Combined Application of Mechanical Deformation and Nitriding to Realize Optimal Mechanical and Anticorrosion Properties for 316 Stainless Steel

Abstract

Thermo-mechanical and thermochemical surface treatments are well-established methods for optimizing the properties of metallic materials. This study examines the effect of cryo-rolling-induced martensite in 316 stainless steel on its corrosion characteristics and the way these characteristics alter after low-temperature nitriding. 316 stainless steel specimens were cryo-rolled to realize varying dislocation densities and martensite fractions followed by salt bath nitriding at 425°C for 4 h. Detailed microstructural and electrochemical characterizations were performed after different stages. Increased martensite content resulted in a thicker nitrided layer, and the martensite diffraction peaks were extensively broadened with relatively less shift towards lower diffraction angles. Subsequent nitriding led to a much higher hardness increase for martensite phase compared to austenite phase. Electrochemical measurements showed that martensite development reduced the corrosion resistance; however, the following nitriding treatment enhanced the corrosion resistance. The distinct electrochemical properties observed were related to the presence of dislocations and binding characteristics of N with dislocations and substitutional elements of austenite and martensite phases. Successive application of cryo-rolling and nitriding can offer optimal combination of mechanical and electrochemical properties.