What is the purpose of tempering martensite in steels?

• A. Increase corrosion resistance.
• B. Increase machinability.
• C. Reduce brittleness and internal stresses.
• D. Retain improved hardness after quenching while reducing brittleness.

Answer: (D)

Tempering martensite is about balancing hardness with toughness. Quenching creates martensite, which is extremely hard but very brittle because the lattice is distorted and carbon is locked in solution, leaving high internal stresses. Tempering lets carbon atoms diffuse and form small carbides, relaxing these stresses and reducing the brittleness. The result is tempered martensite—a structure that stays very hard, but is much tougher and less prone to brittle fracture. So the process aims to keep the improved hardness gained from quenching while significantly lowering brittleness, which is why this option is the best description. Corrosion resistance and machinability aren’t the primary goals of tempering, and while brittleness is reduced, the core idea is achieving a durable, hard, yet tougher steel.