Why does heat treatment of plain carbon steel start from the austenite phase? Ra
ID: 1718971 • Letter: W
Question
Why does heat treatment of plain carbon steel start from the austenite phase?
Rapid cooling from austenite is required to produce martensite. Describe the differences in structure between martensite and the equilibrium structures obtained for a 1080 plain carbon steel.
Describe the process of tempering martensite. Why is it done? What happens to the resulting mechanical properties? What happens to the microstructure?
Describe the Jominy hardenability test. Why is the test performed?
Why does heat treatment of plain carbon steel start from the austenite phase?
Rapid cooling from austenite is required to produce martensite. Describe the differences in structure between martensite and the equilibrium structures obtained for a 1080 plain carbon steel.
Describe the process of tempering martensite. Why is it done? What happens to the resulting mechanical properties? What happens to the microstructure?
Describe the Jominy hardenability test. Why is the test performed?
Explanation / Answer
>> Heat Treatment of Plain Carbon Steel start from the austenite phase because, this phase is at temperature more tha critical temperature and also above recrystallisation temperature.
So, according to cooling conditions, different structure can be formed easily.
>> Martensite is very hard structure. It is extremely brittle and thus, very difficult to work on
Other Equilibrium Structures are:- Pearlite, Bainite
Pearlite is ductile, although strength is somewhat less
Bainite is formed when there is very less diffusivity. It has remarkable strength along with little ductility
>> Tempering Martensite is the process in which martensite is heated slowly upto a particular temperature
It is done to induce some ductile behaviour in Martensite along with no reduction in Strength
Properties are: Ductile, High Toughness, Good Hardness, etc
>> As, the hardenability of a steel is defined as that property which determines the depth and distribution of hardness induced by quenching ftom the austenitic condition. The dependence of hardness upon quenching rate can be understood ftom the time-temperature-transformation characteristics of steel, and, for a particular steel, can be estimated from the T-T-T diagram. A part may be hardened by quenching into water, oil, or other suitable medium. The surface of the part is cooled rapidly, resulting in high hardness, whereas the interior cools more slowly and is not hardened. Because of the nature of the T-T-T diagram, the hardness does not vary linearly from the outside to the center. Hardenability refers to capacity of hardening (depth) rather than to maximum attainable hardness.
It is used to study hardness as a function of quench rate and investigate the hardenability of steels.
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