Consider the following statements:When a metal or alloy is cold worked...
The correct answer is option 'D' - 2 and 4.
Explanation:
When a metal or alloy is cold worked, it means that it is subjected to plastic deformation below its recrystallization temperature. Here is a detailed explanation of the correct statements:
1. It is worked below room temperature.
- This statement is incorrect. Cold working can be performed both below and above room temperature. However, it is more commonly performed at room temperature to avoid the need for additional heating and cooling processes.
2. It is worked below recrystallization temperature.
- This statement is correct. Cold working is carried out below the recrystallization temperature of the metal or alloy. Recrystallization temperature is the temperature at which the strained material undergoes a recovery process, resulting in the formation of new strain-free grains.
3. Its hardness and strength increase.
- This statement is incorrect. While the hardness of a metal or alloy generally increases during cold working, the strength can increase or remain unchanged depending on the specific conditions and materials involved.
4. Its hardness increases but strength does not increase.
- This statement is correct. Cold working leads to an increase in the hardness of the metal or alloy due to the formation of dislocations and grain boundary strengthening. However, the strength may not necessarily increase as it depends on various factors such as the type of material, degree of cold working, and the presence of impurities.
During cold working, the metal or alloy is subjected to mechanical deformation, causing dislocations to move and pile up, resulting in increased hardness. However, after a certain degree of cold working, the dislocations become tangled, making further deformation difficult. This leads to a saturation point where the strength does not increase significantly.
In summary, cold working below the recrystallization temperature of a metal or alloy leads to an increase in hardness but may or may not result in an increase in strength. Therefore, the correct statements are 2 and 4, making option 'D' the correct answer.
Consider the following statements:When a metal or alloy is cold worked...
I think given answer is wrong....as yeild as well as ultimate tensile strength increases with cold working.
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