Which statement regarding heat treatment is true for relieving residual stresses in metal?

Which statement regarding heat treatment is true for relieving residual stresses in metal?

• A. Increase hardness to maximum.
• B. Create porosity.
• C. Relieve residual stresses and improve ductility.
• D. Change color for aesthetics.

Answer: (C)

Relief annealing in heat treatment aims to reduce internal stresses left from forming, welding, or machining. By heating the metal to a moderate temperature and holding it, atoms have time to rearrange and dislocations to rearrange, which relaxes the stresses trapped in the structure. This lowering of residual stress often also softens the metal a bit and increases its ductility, making it less prone to cracking and easier to work with after processing. So the statement that it relieves residual stresses and improves ductility matches what this heat treatment is meant to achieve. The other ideas describe outcomes that aren’t the purpose of stress relief: maximizing hardness comes from hardening, not relieving stresses; creating porosity would be a defect and not a goal of heat treatment; and changing color is a cosmetic effect, not about relieving internal stresses or improving ductility.

Relief annealing in heat treatment aims to reduce internal stresses left from forming, welding, or machining. By heating the metal to a moderate temperature and holding it, atoms have time to rearrange and dislocations to rearrange, which relaxes the stresses trapped in the structure. This lowering of residual stress often also softens the metal a bit and increases its ductility, making it less prone to cracking and easier to work with after processing. So the statement that it relieves residual stresses and improves ductility matches what this heat treatment is meant to achieve.

The other ideas describe outcomes that aren’t the purpose of stress relief: maximizing hardness comes from hardening, not relieving stresses; creating porosity would be a defect and not a goal of heat treatment; and changing color is a cosmetic effect, not about relieving internal stresses or improving ductility.