Gas Nitriding of AISI 420 Martensitic Stainless Steel during the Incubation Period of CrN Precipitation

An incubation nitriding (IN) process was utilized to enhance the surface properties of martensitic stainless steels. This process involved optimizing the process parameters to fabricate a thick nitrided layer with excellent corrosion resistance and wear resistance. The microstructure and phase composition of the IN-treated layers were characterized by using an optical microscope, scanning electron microscope and x-ray diffractometer analysis. The surface properties of the IN-treated layers, such as corrosion resistance and wear resistance, were systematically investigated by the microhardness tester, electrochemical test and wear test, respectively. The results indicate that there is a narrow time window exists in the nitriding of martensitic stainless steels. By nitriding in such a time window, a thick nitrided layer of 50 μm can be formed in a short time without losing corrosion resistance. During the IN process, there is a redistribution of chromium atoms, leading to the recovery of corrosion resistance in the nitrided layers. In addition, the wear resistance of IN-treated layers was improved. The IN process shows a high nitriding efficiency, which provides a good choice for incubation nitriding of martensitic stainless steels.