Improvement of mechanical properties and corrosion resistance of 316L and 304 stainless steel by low temperature plasma cementation

ABSTRACT Low temperature plasma carburizing treatment of austenitic stainless steels is a carbon surface diffusion process for a surface hardness and corrosion and wear resistance. The process is carried out by introducing a mixture of carbon-containing gases and through the use of low temperatures the resulting cemented layer usually contains a single phase of supersaturated austenite with carbon – S-phase. For the present investigation, austenitic stainless steels AISI 316L and 304 were plasma cemented for 8 hours in the gas mixture containing 7.5% CH4 in H2, with a pressure of 500 Pa, at temperatures of 375 ºC and 450 ºC. The phases formed were determined by X-ray diffraction. The corrosion resistance was evaluated through immersion tests over time and cyclic voltammetry. The results indicate that there was no formation of compounds (carbides) in the cemented layer for both steels at any of the temperatures and there was a corrosion resistance improvement.

摘要 奥氏体不锈钢的低温等离子渗碳处理是一种碳表面扩散工艺，旨在提升材料的表面硬度、耐腐蚀性能与耐磨性能。该工艺通过引入含碳气体混合物并在低温环境下实施，所得渗层通常仅含碳过饱和奥氏体单相——即S相。本研究中，研究人员以体积分数7.5%的CH4与H2组成的混合气体为渗剂，在500 Pa压强、375℃与450℃的温度条件下，对AISI 316L与304型奥氏体不锈钢进行了8小时的等离子渗碳处理。采用X射线衍射（X-ray diffraction）对生成的物相进行了鉴定；通过长期浸泡试验与循环伏安法（cyclic voltammetry）对材料的耐腐蚀性能进行了评估。结果表明，两种不锈钢在任一试验温度下的渗层中均未生成化合物（碳化物），且耐腐蚀性能均得到了提升。