低温气体渗碳对304L奥氏体不锈钢抗氢性能的影响

Effects of Low Temperature Gaseous Carburization on Hydrogen Embrittlement Resistance of 304L Austenitic Stainless Steel

对304L奥氏体不锈钢进行低温(470℃)气体渗碳,采用光学显微镜(OM),电子探针显微分析仪(EPMA)以及X射线应力分析仪(IXRD)研究了304L奥氏体不锈钢低温气体渗碳强化层的厚度、碳含量及残余应力分布。通过电化学充氢实验,结合X射线相结构分析(XRD),慢应变单轴拉伸试验,扫描电镜(SEM)观察以及氢含量检测等方法分析低温气体表面渗碳对304L不锈钢抗氢脆性能的影响。研究表明:304L不锈钢经30 h低温气体表面渗碳处理后,形成了约22μm的渗碳层,渗碳层中碳含量和残余应力在表面最高,分别为2%(质量分数)及-1.47 GPa,并沿深度方向梯度减小;低温气体表面渗碳大幅度提高304L不锈钢表面的稳定性,在充氢过程中不产生马氏体相变,从而提高其抗氢性能。此外,渗碳层中的压缩残余应力对抑制H扩散,也起到了积极的作用。

304 L austenitic stainless steel was gaseous carburized at low temperature（LTGC）. The thickness, carbon content and residual stress distributions of the carburized layer of were investigated using optical microscope（OM）, electron probe micro-analyzer（EPMA） and X-ray stress analyzer. Electrochemical hydrogen charging experiments on 304 L austenitic stainless steel before and after LTGC were conducted, combined with slow strain rate uniaxial tensile tests, SEM, XRD and hydrogen analysis instrument, to clarify the effect of LTGC on hydrogen embrittlement resistance of 304 L steel. Results show that a 22 μm thick carburized layer forms on the surface of 304 L stainless steel after LTGC. The carbon content and residual stress are the maximum on the outmost surface, which are about 2% and –1.47 GPa, respectively. The carbon content and residual stress gradiently decrease along the depth direction. Moreover, LTGC enhances the stability of austenite and control martensitic transformation in the hydrogen charging progress, which greatly improves hydrogen resistance of 304 L steel.Additionally, the compressive residual stress in the carburized layer also plays a beneficial role in suppressing the diffusion of hydrogen.