Low-temperature Plasma Nitriding and Plasma Nitrocarburing of 304 Stainless Steel

Objective To study the microstructure,hardness and wear and corrosion properties of plasma nitrided and nitrocarburized layers of 304 austenitic stainless steel,and investigate the wear mechanism of the layers. Methods A nitrided or nitrocarburized layer was formed on 304 stainless steel substrate by low-temperature plasma nitriding( PN) or plasma nitrocarburizing( PNC) technique. The phase structure,hardness and wear and corrosion properties were comparatively analyzed with XRD,OM,microhardness tester and electrochemical measurement system. Results The nitrided or nitrocarburized layer consisted of expanded austenite( S-phase). The composite γN+ γClayer was formed by PNC technique with larger thickness under the same process condition. The hardness of the two layers was 3. 5 times higher than that of the substrate. The wear property of nitrocarburized layer was better than that of the nitrided layer under dry sliding friction condition. The wear mechanism of PN layer was ploughing actions and fracture,while the wear mechanism of PNC layer was ploughing actions and micro-cutting. The corrosion resistance of both the nitrided and nitrocarburized layers was better than that of the substrate as revealed by electrochemical test. Conclusion PN and PNC treatment at 420 ℃ could effectively improve the hardness and wear resistance of 304 stainless steel,and the treatment of PNC was better.