Hot Working and Strain Hardening

Hot working and strain hardening are two important concepts in metallurgy and material science. Let's understand each of these concepts before discussing the assertion and reason given in the question.

Hot Working: Hot working is a metalworking process performed at a temperature above the recrystallization temperature of the material. The recrystallization temperature is the temperature at which the metal grains start to reform and the material becomes softer. Hot working includes processes like forging, rolling, extrusion, and drawing.

Strain Hardening: Strain hardening, also known as work hardening or cold working, is a process of increasing the strength of a metal by plastic deformation. In this process, the metal is deformed at a temperature below the recrystallization temperature. The plastic deformation causes the metal grains to deform and align, which increases the strength of the material.

Assertion and Reason

Now let's discuss the assertion and reason given in the question:

Assertion (A): Hot working does not produce strain hardening.

Reason (R): Hot working is done above the recrystallization temperature.

Both assertion and reason are true, and reason is the correct explanation of the assertion. Let's understand why:

Hot working is done above the recrystallization temperature, which means that the metal is in a soft and ductile state during the process. When the metal is deformed at high temperatures, the grains of the metal deform and recrystallize, which results in a decrease in strength and an increase in ductility. This means that the metal does not undergo strain hardening during hot working.

On the other hand, strain hardening occurs when the metal is deformed at a temperature below the recrystallization temperature. In this case, the metal grains deform and align, which increases the strength of the material. This process is commonly used in cold working processes like rolling, bending, and drawing.

Conclusion

In conclusion, the assertion and reason given in the question are both true, and reason is the correct explanation of the assertion. Hot working is a process performed above the recrystallization temperature, which does not result in strain hardening. Strain hardening occurs at a temperature below the recrystallization temperature, and it increases the strength of the material.

Below the recrystallization temp ie. Cold working have high stress induced in it