1. General

Figure 1 quantifies the possibilities offered by steels through curves showing the evolution of tensile strength as a function of carbon content and after various heat treatments.

After quenching and tempering, the usable range in practice is between :

• a lower limit corresponding to a high-temperature temper which does not lead to very high strength performances (unless the steel contains carburigenic alloying elements), but ensures a high level of ductility characteristics and therefore safety;

• an upper limit corresponding to stress-relieving tempering (180 to 220 C), which preserves high strength characteristics,...