The heat treating process designed to increase toughness by heating and cooling in air is called what?

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

Answer: (A)

The main idea is how controlled heating and cooling in air can reduce brittleness and boost toughness after hardening. Tempering does exactly that: you heat hardened steel to a moderate temperature below the critical point and then let it cool in air. That reheating relieves internal stresses and allows the crystal structure to rearrange, so the material becomes tougher and less prone to shattering, while still retaining useful hardness.

This fits the scenario where toughness is increased after a prior hardening step, with the cooling occurring in air. Quenching, by contrast, is rapid cooling to make the steel very hard but brittle. Annealing softens the steel to increase ductility, which is a different objective. Normalizing refines the grain by heating above critical and air cooling, improving general toughness but not specifically the post-hardening tempering effect.