Heat Treatment | Purpose of Heat Treatment

HEAT TREATMENT

The strength toughness of the base material are determined by its chemical composition and the heat treatment it undergoes. Low carbon steel is easily available and cheap having all material properties that are acceptable for many applications. Low carbon steel contains carbon contain of 0.15% to 0.45%.

Heat treatment on low carbon steel is to increase ductility, to improve toughness, strength, hardness and tensile strength and to relive stress developed in the material.

It is neither externally brittle nor ductile due to its lower carbon content. It has lesser tensile strength and malleable. The increase in carbon content makes the metal to becomes harder and strong but less ductile and more difficult and more difficult to weld. Here MS we use En353, a low carbon alloy steel which contains 0.18 %C, 0.99%Mn, 1.42%Ni, 1.12%Cr, 0.11%Mo, 0.28%Si.

The process that heat treatment is carried out first by heating the material and then cooling it in water, oil and brine water. The use of heat treatment is to soften or harden the material, to modify the size of the grain, to modify the structure of the material and relive the stress setup in the material.

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The most important heat treatment process and purpose.

01 - HEAT TREATMENT PROCESS - PROCESS OF HEAT TREATMENT

STRESS RELIEVING

A low-temperature treatment, to reduce or relive internal stress remaining after casting or work hardening.

ANNEALING

Annealing is a rather generalized term. Annealing consist of heating a metal to a specific temperature and then cooling at a rate that will produce a refined micro structure.

The rate of cooling is generally slow. Annealing is most frequently used to soften a metal for cold working, to increase machinability, or to improve properties like electrical conductivity.

NORMALIZING

Normalizing is technique used to provide uniformity in grain size and composition throughout alloy. The term is frequently used for ferrous alloys that have been austenitized and then cooled in open air.

Normally not only produce pearlier, but also binate and sometimes Mortem site, which gives harder and stronger steel, but with less ductility for some composition then full annealing.

TEMPERING

Untemper martensitic steel, while very hard, is to brittle to be useful for most application. A method for alleviating this problem is called tempering.

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Most application requires that quenched parts be tempered. Tempering contains heating steel below the lower critical temperature to import some touchiness. Higher tempering temperatures, are at times used to import further ductility, although some yield strength is lost.

QUENCHING

To harden by quenching, a metal must essentially be heated beyond the upper critical temperature and then quickly cooled.

Depending on the alloy and other respects, cooling may be done with forced air or other gases, Liquids may be used, due to their better thermal conductivity, such as oil, water, a polymer dissolved in water, or a brine.

Upon being quickly cooled, a percentage of austenite will transform to martensitic, a hard, brittle crystalline structure.

01 - HEAT TREATMENT PROCESS - GRAIN STRUCTURE

CASE HARDENING

Casehardening is a thermo chemical diffusion process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of a monolithic metal.

The subsequent interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing touchiness.

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CARBURIZING

Carburizing is the heat treatment process in which iron or steel absorbs carbon liberated when metal is heated in the presence of a carbon bearing material, such as charcoal or carbon monoxide, with the intent of making the material harder.

Depending on the amount of time and temperature, the affected area can vary in carbon content. Extended carburizing times and higher temperatures lead to greater carbon diffusion into the part as well as increased depth of carbon diffusion.

As soon as the iron or steel is cooled quickly by quenching, the higher carbon content on the outer surface becomes hard via the transformation from austenite to martens tic, while the core remains soft and tough as a ferrite or pearlier microstructure.

Originally posted 2015-06-16 02:51:37.

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