Mechanisms of plastic deformation, hardening, and fracture in single crystals of nitrogen-containing austenitic stainless steels

Abstract

We have carried out a systematic investigation of the mechanisms for solid-solution hardening by nitrogen atoms and dispersion hardening by nitride particles in single crystals of austenitic stainless steels with different stacking fault (SF) energies γ_SF=0.02–0.2 J/m². We show that alloying with nitrogen C_N=0–0.7 mass % and precipitation of dispersed particles leads to the appearance of an orientation dependence of the critical shearing stresses τ_cr, asymmetry phenomena, an orientation dependence of the slip and twinning deformation mechanisms, superelasticity, and transition from ductile fracture to brittle fracture. We develop dislocation models for solid-solution hardening by interstitial atoms, the orientation dependence and the asymmetry of τ_cr, based on taking into account the effect of the external stress field on the splitting of a/2〈110〉 dislocations into partial Schockley a/6〈211〉 dislocations and the change in the position of the interstitial atoms from octahedral interstitial sites to tetrahedral sites with a shift of the twinning a/6〈211〉 dislocations by a Burgers vector. We establish the role of strain localization, splitting of gliding dislocations, twinning, and a high stress level in creation of strain hardening, plastic flow instabilities, and the conditions for the "brittle-ductile" transition.