Components subjected to high and abrupt loads require high strength and toughness at the same time. These properties are achieved by quenching and tempering the appropriate quenched and tempered steels with a heat treatment consisting of hardening and subsequent tempering to temperatures between 500°C and 700°C. The steel is then subjected to a heat treatment process to produce a high degree of strength and high toughness.
The tempering temperatures are significantly higher than for tempering after hardening. Unalloyed and alloyed steels are used for quenching and tempering. Unalloyed quenched and tempered steels contain 0.2% to 0.6% carbon, alloyed quenched and tempered steels additionally contain small amounts of chromium, molybdenum, nickel or manganese.
After quenching, needle-shaped martensite is present. When tempered at 400°C, part of it decomposes into finely distributed ferrite and cementite needles, which are excreted in the remaining martensite. As the tempering temperature increases, martensite decomposition progresses. When tempered to 550°C, it decomposes completely into ferrite and cementite needles. At 700°C, the cementite needles finally bale into cementite grains.