Combination of plasma nitriding and nitrocarburizing treatments of AISI 630 martensitic precipitation hardening stainless steel

Abstract

Low temperature plasma nitriding and nitrocarburizing were experimented to study the effect of these treatments on the surface hardness and the expanded martensite layer (α'N layer) thickness of the AISI 630 martensitic precipitation hardening stainless steel. Plasma nitrided samples show thicker α'N layer thickness (about 16 µm) but their corrosion resistances are worse than the untreated sample. On the other hand, plasma nitrocarburized samples show better corrosion resistance, whereas their α'N layer thickness values (around 10 µm) are very low. But the surface hardness values of both the nitrided and nitrocarburized samples are quite similar (approximately 1250 HV0.05). The purpose of the present study is to combine the beneficial effects of both plasma nitriding and plasma nitrocarburizing. Therefore, in order to get a higher surface hardness and thicker α'N layer thickness with good corrosion behavior, a series of combination of simultaneous nitriding and nitrocarburizing were investigated. This process is termed here as “Multiple Nitriding-Nitrocarburizing process”. The highest surface hardness (around 1350 HV0.05), highest α'N layer thickness (around 16 µm) and best corrosion resistance are achieved when treated with this noble process, compared to single plasma nitriding or single plasma nitrocarburizing process.