Quenching and Tempering

What is quenching and tempering?

When hardening and tempering are applied one after the other, the process is called quenching and tempering. The tempering temperatures chosen cause a significant drop in hardness. The process can be applied not only to structural steels but also to some tool steels.

How is it done?

The part is first heated to hardening temperature (about 820–880 °C depending on the steel), held until the structure has transformed to austenite, and hardened by quenching in oil or water depending on the steel and section. It is then tempered, usually between 500 and 650 °C. The higher the tempering temperature, the lower the hardness and strength and the higher the toughness, so the temperature is chosen to match the hardness or strength required on the drawing.

Because the hardening temperature has to be chosen correctly, the carbon content and alloying of the steel must be known. Stress relieving or normalising before hardening is beneficial, and preheating is necessary for alloy steels in particular.

Which steels and parts?

Medium-carbon quenched and tempered steels such as C45, 42CrMo4 and 34CrNiMo6 are the most common application. Axles, crankshafts and camshafts, gears, bolts, hydraulic piston rods and machine parts working under heavy load are quenched and tempered. The wearing areas of a quenched and tempered part can afterwards be induction hardened.

For a quote

State the steel grade, the part dimensions and weight, and the hardness (HRC or HB) or tensile strength range required after quenching and tempering in the quote form.