2. Tempering

It should be remembered that, for the steels considered here, the purpose of quenching is to prevent carbon precipitation during the return from austenitizing temperature to room temperature, and to do so in as large a cross-section of the part as possible. For economic reasons (savings in alloying elements), it is accepted that a certain proportion of bainite can be substituted for martensite, provided that tempering is carried out at a temperature above 500 C (cf. ).

For a given steel, the two factors that will condition the result of quenching are :

• the hardenability of the steel under the austenitizing conditions adopted;

• austenite cooling conditions.