High Nitrogen Steels. Effect of Nitride (Cr2N) Precipitation on the Mechanical, Corrosion, and Wear Properties of Austenitic Stainless Steel.

High-nitrogen austenitic stainless steels are thermally unstable and susceptible to nitride precipitation (primarily Cr.N) during elevated temperature exposure.This paper describes the effect of Cr.N precipitation on the mechanical, corrosion, and abrasive wear properties of a high-nitrogen austenitic stainless steel, nominally Fe-1 9Cr-5Mn-5Ni-3Mo-0.02C-0.7N.In the annealed state.Cr-rich nitrides (Cr=N) precipitate sequentially as intergranular, cellular, and finally, intragranular precipitates.Cold working, prior to aging, increases grain boundary and intragranular precipitation kinetics, but retards cellular phase formation.Nitride precipitation has only a minor influence on the yield and ultimate tensile strength of annealed materials, but causes embrittlement which is enhancedby high strain rate conditions such as impact testing and by the accelerated precipitation kinetics associated with prior deformation.Nitride precipitation results in sensitization which is also accelerated by prior deformation.The degree of sensitization, as measuredby electrochemical potentiokinetic reactivation (EPR) testing, correlates to intergranular, cellular, and intra- granular Cr-depletion.Although the degree of sensitization is defined by both the Cr-minimumand width of Cr-depleted region, a Cr level below approximate]y 14 wt'/• is required for sensitization.Precipitation also results in a greater corrosion susceptibility as determined by potentiodynamic polarization scans.The wear behavior of the 0.7 wt"/• N alloy is little affected by the precipitation of Cr.N since the volume fraction and size (compared to the abrasive) of the Cr.N precipitates is insufficient to alter the wear resistance of the alloy.