COMBINED EFFECT OF NITROGEN AND SILICON ON LOW-CYCLE FATIGUE OF 12-PERCENT CR MARTENSITIC STAINLESS-STEELS

The low cycle fatigue behaviour of 12% CrMoV type martensitic stainles s steels has been studied at room temperature taking into account the chemical composition, especially carbon, nitrogen and silicon. High va lues of cyclic stress can be obtained in nitrogen plus silicon contain ing steel. The cyclic plasticity is governed by the state of precipita tion and by the interactions of dislocations with silicon atoms. TEM a nalyses show that dislocation arrangements are better formed in the ca rbon plus silicon alloy (C-Si) and in. the nitrogen alloy (N) than in the nitrogen plus silicon alloy (N-Si). As a consequence, the surface plasticity observed in SEM is more difficult to occur in the N-Si allo y leading to earlier fracture.