6. *
*
Depending on the amount of carbon increased A3 temperature, the
structure (α + P or P or P + Fe3C) at room temperature is waited untill
transform to the structure of austenite.
Time
Temprature
(H.S)
α+P
γ
Martenzit
7.
8. *
Tk
After the cooling, to obtain an
entire martenzit structure and
hardness required cooling
speed is crucial cooling speed.
It is depend on alloy elements
of steel.
9. *
In steel of SAE 4340 continuous cooling and
hardness relationship
12. *
After solidification, which is
hard and brittle martensite
phase steel material, as such,
can not be used. Impact
strength, tempering is done to
enhance the elongation ability.
After ward, raising impact
strength, in addition to
elongation ability hardness,
yield and tensile strength
decreases. The tempering
temperature should be done at
a temprature which an
adequate mechanical
values were obtained from.
15. *
*Appiled to the pieces which should remain soft parts of the
surface
-Surface hardening methods without changing chemical feature of
the surface:
-Flame,
-Surface hardening with induction.
-Cold shaping,
-Radiation,
-Surface hardening with surface covering.
26. *Homogenization Annealing
*Especially in austenitic Mn and steanless steel
it is done to ensure homegeneous distribution of alloying
elements in a piece. For this, austenit heat treatment and
rapid cooling is done. Thus, in a piece distribution of alloying
elements homogenization takes place and again rapid
cooling is done to avoid the heterogeneous distribution of.
27. *Normalizing for: Casting, welding, hot forging, etc
*After all is done to refine the structure coarsening upward.
*The first step of the process; austenitizing,
*The second step of the process; cooling in a suitable speed and air.
pearlite
*Normalizing
28. *Softening Annealing
A1 temprature of rigid and difficult to processing steels requires
approximately 30°C tempering for a long time. During the process
cementite transromes to the small pieces as spherical and so border
area gets reduced.
Microstructure, known as spherical, has net soft and ferritic matris
can be proccessed
60 m
(ferrite)
Fe3C
(cementite)
29. *
*During the cold plastic forming strength of metals and alloys,
increases, elongation values decreases. This situation termed
as strain hardening.Due to hardening the cold-forming ability
decreases. By making recrystallization heat treatment cold-
forming ability is increased. The temprature of
recrystalization is ½-1/3 of melting temperature of the alloy.
But, this temprature is not constant, and depend on cold
shaping rate, analysis of steel, time and initial piece
dimension.
31. The effect of annealing temperature on the microstructure
of cold worked metals:
(a) Cold treated
(b) After recovery,
(c) After recrystallization
(d) After grain growth
33. The surface hardening by changing the
chemical structure of surface
1- Hardening with boron
2- Hardening with carbon
3- Hardening with nitrogen
4- Hardening with carbon and
nitrogen
sub-surface
surface
Hardening
region
Example:
carburization
34. *carburization is a heat treatment process in which iron or steel
absorbs carbon while the metal is heated in the presence of a carbon-
bearing material, such as charcoal or carbon monoxide. The intent is to
make the metal harder. Depending on the amount of time and
temperature, the affected area can vary in carbon content. Longer
carburizing times and higher temperatures typically increase the depth
of carbon diffusion. When the iron or steel is cooled rapidly by
quenching, the higher carbon content on the outer surface becomes
hard due to the transformation from austenite to martensite, while the
core remains soft and tough as a ferritic and/or pearlite
microstructure.[2]
*This manufacturing process can be characterized by the following key
points: It is applied to low-carbon workpieces; workpieces are in
contact with a high-carbon gas, liquid or solid; it produces a hard
workpiece surface; workpiece cores largely retain their toughness and
ductility; and it produces case hardness depths of up to 0.25 inches
(6.4 mm). In some cases it serves as a remedy for undesired
decarburization that happened earlier in a manufacturing process.
*
36. *
*Hardening agents
*There are different types of elements or materials that can
be used to perform this process, but these mainly consist of
high carbon content material. A few typical hardening agents
include carbon monoxide gas (CO), sodium cyanide and
barium carbonate, or hardwood charcoal. In gas carburizing,
the CO is given off by propane or natural gas. In liquid
carburizing, the CO is derived from a molten salt composed
mainly of sodium cyanide (NaCN) and barium chloride (BaCl2).
In pack carburizing, carbon monoxide is given off by coke or
hardwood charcoal.
38. *
In general, gas carburizing is used for parts that are
large. Liquid carburizing is used for small and
medium parts and pack carburizing can be used for
large parts and individual processing of small parts
in bulk. Vacuum carburizing (low pressure
carburizing or LPC) can be applied across a large
spectrum of parts when used in conjunction with
either oil or high pressure gas quenching (HPGQ),
depending on the alloying elements within the base
material.
39. *
*Nitriding is a heat treating process that diffuses nitrogen into the surface
of a metal to create a case-hardened surface. These processes are most
commonly used on low-carbon, low-alloy steels. They are also used on
medium and high-carbon steels, titanium, aluminium and molybdenum. In
2015, nitriding was used to generate unique duplex microstructure
(Martensite-Austenite, Austenite-ferrite), known to be associated with
strongly enhanced mechanical properties [1]
*Typical applications include gears, crankshafts, camshafts, cam followers,
valve parts, extruder screws, die-casting tools, forging dies, extrusion dies,
firearm components, injectors and plastic-mold tools.
41. *The processes are named after the medium used to donate.
The three main methods used are: gas nitriding, salt bath
nitriding, and plasma nitriding.
*Gas nitriding
*In gas nitriding the donor is a nitrogen rich gas, usually ammonia (NH3), which is
why it is sometimes known as ammonia nitriding.[2] When ammonia comes into
contact with the heated work piece it dissociates into nitrogen and hydrogen.
The nitrogen then diffuses onto the surface of the material creating a nitride
layer. This process has existed for nearly a century, though only in the last few
decades has there been a concentrated effort to investigate the
thermodynamics and kinetics involved. Recent developments have led to a
process that can be accurately controlled. The thickness and phase constitution
of the resulting nitriding layers can be selected and the process optimized for
the particular properties required.
42. The advantages of gas nitriding over the other variants are:
*Precise control of chemical potential of nitrogen in the nitriding
atmosphere by controlling gas flow rate of nitrogen and oxygen.
*All round nitriding effect (can be a disadvantage in some cases,
compared with plasma nitriding)
*Large batch sizes possible - the limiting factor being furnace size and
gas flow
*With modern computer control of the atmosphere the nitriding results
can be closely controlled
*Relatively low equipment cost - especially compared with plasma
43.
44. *Salt bath nitriding
*In salt bath nitriding the nitrogen donating medium is a nitrogen-containing
salt such as cyanide salt. The salts used also donate carbon to the workpiece
surface making salt bath a nitrocarburizing process. The temperature used is
typical of all nitrocarburizing processes: 550–570 °C. The advantages of salt
nitriding is that it achieves higher diffusion in the same period of time
compared to any other method.
*The advantages of salt nitriding are:
*Quick processing time - usually in the order of 4 hours or so to achieve
*Simple operation - heat the salt and workpieces to temperature and submerge
until the duration has transpired.
*The disadvantages are:
*The salts used are highly toxic - Disposal of salts are controlled by stringent
environmental laws in western countries and has increased the costs involved
in using salt baths. This is one of the most significant reasons the process has
fallen out of favor in recent decades.
*Only one process possible with a particular salt type - since the nitrogen
potential is set by the salt, only one type of process is possible
45. *Plasma nitriding
*Plasma nitriding, also known as ion nitriding, plasma ion nitriding or
glow-discharge nitriding, is an industrial surface hardening treatment
for metallic materials.
*In plasma nitriding, the reactivity of the nitriding media is not due to
the temperature but to the gas ionized state. In this technique intense
electric fields are used to generate ionized molecules of the gas around
the surface to be nitrided. Such highly active gas with ionized
molecules is called plasma, naming the technique. The gas used for
plasma nitriding is usually pure nitrogen, since no spontaneous
decomposition is needed (as is the case of gas nitriding with ammonia).
There are hot plasmas typified by plasma jets used for metal cutting,
welding, cladding or spraying. There are also cold plasmas, usually
generated inside vacuum chambers, at low pressure regimes.
Usually steels are beneficially treated with plasma nitriding.
This process permits the close control of the nitrided
microstructure, allowing nitriding with or without compound
layer formation. Not only is the performance of metal parts
enhanced, but working lifespans also increase, and so do the
strain limit and the fatigue strength of the metals being
treated. For instance, mechanical properties of austenitic
stainless steel like resistance to wear can be significantly
augmented and the surface hardness of tool steels can be
doubled.
47. *Thermomechanical processing, is a metallurgical process
that combines mechanical or plastic deformation process like
compression or forging, rolling etc. with thermal processes
like heat-treatment, water quenching, heating and cooling at
various rates into a single process.
48. *
*The quenching process produces a high strength bar from inexpensive
low carbon steel. The process quenches the surface layer of the bar,
which pressurizes and deforms the crystal structure of intermediate
layers, and simultaneously begins to temper the quenched layers using
the to heat from the bar's core.
*Steel billets 130mm² ("pencil ingots") are heated to approximately
1200°C to 1250°C in a reheat furnace. Then, they are progressively
rolled to reduce the billets to the final size and shape of reinforcing
bar. After the last rolling stand, the billet moves through a quench box.
The quenching converts the billet's surface layer to martensite, and
causes it to shrink. The shrinkage pressurizes the core, helping to form
the correct crystal structures. The core remains hot, and austenitic. A
microprocessor controls the water flow to the quench box, to manage
the temperature difference through the cross-section of the bars. The
correct temperature difference assures that all processes occur, and
bars have the necessary mechanical properties.
49.
50. *High temperature TMT
Heating 70-100°C above Ac3
Cooling to T deform. (800-900°C)
Deformation about 30-50%
Martenzite cooling
Low tempering (200-300 °C)
Rm= 1800-2200 MPa
A = 8-12%
K1c = 50-90 J/cm2
• Low temperature TMT
• 50NiCrMn16
Heating 70-100°C above Ac3
Cooling to T deform. (450°C) below TR
Deformation about 30-50%
Martenzite cooling
Low tempering (200-300 °C)
Rm= 2700 MPa
A = 10%
K1c = 0,4 MJ/cm2
*
61. *
Historically, katana (刀 or かたな)
were one of the traditionally made
Japanese swords (日本刀 nihontō) that
were used by the samurai of ancient
and feudal Japan.
The katana is characterized by its
distinctive appearance: a curved,
single-edged blade with a circular or
squared guard and long grip to
accommodate two hands.
62. *The Katana, also known as "samurái sword", is the quintessential
Japanese sword and is defined as a curved single-edged sword. The
Katana has been considered the most perfect and effective hand held
weapon that man has developed throughout history.
Katanas combines three elements.
Their artistic beauty as a piece of craftsmanship. The strength that
allows you to split a body in two just by removing the sheath. And the
accuracy, that allows you to split a single human hair.
The manufacturing process of the Katana is
long, complex and marked by a strong
symbolic component. The craftsmen were
alchemists who thanks to their experience
were able to learn the secrets of metal,
passing them down from generation to
generation. The swordsmith would say a
prayer to Buddah before beginning to make
every sword, which shows the spirituality
that surrounded the whole forging process.
63.
64. * The manufacturing can be divided into four fundemental phases:
* 1ª Casting: The steel of the Katana comes from a very fine iron sand. To achieve the distinctive
steel it is necessary to remove the oxygen and make carbon. This is accomplished by melting
the steel at low temperature in a furnace called "Tatara".
* 2ª Folding:This is a process that is done by hand and requires great precision by the craftsman.
It consists in heating the material, hammering it and then cooling it in water to make it thinner
and elongated. When it has reached twice its length, the metal is bent upon itself to form
exactly the same original block, but with two layers of steel together. This operation is
performed at least twelve times. The length achieved is similar to that of the original block but
the number of layers can be anywhere up to 5000 for every centimetre of steel. This process
seeks to mix the iron and the steel so that the block is equal throughout it's entire structure
and to eliminate, at the same time, it's impurities. Thus achieveing a very low carbon content
(less than 0.7%) which gives flexibility to the sword.
* 3ª Differential Tempering: This process seeks to harden the blade of the sword and in turn
maintain the flexibility of the spine. In order to achieve this flexibility, at the time of
hardening the weapon a thick layer of a mixture of clay, sand and ash is laid over the spine;
whereas on the blade, the mixture is of coal dust and the layer spread is much thinner. After
the heating and cooling process, you get a hard temper on the blade and softer edge to the
spine,and thus the curve of the sword develops naturally .
*
4ª Polishing: Sharpening the sword to give it it's final form. The end result provides a process
characterized by the Katana, combining iron and carbon, and gives the sword it's hardness and
flexibility which is difficult to match.
