Q1: In cold working of metal as compared to its hot working

ANS:D - yield stress, hardness and fatigue strength is not at all affected.

In cold working of metal compared to its hot working:

• Cracks and blow holes are eliminated: This statement is generally incorrect. Cold working can introduce cracks or surface defects in the metal due to the high stresses applied during deformation. However, hot working can help reduce the likelihood of cracks and blowholes because the metal is more ductile at elevated temperatures.
• Ductility and impact strength improve: This statement is generally incorrect. Cold working typically reduces the ductility of the metal due to the introduction of dislocations and strain hardening. While cold working may improve certain mechanical properties like hardness and tensile strength, it often leads to a reduction in ductility and impact strength.
• Appreciable strain hardening is produced: This statement is correct. Cold working induces strain hardening in the metal, which strengthens the material by increasing dislocation density and hindering dislocation movement. This results in improved mechanical properties such as tensile strength and hardness.
• Yield stress, hardness, and fatigue strength are not at all affected: This statement is incorrect. Cold working can significantly increase yield stress, hardness, and fatigue strength due to strain hardening. The material becomes stronger and more resistant to deformation and fatigue failure after cold working.

In summary, while cold working can introduce certain drawbacks such as cracks and reduced ductility, it can also improve mechanical properties like yield stress, hardness, and fatigue strength through strain hardening. Therefore, appreciable strain hardening is produced during cold working, and it affects various mechanical properties of the metal.