Enhanced performances of deep nitriding austenitic stainless steel by a novel complex treatment

Abstract

A novel combination of plasma nitriding and solution treatment was primarily developed for preparing deep nitriding austenitic stainless steel. Plasma nitriding was used to get high concentration of nitrogen in the surface layer of austenitic stainless steel at higher rate, and solution treatment was used to fully decompose the chromium nitrides formed during plasma nitriding and let nitrogen atoms dissolve into the matrix, and thus possible to get deep nitriding austenitic stainless steel. The performances of the treated samples were evaluated by optical microscopy, x-ray diffraction (XRD), micro-hardness test, electrochemical polarization and pin-on-disk tribotester. The results showed that a deep nitriding layer with effective hardening thickness of 1.0 mm composed of nitrogen expanded austenite (γN) was obtained for austenitic stainless steel by the novel complex treatment. Furthermore, the surface hardness of the PN+ST sample was up to 747 HV, 547 HV higher than 200 HV of untreated sample. The surface hardness of the specimen treated by the novel complex treatment was significantly improved, and the friction coefficient decreased from 0.8 to 0.7, the deep nitriding austenitic stainless steel had better corrosion resistance, the corrosion potential was increased from −0.534 V to −0.445 V, and the current density was decreased from 1.589 × 10−6 A cm−2 to 0.916 × 10−6 A cm−2.