The process of heating hardened steel or cast iron below its melting point to decrease hardness and increase toughness is called?

The process of heating hardened steel or cast iron below its melting point to decrease hardness and increase toughness is called?

• A. Quenching
• B. Annealing
• C. Tempering
• D. Normalizing

Answer: (C)

Tempering is heating hardened steel or cast iron to a temperature below its melting point and holding there to relieve internal stresses, reduce the hardness of the martensitic structure, and increase toughness and ductility. This step follows quenching, which produces a very hard but brittle material; tempering loosens the brittle structure just enough to improve toughness while retaining useful strength. The exact tempering temperature and time determine the balance between hardness and toughness: lower temperatures preserve more hardness, while higher temperatures yield greater toughness. Other heat treatments—annealing softens by heating to a high temperature and slow cooling, and normalizing refines the grain by heating above the transformation range and air cooling—work with different goals, so they don’t fit the description as precisely as tempering does.

Tempering is heating hardened steel or cast iron to a temperature below its melting point and holding there to relieve internal stresses, reduce the hardness of the martensitic structure, and increase toughness and ductility. This step follows quenching, which produces a very hard but brittle material; tempering loosens the brittle structure just enough to improve toughness while retaining useful strength. The exact tempering temperature and time determine the balance between hardness and toughness: lower temperatures preserve more hardness, while higher temperatures yield greater toughness. Other heat treatments—annealing softens by heating to a high temperature and slow cooling, and normalizing refines the grain by heating above the transformation range and air cooling—work with different goals, so they don’t fit the description as precisely as tempering does.