Tempering

What is tempering?

Quench-hardened steel is very hard but brittle: martensite and internal stresses make the part fragile against impact and vibration. Tempering heats the hardened part to a set temperature below the transformation range, holds it there and then cools it. Internal stresses fall, toughness rises and hardness is adjusted to the required value.

Temperature and result

• Low temperature (about 150–250 °C): most of the hardness is kept and stresses are reduced. Used for induction and case hardened surfaces and for tools.
• Medium temperature (about 350–500 °C): springs and parts that need elasticity.
• High temperature (about 500–650 °C): together with hardening it forms quenching and tempering, giving high toughness and strength.

Why straight away?

Leaving a hardened part untempered increases the risk of delayed cracking, so tempering follows hardening as soon as possible. Some tool steels are tempered two or more times to reach the required structure.

For a quote

State the steel grade and the hardness range required after tempering (e.g. HRC) in the quote form.