P4 The tempering of steel

Reheating the steel after quenching to improve the microstructure

thermally or transformation induced stresses

1. The precipitation of transition epsilon-carbides(<250°C)

2. The decompositon of reatined austenite (200-300°C)

3. replacement of epsilon with Fe3C (250-350°C)

4. The coarsening and spheroidization of Fe3C (300-400°C)

5. Precipitation of secondary alloy carbides form martensite and/or retained austenite

C content -0.2%

Common for tempered steels in the range od 260°C -370°C

Decrease in impact thoughness due to the formation of cementit particles at the martensite lath boundaries.

Can be avoided by adding 0.5% Mo to the steel

Embrittlement through heat treatment of impure steels (containing phosphorus, anitmony, tin, sulfur)

Impurities segregate the grain boundaries and reduce cohesion.

Can be minimized by the addition of 0.5% Mo