Heat Treatment Processes E-Book

Dr. Chandan Deep Singh

• Herausgeber: BookRix
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2018

Beschreibung

It may be defined as an operation of heating and cooling of metals or alloys in the solid state to induce certain desired properties into them. Heat treatment can alter the mechanical properties of steel by changing the shape and size of grains of which it is composed, or by changing its micro-constituents.

Leseprobe

Dr. Chandan Deep Singh, Jasveer Singh

Heat Treatment Processes

BookRix GmbH & Co. KG80331 Munich

Chapter 1

RAW MATERIALS

2.1 AN INTRODUCTION:

The raw material is the first requirement to start the production as per planning. For an economical production the raw material should be of good quality and should be of the required specifications.

The raw material used in STELCO is hot rolled coils, which are imported from Jamshedpur. The hot rolled coils are inspected in the chemical analysis lab for the content of carbon and manganese. The hot rolled coils are bigger in size, which are then slitted as per required width by H.R. slitting machine.

GRADE

C%

Mn%

Si%

P%

C-40

0.35-0.45

0.50-0.70

0.15-0.35

0.04-0.04

C-55

0.50-0.60

0.50-0.80

0.15-0.35

0.04-0.04

C-60

0.55-0.65

0.50-0.80

0.15-0.35

0.04-0.04

C-80

0.75-0.85

0.60-0.90

0.15-0.35

0.04-0.04

C-120

1.1-1.3

0.60-0.90

0.15-0.35

0.04-0.04

Width-As per the requirement of the customer.

2.2 DUCTILITY OF PLAIN CARBON STEELS

Carbon Content

Elongation in tensile test

Nil

0.2

0.4

0.6

0.8

1.2

42%

37%

31%

22%

17%

03%

Chapter 2

HEAT TREATMENT

AN INTRODUCTION:

It may be defined as an operation of heating and cooling of metals or alloys in the solid state to induce certain desired properties into them. Heat treatment can alter the mechanical properties of steel by changing the shape and size of grains of which it is composed, or by changing its micro-constituents. It is generally employed for following purposes:-

To improve machinabilityTo change or refine the grain sizeTo relieve the stresses of the metal induced during cold or hot working.To improve the mechanical properties e.g. tensile strength, hardness, ductility, shock resistance etc.To improve magnetic and electrical properties.To increase resistance to wear, heat and corrosion.To produce a hard surface on a ductile interior.

Heat treatment refers to a combination of heating and cooling of a metal or alloy in the solid state for the purpose of obtaining desired properties. Changes in properties result from micro structural changes in the material produced by heat treatment operations.

The various improvements from heat treatment are a result of the development of certain micro constituents which have desired qualities. These micro constituents are obtained by different rates of heating and cooling.

The most commonly used operations of heat treatment are as follows:-

AnnealingHardeningTemperingNormalizingCarburizingCyanidingNitridingInduction hardeningFlame hardening

PROCESSES

4.1 ANNEALING

4.1.1 AN INTRODUCTION:

Annealing is one of the most important widely used operations in the heat treatment of steel. The purpose of annealing is to obtain one or more of the following effects:

Soften the steelImprove machinabilityIncrease of restore ductility and toughnessRelieve internal stressesReduce or eliminate structural inhomogeneity.Refine grain size.Prepare steel for subsequent heat treatment.

The various types of annealing that serve one or more of these problems are explained in the following discussions.

4.1.2 FULL ANNEALING

This process is known as full annealing because it wipes out all traces of previous structure by complete phase recrystallisation. Full annealing consists of:

Heating the steel slightly above the critical pointHolding it at this temperature for a considerable periodSlowly cooling

4.1.3 PROCESS ANNEALING

When steel is cold worked the hardness and elastic properties particularly considerably increase, while the ductility remarkably suffers and the steel becomes unsuitable for further plastic deformation. The ductility of steel may then be restored by so-called recrystallisation or process annealing. Furthermore, the effect of process annealing is to relieve internal successes resulting from any previous heat treatment.

Process annealing consists in heating the steel to a temperature usually in the range of 5000C to 7000C holding at this temperature for a prolonged period and slow cooling. This causes the grains of steel, broken up or distorted in the process of deformation, to come back into their normal state. Process of recrystallisation annealing is frequently applied in the production of cold rolled steel which, in deep drawing, and in wire drawing operations is an intermediate process with the aim of increasing the plasticity of the steel. It should be pointed out that this process is applied to low carbon steels only. Medium and high carbon steels, however, require full annealing for recrystallisation.

In process annealing, new equiaxial grains gradually grows from the fragments of the original elongated grains, forming centers, or nuclei. These new grains become equiaxial. It must, therefore, be remembered that this process does not produce ay new structure by phase transformations but produces only new crystals of the same structure.