The structure, properties and change in the cross-sectional corrosion resistance of a nitrided layer produced on AISI 321 steel

The paper presents the results of an investigation into the structure and physicochemical properties of surface layers on AISI 321 stainless steel obtained from the process of glow-discharge nitriding. The thickness and structure of the resulting surface layer were evaluated based on: microscopic observations, changes in microhardness, x-ray analysis and the local analysis of nitrogen content in the surface layer cross-section. The evaluation of the corrosion resistance of this nitrided stainless steel used the progressive thinning method with determination the potentiodynamic polarisation characteristics of the nitrided surface in stages from the outer surface through the coating thickness into the bulk material. The rate of general corrosion of the outer nitrided layers of AISI 321 stainless steel in acidified sulphate solutions is approximately four to seven times as high as that of the bulk material. Current values show the maximum at depths of 100-200 mu m where the structure is dominated by nitride precipitates Cr2N.