Question

Which of the following characterize a hot-worked steel part in comparison with a cold-worked part?

I. higher yield strength
II. better surface finish
III. greater hardness
IV. greater toughness
V. less ductility
A) I and V
B) II only
C) III and IV
D) none of the above

Answer 1

Hot-worked and cold-worked steel parts differ in their mechanical properties. Hot-working results in lower yield strength and higher ductility, while cold-working increases yield strength, hardness, and toughness.

Step-by-step explanation:

Hot-worked and cold-worked steel parts differ in their mechanical properties. Hot working involves plastic deformation of steel at high temperatures, while cold working is done at room temperature.

I. Higher yield strength: Hot-worked steel parts generally have lower yield strength compared to cold-worked parts. The high temperature during hot working can result in grain growth and reduced strength.

II. Better surface finish: Cold-working processes like rolling, drawing, and grinding can improve the surface finish of steel parts.

III. Greater hardness: Cold-working processes increase the hardness of steel parts as the plastic deformation leads to dislocation motion and strain hardening.

IV. Greater toughness: Cold-worked steel parts generally exhibit greater toughness due to the strain hardening effect.

V. Less ductility: Hot-working at high temperatures can reduce the ductility of steel, while cold-working can increase the ductility.

Therefore, the correct answer is A) I and V.