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In heat treatment, the sudden cooling of plain carbon steel after attaining the upper critical temperature is to
- a)increase the hardness
- b)increase toughness
- c)reduce the brittleness
- d)improve machinability
Correct answer is option 'A'. Can you explain this answer?
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In heat treatment, the sudden cooling of plain carbon steel after att...
The temperature, at which the change of structure to austenite starts, 723°C, is called the lower critical temperature for all plain carbon steels.
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The temperature at which the structure of steel completely changes to AUSTENITE is called the upper critical temperature. This varies depending on the percentage of carbon in the steel.
- 0.57% and 1.15% carbon steel: In these cases, the lower critical temperature is 723°C and the upper critical temperature is 800°C.
- For 0.84% carbon steel, both lower critical temperature and upper critical temperature are 723°C. This steel is called eutectoid steel.
If steel is heated, a change in its structure commences from 723°C. The new structure formed is called ‘AUSTENITE’. Austenite is non-magnetic.
- If the hot steel is cooled slowly, the old structure is retained and it will have fine grains which makes it easily machinable.
- If the hot steel is cooled rapidly the austenite changes into a new structure called ‘MARTENSITE’. This structure is very fine-grained, very hard and magnetic. It is extremely wear-resistant and can cut other metals.
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In heat treatment, the sudden cooling of plain carbon steel after att...
Heat Treatment of Plain Carbon Steel
Heat treatment is a process of heating and cooling a material to alter its properties such as hardness, toughness, ductility, and machinability. Plain carbon steel is a type of steel that contains only carbon as the main alloying element. The sudden cooling of plain carbon steel after attaining the upper critical temperature is known as quenching. This process is used to increase the hardness of the steel.
Increase in Hardness
Quenching is a process of sudden cooling of a metal to achieve a certain hardness level. In the case of plain carbon steel, the upper critical temperature is around 723°C. Above this temperature, the steel becomes austenitic, which is a face-centered cubic crystal structure. When the steel is quenched, it rapidly cools down, and the austenitic structure transforms into martensite. Martensite is a body-centered tetragonal crystal structure that is extremely hard and brittle.
The quenching process traps the carbon atoms in the martensite structure, causing the steel to become harder. The hardness level achieved depends on the cooling rate and the carbon content of the steel. Higher carbon content results in higher hardness levels.
Conclusion
In conclusion, the sudden cooling of plain carbon steel after attaining the upper critical temperature is to increase the hardness of the steel. Quenching is a process of rapid cooling that transforms the austenitic structure into martensite, resulting in a harder and more brittle steel. The hardness level achieved depends on the cooling rate and the carbon content of the steel.
Heat treatment is a process of heating and cooling a material to alter its properties such as hardness, toughness, ductility, and machinability. Plain carbon steel is a type of steel that contains only carbon as the main alloying element. The sudden cooling of plain carbon steel after attaining the upper critical temperature is known as quenching. This process is used to increase the hardness of the steel.
Increase in Hardness
Quenching is a process of sudden cooling of a metal to achieve a certain hardness level. In the case of plain carbon steel, the upper critical temperature is around 723°C. Above this temperature, the steel becomes austenitic, which is a face-centered cubic crystal structure. When the steel is quenched, it rapidly cools down, and the austenitic structure transforms into martensite. Martensite is a body-centered tetragonal crystal structure that is extremely hard and brittle.
The quenching process traps the carbon atoms in the martensite structure, causing the steel to become harder. The hardness level achieved depends on the cooling rate and the carbon content of the steel. Higher carbon content results in higher hardness levels.
Conclusion
In conclusion, the sudden cooling of plain carbon steel after attaining the upper critical temperature is to increase the hardness of the steel. Quenching is a process of rapid cooling that transforms the austenitic structure into martensite, resulting in a harder and more brittle steel. The hardness level achieved depends on the cooling rate and the carbon content of the steel.
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In heat treatment, the sudden cooling of plain carbon steel after attaining the upper critical temperature is toa)increase the hardnessb)increase toughnessc)reduce the brittlenessd)improve machinabilityCorrect answer is option 'A'. Can you explain this answer?
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