Plastic deformation and fracture behaviour of high-nitrogen nickel-free austenitic stainless steel

Abstract

The plastic deformation and fracture behaviour of a high-nitrogen nickel-free austenitic stainless steel were examined by performing tensile testing at room temperature and at a wide strain rate range. The tensile testing demonstrated that this steel shows a significant strain rate dependence of the strength and ductility. With increasing strain rate from 10⁻⁴ to 1s⁻¹, the yield strength increases from 673 to 801 MPa and the ultimate tensile strength increases from 958 to 1003 MPa; the uniform elongation decreases from 75 to 44% and the total elongation decreases from 86 to 58%. The analysis of the stress–strain curve by using the Ludwigson equation showed that this steel exhibits a two-stage strain hardening behaviour, the strain hardening exponents at low and high strain regions ( and ) and the transition strain () decrease with increasing strain rate. Based on the analysis results of the stress–strain curve, the transmission electron microscopy characterisation of the microstructure and the scanning electron microscopy observation of the deformation and fracture surfaces, the significant strain rate dependence of the strength and ductility of this steel was discussed and connected with the variation in the dislocation activity with strain rate.