This document discusses heat treatment processes for metals. It covers various heat treatment methods like annealing, normalizing, hardening and tempering. It describes processes like case hardening, through hardening, induction hardening and vacuum heat treatment. Key information covered includes different heat treatment methods for ferrous and non-ferrous metals, advantages of various processes, factors influencing heat treatment selection, and details of specific processes like carburizing and quenching methods.

1. HEAT TREATMENT
MANUFATURING PROCESS

2. METALS:
FERROUS NON FERROUS
STEEL IRON
LOW ALLOY HIGH ALLOY CAST
STEEL
CAST IRON MALLEABLE
IRON
Copper, Lead, Zinc, Tin,
Nickel, Aluminium
Structural Steel ( Low) Tool Steel
Grey Cast
Iron
White heart
malleable Iron
Copper Alloys, Zinc alloys,
Aluminium alloys
Carbon Steel (Medium) Alloy Tool
Steel Alloy Cast
Iron
Black heart
Malleable Iron
Solders
Alloy Steel(High) Stainless
Steel
ADVANTAGES DIS ADVANTAGES
 Low cost
 High Strength
 Relatively High Toughness
 Weldable
 Heavy(High Density)
 Poor Corrosion Resistance
STEELS:

3. PROPERTIES OF MATERIALS :
MECHANICAL PHYSICAL TECNOLOGICAL
Tensile Strength Wear Resistance Machinability
Bending Strength Hardenability Weldability
Shear Strength Thermal Conductivity Castability
Impact Strength Specific gravity Formability
Compressive Strength Coefficient of friction Malleability
Bearing Strength Coefficient of Thermal expansion
Torsion Strength Rust and corrosion inhibition
Damping Property

4. WHY HEAT TREATMENT:
 To relieve the INTERNAL STRESS due to manufacturing process such as Welding, Casting , Forming etc.,
 To HOMOGENIZE the structure which is dislocated due to Cold Forming & Semi Hot and Hot Forgings,
 To aid MACHINABILITY,
 To eliminate the non conformities present in Micro Structure such as BANDING,
 To facilitate COLD FORMING,
 To improve the MECHANICAL PROPERTIES,
 To impart WEAR RESISTANCE,
 To increase the STRENGTH,
 To improve the TOUGHNESS
 To impart ANTI SCUFFING and ANTI SEIZURE Properties,
 To improve the PERFORMANCE LEVEL AT ELEVATED TEMPERATURE OF OPERATION.

5.  Stress Relieving
 Annealing
 Full annealing
 Process Annealing
 Spheroidize Annealing
 ISO Thermal Annealing
 Normalizing
 Hardening & Tempering
 Martempering
 Austempering
 Case Hardening
 Carburising
 Carbo Nitriding
 Induction Hardening
 Gas Nitriding
 Liquid Nitriding
 Gas Nitrocarburising
 Special process like Low
pressure Carburising
 Plasma Nitriding
HEAT TREATMENT PROCESS:

6. CASE HARDENING / SURFACE HARDENING :
(Carburizing, Hardening and Tempering)
Case-hardening or surface hardening is the process of hardening the surface of a metal object while
allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal (called the
"case") at the surface. (Mainly increasing the carbon from < 0.2% to 0.7% ~ 1 % of the surface )
THROUGH HARDENING :
Through hardening is the process of using a rapid quench to increase hardness throughout a steel alloy
for the purpose of increasing its strength. As opposed to case hardening, which gives steel a hard outer
layer while preserving a softer, more ductile core, through hardening diffuses carbon throughout the entire
section of steel.
Through hardening typically consists of three steps: the heating of an alloy to alter its physical
properties, a rapid quench in a medium, such as oil, salt or caustic, and a reheating, or tempering, to
eliminate excess brittleness from the treated alloy.

10. ISO THERMAL ANNEALING:
PURPOSE:
 Used for low carbon alloy steels which are HOT FORGED
OBJECT:
 To Improve Machinability
 To Eliminate Banding
 To Achieve uniform Micro Structure,
 Which gives DIMENSIONAL STABILITY during critical machining
 Also IMPROVES THE LIFE of GEAR HOBBING / BROACHING Tools

14. MAR TEMPERING:
OBJECT: To minimise Distortion, to eliminate Crack during quenching, and to maintain high degree of
Dimensional accuracy.
PROCESS:
 Heat the components to the Hardening Temperature and Soak for the required time
 Quench in Molten Salt bath or Hot oil maintained at 10°C above or below the Martensite starting point
 Adequately soak to get temperature uniformity
 Take out and cool in Air
APPLICATIONS:
 Tools of Intricate design and non uniform cross section like High speed Steel Cutters
 Die steels, High alloy Tools and Dies
 Case hardening of Gears, Shafts, Spline shafts, Cams made out of low alloy steels.

15. CARBURISING METHOD:
 Salt bath Technology or Liquid
Carburising
 Gas Carburising,
 Vaccum or Low Pressure
Carburising.

16. LIQUID CARBURISING:
 This process is mostly used for producing shallow case depths in thin sections.
 The components are heated in a bath containing a suitable mix of SODIUM CYANIDE SALTS and SODIUM CARBONATE.
 The normal case depth for this process are around 0.25 to 0.50mm with bath strengths of 20% to 30% NaCN.
High bath strengths of 40 % to 50 % NaCN are required for case depth of 0.50mm and above.
 The case resulting from this process includes CARBON and NITROGEN. Which makes this process ideal for low carbon
sheet metal pressed and Machined components.
 This process normally works with bath temperature of 800°C to 930°C for immersion time from 2 to 7 hrs depending on
the depth required.
 However the DISPOSAL PROBLEMS in eliminating the SOLID WASTE & WASTE WATER have made this process
not environmental friendly and becoming obsolete.

17. GAS CARBURISING:
 Gas carburising is very popular and widely used for case depth varying from 0.20 mm to 3.0 mm.
 Possible to achieve very narrow bands of case depth requirements.
 GOOD REPEATABILITY of end result possible.
 Different Furnaces and atmospheres are used to suit the end requirements of the Product and Cost
CARBURISING APPLICATIONS:
APPLICATIONS CASE DEPTH
 High wear resistance, Low to Moderate loading Up to 0.50 mm
 Small and delicate parts subject to wear
 High wear resistance, Moderate to Heavy loading. 0.50mm to 1.0 mm
 Light Industrial Gearing
 High wear resistance, Heavy loading, Crushing loads or 1.0 mm to 1.50 mm
High magnitude alternate bending stress
 Heavy duty Industrial Gearing
 High wear resistance, Shock resistance, High crushing loads, 1.50 mm to 6.25 mm
Bearing surfaces, Mill gearing , Rollers.

18. CARBONITRIDING:
ADVANTAGES:
 Addition of NITROGEN into the SURFACE INCREASES THE HARDENABILITY OF CASE and hence Low Carbon
Sheet Metal and Machined Components respond well to CARBONITRIDING even with OIL as QUENCHING medium.
 This process is good alternate to SALT BATH CYANIDE HARDENING of Low Carbon materials.
 NITROGEN lowers the Austenite temperature by 50°C , allowing process to be done at lower temperature for the
same case depth REDUCING the DISTORTION
 Carbonitriding layer has Temper resistant and can be Tempered at higher temperatures for the same hardness of
Carburised layer by reducing brittleness.
CARBONITRIDED PARTS

19. TYPES OF QUENCHING MEDIA:
 Water Quenching
 Oil Quenching
 Hot Oil Quenching
 Polymer Quenching
 Salt Quenching
 Gas Quenching
POLYMER QUENCHING:
 Polymer Quenchants are Water base Organic chemicals known as POLY ALKALINE GLYCOLS
 It dissolves in water at room temperature
 Cooling rate of Polymer quenchant depends on the percentage of Glycol in water
 Higher the concentration, lower the rate of cooling
 By varying the concentration, the required quenching characteristics can be achieved to suit the
specific requirements
 Recommended room temperature is 35°C to 50°C
 Eliminates washing before tempering as it does not adhere to the surface and generate smoke on
heating

22. FIXTURING METHOD IN PIT TYPE FURNACES:

24. INDUCTION HARDENING:
 The basic components of an Induction Heating system are an AC POWER supply, INDUCTION COIL, and WORK
PIECE( Part to be heat treated)
 The Power supply sends an Alternative current through the coil, Generating Magnetic field in the work piece,
which is placed in the coil
 The magnetic field induces EDDY CURRENTS in the work piece, generating precise amount of Clean Localised heat
without any physical contact between Coil and work piece
 After Heating, the work piece is QUENCHED by PASSING WATER or POLYMER JET as coil withdraws from the
stationary /rotating work piece
APPLICATION:
 Medium Carbon and Alloy Steels
 Core remains undisturbed
 Selective Heat treatment possible
 Economical
 Some cases unique
ADVANTAGES:
 Low distortion and Low risk of scaling (These two advantages may allow final Mc/g
before hardening
 Localised hardening and Good reproducibility of the HT process
 Easy integration in production line and Fully automatic process easily attainable
 Easy to operate and Less harmful, compared to other hardening process
 Use of non alloyed steels

26. VACUUM HEAT TREATMENT:
 In protective atmosphere the induced gases replace the air in the furnace and reduces the concentration of Oxygen
and Moisture. Best way to do this could be to eliminate the air itself , thereby eliminating the Oxygen and Moisture,
which are the real culprits
 In physics, it is called Vacuum, absence of everything, so absence of Air and Moisture
 In vacuum, a partial order of vacuum level is achieved and maintained, which ensures integrity and consistency of the
process
 Vacuum is reduction of atmospheric pressure of 1 bar/760 tar to the order of 10¯2 - 10¯3
VACUUM PROCESS SEQUENCE:
 Charge arranged in Fixture and loaded in the furnace in Cold condition
 Furnace is cold evacuated to 10¯2tar
 Heating is initiated in Vacuum condition
 Once the Soak is over, Heating and evacuation are stopped
 The Inert gas at certain pressure is made to enter the furnace and the quenching process starts
 Once the quenching time is over, the flow of Gases stopped & the furnace is allowed cool down below 70° and the
charge is removed

27. ANY QUERY
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