CO浓度对316L不锈钢准平衡气体渗碳的影响

Effect of CO concentration on paraequilibrium gas carburization of 316L stainless steel

采用准平衡气体渗碳工艺,在不同CO浓度的CO/H2/N2混合气体条件下制备了表面强化层,研究CO浓度对316L奥氏体不锈钢渗碳层的微观结构、碳浓度分布、表面纳米硬度和残余应力的影响。结果表明,准平衡气体渗碳层为单一的扩张奥氏体相;当CO浓度小于30%时,渗碳层厚度、表面纳米硬度和压缩残余应力均随CO浓度的提高而提高,当CO浓度高于35%时,渗碳气体碳活度降低,渗碳表面强化效果降低;经470℃条件下准平衡渗碳20 h后,316L不锈钢渗碳层厚度最高可达30μm,表面碳浓度增加至2.6 mass%,导致表面纳米硬度从3 GPa增加至9 GPa,并产生1300 MPa以上的压缩残余应力。

Surface strengthened layers were prepared by paraequilibrium gas carburization in mixture of CO / H2/ N2 with different CO concentration. The effect of CO concentration on microstructure,carbon profile,surface nano-hardness and residual stress of the carburized layer on 316 L stainless steel surface was investigated. The results show that the paraequilibrium carburized layer consists of single expanded austenite. With increase of the CO concentration,the thickness,surface nano-hardness and compressive residual stress of the carburized layer increase when the CO concentration is less than 30%,but when the CO concentration continues to increase to 35%,the surface strengthening effect decreases because of lower carbon activity of the carburizing atmosphere. After the paraequilibrium carburization at 470 ℃ for 20 h,the thickness of carburized layer can reach 30 μm,the surface carbon concentration increases to 2. 6mass%,leading to an increase in surface nano-hardness from 3 GPa to 9 GPa and compressive residual stress more than 1300 MPa.