53979847 Case Hardening Heat Treatment

8/2/2019 53979847 Case Hardening Heat Treatment

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TERM PAPER

TOPIC

Write a report on case hardening heat treatments

COURSE CODE=MEC 208

SUMMITTED TO: SUBMITTED BY:

MR.HARPREET SINGH Mohit Kumar

. ROLL NO:RM3R17B59

REG.NO.11011215


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CONTENTS

ITEMS PAGES NO:

1. ACKNOWLEDGEMENT 32. INTRODUCTION 43. WHAT IS CASE HARDENING 54. TYPES OF CASE HARDENING AND APPLICATION 65. PROCESS 86. WHAT IS HEAT TREATMENT 97. RELATION OF HEAT TREATMENT AND CASE HARDENING 108. HAET TREATMENT WITH THE HELP OF CASE HARDENING 119. CONCLUTION 1410.REFERENCES AND SOURCES 14


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ACKNOWLEDGMENT

I, Mohit Kumar, a student of LOVELY PROFESSIONAL UNIVERSITY in my

acknowledgement thank all the people who have helped me in making this term

paper a success

My first and foremost acknowledgement goes to our subject teacher

Mr.HARPREET sir for the assistance and guidance that she provided

throughout the session. I am ever grateful to him for that. I owe him a lot for the

successful completion of the term paper.

I am also thankful to many of my fellow college mates for their active support

and valuable inputs and the help that they provided. I am ever thankful to all of

them.

I am thankful too much thankful to the library of the college which acted as a

database of knowledge and information for me .The internet and the various

educational sites visited by me also deserve a lot of appreciation and thank for

the help they provided in completing this term paper. I thank you one and all.

Thank you.


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What is Case hardening?

Case hardening or surface hardening is the process of hardening the surface of ametal, often a low carbon steel, by infusing elements into the material's surface,forming a thin layer of a harder alloy. Case hardening is usually done after the

part in question has been formed into its final shape, but can also be done to

increase the hardening element content of bars to be used in a pattern welding or

similar process. The term face hardening is also used to describe this technique,when discussing modern armour.

Process:-

Case hardening is a process that is used to harden the outer layer of casehardening steel while maintaining a soft inner metal core. The case hardening

process uses case hardening compounds for the carbon addition. Steel casehardening depth depends upon the application of case hardening depth.

Case hardening is a technique in which the metal surface is reinforced by the

adding of a fine layer at the top of another metal alloy that is generally more

durable. Case hardening steel is normally used to increase the object life. This is

particularly significant for the manufacture of machine parts, carbon steel

forgings, and carbon steel pinions. Case hardening is also utilized for other

applications. Case hardening is also called surface hardening. Case hardeninghas been in use for many centuries, and was frequently used for producing

horseshoes and different kinds of cooking utensils that were subjected to

substantial wear and tear. Case hardening is essentially a group of processes that

are used to increase the surface hardness to an extent that is higher than that of

the bulk material. Case hardening is performed normally locally on the top


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surface, and for a limited depth. Greater hardness is usually related with betterwear and fatigue resistance.

The addition of carbon to the iron surfaces is common. Case hardening involves

the use of metal that has low carbon contents, and combining it with a metal thathas more carbon content. The grouping of metals is likely to produce the

product that is much harder. The adding of the low carbon metal creates a

material that can be molded easily into the desired shapes. The surface

improvement not only increases the product strength, but also assists to avoidthe iron weakening.

Components that are subjected to severe impacts and high pressures are

generally case hardened. The surfaces that need special hardness may be

selectively hardened, without performing case hardening of the remaining

object.

Types of Case hardening:-

Steel Case Hardening

Carbon is penetrated into the metal skin to create mild steel that has an external

covering with more carbon than the nucleus. The mild steel is subjected to

heating at a particular temperature, till it is bright red. While the mild steel issoft, it is immersed into a carbon compound that covers the outer surface. One

dipping may not be adequate, and several re-heating and dipping may be

necessary. This heat treatment procedure will produce a skin that is rich in

carbon. Subsequently, the metal is reheated and dropped in water for hardening.

Case hardening is useful for objects that need to be hardened externally to

endure wear and tear, but soft internally to withstand shock.

Heat-treatable Steels

Heat-treatable steels are steels for mechanical engineering which, as a result of

their chemicalcomposition, are suitable for hardening and in heat-treated condition show good

toughness

characteristics for a given tensile strength. In general, the steels are used in softcondition to


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produce parts which are subsequently subjected to heat treatment to obtain the

desired functional properties.

Boron-containing Heat-treatable Steels

Boron-containing heat-treatable steels are alloyed with a low mass percentage

of boron to improve hardenability. This automatically increases the core

strength of the steel. Prior to heat treatment, the steel grades show good cold

formability characteristics. More detailed information is available upon request.

Applications

1.Chain saws

2.Springs

3.Mowing blades

4.Flywheels5.Gear parts

6.Punched parts

The most widely used case hardening methods are: carburizing, nitriding and

carbonitriding.

Carburizing

Carburizing is the process of diffusion enrichment of the surface layer of a partwith carbon followed by heat treatment of the part.

As carburizing medium the following substances are used:

Charcoal or other carbon-containing solids mixed with sodium carbonateand barium carbonate accelerating the process of dissolving the carbon insteel.

The process is carried out in steel or cast iron boxes placed into a furnace at the

temperature 1650F - 1750F (900C - 950C) resulting in formation of hard


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case of the thickness 0.02-0.08 (0.5mm 2mm) and containing 0.8-1% ofcarbon.

Kerosene or benzeneliquid carbonizing mediums, which are usuallyused in dispersed form;

Methane (CH4), propane (C3H8)gaseous carbonizing mediums.The process is carried out in a furnace (batch or continuous) at the temperature1650F - 1750F (900C - 950C) for 3-4 hrs.

Thickness of the hard layer formed in the gaseous carburizing may reach 0.15

(4mm).

Heat treatment after carburizing involves hardening-tempering treatments with

purpose of controlling structure and properties of both the hard layer and theductile core.

Nitriding

Nitriding is the process of diffusion enrichment of the surface layer of a part

with Nitrogen.

Gas nitriding is carried out at 930F - 1110F (500C - 600C) for 40-100 hrs.in

the atmosphere of Ammonia, which dissociates to Hydrogen and nitrogen. The

latter diffuses into the steel forming nitrides of iron, aluminum, chromium and

vanadium.

Ion nitriding (plasma nitriding) is a surface Hardening heat treatment, in which

Nitrogen is delivered to the workpiece surface in form of ionized gas (plasma).

The case formed as a result of nitriding has a hardness of about 1100 HV whichis higher than the hardness after carburizing.

Nitrided part possess also better wear resistance, increased fatigue strength,enhanced toughness and good resistance to corrosion.

No additional heat treatment is required after nitriding.


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Carbonitriding

Carbonitriding is the process of diffusion enrichment of the surface layer of a

part with carbon and nitrogen.

Gaseous carbonitriding is carried out in gaseous medium, consisting ofcarburizing gas (methane, propane) with addition of 3-8% of Ammonia.

There are two principal methods of the gaseous carbonitriding:

Low temperature gaseous carbonitriding, conducted at 930F - 1110F(500C - 600C). The steel surface is enriched mostly with nitrogen inthis process.

High temperature gaseous carbonitriding, conducted at1470F - 1750F(800C - 950C). The steel surface is enriched mostly with carbon in thisprocess. This process is followed by heat treatment.

Cyaniding is the carbonitriding process, conducted in molten salt, containing20-25% of sodium cyanide (extremely toxic substance).

The process is carried out at the temperatures 1500F - 1580F (820C - 860C)for 1 hour.

Carbonitrided parts possess better (than carburized parts) wear resistance.

What is Heat Treatment?

Heat Treatment is the controlled heating and cooling of metals to alter theirphysical and mechanical properties without changing the product shape. Heat

treatment is sometimes done inadvertently due to manufacturing processes thateither heat or cool the metal such as welding or forming.

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, 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.


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Steels are particularly suitable for heat treatment, since they respond well to

heat treatment and the commercial use of steels exceeds that of any other

material. Steels are heat treated for one of the following reasons:

1. Softening

2. Hardening

3. Material Modification

Common Heat Treatments

Softening: Softening is done to reduce strength or hardness, remove residual

stresses, improve toughness, restore ductility, refine grain size or change theelectromagnetic properties of the steel.

Restoring ductility or removing residual stresses is a necessary operation when

a large amount of cold working is to be performed, such as in a cold-rolling

operation or wiredrawing. Annealingfull Process, spheroidizing,

normalizing and temperingaustempering, martempering are the principalways by which steel is softened.

Hardening: Hardening of steels is done to increase the strength and wear

properties. One of the pre-requisites for hardening is sufficient carbon and alloycontent. If there is sufficient Carbon content then the steel can be directly

hardened. Otherwise the surface of the part has to be Carbon enriched usingsome diffusion treatment hardening techniques.

Material Modification: Heat treatment is used to modify properties of materials

in addition to hardening and softening. These processes modify the behavior of

the steels in a beneficial manner to maximize service life, e.g., stress relieving,or strength properties, e.g., cryogenic treatment, or some other desirableproperties, e.g., spring aging.

Full Annealing a heat treatment process:-

Full annealing is the process of slowly raising the temperature about 50 C (90
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F) above the Austenitic temperature line A3 or line ACM in the case of

Hypoeutectoid steels (steels with < 0.77% Carbon) and 50 C (90 F) into the

Austenite-Cementite region in the case of Hypereutectoid steels (steels with >0.77% Carbon).

It is held at this temperature for sufficient time for all the material to transform

into Austenite or Austenite-Cementite as the case may be. It is then slowly

cooled at the rate of about 20 C/hr (36 F/hr) in a furnace to about 50 C (90 F)

into the Ferrite-Cementite range. At this point, it can be cooled in roomtemperature air with natural convection.

The grain structure has coarse Pearlite with ferrite or Cementite (depending on

whether hypo or hyper eutectoid). The steel becomes soft and ductile.

Normalizing

Normalizing is the process of raising the temperature to over 60 C (108 F),above line A3 or line ACM fully into the Austenite range. It is held at this


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temperature to fully convert the structure into Austenite, and then removed form

the furnace and cooled at room temperature under natural convection. This

results in a grain structure of fine Pearlite with excess of Ferrite or Cementite.

The resulting material is soft; the degree of softness depends on the actual

ambient conditions of cooling. This process is considerably cheaper than fullannealing since there is not the added cost of controlled furnace cooling.

The main difference between full annealing and normalizing is that fully

annealed parts are uniform in softness (and machinablilty) throughout the entire

part; since the entire part is exposed to the controlled furnace cooling. In the

case of the normalized part, depending on the part geometry, the cooling is non-

uniform resulting in non-uniform material properties across the part. This may

not be desirable if further machining is desired, since it makes the machining

ob somewhat unpredictable. In such a case it is better to do full annealing.

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 C (1341 F) so heating it to about 700C (1292 F) 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 process is cheaper than either

full annealing or normalizing since the material is not heated to a very hightemperature or cooled in a furnace.

Stress Relief Annealing

Stress Relief Anneal is used to reduce residual stresses in large castings, welded

parts and cold-formed parts. Such parts tend to have stresses due to thermal

cycling or work hardening. Parts are heated to temperatures of up to 600 - 650 C

(1112 - 1202 F), and held for an extended time (about 1 hour or more) and thenslowly cooled in still air.

Spheroidization

Spheroidization is an annealing process used for high carbon steels (Carbon >0.6%) that will be machined or cold formed subsequently. This is done by one of


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the following ways:

1. Heat the part to a temperature just below the Ferrite-Austenite line, line A1or below the Austenite-Cementite line, essentially below the 727 C (1340

F) line. Hold the temperature for a prolonged time and follow by fairlyslow cooling. Or

2. Cycle multiple times between temperatures slightly above and slightly

below the 727 C (1340 F) line, say for example between 700 and 750 C

(1292 - 1382 F), and slow cool. Or

3. For tool and alloy steels heat to 750 to 800 C (1382-1472 F) and hold for

several hours followed by slow cooling.

All these methods result in a structure in which all the Cementite is in the form of

small globules (spheroids) dispersed throughout the ferrite matrix. This structure

allows for improved machining in continuous cutting operations such as lathesand screw machines. Spheroidization also improves resistance to abrasion.

Heat Treatment With The Help Of Case Hardening

There are a number if useful and effective devices and systems. Our life has

changed with the introduction of these systems and tools. Thanks to the

technological advancement. It has gifted us with a number of valuable anduseful tools and systems. Induction hardening is one of the popular heat treating

operations. It is basically designed to harden parts.

There are a number of factors that make the process a successful one. These

include the general ability and chemistry of the material or item to hardenproperly, cooling the material so that the transformation of martensite can occur

and adjusting the temperature of the material. If one or more of these crucial

factors or features are not present, the material may remain soft entirely or soft

spots may develop on the material. These factors have control over quenchingand heating of the parts.
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It is quite necessary to adjust the temperature of the materials so that the

austenitic phase can occur. Depending on the material, in some cases, it may be

essential to hold the temperature for a certain amount of time so that the

material may fully transform. By doing so, undesirable buy-products can beavoided.

There are a number ofheat treatment processes, like Induction Annealing,

Homogenising, Carbonitriding, Hardening, Ageing, Annealing, Induction

Annealing, Normalizing, Induction Hardening, Shot Blasting, Case Hardening,

Tempering, Stress Relieving etc to materials including Carbon Steels, Stainless

Steels, Alloy Steels, Cast Irons, Die Steels and Tool Steels.

Case hardening is one of the most popular heat treatment procedures. It is really

an effective process that is used in a number of cases. Carbonitriding is actually

a case hardening process. In this process the steel is heated in a particularatmosphere containing both nitrogen and carbon.

The case hardening type steels are normally used. AC is depressed with the

absorption of the nitrogen. The harden ability is increased as a result of this. It isnot essential to include too much of alloy. It is one of the most useful and

popular procedures of heat treatment.

The hardening process is quite similar to any other type of heat treating

operations. It is specifically designed to harden parts. There are several factors

that make the procedure successful. These include, cooling the material so thatthe transformation of the martensite can occur, adjusting the temperature and

finally the general ability and chemistry of the material to harden. When one or

more than one of these crucial factors are not present, then the material may

remain soft entirely or soft spots may develop on the material.

Induction Heat Treatment Services (inductionheattreatmentservices.co.uk) isone of the leading heat treatment organizations. They offer a number of heat

treatment processes including Annealing, Ageing, Tempering, Carburising,

Carbonitriding, Hardening, Induction Annealing, Homogenising, Induction

Hardening, Stress Relieving, Case Hardening, Normalizing and Shot Blasting to

materials including Die Steels, Alloy Steels, Cast Irons, Carbon Steels, StainlessSteels and Tool Steels. They have a selection of protective gas/vertical

controlled atmosphere furnaces and both rectangular and vertical tempering

furnaces.
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Conclution:-

Its a predict feels highghly oblisised that I am try to complete my term paper

about the topic WRITE A REORT OF CASE HARDENING HEAT TREATMENT,itsmy glad to do this term paper with the help of internet and some books and

somes pdf files.i hope that I have done my best hard work to do this work hard

to hardest to achieve my goal.And thanx to my sir that he has given to me this

work to better myself.

Refferences

Links-

1.en.wikipedia.org/wiki/Case_hardening

2.www.thefreedictionary.com/Case+hardening

3.www.welding-advisers.com/Case-hardening.html

4.www.finishing.com/260/89.shtm

Books and others

1.Hardening, Tempering and Heat Treatment (Workshop Practice)

2. Heat treater's guide: practices and procedures for irons and steels

By Harry Chandler


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53979847 Case Hardening Heat Treatment

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