A

Summer Intern Project Report

On

HEAT TREATMENT

at

Submitted by

NEERAJ VIJAYVARGIYA ID No: 2010UMT258

of

BACHELOR OF TECHNOLOGY

in

METALLURGICAL & MATERIALS ENGINEERING

Malaviya National Institute of Technology

Jaipur

July, 2013

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ACKNOWLEDGEMENTS

First and Foremost, I would like to thank Vardhman Special Steels Limited for giving me an

opportunity to accomplish my Project. Working here has been a great learning experience.

I take this opportunity to express a deep sense of gratitude to Mr. Mal Singh Rathore, for

assigning to me an interesting project and for his helpful guidance, criticism, encouragement

throughout the every stage of this study.

I would also like to express my profound gratitude to Mr. B. D. Chawla (VP Tech.), Mr. Rishu,

Mr. Vikram Mahajan, Mr. Pawan Kishore, Mr. Tilak Raj and Miss. Amrit Jallawalia for their

cordial support, valuable information and guidance throughout the course of this project.

I am obliged to all members of the Metallurgical Services Department of VSSL for the valuable

information provided by them in their respective fields. I am grateful for their cooperation during

the period of my project.

Finally, I wish to express my gratitude to my family for their complimentary love and unshakable

faith in me during my life.

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ABSTRACT

This document describes the various heat treatment processes which are being done or to be done

in future at Vardhman Special Steels Limited. Study of various spherodising cycles which are

being used at VSSL is analyzed and study is done to reduce the cycle time for the same.

Effect of the alloying elements on hardness(before and after spherodisation) is studied from the

data of 5 months and conclusion was made to reduce the percentage of alloying element keeping

the aim and standard chemistry in mind to reduce the cycle time.

Full annealing and normalizing are also discussed in this report along with the problem of ferrite

banding. Reduction in banding to a great extent due to application of magnetic field is also studied

and conclusions were made.

Apart from this, futuristic projects of VSSL like quenching and tempering are also discussed in

short.

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TABLE OF CONTENTS

ACKNOWLEDGEMENT……………………………………....………….....…...2

ABSTRACT……………………………………………………………………......3

TABLE OF CONTENTS…………………………………………………………..4

1. INTRODUCTION

1.1 Introduction to heat treatment…………………………………………………..5

1.2 Vardhman Special Steels Limited………………………………………………6

2. PURPOSE OF HEAT TREATMENT……………………………………………7

3. TYPES OF HEAT TREATMENT ……………………………………………….9

3.1 Normalising………………………………………………………………………9

3.2 Full Annealing…………………………………………………………………..13

3.3Problem of ferrite banding in full annealing…………………………………….15

a.) Cause…………………………………………………………………………….15

b.) Remedies………………………………………………………………………...16

C.) Conclusion………………………………………………………………………17

3.4 Process annealing………………………………………………………………..17

3.5 Stress relief annealing…………………………………………………………...18

3.6 Spheroidizing……………………………………………………………………..18

a) Various methods of spheroidizing………………………………………………….19

b) Some of the cycles which are being used at VSSL……………………………….22

c) Conclusions based upon the study of spherodisation from Jan’13 to May’13 at VSSL..24

3.7Quenchig…………………………………………………………………………..25

a) Types of quenching………………………………………………………………...26

3.8 Tempering and various stages of tempering……………………………………...27.

4. REFERENCES…………………………………………………………………….29

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INTRODUCTION

1.1Introduction to heat treatment

A STEEL is usually defined as an alloy of iron and carbon with the carbon content between a few

hundreds of a percent up to about 2 wt%. Other alloying elements can amount in total to about 5

wt% in low-alloy steels and higher in more highly alloyed steels such as tool steels and stainless

steels. Steels can exhibit a wide variety of properties depending on composition as well as the

phases and microconstituents present, which in turn depend on the heat treatment.

Heat treatment is an operation or combination of operations involving heating at a specific rate,

soaking at a temperature for a period of time and cooling at some specified rate. The aim is to

obtain a desired microstructure to achieve certain predetermined properties.

Steels can be heat treated to produce a great variety of microstructures and properties. Generally,

heat treatment uses phase transformation during heating and cooling to change a microstructure in

a solid state.

Heat Treatment is often associated with increasing the strength of material, but it can also be used

to alter certain manufacturability objectives such as improve machining, improve formability, and

restore ductility after a cold working operation. Thus it is a very enabling manufacturing process

that can not only help other manufacturing process, but can also improve product performance by

increasing strength or other desirable characteristics.

Figure: Various heat treatment processes

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1.5 Vardhman Special Steels limited

Vardhman Special Steels limited is a part of the Vardhman Group of Companies, over 24

manufacturing facilities in five states across India. The Group business portfolio includes Yarn,

Grieve & processed Fabric, Garments, Sewing Thread, Acrylic Fiber and Alloy Steel. It is the

largest producer and exporter of Yarns and Grey woven Fabrics from India. Vardhman is also the

largest producer of Tyercord yarns and the second largest producer of sewing Threads in India.

Vardhman Special Steels limited is one of the secondary steel making companies that produces

Special and Alloy steel long products that find end use in the Automotive, Tractor and other

Engineering sectors. The company is an approved source of steel for several Original Equipment

Manufacturers. Vardhman Special Steels comprises a Steel Melt shop having a 30 ton UHP

Electric arc furnace with EBT, Ladle Refining Furnace, and Vacuum Degassing unit. Company

has a three strand Continuous Casting Machine, a rolling mill and a Bright Bar Unit facility.

It was Vardhman Group's faith in the economy of the country, specifically in core industrial sector

that initiated the Group's venture into the steel industry. The story of Vardhman Special Steels

began way back in the year 1972 with the commissioning of Oswal Steels at Faridabad to

manufacture Special & Alloy Steels; with an initial capacity of 50,000 Metric tonnes per

annum.1986 was the turning point in the history of Vardhman Special Steels. The Company

acquired another plant at Ludhiana, which was later upgraded with the latest state-of-the-art

technology to an installed capacity of 1, 00,000 Metric tonnes per annum.

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2. PURPOSE OF HEAT TREATMENT

Various types of heat treatment processes are used to change the following properties or

conditions of the steel:

Improve the toughness

Increase the hardness

Increase the ductility

Improve the machinability

Refine the grain structure

Remove the residual stresses

Improve the wear resistance

The following are the general reasons for heat treatment:

Hardening (Steels can be heat treated to high hardness and strength levels. The reasons for doing

this are obvious. Structural components subjected to high operating stress need the high strength

of a hardened structure. Similarly, tools such as dies, knives, cutting devices, and forming devices

need a hardened structure to resist wear and deformation.)

Tempering (As-quenched hardened steels are so brittle that even slight impacts may cause

fracture. Tempering is a heat treatment that reduces the brittleness of a steel without significantly

lowering its hardness and strength. All hardened steels must be tempered before use.)

Softening a Hardened Structure (Hardening is reversible. If a hardened tool needs to be

remachined, it may be softened by heat treatment to return it to its machinable condition. Most

steels weld better in their soft state than in their hardened state; softening may be used to aid

weldability.)

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Recrystallization (If a metal is cold worked, grains or crystals deform, become elongated, and in

doing so harden and strengthen a metal. There is a limiting amount of cold work that a particular

metal can be subjected to. In rolling of steel into thin sheets, you can only reduce the cross-

sectional area so much before it gets too hard to roll. At this point it would be desirable to return

the grains to their original shape. Heat treatment can accomplish this. The transformation of cold-

worked grains to an undistorted shape is called recrystallization. Very large coarse grains can also

be refined by recrystallization.This type of heat treatment is essential if a steel is to be subjected to

severe cold working in rolling, drawing, etc.)

Stress Relief (One of the most frequent reasons for heat treatment is to remove internal stress

from a metal that has been subjected to cold working or welding. Stress relieving is a heat

treatment used to remove internal strains without significantly lowering the strength. It is used

where close dimensional control is needed on weldments, forgings, castings, etc.)

Hot-Working Operations (Most metal shapes produced by steel mills are at least rough shaped at

elevated temperatures. Heat treating is required to bring the rough metal shapes to the proper

temperature for hot-forming operations.Forging, hot rolling, roll welding, and the like are all

performed at temperatures of sufficient magnitude as to prevent the formation of distorted grains

that will harden the metals. Hot-working operations require dynamic recrystallization which is

achieved by working at the proper hot-work temperatures.)

Diffusion of Alloying Elements (One of the criteria for hardening a steel is that it have sufficient

carbon content. Low carbon steels can be hardened, at least on the surface, by heat treating at an

elevated temperature in an atmosphere containing an alloying element that will diffuse into the

steel and allow surface hardening on quenching. Carbon is frequently diffused into the surface of

soft steels for surface hardening. Using this same principle, elements such as chromium, boron,

nitrogen, and silicon can be diffused in the surface of a steel for special purposes.)

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3.TYPES OF HEAT TREATMENT

Common heat treatment processes:

Normalizing

Spheroidising

Full annealing

Process annealing

Stress relieving

Direct Hardening

Tempering

Austempering

Martempering

Diffusion Hardening

Selective hardening

3.1 NORMALIZING

NORMALIZING OF STEEL is a heat-treating process that is often considered from both thermal

and microstructural standpoints. In the thermal sense, normalizing is an austenitizing heating cycle

followed by cooling in still or slightly agitated air. Typically, the work is heated to a temperature

about 55 °C (100 °F) above the upper critical line of the iron-iron carbide phase diagram, that is,

above Ac3 for hypoeutectoid steels and above Acm for hypereutectoid steels. To be properly

classed as a normalizing treatment, the heating portion of the process must produce a

homogeneous austenitic phase (face-centered cubic, or fcc, crystal structure) prior to cooling.

Figure : Normalizing temperatures for hypoeutectoid and hypereutectoid steels.

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The following is the list of the reasons for normalizing the steel :

To produce a harder and stronger steel than full annealing

To improve the machinability

To modify and refine the grain structure

To obtain a relatively good ductility without reducing the hardness and strength

Figures a, b, c and d show the effect of annealing and normalizing on the ductility, tensile

strength, hardness and yield point of steels.

Figure a: Ductility of annealed and normalized steels.

As indicated in Figure (a), annealing and normalizing do not present a significant difference on the

ductility of low carbon steels. As the carbon content increases, annealing maintains the %

elongation around 20%. On the other hand, the ductility of the normalized high carbon steels drop

to 1 to 2 % level.

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Figure b : Tensile strength of normalized and annealed steels.

Figure c: yield point of annealed and normalized steels

Figures (b) and (c) show that the tensile strength and the yield point of the normalized steels are

higher than the annealed steels. Normalizing and annealing do not show a significant difference on

the tensile strength and yield point of the low carbon steels. However, normalized high carbon

steels present much higher tensile strength and yield point than those that are annealed.

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Figure d: Hardness of normalized and annealed steels.

As seen from Figure (d), low and medium carbon steels can maintain similar hardness levels when

normalized or annealed. However, when high carbon steels are normalized they maintain higher

levels of hardness than those that are annealed.

3.2 Full Annealing

A common annealing practice is to heat hypoeutectoid steels above the upper critical temperature

(A3) to attain full austenitization. The process is called full annealing. In hypoeutectoid steels

(under 0.77% C), supercritical annealing (that is, above the A3 temperature) takes place in the

austenite region (the steel is fully austenitic at the annealing temperature).

However, in hypereutectoid steels (above 0.77% C), the annealing takes place above the A1

temperature, which is the dual-phase austenite-cementite region. In general, an annealing

temperature 50 °C (90 °F) above the A3 for hypoeutectic steels and A1 for hypereutectoid steels is

adequate.

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Figure: Full annealing range

Full annealing process consists of three steps. First step is heating the steel component to above A3

(upper critical temperature for ferrite) temperature for hypoeutectoid steels and above A1 (lower critical

temperature) temperature for hypereutectoid steels by 30-500

C .

The second step is holding the steel component at this temperature for a definite holding (soaking)

period of at least 20 minutes per cm of the thick section to assure equalization of temperature

throughout the cross-section of the component and complete austenization. Final step is to cool the

hot steel component to room temperature slowly in the furnace, which is also called as furnace

cooling. The full annealing is used to relieve the internal stresses induced due to cold working,

welding, etc, to reduce hardness and increase ductility, to refine the grain structure, to make the

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material homogenous in respect of chemical composition, to increase uniformity of phase

distribution, and to increase machinability.

3.3 Problem of ferrite banding in full annealing:

Ferrite banding: Parallel bands of free ferrite aligned in the direction or working. Sometimes

referred to as ferrite streaks.

Figure: Pearlite and ferrite band in a medium carbon steel

This is a medium carbon steel, consisting of ferrite and pearlite (a lamellar mixture of ferrite and

cementite). It is banded (dark bands = pearlite; light bands = ferrite) an undesirable condition.

As the piece cooled below the all-austenite region within which the hot rolling had been

performed, ferrite was first precipitated at the austenite grain boundaries, thereby causing carbon

to be rejected into the remaining austenite. Once the piece cooled below the eutectoid temperature

(727C) the 0.8% carbon austenite transformed discontinuously via coupled growth of ferrite and

cementite in a lamellar (layered) morphology called pearlite because of its appearance to the

unaided eye after etching.

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a) Cause:

The banding is the result of microsegregagtion of manganese during solidification of the original

sample. Slow cooling in annealing makes ferrite formation preferentially in the manganese

depleted regions, i.e., produces bands of ferrite where Mg is low, and bands of pearlite where Mg

is high.

As this piece cooled from the all-austenite region, alpha ferrite was precipitated - more so, the less

the local manganese content. Therefore, the last areas to transform were richer in both manganese

and carbon, so those regions are now mostly pearlite.

b) Remedies:

1.) Banding can be eliminated by prolonged heating and/or extensive hot working to homogenize

the metal with respect to the manganese, or it can be circumvented by short time, high temperature

austenitization, which levels out the local carbon content but not the manganese variations.

2.)Magnetic annealing can be done in which magnetic field is applied parallel to hot rolling

direction of rods.A magnetic field of 14T was applied in the experiment** .

A cooling rate of

46oC/Min can be achieved for full annealing.

Figure : Microstructure of 42CrMo steel after being austenitized at 860oC for 30 min and cooled naturally at about

1oC/min (the hot-rolling direction is horizontal in the micrograph). Bright areas -ferrite grains; dark areas - pearlite

colonies.

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Figure : Microstructure of 42CrMo steel after being austenitized at 880 oC for 33 min and cooled at 46

o_C/min, with

magnetic field of 14 T (the magnetic-field direction is horizontal in the micrograph). Bright areas=ferrite grains; dark

areas=pearlite colonies.

c) Conclusions:

1.) Banding resulted from hot processing can be eliminated upto a very good extent by this

method as seen in the figure.

2.)A very high cooling rate of 46oC/Min can be obtained with desirable microstructure while we

are having cooling rate of 1oC/Min at VSSL.

3.4 Process Annealing

Process annealing is used to treat work-hardened parts made out of low-Carbon steels (< 0.25%

Carbon). This allows the parts to be soft enough to undergo further cold working without

fracturing. Process annealing is done by raising the temperature to just below the Ferrite-Austenite

region, line A1on the diagram. This temperature is about 727 ºC (1341 ºF) so heating it to about

700 ºC (1292 ºF) should suffice. This is held long enough to allow recrystallization of the ferrite

phase, and then cooled in still air. Since the material stays in the same phase through out the

process, the only change that occurs is the size, shape and distribution of the grain structure. This

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process is cheaper than either full annealing or normalizing since the material is not heated to a

very high temperature or cooled in a furnace. Process annealing relieves the internal stresses in the

cold worked steels and weldments, and improves the ductility and softness of the steel. Refinement

in grain size is also possible by the control of degree of cold work prior to annealing or by control of

annealing temperature and time.

3.5 Stress relief annealing

Stress relief annealing process consists of three steps. The first step is heating the cold worked

steel to a temperature between 5000

C and 5500

C i.e. below its recrystallization temperature. The

second step involves holding the steel component at this temperature for 1-2 hours. The final step

is to cool the steel component to room temperature in air.The stress relief annealing partly relieves

the internal stress in cold worked steels without loss of strength and hardness i.e. without change

in the microstructure. It reduces the risk of distortion while machining, and increases corrosion

resistance. Since only low carbon steels can be cold worked, the process is applicable to

hypoeutectoid steels containing less than 0.4% carbon. This annealing process is also used on

components to relieve internal stresses developed from rapid cooling and phase changes.

3.6 Spheroidizing:

Hypereutectoid steels consist of pearlite and cementite. The cementite forms a brittle network

around the pearlite. This presents difficulty in machining the hypereutectoid steels. To improve

the machinability of the annealed hypereutectoid steel spheroidize annealing is applied. This

process will produce a spheroidal or globular form of a carbide in a ferritic matrix which makes

the machining easy. Prolonged time at the elevated temperature will completely break up the

pearlitic structure and cementite network. The structure is called spheroidite. This structure is

desirable when minimum hardness, maximum ductility and maximum machinability are required.

It is also called as Soft Annealing.

The majority of all spheroidizing activity is performed for improving the cold formability of

steels. It is also performed to improve the machinability of hypereutectoid steels, as well as tool

steels. A spheroidized microstructure is desirable for cold forming because it lowers the flow

stress of the material. The flow stress is determined by the proportion and distribution of ferrite

and carbides. The strength of the ferrite depends on its grain size and the rate of cooling. Whether

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the carbides are present as lamellae in pearlite or spheroids radically affects the formability of

steel.

Steels may be spheroidized, that is, heated and cooled to produce a structure of globular carbides in a

ferritic matrix. Figure shows 1040 steel in the fully spheroidized condition.

Figure : Spheroidized microstructure of 1040 steel after 21 h at 700 °C (1290 °F). 4% picral etch. 1000×

a) Spheroidization can take place by the following method

Method 1.)

Prolonged holding at a temperature just below Ae1 and slow cooling.

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Method 2.)

Heating and cooling alternately between temperatures that are just above Ac1 and just below Ar1

Method 3.)

A more common commercial method consists of heating to a temperature of 50°F (13-26°C)

below Ac1, hold at this temperature, then increase the temperature set point between Ac1 and Ac3

and hold again. Following the second soak period, the temperature is decreased slowly.

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Method 4.)

Heating to a temperature just above Ac1, and then either cooling very slowly (30-50 °C/Hr) in the

furnace or holding at a temperature just below Ar1 or just above Ar1.

Method we use at VSSL:

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b) Some of the cycles which are being used at VSSL:

1.)Cycle for 16MnCr5,20MnCr5, 20MnCr5H,16MnCr5H,SAE1020

2.) Cycle for S25C

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3.)Cycle for SAE1010 and AISI1010

c) Conclusions based upon the study of spherodisation from

Jan’13 to May’13 at VSSL:

As we know that

Ac1 ( 0C ) = 723 – 10.7Mn – 16.9Ni + 29.1Si + 16.9Cr + 6.38W + 290As

And Ac3 ( 0C ) = 910 - 203√C – 15.2Ni + 44.7Si + 104V + 31.5Mo + 13.1W – 30Mn + 11Cr –

20Cu - 700P - 120As – 400Al- 400Ti

1.) Percentage of alloying elements like Si,Cr,Mn,W,Mo,V which impart hardness to structure can

be reduce somewhat according to aim and standard chemistry for the ease of further

spherodisation.

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3.7 Quenching:

QUENCHING refers to the process of rapidly cooling metal parts from the austenitizing or

solution treating temperature, typically from within the range of 815 to 870 °C (1500 to 1600 °F)

for steel. Stainless and high-alloy steels may be quenched to minimize the presence of grain

boundary carbides or to improve the ferrite distribution but most steels including carbon, low-

alloy, and tool steels, are quenched to produce controlled amounts of martensite in the

microstructure. Successful hardening usually means achieving the required microstructure,

hardness, strength, or toughness while minimizing residual stress, distortion, and the possibility of

cracking.The selection of a quenchant medium depends on the hardenability of the particular

alloy, the section thickness and shape involved, and the cooling rates needed to achieve the

desired microstructure. The most common quenchant media are either liquids or gases. The liquid

quenchants commonly used include:

· Oil that may contain a variety of additives

· Water

· Aqueous polymer solutions

· Water that may contain salt or caustic additives

The most common gaseous quenchants are inert gases including helium, argon, and nitrogen.

These quenchants are sometimes used after austenitizing in a vacuum. The ability of a quenchant

to harden steel depends on the cooling characteristics of the quenching medium.

Quenching effectiveness is dependent on the steel composition, type of quenchant, or the

quenchant use conditions. The design of the quenching system and the thoroughness with which

the system is maintained also contribute to the success of the process.

Fundamentals of Quenching and Quenchant Evaluation

Fundamentally, the objective of the quenching process is to cool steel from the austenitizing temperature

sufficiently quickly to form the desired microstructural phases, sometimes bainite but more often

martensite. The basic quenchant function is to control the rate of heat transfer from the surface of the

part being quenched.

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Types of quenching

· Direct quenching

· Time quenching

· Selective quenching

· Spray quenching

· Fog quenching

· Interrupted quenching

Direct quenching refers to quenching directly from the austenitizing temperature and is by far

the most widely used practice. The term direct quenching is used to differentiate this type of

cycle from more indirect practices which might involve carburizing, slow cooling, reheating,

followed by quenching.

Time quenching is used when the cooling rate of the part being quenched needs to be abruptly

changed during the cooling cycle. The change in cooling rate may consist of either an increase or

a decrease in the cooling rate depending on which is needed to attain desired results. The usual

practice is to lower the temperature of the part by quenching in a medium with high heat

removal characteristics (for example, water) until the part has cooled below the nose of the time

temperature- transformation (TTT) curve, and then to transfer the part to a second medium(for

example, oil), so that it cools more slowly through the martensite formation range. In some

applications, the second medium may be air or an inert gas. Time quenching is most often used

to minimize distortion, cracking, and dimensional changes.

Selective quenching is used when it is desirable for certain areas of a part to be relatively

unaffected by the quenching medium. This can be accomplished by insulating an area to be more

slowly cooled so the quenchant contacts only those areas of the part that are to be rapidly

cooled.

Spray quenching involves directing high-pressure streams of quenching liquid onto areas of the

workpiece where higher cooling rates are desired. The cooling rate is faster because the

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quenchant droplets formed by the high-intensity spray impact the part surface and remove heat

very effectively. However, low-pressure spraying, in effect a flood-type flow, is preferred with

certain polymer quenchants.

Fog quenching utilizes a fine fog or mist of liquid droplets in a gas carrier as the cooling agent.

Although similar to spray quenching, fog quenching produces lower cooling rates because of the

relatively low liquid content of the stream.

Interrupted quenching refers to the rapid cooling of the metal from the austenitizing

temperature to a point above the Ms where it is held for a specified period of time, followed by

cooling in air. There are three types of interrupted quenching: austempering, marquenching

(martempering), and isothermal quenching.

3.8 Tempering and its various stages

In this process quenched component heats or tempers in order to relieve the internal stresses and

reduce the brittleness. During tempering, which is always carried out below the lower critical

temperature, martensite tends to transform to the equilibrium structure of ferrite and cementite.

The higher the tempering temperature the more closely will the original martensitic structure

revert to this ferrite and cementite mixture and so strength and hardness fall progressively, whilst

toughness and ductility increase.Thus by choosing the appropriate tempering temperature a wide

range of mechanical properties can be achieved in carbon steels. The structural changes which

occur during the tempering of martensite containing more than 0.3% carbon, take place in three

stages:

First Stage (100 to 250 °C, or 210 to 480 °F)

First stage occurs at temperatures below 200 °C. This stage involves conversion of the martensite

to low carbon martensite (0.25%C) plus epsilon carbide (є). Є-carbide is metastable and richer in

carbon than cementite and is described by the formula Fe2.5C (or Fe5C2). low carbon martensite

retains some degree of tetragonality because it still contains more carbon in solid solution than

would ferrite; there are no changes in the morphology of the martensite crystals. At this stage a

slight increase in hardness may occur because of the presence of the finely-dispersed but hard є-

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carbide. Brittleness is significantly reduced as quenching stresses disappear in consequence of the

transformation. At 100°C the transformation proceeds very slowly but increases in speed up to

200°C.

Second Stage (200 to 300 °C, or 390 to 570 °F)

The transformation of retained austenite to ferrite and cementite.

Third Stage

Third stage start at 300°C. At this stage є-carbide begins to transform to ordinary cementite and

this continues as the temperature rises. In the mean time the remainder of the carbon begins to

precipitate from the low carbon martensite also as cementite and in consequence the martensite

structure gradually reverts to one of ordinary BCC ferrite. Above 500°C the cementite particles

coalesce into larger rounded globules in the ferrite matrix. This structure was formerly called

sorbite or tempered martensite. Due to the increased carbide precipitation which occurs as the

temperature rises the structure becomes weaker but more ductile, though above 550°C strength

falls fairly rapidly with little rise in ductility.

Figure. Variation in properties with tempering temperature

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REFERENCES:

1. Nandita Gupta,S.K. Sen(2006)Defence Science Journal, Vol. 56, No. 4, October 2006, pp. 665-676

2. ASM Metals Handbook Volume 4 : Heat Treating

3. Yudong Zhang, Changshu He, Xiang Zhao, Claude Esling and Liang Zuo(2003)

(A New Approach for Rapid Annealing of Medium Carbon Steels)

4. Sidney H. Avner (Introduction to physical metallurgy,2nd edition)

5. http://info.lu.farmingdale.edu/depts/met/met205/ANNEALING.html

6. Vardhman Special Steels Limited, || http://www.vardhmansteel.com/