Mechanical Engineering Exam > Mechanical Engineering Questions > Select the WRONG statement:a)The main purpose...
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Select the WRONG statement:
- a)The main purpose of heat treatment is to change the mechanical properties.
- b)Tempering is the process of annealing martensite at low temperatures.
- c)Case hardening is the only method suitable for (ow carbon steel.
- d)A eutectoid steel consists of wholly austenite.
Correct answer is option 'D'. Can you explain this answer?
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Most Upvoted Answer
Select the WRONG statement:a)The main purpose of heat treatment is to ...
Explanation:
Heat treatment is a process used to alter the physical and mechanical properties of materials, specifically metals and alloys. It involves heating and cooling the material in a controlled manner to achieve the desired properties. The main purpose of heat treatment is indeed to change the mechanical properties of the material.
Incorrect Statement:
d) A eutectoid steel consists of wholly austenite.
Explanation:
Eutectoid steel is a type of steel that contains a eutectoid composition, which is approximately 0.76% carbon. It undergoes a phase transformation during heat treatment, where it is heated above the critical temperature (known as the upper critical temperature) and then cooled at a controlled rate. The phase transformation involves the formation of a mixture of ferrite and cementite known as pearlite.
During the heat treatment process, when the eutectoid steel is heated above the upper critical temperature (around 727°C for plain carbon steels), the existing microstructure (typically ferrite and pearlite) transforms into austenite, which is a face-centered cubic (FCC) crystal structure. This austenite is not wholly austenite, but rather a temporary phase formed during the heating process.
As the eutectoid steel is cooled, the austenite transforms back into a two-phase mixture of ferrite and cementite, known as pearlite. This transformation occurs at a specific temperature called the lower critical temperature. The resulting microstructure of eutectoid steel consists of ferrite and pearlite, not wholly austenite.
Therefore, statement d) is incorrect because a eutectoid steel does not consist of wholly austenite.
Heat treatment is a process used to alter the physical and mechanical properties of materials, specifically metals and alloys. It involves heating and cooling the material in a controlled manner to achieve the desired properties. The main purpose of heat treatment is indeed to change the mechanical properties of the material.
Incorrect Statement:
d) A eutectoid steel consists of wholly austenite.
Explanation:
Eutectoid steel is a type of steel that contains a eutectoid composition, which is approximately 0.76% carbon. It undergoes a phase transformation during heat treatment, where it is heated above the critical temperature (known as the upper critical temperature) and then cooled at a controlled rate. The phase transformation involves the formation of a mixture of ferrite and cementite known as pearlite.
During the heat treatment process, when the eutectoid steel is heated above the upper critical temperature (around 727°C for plain carbon steels), the existing microstructure (typically ferrite and pearlite) transforms into austenite, which is a face-centered cubic (FCC) crystal structure. This austenite is not wholly austenite, but rather a temporary phase formed during the heating process.
As the eutectoid steel is cooled, the austenite transforms back into a two-phase mixture of ferrite and cementite, known as pearlite. This transformation occurs at a specific temperature called the lower critical temperature. The resulting microstructure of eutectoid steel consists of ferrite and pearlite, not wholly austenite.
Therefore, statement d) is incorrect because a eutectoid steel does not consist of wholly austenite.
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Select the WRONG statement:a)The main purpose of heat treatment is to change the mechanical properties.b)Tempering is the process of annealing martensite at low temperatures.c)Case hardening is the only method suitable for (ow carbon steel.d)A eutectoid steel consists of wholly austenite.Correct answer is option 'D'. Can you explain this answer?
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