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Heat Treatment
The strength and 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 the material properties that are acceptable for many applications. Low-carbon steel contains a carbon content of 0.15% to 0.45%.
Heat treatment on low carbon steel is to increase ductility, 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 less tensile strength and is 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 at MS, we use En353, a low-carbon alloy steel that contains 0.18 %C, 0.99%Mn, 1.42%Ni, 1.12%Cr, 0.11%Mo, and 0.28%Si.
The process of 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, modify the structure of the material, and relieve the stress set up in the material.
The most important heat treatment process and purpose.
STRESS RELIEVING
A low-temperature treatment, to reduce or relieve internal stress remaining after casting or work hardening.
ANNEALING
Annealing is a rather generalized term. Annealing consists of heating a metal to a specific temperature and then cooling it at a rate that will produce a refined microstructure.
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 a technique used to provide uniformity in grain size and composition throughout the alloy. The term is frequently used for ferrous alloys that have been austenitized and then cooled in the open air.
Normally, it produces pearlite but also binate and sometimes martensite steel, which gives harder and stronger steel but with less ductility for some compositions than full annealing.
TEMPERING
Untempered martensitic steel, while very hard, is too brittle to be useful for most applications. A method for alleviating this problem is called tempering.
Most applications require quenched parts to be tempered. Tempering involves heating steel below the lower critical temperature to impart some touchiness. Higher tempering temperatures are sometimes used to achieve 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.
CASE HARDENING
Casehardening is a thermo-chemical diffusion process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of the monolithic metal.
The subsequent interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing touchiness.
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.
It’s awesome that you talked about how heat treatment is a process where a material’s toughness is improved. In my opinion, it’s interesting to know how rising the temperature of steel and then slowly cooling it down can make the material harden but refine its structure. I appreciate you helping me learn about the purpose of heat treatment and how it’s done.
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Interesting article! Heat treatment indeed has multiple uses ranging from softening or hardening material to relieving the stress set up in it. We can’t think of metalwork without heat treatment. That’s why it has been in use for ages as early as around 1,200 BC when the process of ironworking was discovered. It was marked as the beginning of the Iron Age.