Effect of Plasma Nitriding Temperature on Surface Properties of Austenitic Stainless Steel

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Abstract
A chromium–nickel austenitic stainless steel was plasma nitrided at 535, 585, 650, 735, and 785°C. After nitriding, the structure, thickness, and hardness of the surface layer, as well as the appearance and height of surface irregularities, were determined. The wear and corrosion resistance of the nitrided steels were tested and the percentage of magnetic phases present was determined. It has been established that nitriding markedly raises the wear resistance of the steel at pressures of 50, 200, and 400 MPa. The corrosion resistance of the steel in 0.05 M Na2SO4 at pH 3 decreases as a result of nitriding. Nitriding leads to the appearance of a multi phase structure in the surface layer, the proportion of the ferromagnetic a and γ’ phases being dependant on nitriding temperature. After nitriding at 785°C the proportion of these phases is minimal. At the same time, the steel has a high hardness and wear resistance and is susceptible to passivation.