Heat Treatment Glossary
A    Acicular ferrite    A highly sub-structured non-equiaxed ferrite that forms upon continuous cooling by a mixed    dif...
Air hardening steel    A	steel	containing	sufficient	carbon	and	other	alloying	elements	to	harden	fully	during	cooling	   ...
cold	working;	improvement	of	mechanical	or	electrical	properties;	or	increase	in	stability	       of dimensions. The time–...
ature	an	isothermal	hold	is	set	up	for	a	specified	time	in	order	to	achieve	the	desired	micro-        structure	(bainite	f...
•	 A metastable aggregate of ferrite and cementite resulting from the transformation of aus-       tenite at temperatures ...
Boronizing    A thermo-chemical surface hardening process used to diffuse boron atoms into the surface of    the	metal	to	...
Carbide coating    TiC and SiC coating is a vacuum deposition process where titanium or silicon carbide compound    is for...
is absorbed and diffused inward from the surface. This is generally followed by quench-       ing to produce a hardened ca...
Ceramic An inorganic, nonmetallic, thermally-stable material, usually in a crystalline structure. Ceramic consists of one ...
Continuous mill A	rolling	mill	consisting	of	a	number	of	stands	of	synchronized	rolls	(in	tandem)	in	which	metal	 undergoe...
Cryogenic treatment A	secondary	cooling	process	that	exposes	the	ferrous	material	to	subzero	temperatures	(typi- cally	–19...
Diffusion bonding A joining process that involves atomic movement from one metal part in intimate contact with another met...
E Elastic deformation A change in dimensions directly proportional to and in phase with an increase or decrease in applied...
Eutectic alloy     •	 The alloy composition that freezes at constant temperature similar to a pure metal. The        lowes...
Flame hardening     •	 A	localised	hardening	process	where	components	are	subject	to	mainly	an	acetylene	fla-        me an...
G Gage length The original length of that portion of the specimen over which strain, change of length and oth- er characte...
H Hardenability     •	 This	relates	to	the	ability	of	steel	to	harden	deeply	upon	quenching,	and	takes	into	con-        si...
also refer to stiffness or temper, or to resistance to scratching, abrasion or cutting. Indentation hardness	tests,	such	a...
Honing A	low-speed	finishing	process	used	chiefly	to	produce	uniform	high	dimensional	accuracy	and	 fine	finish,	most	ofte...
Indirect gas fired A	heating	system	where	the	products	of	combustion	(a	by-product	of	the	burner	system),	are	 NOT	circula...
J     K Knoop Hardness Microhardness determined from the resistance of metal to indentation by a pyramidal diamond indente...
Magnetic-particle inspection A non-destructive method of inspection for determining the extistence and extent of surface c...
Martensite     •	 A microconstituent or structure in quenched steel which has the maximum hardness of ally        of the o...
•	 From	the	chemical	viewpoint,	and	elemental	substance	whose	hydroxide	is	alkaline.     •	 An alloy. Metallography The sc...
Mill scale The heavy oxide layer formed during hot fabrication or heat treatment of metals. Modulus of elasticity A measur...
Nitrocarburizing Any of several processes in which both nitrogen and carbon are absorbed into the surface lay- ers of a fe...
O Offset The distance along the strain coordinate between the initial portion of a stress-strain curve and a parallel line...
or	cast	iron	shavings	and	heated	in	a	furnace	for	12	to	72	hours	at	900	ºC	(1652	ºF).		Carbon	 monoxide	gas	(CO)	is	produc...
Pitting Forming small sharp cavities in a metal surface by non-uniform electrode position or by corro- sion. Pit Type Furn...
Proof stress     •	 The	stress	that	will	cause	a	specified	small	permanent	set	in	a	material.	     •	 A	specified	stress	t...
Quenching     •	 In the heat treating of metals, the step of cooling metals rapidly in order to obtain desired        prop...
Reduction of area     •	 Commonly, the difference, expressed as a percentage of original area, between the        original...
Retort furnace This is a vertical type of furnace provided with a cylindrical metal retort into which the parts to be heat...
Selective quenching Quenching	only	certain	portions	of	a	workpiece.	 Sensitization In austenitic stainless steels, the pre...
Soaking Prolonged heating of a metal at a selected temperature. Soldering A process designed for joining more than one met...
Spheroidizing Heating and cooling in a cycle designed to produce a spheroidal or globular form of carbide in steel. Sphero...
Stainless steel     •	 Corrosion resistant steel of a wide variety, but always containing a high percentage of chro-      ...
degree of embrittlement is a function of aging time and temperature, occurring in a matter of minutes	at	about	200	degrees...
Subcritical annealing     •	 Stress Relief Annealing. A heat treating operation used to relieve or dissipate stresses in  ...
Temper brittleness Brittleness that results when certain steels are held within, or are cooled slowly through, a certain r...
Solo swiss heat treatment glossary
Solo swiss heat treatment glossary
Solo swiss heat treatment glossary
Solo swiss heat treatment glossary
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Solo swiss heat treatment glossary

  1. 1. Heat Treatment Glossary
  2. 2. A Acicular ferrite A highly sub-structured non-equiaxed ferrite that forms upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature slightly higher than the temperature transformation range for upper bainite. It is distinguished from bainite in that it has a limited amount of carbon available; thus, there is only a small amount of carbide present. Acicular ferrite steels Those steels having a microstructure consisting of either acicular ferrite or a mixture of acicu- lar ferrite and equiaxed ferrite. Age hardening • A process in which certain nonferrous and ferrous alloys are heated, quenched and then aged at a relatively low temperature above room temperature, to allow precipitation hard- ening to occur. Can significantly increase work-piece strength without affecting work-piece ductility. The hardening process can be halted by refrigeration of the component. • Hardening by aging, usually after rapid cooling or cold working. The term as applied to soft, or low carbon steels, relates to a wide variety of commercially important, slow, gradual changes that take place in properties of steels after the final treatment. These changes, which bring about a condition of increased hardness, elastic limit, and tensile strength with a consequent loss in ductility, occur during the period in which the steel is at normal temperatures. • The hardening of a material via precipitation from solid solution of coherent transitional phases which produce a strain in the atomic lattice. Aging • A change in properties that occurs at ambient or moderately elevated temperatures after hot working or a heat treating operation (quench aging in ferrous alloys), or after a cold working operation (strain aging). The change in properties is often, but not always, due to a phase change (precipitation), but does not involve a change in chemical composition. In a metal or alloy, a change in properties that generally occurs slowly at room tempera- ture and more rapidly at higher temperatures. • Describes a time–temperature-dependent change in the properties of certain alloys. Except for strain aging and age softening, it is the result of precipitation from a solid solution of one or more compounds whose solubility decreases with decreasing temperature. For each alloy susceptible to aging, there is a unique range of time–temperature combinations to which it will respond.2 Heat Treatment Glossary www.soloswiss.com
  3. 3. Air hardening steel A steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous mediums from a temperature above its transformation range. The term should be restricted to steels that are capable of being hardened by cooling in air in fairly large sections, about 2 inches or more in diameter. Same as self-hardening steel. Alloy A substance of metallic properties composed of two or more elements, at least one of which is a metal. Alloy steel Steel containing specified quantities of alloying elements (other than carbon and the com- monly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus) within the limits recognized for constructional alloy steels, added to effect changes in mechanical or physical properties. Alpha iron The body-centered cubic form of pure iron, stable below 910 degrees Celsius (1670 degrees F) Annealing • A term used to describe a variety of softening heat treatments by changing the microstruc- ture of an alloy. • A heat treatment process used to soften the metal and produce desired changes in its microstructure. Annealing is used to improve machinability, dimensional stability, relieve stresses and define the crystalline grain structure of the material. • Heating to and holding at a suitable temperature and then cooling at a suitable rate, for such purposes as reducing hardness, improving machinability, facilitating cold working, pro- ducing a desired microstructure, or obtaining desired mechanical, physical, or other proper- ties. When applicable, the following more specific terms should be used: black annealing, blue annealing, box annealing, bright annealing, flame annealing, graphitizing, intermedi- ate annealing, isothermal annealing, malleablizing, process annealing, quench annealing, recrystallization annealing, and spheroidizing. When applied to ferrous alloys, the term annealing, without qualification, implies full annealing. When applied to nonferrous alloys, the term annealing implies a heat treatment designed to soften an age-hardened alloy by causing a nearly complete precipitation of the second phase in relatively coarse form. Any process of annealing will usually reduce stresses, but if the treatment is applied for the sole purpose of such relief, it should be designated stress relieving. • A term denoting a treatment, consisting of heating to and holding at a suitable tempera- ture followed by cooling at a suitable rate, used primarily to soften but also to simultane- ously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to, improvement of machinability; facilitation of 3 Heat Treatment Glossary www.soloswiss.com
  4. 4. cold working; improvement of mechanical or electrical properties; or increase in stability of dimensions. The time–temperature cycles used vary widely both in maximum tempera- ture attained and in cooling rate employed, depending on the composition of the material, its condition, and the results desired. When applicable, the following more specific process names should be used: black annealing, blue annealing, box annealing, bright annealing, cycle annealing, flame annealing, full annealing, graphitizing, intermediate annealing, iso- thermal annealing, process annealing, quench annealing, and speroidizing. When the term is used without qualification, full annealing is implied. When applied only for the relief of stress, the process is properly call stress relieving. • A generic term denoting a treatment, consisting of heating to and holding at a suitable tem- perature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to: improvement of machin- ability, facilitation of cold work, improvement of mechanical or electrical properties, and/ or increase in stability of dimensions. When the term is used without qualification, full an- nealing is implied. When applied only for the relief of stress, the process is properly called stress relieving, or stress-relief annealing. In ferrous alloys, annealing usually is done above the upper critical temperature, but the time-temperature cycles vary widely in both maximum temperature attained and in cooling rate employed, depending on composition, material condition, and results desired. When applicable, the following commercial process names should be used: black annealing, blue annealing, box annealing, bright annealing, cycle annealing, flame annealing, full annealing, graphitizing, in-process annealing, isothermal annealing, malleablizing, orientation annealing, process annealing, quench annealing, spheroidizing, sub-critical annealing. In nonferrous alloys, annealing cycles are designed to: (a) remove part or all of the ef- fects of cold working (re-crystallization may or may not be involved); (b) cause substan- tially complete coalescence of precipitates from solid solution in relatively coarse form; or (c) both, depending on composition and material condition. Specific process names in commercial use are final annealing, intermediate annealing, partial annealing, recrystal- lization annealing, stress-relief annealing, anneal to temper. Austempering • This is a method of hardening steel by quenching from the austenitizing temperature into a heat extracting medium (usually salt) which is maintained at some constant temperature level between 400” and 800” and holding the steel in this medium until austenite is trans- formed to bainite. • Quenching from a temperature above the transformation range, in a medium having a rate of heat abstraction high enough to prevent the formation of high temperature transforma- tion products, and then holding the alloy, until transformation is complete, at a temperature below that of pearlite formation and above that of martensite formation. • A heat treating process for ferrous metals which increase hardness, fatigue strength, and impact resistance while reducing distortion of the parts. Typically the part is heated high enough to change the microstructure to the austenitic phase and cooled rapidly to avoid the pearlite phase. When it cools to a temperature slightly above the martensitic start temper-4 Heat Treatment Glossary www.soloswiss.com
  5. 5. ature an isothermal hold is set up for a specified time in order to achieve the desired micro- structure (bainite for steel). • A heat treatment for ferrous alloys in which a part is quenched from the austenitizing tem- perature at a rate fast enough to avoid formation of ferrite or pearlite and then held at a temperature just above M until transformation to bainite is complete. Austenite • The solid solution of iron and carbon which is attained by heating to high temperatures above the upper critical temperature. This temperature or temperature range is called the austenitizing temperature and must be attained to obtain the proper microstructure and full hardness of steel in heat treating. The austenitizing temperature varies for the differ- ent grades of carbon, alloy and tool steels. • A solid solution of one or more elements in face-centered cubic iron. Unless otherwise des- ignated (such as nickel austenite), the solute is generally assumed to be carbon. Austenitic grain size The size attained by the grains of steel when heated to the austenitic region; may be revealed by appropriate etching of cross sections after cooling to room temperature. Austenitic steel An alloy steel whose structure is normally austenitic at room temperature. Austenitising Forming austenite by heating a ferrous alloy into the transformation range (partial austenitiz- ing) or above the transformation range (complete austenitizing). When used without qualifica- tion, the term implies complete austenitizing. B Bainite • A eutectoid transformation product of ferrite and a fine dispersion of carbide, generally formed at temperatures below 840 to 930 F (450 to 500 C): upper bainite is an aggregate containing parallel lath-shape units of ferrite, produces the so-called feathery appearance in optical microscopy, and is formed at temperatures above about 660 F (350 C) ; lower bain- ite consists of individual plate-shape units and is formed at temperatures below about 660 F (350 C). Also, a slender, needle-like (acicular) microstructure appearing in spring steel strip characterized by toughness and greater ductility than tempered Martensite. Bainite is a de- composition product of Austenite best developed at interrupted holding temperatures below those forming fine pearlite and above those giving Martensite.5 Heat Treatment Glossary www.soloswiss.com
  6. 6. • A metastable aggregate of ferrite and cementite resulting from the transformation of aus- tenite at temperatures below the pearlite range but above Ms. Its appearance is feathery if formed in the upper part of the bainite transformation range; acicular, resembling tem- pered martensite, if formed in the lower part. Baking Heating to a low temperature in order to remove entrained gases. Bath annealing Is immersion is a liquid bath (such as molten lead or fused salts) held at an assigned tempera- ture-when a lead bath is used, the process is known as lead annealing. Bend test A test for determining relative ductility of metal that is to be formed (usually sheet, strip, plate or wire) for determining soundness and toughness of metal (after welding, for example). The specimen is usually bent over a specified diameter through a specified angle for a specified number of cycles. Black annealing • A process of box annealing or pot annealing ferrous alloy sheet, strip or wire after hot working and pickling. • Box annealing or pot annealing, used mainly for sheet, strip, or wire. Blue annealing Heating hot rolled ferrous sheet in an open furnace to a temperature within the transforma- tion range and then cooling in air, in order to soften the metal. The formation of a bluish oxi- de on the surface is incidental. Blue brittleness Brittleness exhibited by some steels after being heated to some temperature within the range of about 200 to 370 degree Celsius (400 to 700 F), particularly if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness. Bluing • Subjecting the scale-free surface of a ferrous alloy to the action of air, steam, or other agents at a suitable temperature, thus forming a thin blue film of oxide and improving the appearance and resistance to corrosion. • A treatment of the surface of iron-base alloys, usually in the form of sheet or strip, on which, by the action of air or steam at a suitable temperature, a thin blue oxide film is formed on the initially scale-free surface, as a means of improving appearance and resis- tance to corrosion. This term is also used to denote a heat treatment of springs after fabri- cation, to reduce the internal stress created by coiling and forming.6 Heat Treatment Glossary www.soloswiss.com
  7. 7. Boronizing A thermo-chemical surface hardening process used to diffuse boron atoms into the surface of the metal to form complex metal borides (i.e. – FeB/FeB2). The benefits of boronizing include good corrosion resistance, reduced coefficient of friction, and increased fatigue life Box annealing Annealing in a sealed container under conditions that minimize oxidation. In box annealing, the charge is usually heated slowly to a temperature below the transformation range, but some- times above or within it, and is then cooled slowly; this process is also called “close annealing” or “pot annealing.” Brazing • Joining metals by fusion of nonferrous alloys that have melting points above 800 F (425C), but lower than those of the metals being joined. May be accomplished by a torch. Filler metal is ordinarily in rod form in torch brazing; whereas in furnace and dip brazing the work material is first assembled and the filler metal may then be applied as wire, washers, clips, bands, or may be bonded, as in brazing sheet. • A metal joining process whereby a filler metal is heated above the solidus and the liquid is distributed between two or more close-fitting parts via capillary action. The filler metal is brought slightly above its melting temperature in a protective atmosphere; this can be in vacuum or in inert gas atmosphere free of oxygen. Bright annealing • The process of annealing in a protective atmosphere or vacuum so as to prevent discolor- ation of the bright surface desired. • Annealing in a protective medium to prevent discoloration of the bright surface. Brinell hardness test A test for determining the hardness of a material by forcing a hard steel or carbide ball of speci- fied diameter into it under a specific load. The result is expressed as the Brinell hardness num- ber, which is the value obtained by dividing the applied load in kilograms by the surface area of the resulting impression in square millimeters. Brittleness The quality of a material that leads to crack propagation with appreciable plastic deformation. C Carbide A compound of carbon with one or more metallic elements.7 Heat Treatment Glossary www.soloswiss.com
  8. 8. Carbide coating TiC and SiC coating is a vacuum deposition process where titanium or silicon carbide compound is formed on graphite components. Carbonitriding • A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause si- multaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the de- sired properties in the work piece. • A case hardening process that introduces carbon and nitrogen into the surface of a solid ferrous alloy by heating the alloy in contact with a gaseous carbonaceous material and am- monia. The heat treating process is completed by quenching at a set rate to produce the desired properties of the work piece. Carbon potential A measure of the ability of an environment containing active carbon to alter or maintain, under prescribed conditions, the carbon content of the steel exposed to it. In any par- ticular environment, the carbon level attained will depend on such factors as tempera- ture, time, and steel composition. Carbon restoration Replacing the carbon lost in the surface layer from previous processing by carburizing this layer to substantially the original carbon level. Carbon steel Steel having no specified minimum quality for any alloying element (other than the commonly accepted amounts of manganese, silicon, and copper) and that contains only an incidental amount of any element other than carbon, silicon, manganese, copper, sulfur and phosphorus. Carburizing (Cementation) • Adding carbon to the surface of iron-base alloys by absorption through heating the metal at a temperature below its melting point in contact with carbonaceous solids, liquids or gas- es. The oldest method of case hardening. • A process in which carbon is introduced into a solid iron-base alloy by heating above the transformation temperature range while in contact with a carbonaceous material that may be a solid, liquid, or gas. Carburizing is frequently followed by quenching to pro- duce a hardened case. • A surface hardening process that introduces carbon into the surface of a solid ferrous al- loy by heating the alloy in contact with a carbonaceous material to a temperature above the transformation range and holding at that temperature until a desired level of carbon8 Heat Treatment Glossary www.soloswiss.com
  9. 9. is absorbed and diffused inward from the surface. This is generally followed by quench- ing to produce a hardened case. • Absorption and diffusion of carbon into solid ferrous alloys by heating to a temperature usu- ally above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then re-austenitizing and quenching. Case • The surface layer of an iron-base alloy that has been suitably altered in composition and can be made substantially harder than the interior or core by a process of case hardening. • The term case is also used to designate the hardened surface layer of a piece of steel that is large enough to have a distinctly softer core or center. • That portion of a ferrous alloy, extending inward from the surface, whose composition has been altered so that it can be case hardened. Typically considered to be the portion of the alloy (a) whose composition had been measurably altered from the original composition, (b) that appears dark on an etched cross section, or (c) that has a hardness, after harde- ning, equal to or greater than a specified value. Contrast with core. Case hardening • One of a number of heat treatment processes which improve the surface hardness of a steel alloy without affecting the properties of the core material. • A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon or nitrogen, or a mixture of the two, and, by diffusion, create a concentration gradient. A heat treatment or a combination of heat treatments of surface hardening involving a change in the composition of the outer layer of an iron-base alloy in which the surface is made substantially harder by inward dif- fusion of a gas or liquid followed by appropriate thermal treatment. Typical case-hardening processes are carburizing, cyaniding, carbonitriding, quench hardening and nitriding. • A process of surface hardening involving a change in the composition of the outer layer of an iron-base alloy followed by appropriate thermal treatment. Cementation The process of introducing elements into the outer layer of metal objects by means of high- temperature diffusion. Cementite A compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it oc- curs as a phase in steel, the chemical composition will be altered by the presence of manga- nese and other carbide-forming elements.9 Heat Treatment Glossary www.soloswiss.com
  10. 10. Ceramic An inorganic, nonmetallic, thermally-stable material, usually in a crystalline structure. Ceramic consists of one or more metals in combination with a non-metal, usually oxygen, but can in- clude nitrides, borides, carbides, silicides, and sulfides. They are characterized by a high tem- perature strength, good electro-thermal insulation, and high chemical stability. Charging Placing materials into a furnace. Charpy test A pendulum-type single-low impact test in which the specimen, usually notched, is supported at both ends as a simple beam and broken by a falling pendulum. The energy absorbed, as determined by the subsequent rise of the pendulum, is a measure of impact strength or notch toughness. Contrast with Izod Test. Chemical vapor deposition A chemical process used to produce a non-volatile solid thin film of various materials on a sub- strate. In a typical CVD process the substrate is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired thin film. Fre- quently, volatile byproducts are also produced, which are removed by gas flow through the re- action chamber. Chevron pattern A fractographic pattern of radial marks (shear ledges) that looks like nested letters “V”; some- times called a herringbone pattern. Chevron patterns are typically found on brittle fracture surfaces in parts whose widths are considerably greater than their thickness. The points of the chevrons can be traced back to the fracture origin. Cold treatment • Exposing to suitable subzero temperatures for the purpose of obtaining desired conditions or properties, such as dimensional or microstructural stability. When the treatment involves the transformation of retained austenite, it is usually followed by a tempering treatment. • A secondary cooling process that exposes the ferrous material to subzero temperatures (typically –84°C (-120°F) to either impart or enhance specific conditions or properties of the material. Increased strength, greater dimensional or micro-structural stability, improved wear resistance, and relief of residual stress are among the benefits of the cold treatment of steel. Conditioning heat treatment A preliminary heat treatment used to prepare a material for a desired reaction to a subsequent heat treatment. For the term to be meaningful, the treatment used must be specified. Continuous casting A casting technique in which a cast shape is continuously withdrawn through the bottom of the mold as it solidifies, so that its lengths not determined by mold dimensions. Used chiefly to produce semi-finished mill products such as billets, blooms, ingots, slabs and tubes.10 Heat Treatment Glossary www.soloswiss.com
  11. 11. Continuous mill A rolling mill consisting of a number of stands of synchronized rolls (in tandem) in which metal undergoes successive reductions as it passes through the various stands. Controlled cooling • A term used to describe a process by which a steel object is cooled from an elevated tem- perature, usually from the final hot-forming operation in a predetermined manner of cooling to avoid hardening, cracking, or internal damage. • Cooling from an elevated temperature in a predetermined manner, to avoid hardening, cracking, or internal damage, or to produce desired microstructure or mechanical proper- ties. Cooling curve A curve shoeing the relation between time and temperature during the cooling of a material. Cooling stresses Residual stresses resulting from non-uniform distribution of temperature during cooling. Core • The interior portion of an iron-base alloy that after case hardening is substantially softer than the surface layer or case. • The term core is also used to designate the relatively soft central portion of certain hard- ened tool steels. Critical cooling rate The rate of continuous cooling required to prevent undesirable transformation. For steel, it is the minimum rate at which austenite must be continuously cooled to suppress transformations above the Ms temperature. Critical point The temperature or pressure at which a change in crystal structure, phase or physical proper- ties occurs. Same as transformation temperature. Critical range or critical temperature range Synonymous with transformation range, which is preferred.11 Heat Treatment Glossary www.soloswiss.com
  12. 12. Cryogenic treatment A secondary cooling process that exposes the ferrous material to subzero temperatures (typi- cally –190°C (-310°F) to either impart or enhance specific conditions or properties of the material. This is typically used to eliminate retained austenite in carburized parts. Increased strength, greater dimensional or micro-structural stability, improved wear resistance, and relief of residual stress are among the benefits of the cold treatment of steel. Crystallization The formation of crystals by the atoms assuming definite positions in a crystal lattice. This is what happens when a liquid metal solidifies. (Fatigue, the failure of metals under repeated stresses, is sometimes falsely attributed to crystallization.) Cyaniding • Surface hardening by carbon and nitrogen absorption of a steel article or a portion of it by heating at a suitable temperature in contact with cyanide salt, followed by quenching. • A process of case hardening an iron-base alloy by the simultaneous absorption of carbon and nitrogen by heating in a cyanide salt. Cyaniding is usually followed by quenching to produce a hard case. Cycle Annealing An annealing process employing a predetermined and closely controlled time–temperature cy- cle to produce specific properties or microstructure. D Decarburization • When steel is subjected to high temperatures, such as are used in hot rolling, forging, and heat treating in a media containing air, oxygen, or hydrogen there is a loss of carbon at the surface which is known as decarburization. This resultant loss of carbon or chemistry change at the surface of the steel part reduces the strength of the part by reducing the size of the section and produces a softer surface hardness than the core of the part. • The loss of carbon from the surface of an iron-base alloy as the result of heating in a me- dium that reacts with the carbon. Degassing A heat treatment process that removes gas from the metal; vacuum processing is used to de- gas titanium, copper, and tantalum. Differential heating A heating process by which the temperature is made to vary throughout the object being heated so that on cooling, different portions may have such different physical properties as may be desired.12 Heat Treatment Glossary www.soloswiss.com
  13. 13. Diffusion bonding A joining process that involves atomic movement from one metal part in intimate contact with another metal part, typically in the same alloy family, to form a strong metallurgical bond. This occurs at high temperature (but below the melting point) and pressure. The process is particu- larly facilitated in a vacuum because of the elimination of oxygen, allowing for a high integrity bond. Direct gas fired A heating system where the products of combustion (a by-product of the burner system), are circulated through the work chamber. Direct quenching Quenching carburized parts directly from the carburizing operation. Double aging Employment of tow different aging treatments to control the type of precipitate formed from a sub-persaturated matrix in order to obtain the desired properties. The first aging treatment, sometimes referred to as intermediate or stabilizing, is usually carried out at a higher tempera- ture than the second. Double tempering • A treatment in which quench hardened steel is given two complete tempering cycles at sub- stantially the same temperature for the purpose of ensuring completion of the tempering reaction and promoting stability of the resulting microstructure. • A treatment in which a quench-hardened ferrous metal is subjected to two complete tempering cycles, usually at substantially the same temperature, for the purpose of ensuring completion of the tempering reaction and promoting stability of the resulting microstructure. Drawing Drawing, or drawing the temper, is synonymous with tempering, which is preferable. Ductility The property of metals that enables them to be mechanically deformed when cold, without fracture. In steel, ductility is usually measured by elongation and reduction of area as deter- mined in a tensile test.13 Heat Treatment Glossary www.soloswiss.com
  14. 14. E Elastic deformation A change in dimensions directly proportional to and in phase with an increase or decrease in applied force. Elasticity Ability of a solid to deform in direct proportion to and in phase with increases or decreases in applied force. Elastic limit The maximum stress to which a material may be subjected without any permanent strain re- maining upon complete release of stress. Elastic modulus Same as modulus of elasticity. Elastic ratio Yeild point divided by tensile strength. Emissivity A measure of thermal emittance; measured by the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody (a surface that emits all the heat energy that it absorbs) under the same conditions. End-quench hardenability test A laboratory procedure for determining the hardenability of a steel or other ferrous alloy; widely referred to as the Jominy test. Hardenability is determined by heating a standard speci- men above the upper critical temperature, placing the hot specimen in a fixture so that a stream of cold water impinges on one end, and after cooling to room temperature is completed, measuring the hardness near the surface of the specimen at regularly spaced intervals along its length. The data are normally plotted as hardness versus distance from the quenched end. Etching • Subjecting the surface of a metal to preferential chemical or electrolytic attack in order to reveal structural details for metallographic examination. • Chemically or electrochemically removing tenacious films from a metal surface to condition the surface for a subsequent treatment, such as painting or electroplating.14 Heat Treatment Glossary www.soloswiss.com
  15. 15. Eutectic alloy • The alloy composition that freezes at constant temperature similar to a pure metal. The lowest melting (or freezing) combination of two or more metals. The alloy structure (homo- geneous) of two or more solid phases formed from the liquid eutectically. • An alloy of two or more elements that exhibits isothermal freezing with the simultaneous precipitation of alternate phases at a lower temperature than any of the pure elements in the alloy. In the liquid form, a eutectic usually exhibits high fluidity. Extensometer An instrument for measuring changes in length caused by application or removal of a force. Commonly used in tension testing of metal specimens. F Ferrite • A solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated (for instance, as chromium ferrite) the solute is generally assumed to be carbon. On some equilibrium diagrams, there are two ferrite regions separated by an austenite area. The lower area is alpha ferrite; the upper, delta ferrite. If there is no designation, alpha ferrite is assumed. • In the field of magnetics, substances having the general formula: M++ O2+++ O3 The trivalent metal often being iron. Ferritic nitrocarburizing A case hardening process that diffuses nitrogen and carbon into ferrous alloys at sub-critical temperatures. The resultant hardened surface show increased resistance to wear, corrosion, and fatigue. File hardness Hardness as determined by the use of a file of standardized hardness on the assumption that a material that cannot be cut with the file is as hard as, or harder than, the file. Files covering a range of hardnesses may be employed. Flame annealing Annealing in which the heat is applied directly by a flame. 15 Heat Treatment Glossary www.soloswiss.com
  16. 16. Flame hardening • A localised hardening process where components are subject to mainly an acetylene fla- me and then spray quenched. • A process of heating the surface layer of an iron-base alloy above the transformation tem- perature range by means of a high-temperature flame, followed by quenching. Fluorescent magnetic particle inspection Inspection with either dry magnetic particles or those in a liquid suspension, the particles being coated with a fluorescent substance to increase the visibility of the indications. Fluorescent penetrant inspection Inspection using a fluorescent liquid that will penetrate any surface opening; after wiping the surface flaws may be detected by the fluorescence, under ultraviolet light, of back-seepage of the fluid. Fog quenching Quenching in a mist. Forging Plastically deforming metal, usually hot, into desired shapes with compressive force, with or without dies. Full annealing Austenitizing and then cooling at a rate such that the hardness of the product approaches a minimum.16 Heat Treatment Glossary www.soloswiss.com
  17. 17. G Gage length The original length of that portion of the specimen over which strain, change of length and oth- er characteristics are measured. Gamma iron The face-centered cubic form of pure iron, stable from 910 to 1400 degrees Celsius (1670 to 2550 F). Gas carburizing Carburizing in the presence of hydrocarbon gases which react on the surface of the steel to release nascent carbon which diffuses into the surface of the steel to improved wear and fa- tigue resistance. Gas nitriding A process of case hardening in which ferrous alloys, metals or non ferrous alloys, usually of special composition, is heated in an atmosphere of ammonia to produce absorption of nitrogen on the surface which hardens the material without quenching. Glass A super-cooled liquid ceramic material commonly composed of silicates and oxides that form by cooling the viscous materials without sufficient time for a crystalline lattice structure to form. Grain growth An increase in the average size of the grains in polycrystalline metal, usually as a result of heat- ing at elevated temperature. Grain size • For metals, a measure of the areas or volumes of grains in a polycrystalline material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, the grain size refers to that of the matrix unless other- wise specified. Grain sizes are reported in terms of number of grains per unit area or volume, average diameter, or as a grain-size number derived from area measurements. • For grinding wheels, see preferred term, grit size. Graphitizing Annealing in such a way that some or all of the carbon is precipitated as graphite.17 Heat Treatment Glossary www.soloswiss.com
  18. 18. H Hardenability • This relates to the ability of steel to harden deeply upon quenching, and takes into con- sideration the size of the part and the method of quenching. The test used to deter- mine the hardenability of any grade of steel is the Jominy Test. • In a ferrous alloy, the property that determines the depth and distribution of hardness in- duced by quenching. • The relative ability of a ferrous alloy to form martensite when quenched from a tempe- rature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surface where the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure. Hardening • One of a number of processes used to improve the hardness of an alloy superior to that normally present in the core stock. Usually achieved by quenching material from above its upper critical temperature. • Increasing hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening, case hardening, flame hardening, induction hardening, precipitation hardening, quench hardening. • Any process of increasing hardness of metal by suitable treatment, usually involving heating and cooling. Also: see aging. Hardening and Tempering A common heating and cooling treatment used to harden and strengthen the metal. One way to measure is by using various hardness scales including Brinell and Rockwell. Hard- ened metal is reheated in order to temper it; hardness is lowered but the ductility is in- creased. Vacuum process will result in bright finishes. Temperature of the temper operation determines the final strength, hardness, and ductility. Hardfacing A process where harder or tougher material is applied to the surface a base metal. Hardness Resistance of metal to plastic deformation, usually by indentation. However, the term may18 Heat Treatment Glossary www.soloswiss.com
  19. 19. also refer to stiffness or temper, or to resistance to scratching, abrasion or cutting. Indentation hardness tests, such as Brinell, Rockwell and Vickers. Heat treatable alloy An alloy that can be hardened by heat treatment. Heat treatment • Altering the properties of a metal by subjecting it to a sequence of termperature changes, time of retention at specific temperature and rate of cooling therfrom being as important as the temperature itself. Heat treatment usually markedly affects strength, hardness, ductility, malleability, and similar properties of both metals and their alloys. • A combination of heating and cooling operations applied to a metal or alloy in the solid state to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition. • Modifies the microstructure of the material or changes the phase structure to improve he t mechanical properties for specific applications or further work processes. • heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the mea- ning of this definition. • Process in which a metal is heated to a certain temperature and the cooled in a particular manner to alter its internal structure for obtaining desired degree of physical and mechani- cal properties such as brittleness, hardness, and softness. High pressure gas quenching Gas quenching at pressures greater than 1 bar; typically 2-20 bar. HPGC is used to eliminate distortion typically found with oil quenching, and to produce a clean esthetically desirable sur- face. Homogenisation Primarily used to equalise temperature in stock material prior to hot working, or to reduce ex- cessive coring, which can occur in ingots and continuously cast alloys. Homogenizing • A high-temperature heat-treatment process intended to eliminate or to decrease chemi- cal segregation by diffusion. • Heating a metal to high temperature in order to ensure uniform distribution of components. This process is typically used to reduce chemical segregation and coring in cast structures and to produce a more homogeneous microstructure in hot worked materials. Homogenizing annealing An annealing treatment carried out at a high temperature, approaching the solidus tempera- ture, for a sufficiently long time that inhomogeneous distributions of alloying elements are re- duced by diffusional processes.19 Heat Treatment Glossary www.soloswiss.com
  20. 20. Honing A low-speed finishing process used chiefly to produce uniform high dimensional accuracy and fine finish, most often on inside cylindrical surfaces. In honing, very thin layers of stock are removed by simultaneously rotating and reciprocating a bonded abrasive stone or stick that is presses against the surface being honed with lighter force than is typical of grinding. Hooke’s law Stress is proportional to strain. The law holds up to the proportional limit only. Hot Iso Static Processing (HIPping) This process is used for the densification of castings and pre-sintered components, as well as in the diffusion bonding of alloys. The process usually uses very high temperatures and pres- sures within a specially designed vessel. Hot quenching An imprecise term used to cover a variety of quenching procedures in which a quenching me- dium is maintained at a prescribed temperature above 160 degrees F (70 degrees C). Hydriding/Dehydriding Hydriding is the addition of hydrogen to metal to embrittle it for pulverizing. After pulverizing, hydrogen is removed through dehydriding so the material becomes ductile. Hydrogen annealing Annealing under a controlled atmosphere of hydrogen to prevent oxidation or discoloration of parts. I Impact energy The amount of energy required to fracture a material, usually measured by means of an Izod or Charpy test. The type of specimen and test conditions affect the values and therefore should be specified. Impact test A test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in the Charpy or Izod tests. Inclusions Particles of foreign material in a metallic matrix. The particles are usually compounds (such as oxides, sulfides, or silicates), but may be of any substance that is foreign to (and essentially in- soluble in) the matrix. Indentation hardness The resistance of a material to indentation. This is the usual type of hardness test, in which a pointed or rounded indenter is pressed into a surface under a substantially static load. Indication In inspection, indication is a response to nondestructive stimulus that implies the presence of an imperfection. The indication must be interpreted to determine if (a) it is a true indication or a false indication and (b) whether or not a true indication represents an unacceptable deviation.20 Heat Treatment Glossary www.soloswiss.com
  21. 21. Indirect gas fired A heating system where the products of combustion (a by-product of the burner system), are NOT circulated through the work chamber. Induction furnace An ac electric furnace in which the primary conductor is coiled and generates, by electromag- netic induction, a secondary current that develops heat within the metal charge. Induction hardening A widely used process particularly in the automotive and tools market for the surface hardening of steel. The components are heated by means of an induction set which applies an alternating magnetic field to the work-piece. The temperature of the components increases to the transfor- mation range or just above before being immediately quenched. The physical properties of the core material remain unaffected by the process. Induction heating A process of local heating by electrical induction. Intermediate annealing Annealing at one or more stages during manufacture and before final thermal treatment. Interrupted quenching A quenching procedure in which the workpiece is removed from the first quench at a tempera- ture substantially higher than that of the quenchant and is then subjected to a second quench- ing system having a different cooling rate than the first. Ion nitriding A vacuum heat treatment process in which a high-voltage glow discharge is used to bombard low and medium alloy steels, tool steels, and stainless steel surfaces with nitrogen ions. The nitrogen ions form nitrides with the alloy elements and diffuse into the part resulting in clean, hardened surface. Isothermal annealing • A process in which a ferrous alloy is heated to produce a structure partly or wholly auste- nitic, and is then cooled to and held at a temperaure that causes transformation of the aus- tenite to a relatively soft ferrite-carbide aggregate. • Austenitizing a ferrous alloy and then cooling to and holding at a temperature at which aus- tenite transforms to a relatively soft ferrite-carbide aggregate. Isothermal transformation A change in phase that takes place at a constant temperature. The time required for transfor- mation to be completed, and in some instances the time delay before transformation begins, depends on the amount of super-cooling below (or superheating above) the equilibrium tem- perature for the same transformation. Izod test A pendulum-type single-blow impact test in which the specimen, usually notched, is fixed at one end and broken by a falling pendulum, is a measure of impact strength or notch toughness. Contrast with Charpy test.21 Heat Treatment Glossary www.soloswiss.com
  22. 22. J K Knoop Hardness Microhardness determined from the resistance of metal to indentation by a pyramidal diamond indenter, having edge angles of 172 degrees 30’ and 130 degrees, making a rhombohedral im- pression with one long and one short diagonal. L Lap A surface imperfection, appearing as a seam, caused by folding over hot metal, fins or sharp corners and then rolling or forging them into the surface, but not welding them. Longitudinal direction The principal direction of flow in a worked metal. Low pressure carburizing Low Pressure Vacuum Carburizing, also known as LPVC, which is a heat treat process that sup- plies additional carbon to the surface of the steel. Performed in a vacuum furnace, this vacuum carburizing process is designed to achieve optimum case hardening properties for various al- loy materials. M Magnetic annealing An annealing process utilized on certain ferrous materials to achieve uniform magnetic proper- ties. This is usually done in vacuum or in a hydrogen atmosphere in order to avoid decarbur- ization. This process requires tight temperature uniformity, extended soak times and accurate control of the cooling rates to control the microstructure of the material without loss of mag- netic properties.22 Heat Treatment Glossary www.soloswiss.com
  23. 23. Magnetic-particle inspection A non-destructive method of inspection for determining the extistence and extent of surface cracks and similar imperfections in ferromagnetic materials. Finely divided magnetic, applied to the magnetized part, are attracted to and outline the pattern of any magnetic-leakage fields created by discontinuities. Malleablizing A process of annealing white cast iron in which the combined carbon is wholly or in part trans- formed to graphitic or free carbon and, in some cases, part of the carbon is removed complete- ly.See temper carbon. Maraging A precipitation hardening treatment applied to a special group of iron-base alloys to precipi- tate one or more intermetallic compounds in a matrix of essentially carbon-free martensite. . NOTE: the first developed series of maraging steels contained, in addition to iron, more than 10% nickel and one or more supplemental hardening elements. In this series, aging is done at 480 degrees Celsius (900 F) Martempering or marquenching • This is a method of hardening steel by quenching from the austenitizing temperature into some heat extracting medium, usually salt, which is maintained at some constant tempera- ture level above the point at which martensite starts to form (usually about 450” F.), hold- ing the steel in this medium until the temperature is uniform throughout, cooling in air for the formation of martensite and tempering by the conventional method. The advantages of this method of interrupted quenching are a minimum of distortion and residual strains. The size of the part can be considerably larger than for austempering. • A hardening procedure in which an austenitized ferrous workpiece is quenched into an ap- propriate medium whose temperature is maintained substantially at the M3 of the workpiece, held in the medium until its temperature is uniform throughout but not long enough to permit bainite to form, and then cooled in air. The treatment is frequently followed by tempering. When the process is applied to carburized material, the control- ling Ms temperature is that of the case. This variation of the process is frequently called marquenching. • A heat treatment involving transformation of austenite to martensite followed by step quenching, at a rate fast enough to avoid the formation of ferrite, pearlite or bainite. This is typically performed at temperatures slightly above the Ms point. Soaking must be short enough to avoid the formation of bainite before the temperature is lowered below Ms. The advantage of martempering is the reduction of thermal stresses compared to normal quenching. This prevents cracking and minimizes distortion.23 Heat Treatment Glossary www.soloswiss.com
  24. 24. Martensite • A microconstituent or structure in quenched steel which has the maximum hardness of ally of the other steel structures resulting from the transformation of austenite. • A generic term for microstructures formed by diffusion-less phase transformation in which the parent and product phases have a specific crystallographic relationship. Martensite is characterized by an acicular pattern in the microstructure in both ferrous and nonferrous alloys. In alloys where the solute atoms occupy interstitial positions in the martensitic lattice (such as carbon in iron), the structure is hard and highly strained; but where the solute atoms occupy substitutional positions (such as nickel and iron), the martensite is soft and ductile. T he amount of high temperature phase that transforms to martensite on cooling depends on the lowest temperature attained, there being a rather distinct beginning temperature (Ms) and a temperature at which the transformation is es- sentially complete (Mf). Martensite range The temperature interval between Ms and Mf. Martensitic transformation A reaction that takes place in some metals on cooling, with the formation of an acicular struc- ture called martensite. Mechanical properties The properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit. Compare with physical properties. Mechanical testing Determination of mechanical properties. Melting point The temperature upon which a chemically pure substance, eutectic or maximum melting point material changes from a solid state to a liquid state. Metal • An opaque lustrous elemental chemical substance that is a good conductor of heat and electricity and, when polished, a good reflector of light. Most elemental metals are mal- leable and ductile and are, in general, denser than the other elemental substances. • As to structure, metals may be distinguished from nonmetals by their atomic binding and electron availability. Metallic atoms tend to lose electrons form the outer shells, the posi- tive ions thus formed being held together by the electron gas produced by the separation. The ability of these “free electrons” to carry an electric current, and the fact that this ability decreases as temperature increases, establish the prime distinctions of a metallic solid.24 Heat Treatment Glossary www.soloswiss.com
  25. 25. • From the chemical viewpoint, and elemental substance whose hydroxide is alkaline. • An alloy. Metallography The science dealing with the constitution and structure of metals and alloys as revealed by un- aided eye or by such tools as low-powered magnification, optical microscope, electron micro- scope and diffraction or x-ray techniques. Metallurgy The science and technology of metals and alloys. Process metallurgy is concerned with the extraction of metals from their ores and with the refining of metals; physical metallurgy, with the physical and mechanical properties of metals as affected by composition, processing and environmental conditions; and mechanical metallurgy, with the response of metals to applied forces. Metal oxide A compound of oxygen with a metal. Most metals react with oxygen under appropriate tem- perature and pressure conditions, and oxidation can occur slowly at room temperature to form a thin oxide coat that can serve to protect the metal. Mf temperature For any alloy system, the temperature at which martensite formation on cooling is essentially finished. See transformation temperature for the definition applicable to ferrous metals. Micro-hardness The hardness of material as determined by forcing an indenter such as Vickers or Knoop indent- er into the surface of a material under very light load; usually the indentations are so small that they must be measured with a microscope. Capable of determining hardness of different micro-constituents within a structure, or of measuring steep hardness gradients such as those encountered in case hardening. Micro-structure The structure of metals as revealed by microscopic examination of the etched surface of a pol- ished specimen. Micro structure states Heat treatments are used to change the micro structural state of steels and alloys. Each of the states holds advantages in different applications and metals may be produced which exhibit combinations of the states. Mild steel Carbon steel with a maximum of about 0.25% C.25 Heat Treatment Glossary www.soloswiss.com
  26. 26. Mill scale The heavy oxide layer formed during hot fabrication or heat treatment of metals. Modulus of elasticity A measure of the rigidity of metal. Ratio of stress below the proportional limit, to correspond- ing strain. Specifically, the modulus obtained in tension or compression is Young’s modulus, stretch modulus or modulus of extensibility; the modulus obtained in torsion or shear is modu- lus of rigidity, shear modulus or modulus of torsion; the modulus covering the ratio of the mean normal stress to the change in volume per unit volume is the bulk modulus. The tangent modulus and secant modulant are not restricted within the proportional limit; the former is the slope of the stress-strain curve at a specified point; the latter is the slope of a line from the or- igin to a specified point on the stress-strain curve. Also called elastic modulus and coefficient of elasticity. Ms temperature For any alloy system, the temperature at which martensite starts to form on cooling. See transformation temperature for the definition applicable to ferrous alloys. N Nitriding • Introducing nitrogen into the surface of a solid ferrous alloy by holding at a suitable tem- perature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually am- monia of molten cyanide of appropriate composition. Quenching is not required to produce a hard case. Process of surface hardening certain types of steel by heating in ammonia gas at about 935-1000 (degrees) F., the increase in hardness being the result of surface nitride formation. Certain alloying constituents, principal among them being aluminum, greatly facilitate the hardening reaction. In general, the depth of the case is less than with carbur- izing. • A process of case hardening in which an iron-base alloy of special composition is heated in an atmosphere of ammonia or in contact with nitrogenous material. Surface hardening is produced by the absorption of nitrogen without quenching. • A chemical process which diffuses nascent nitrogen into the surface layers of low carbon steels, other metals, or alloys in order to improve surface hardness and wear resistance. Nitriding potential The nitriding potential is directly proportional to the nitrogen activity in the gas mixture con- taining ammonia as the nitriding species. It is defined as K = pNH3/pH23/2, where “p” is the partial pressure of the ammonia and hydrogen.26 Heat Treatment Glossary www.soloswiss.com
  27. 27. Nitrocarburizing Any of several processes in which both nitrogen and carbon are absorbed into the surface lay- ers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is done mainly to provide an anti-scuffing sur- face layer ant to improve fatigue resistance. Compare with carbonitriding. Nondestructive inspection Inspection by methods that do not destroy the part nor impair its serviceability. Nondestructive testing Same as non-destructive inspection, but implying use of a method in which the part is stimu- lated and its response measured quantitatively or semi-quantitatively. Normalizing • A treatment used to remove undesired microstructure effects of previous heat treatments and performed to produce a uniform grain structure. • Heating steels to approximately 100 F above the critical temperature range followed by cooling to below that range in still air at ordinary temperatures. This heat treat operation is used to erase previous heat treating results in carbon steels to .40% carbon, low alloy steels, and to produce a uniform grain structure in forged and cold worked steel parts. • A process in which an iron-base alloy is heated to a temperature above the transformation range and subsequently cooled in still air at room temperature. • Heating a ferrous alloy to a temperature above the transformation range in order to create a phase change in the metal’s microstructure and refinement of the grain structure. After heating for the required time the material is cooled in air, or in vacuum at a rate equiva- lent to air cooling. • Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range. Notch depth The distance from the surface of a test specimen to the bottom of the notch. In a cylindrical test specimen, the percentage of the original cross-sectional area removed by machining an an- nular groove.27 Heat Treatment Glossary www.soloswiss.com
  28. 28. O Offset The distance along the strain coordinate between the initial portion of a stress-strain curve and a parallel line that intersects the stress-strain curve at a value of stress that is used as a mea- sure of the yield strength. It is used for materials that have no obvious yield point. A value of 0.2% is commonly used. Oil hardening A process of hardening a ferrous alloy of suitable composition (generally alloys) by heating within or above the transformation range and quenching in oil. Overaging • Aging at a higher temperature, and/or for a longer time than required for formation of a coherent precipitate, thus causing loss of coherency in the precipitating phase (coarsen- ing) and loss of strength and hardness. • Aging under conditions of time and temperature greater than those required to obtain max- imum change in a certain property, so that the property is altered in the direction of the initial value. See aging. Overheated A metal is said to have been overheated if, after exposure to an unduly high temperature, it develops an undesirably coarse grain structure but is not permanently damaged. The structure damaged by overheating can be corrected by suitable heat treatment or by mechanical work or by a combination of the two. In this respect it differs from a burnt structure. Overheating Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working or by a combination of working and heat treating, the overheating is known as burning. Oxidation The addition of oxygen to a compound. Exposure to atmosphere sometimes results in oxidation of the exposed surface, hence a staining or discoloration. This effect is increased with tempera- ture increase. P Pack carburizing A carburizing process where Parts are packed in a high carbon medium such as carbon powder 28 Heat Treatment Glossary www.soloswiss.com
  29. 29. or cast iron shavings and heated in a furnace for 12 to 72 hours at 900 ºC (1652 ºF). Carbon monoxide gas (CO) is produced and reacts on the surface of the steel part releasing nascent carbon, which is then diffuses into the surface. Partial annealing An imprecise term used to denote a treatment given cold worked material to reduce the strength to controlled level or to effect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated. Partial pressure The partial pressure of a gas introduced into a vacuum furnace is the force exerted by the gas (or gases) constrained in the vacuum vessel. If only a single gas is present, the partial pressure of the system is the same as the total pressure. In vacuum systems, partial pressure usually refers to the operation of a vacuum furnace at or above 1 torr (1000 microns). The chamber is usually evacuated to a higher vacuum level; commonly between 10-3 torr and 10-5 torr (0.1 to 0.01 microns) then an inert gas is introduced at a controlled rate to a set partial pressure range which is maintained during the heating cycle. Patenting A process of heat treatment applied to medium- or high-carbon steel in wire making prior to the wire drawing or between drafts. It consists in heating to a temperature above the transfor- mation range, followed by cooling to a temperature below that range in air or in a bath of mol- ten lead or salt maintained at a temperature appropriate to the carbon content of the steel and the properties required of the finished product. Pearlite • Microscopic structure of steel which is produced by slow cooling or air cooling low to me- dium carbon and low alloy steels from the austenitic state. • A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range. Phase A homogeneous portion of matter separated from other matter by an interface. Physical properties Properties of a metal or alloy that are relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of ther- mal expansion, magnetic permeability and lattice parameter. Does not include chemical reac- tivity. Compare with mechanical properties. Physical vapor deposition A vaporization coating process, involving transfer of solid material on an atomic level. The coatings are generally used to improve hardness, wear resistance and oxidation and corrosion resistance.29 Heat Treatment Glossary www.soloswiss.com
  30. 30. Pitting Forming small sharp cavities in a metal surface by non-uniform electrode position or by corro- sion. Pit Type Furnace This is a vertical furnace arranged for the loading of parts in a metal basket, when lowered into place, fitting into the furnace chamber in such a way as to provide a dead-air space to prevent direct heating. Precipitation hardening • A prtocess in which the hardness and stressrupture strength can be improved of harden- able high-temperature steels, as well as titanium, nickel and cobalt alloys. The process con- sists of a solution heat treatment followed by aging, during which the constituents of the structure form a solid solution that is frozen during rapid cooling. The hardness increase is caused by the aging cycle. • A process of hardening an alloy in which a constituent precipitates from a supersaturat- ed solid solution. See also aging. • A process of hardening by precipitating an element from a supersaturated solid solution to form coherent transitional precipitates, which produces a strain in the atomic lattice. • Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging. Preheating • Heating before some further thermal or mechanical treatment. For tool steel, heat- ing to an intermediate temperature immediately before final austenitizing. For some nonferrous alloys, heating to a high temperature for a long time, in order to homog- enize the structure before working. In welding and related processes, heating to an inter- mediate temperature for a short time immediately before welding, brazing, soldering, cut- ting or thermal spraying. • Heating to an appropriate temperature immediately prior to austenitizing when hardening high-hardenability constructional steels, many of the tool steels, and heavy sections. Press quenching An oil quench process using a quench press that holds the object under pressure as it is cooled. These are used to quench large gears and other circular or flat parts to prevent distortion and maintain the part integrity. Process annealing An imprecise term used to denote various treatments that improve workability. For the term to be meaningful, the condition of the material and the time-temperature cycle used must be stated.30 Heat Treatment Glossary www.soloswiss.com
  31. 31. Proof stress • The stress that will cause a specified small permanent set in a material. • A specified stress to be applied to a member or structure to indicate its ability to withstand service loads. Q Quench-age embrittlement Embrittlement of low-carbon steel evidenced by a loss of ductility on aging at room tempera- ture following rapid cooling from a temperature below the lower critical temperature. Quench aging Aging induced by rapid cooling after solution heat treatment. Quench annealing Annealing an austenitic ferrous alloy by solution heat treatment followed by rapid quenching. Quench cracking Fracture of a metal during quenching from elevated temperature. Most frequently observed in hardened carbon steel, alloy steel or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners or other stress raisers and result from high stresses due to the volume changes accompanying transformation to martensite. Quench hardening • The objective of this treatment is to produce a fully Martensitic micro-structure in the steel. To achieve this the steel must be cooled rapidly from the austenitic condition. The process is suitable for ferrous metal and alloys in which steel and cast iron alloys are heated above a certain critical temperature and rapidly cooled to produce a hardened structure. Either surface hardening or full-hardening can result, depending on the cooling rate. The process requires close control of temperature during heating and quenching. • A process of hardening a ferrous alloy of suitable composition by heating within or above thiiIe transformation range and cooling at a rate sufficient to increase the hardness substantially. The process usually involves the formation of martensite. • Hardening suitable alpha-beta alloys (most often certain copper or titanium alloys) by solu- tion treating and quenching to develop a martensite-like structure. • In ferrous alloys, hardening by austenitizing and then cooling at a rate such that a substan- tial amount of austenite transforms to martensite.31 Heat Treatment Glossary www.soloswiss.com
  32. 32. Quenching • In the heat treating of metals, the step of cooling metals rapidly in order to obtain desired properties; most commonly accomplished by immersing the metal in oil or water. In the case of most copper base alloys, quenching has no effect other than to hasten cooling. • Rapid cooling. When applicable, the following more specific terms should be used: direct quenching, fog quenching, hot quenching, interrupted quenching, selective quenching, slack quenching, spray quenching, interrupted quenching and time quenching, Quenching and tempering In this operation the procedure consists of heating the material to the proper austenitizing tem- perature, holding at that temperature for a sufficient time to effect the desired change in crys- talline structure, and quenching in a suitable medium - water, oil or air depending on the che- mical composition. After quenching, the material is reheated to a predetermined temperature below the critical range and then cooled under suitable temperatures (tempering). Quench time In resistance welding, the time from the finish of the weld to the beginning of temper. Also called chill time. R Recrystallization • The formation of a new, strain-free grain structure from that existing in cold worked met- al, usually accomplished by heating. • The change from on crystal structure to another, as occurs on heating or cooling through a critical temperature. Recrystallizing anneal A heat treatment process used to transfer heavily distorted, cold worked grains into a uniform equiaxed grain stress-free structure. Recrystallization annealing Annealing cold worked metal to produce a new grain structure without phase change. Recrystallization temperature The approximate minimum temperature at which complete recrystallization of a cold worked metal occurs within a specified time32 Heat Treatment Glossary www.soloswiss.com
  33. 33. Reduction of area • Commonly, the difference, expressed as a percentage of original area, between the original cross-sectional area of a tensile test specimen and the minimum cross sectio- nal area measured after complete separation. • The difference, expressed as a percentage of original area, between original cross-sectio- nal area and that after straining the specimen. Refractory • A material of very high melting point with properties that make it suitable for such uses as furnace linings and kiln construction. • The quality of resisting heat. Refractory alloy A term applied to those alloys which due to hardness or abrasiveness present relative difficulty in maintaining close dimensional tolerances. Refractory metal A metal that has a melting point well above the common alloying bases (i.e. iron, cobalt, and nickel). They include niobium (columbium), tantalum, molybdenum, tungsten, and rhenium. These metals maintain high strength and hardness at elevated temperatures. Residual elements Elements present in an alloy in small quantities, but not added intentionally. Residual stress • Stress present in an alloy in small quantities, but not added intentionally. • Stress present in a body that is free of external forces or thermal gradients. Resilience The tendency of a material to return to its original shape after the removal of a stress that has produced elastic strain.33 Heat Treatment Glossary www.soloswiss.com
  34. 34. Retort furnace This is a vertical type of furnace provided with a cylindrical metal retort into which the parts to be heat-treated are suspended either individually, if large enough, or in a container of some sort. The use of a retort permits special gas atmosphere to be employed for carburizing, nitrid- ing, etc. Rockwell hardness test An indentation hardness test based on the depth of penetration of a specified penetrator into the specimen under certain arbitrarily fixed conditions. Rolling Reducing the cross-sectional area of metal stock, or otherwise shaping metal products, through the use of rotating rolls. Roll Straightening Straightening of metal stock of various shapes by (1) passing it through a series of stag- gered rolls, the rolls usually being in horizontal and vertical planes; or (2) by reeling in two-roll straightening machines. S Salt bath A method of providing thermal processing of steels using a bath of molten salts. The process prevents oxidation and provides a very uniform heating environment for hardening and temper- ing. Sample One or more units of product (or a relatively small quantity of a bulk material) that is with- drawn from a lot or process stream, and that is tested or inspected to provide information about the properties, dimensions or other quality characteristics of the lot or process stream. Not to be confused with specimen. Scaling • Forming a thick layer of oxidation products on metals at high temperature. • Depositing water-insoluble constituents on a metal surface, as in cooling tubes and water boilers. Secondary hardening An increase in hardness following the normal softening that occurs during the tempering of cer- tain alloy steels.34 Heat Treatment Glossary www.soloswiss.com
  35. 35. Selective quenching Quenching only certain portions of a workpiece. Sensitization In austenitic stainless steels, the precipitation of chromium carbides, usually at grain boundar- ies, upon exposure to temperatures of about 550 to 850 °C (100 to 1550 °F), leaving the grain boundaries depleted of chromium and therefore susceptible to preferential attack by a corrod- ing (oxidizing) medium. Shear fracture A ductile fracture in which a crystal (or a polycrystalline mass) has separated by sliding or tear- ing under the action of shear stresses. Shear strength The stress required to produce fracture in the plane of cross section, the conditions of load- ing being such that the directions of force and of resistance are parallel and opposite although their paths are offset a specified minimum amount. The maximum load divided by the original cross-sectional area of a section separated by shear. Sintering • The thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding togeth- er of the particles. • Treatments which strengthen the molecular bonding of powder compacted components. Many productswith complex cross sectional forms are manufactured from powdered, core material, which is pressed or moulded into the component shape. Sintering takes place in an atmosphere controlled environment and is used to strengthen the bonding of powder compacted components over a times, temperature process cycle. • A heating process used to bonds adjacent particles in a “green” compacted powder mass; in order to increase strength and density. High temperature vacuum sintering is performed at elevated temperatures below the melting point of the metal, up to 2650°F, and even higher for refractory metals. Slack quenching The incomplete hardening of steel due to quenching from the austenitizing temperature at a rate slower than the critical cooling rate for the particular steel, resulting in the formation of one or more transformation products in addition to martensite. Snap temper A precautionary interim stress-relieving treatment applied to high hardenability steels immedi- ately after quenching to prevent cracking because of delay in tempering them at the prescribed higher temperature.35 Heat Treatment Glossary www.soloswiss.com
  36. 36. Soaking Prolonged heating of a metal at a selected temperature. Soldering A process designed for joining more than one metal. This is accomplished by the fusion of a filler metal alloy that has a melting point less than about 800°F (425°C). Solid solution A constituent of alloys is formed when atoms of one metal are incorporated into the crystals of another metal as a single phase. Solution heat treatment • A process in which certain alloys, mainly some stainless steels and copper based alloys, are heated to a suitable temperature to allow their constituents to enter into solid solution. The process is then held at the defined temperature for a specified length of time, dependent on the alloy mix, to allow the various components to form a coherent solid but soluble mass before rapid cooling (precipitation). • A treatment in which an alloy is heated to a suitable temperature and held at this tempera- ture for a sufficient length of time to allow a desired constituent to enter into solid solution, followed by rapid cooling to hold the constituent in solution. The material is then in a super- saturated, unstable state, and may subsequently exhibit age hardening. • Heating an alloy to a suitable temperature, holding at that temperature long enough o cause one or more constituents to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution. Solution treating A process of heating an alloy and holding it at a suitable temperature until one or more of the constituents enters a solid solution, at which point the solution is cooled rapidly to hold the al- loy in a supersaturated condition. Specimen A test object, often of standard dimensions or configuration, that is used for destructive or non- destructive testing. One or more specimens may be cut from each unit of a sample. Spheroidite An aggregate of iron or alloy carbides of essentially spherical shape dispersed throughout a ma- trix of ferrite. Spheroidize annealing A heat treating process used to soften metals for ease of stamping and forming. Heating to a set temperature followed by cooling very slowly changes the metallurgical structure such that the end product looks like spheres or balls36 Heat Treatment Glossary www.soloswiss.com
  37. 37. Spheroidizing Heating and cooling in a cycle designed to produce a spheroidal or globular form of carbide in steel. Spheroidizing methods frequently used are: 1. Prolonged holding at a temperature just below Ae1 2. Heating and cooling alternately between temperatures that are just above and below Ae1 3. Heating to a temperature above Ae1 or Ae3 and then cooling very slowly in the furnace or holing at a temperature just below Ae1 4. Cooling at a suitable rate from the minimum temperature at which all carbide is dissolved, to prevent the reformation of a carbide network, and then reheating in accordance with method 1 or 2 above. (Applicable to hypereutectoid steel containing a carbide network.) Spray quenching Quenching in a spray of liquid. Spring temper A steel temper process which results in an increased upper limit of elasticity; obtained by hard- ening and tempering in the usual way followed by reheating until the steel turns blue. Stabilizing treatment • A thermal treatment designed to precipitate material from solid solution, in order to im- prove the workability, to decrease the tendency of certain alloys to age harden at room temperature, or to obtain dimensional stability under service at slightly elevated tempera- tures. • A treatment applied to stabilize the dimensions of a workpiece or the structure of a material such as 1) before finishing to final dimensions, heating a workpiece to or somewhat beyond its operating temperature and then cooling to room temperature a sufficient number of times to ensure stability of dimensions in service; 2 ) transforming retained austenite in those materials that retain substantial amounts when quench hardened (see cold treatment); and 3) heating a solution-treated austenitic stainless steel that contains controlled amounts of titanium or niobium plus tantalum to a temperature be- low the solution heat-treating temperature to cause precipitation of finely divided, uniformly distributed carbides of those elements, thereby substantially reducing the amount of carbon available for the formation of chromium carbides in the grain boundaries on subsequent ex- posure to temperatures in the sensitizing range. • Before finishing to final dimensions, repeatedly heating a ferrous or nonferrous part to or slightly above its normal operating temperature and then cooling to room temperature to ensure dimensional stability in service. (2) Transforming retained austenite in quenched hardenable steels, usually by cold treatment. (3) Heating a solution-treated stabilized grade of austenitic stainless steel to 870 to 900 degrees Celsius (1600 to 1650 F) to pre- cipitate all carbon as TiC, NbC, or TaC so that sensitization is avoided on subsequent ex- posure to elevated temperature.37 Heat Treatment Glossary www.soloswiss.com
  38. 38. Stainless steel • Corrosion resistant steel of a wide variety, but always containing a high percentage of chro- mium. These are highly resistant to corrosion attack by organic acids, weak mineral ac- ids, atmospheric oxidation, etc. • Any of several steels containing 12 to 30% chromium as the principle alloying element; they usually exhibit passivity in aqueous environments. Steel An iron base alloy, malleable in some temperature ranges as initially cast, containing manga- nese, usually carbon, and often other alloying elements. In carbon steel and low-alloy steel, the maximum carbon is about 2.0%; in high-alloy steel, about 2.5%. The dividing line between low-alloy and high-alloy steels is generally regarded as being about 5% metallic alloying ele- ments. Steel is to be differentiated from two general classes of “irons”: the cast irons, on the high car- bon side, and the relatively pure irons such as ingot iron, carbonyl iron, and elecrtrolytic iron, on the low-carbon side. In some steels containing extremely low carbon, the manganese con- tent is the differentiating factor, steel usually containing at least 0.25%; Ingot iron, consider- ably less. Step aging Aging at two or more temperatures, by steps, without cooling to room temperature after each step. Stopping off Applying a physical barrier (copper plate, specialized paints) to selected areas of a part to pre- vent unwanted hardening during carburization, or to prevent adverse reactions between the parts and the furnace supports. Straightening A post-heat treatment process utilized to ensure that elongated parts meet straightness re- quirements. This is typically done with the use of weights. A special case is “tempering plas- ticity”, where distorted thin steel products (i.e. quenched circular saw blades) are clamped flat and tempered. The result is flat saw blades. Strain A measure of the relative change in the size or shape of a body. Linear strain is the change per unit length of a linear dimension. True strain (or natural strain) is the natural logarithm of the ratio of the length at the moment of observation to the original gage length. Conventional strain is the linear strain over the original gage length. Shearing strain (or shear strain) is the change in angle (expressed in radians) between two lines originally at right angles. When the term “strain” is used alone it usually refers to the linear strain in the direction of applied stress. Strain age embrittlement A loss in ductility accompanied by an increase in hardness and strength that occurs with low- carbon steel (especially rimmed or capped steel) is aged following plastic deformation. The 38 Heat Treatment Glossary www.soloswiss.com
  39. 39. degree of embrittlement is a function of aging time and temperature, occurring in a matter of minutes at about 200 degrees Celsius (400 F) but requiring a few hours to a year at room tem- perature. Strain aging Aging induced by cold working. Strain energy • The work done in deforming a body. • The work done in deforming a body within the elastic limit of the material. It is more pro- perly termed elastic strain energy and can be recovered as work rather than heat. Strain rate The time rate of straining for the usual tensile test. Strain as measured directly on the speci- men gage length is used for determining strain rate. Because strain is dimensionless, the units of strain are reciprocal time. Stress Force per unit area, often thought of as force acting through a small area within a plane, called normal stress and shear stress, respectively. True stress denotes the stress where force and area are measured at the same time. Conventional stress, as applied to tension and com- pression tests, is force divided by the original area. Nominal stress is the stress computed by simple elasticity formulas, ignoring stress raisers and disregarding plastic flow; in a notch bend test, for example it is bending moment divided by minimum section modulus. Stress relief Low temperature annealing for removing internal stresses, such as those resulting on a metal from work hardening or quenching. Stress relieving • A process used to remove stresses in welded, rapidly cooled components or cold work products. • A process to reduce internal residual stresses in a metal object by heating the object to a suitable temperature and holding for a proper time at that temperature. This treatment may be applied to relieve stresses induced by casting, quenching, normalizing, machi- ning, cold working or welding. • A uniform heating process followed by slow, uniform cooling; the process reduces stres- ses in fabricated or machined parts, and results in dimensional stability. • Heating to a suitable temperature, holding long enough to reduce residual stresses and then cooling slowly enough to minimize the development of new residual stresses.39 Heat Treatment Glossary www.soloswiss.com
  40. 40. Subcritical annealing • Stress Relief Annealing. A heat treating operation used to relieve or dissipate stresses in weldaments, heavily machined parts, castings and forgings. The parts are heated to 1150” F., uniformly heated through, and are either air cooled from temperature or slow cooled from temperature depending on the type of part and subsequent finishing or heat treat- ing operations. • A heat treatment process typically in the temperature range of 1300 F-1400 F used to pro- duce a softened condition with less microstructural refinement than a full anneal process. Also referred to as a “process anneal” it is used to improve ductility to the material for sub- sequent cold-working/forming operations. • a process anneal performed on ferrous alloys at a temperature below Ac1. Surface hardening A generic term covering several processes applicable to a suitable ferrous alloy that produces, by quench hardening only, a surface layer that is harder or more wear resistant than the core. There is no significant alteration of the chemical composition of the surface layer. The processes commonly used are induction hardening, flame hardening and shell hardening. Use of the appli- cable specific process name is preferred. T Temper • In heat treatment, re-heating hardened steel or hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing the hardness and increasing the toughness. The process also is sometimes applied to normal- ized steel. • In tool steels, temper is sometimes used, but inadvisedly, to denote the carbon content. • In nonferrous alloys (steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties, or reduction in area during cold working. • To moisten sand for casting molds with water. • Tempering is a post-heat treat process used after a hardening process. The secondary heating cycle reduces hardness slightly and increases ductility.40 Heat Treatment Glossary www.soloswiss.com
  41. 41. Temper brittleness Brittleness that results when certain steels are held within, or are cooled slowly through, a certain range of temperatures below the transformation range. The brittleness is revealed by notched-bar impact tests at or below room temperature. The brittleness is manifested as an upward shift in ductile-to-brittle transition temperature, but only rarely produces a low value of reduction area in a smooth-bar tension test of the embrittled material. Temper carbon The free or graphitic carbon that comes out of solution usually in the form of rounded nodules in the structure during graphitizing or malleablizing. Tempering • A treatment used to remove brittleness from mainly quench hardened steels and achieved by thoroughly soaking the material, at an alloy dependent temperature, prior to cooling. Also referred to as the Draw Process. • Reheating hardened, usually quenched, steel to some temperature below the lower criti- cal temperature followed by any desired rate of cooling after the steel has been thoroughly soaked at temperature. Usual tempering temperatures are 300” to 1100” F. • Heating a quench-hardened or normalized ferrous alloy to a temperature below the trans- formation range to produce desired changes in properties. The object of tempering or draw- ing is to reduce the brittleness in hardened steel and to remove the internal strains caused by the sudden cooling in the quenching bath. The tempering process consists in heating the steel by various means to a certain temperature and then cooling it. When steel is in a fully hardened condition, its structure consists largely of martensite. On reheating to a tem- perature of from about 300 to 750°F., a softer and tougher structure known as troostite is formed. If the steel is reheated to a temperature of from 750 to 1290°F, a structure known as a sorbite is formed, which has somewhat less strength than troostite, but much greater ductility. Tensile strength In tensile testing, the ratio of maximum load to the original cross-sectional area. Thermocouple • A device for measuring temperatures made of two dissimilar metal or alloy wires joined at one end and connected to a voltage-measuring instrument at the other end. Common types include J, K, N, R, S, and W (also known as C). • A device for measuring temperatures, consisting of lengths of two dissimilar metals or al- loys that are electrically joined at one end and connected to a voltage-measuring instru- ment at the other end. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions. Time quenching Interrupted quenching in which the duration of holding in the quenching medium is controlled.41 Heat Treatment Glossary www.soloswiss.com

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