Improvement of the Surface Properties of Low Temperature Plasma Nitrocarburized Martensitic Precipitation-Hardening Stainless Steel by Aging Treatment

Abstract

Various aging treatments were conducted on AISI 630 martensitic precipitation hardening stainless steel in order to optimize aging condition. Aging treatment was carried out with Ar gas in the chamber at temperature of 380°C, 400°C and 430°C and times of 2, 4 and 8 h. After obtaining the optimized aging condition, several nitrocarburizing treatments were done with and without the aging treatment. Nitrocarburizing was performed on the samples at 400V with a gas mixture of H2, N2 and CH4 for 15 hrs at 4.0 Torr vacuum pressure. The aging condition was optimized as 400°C temperature for 4 h. Better results were found when the samples were experimented with aging + nitrocarburizing treatment. In this combined process, the corrosion resistance improved noticeably which is confirmed by potentiodynamic polarization test and by observing the surface of the samples after corrosion test. Moreover, the surface hardness increases up to 1300 HV0.05 approximately and α'N layer thickness increases up to 11 μm (approximately).