S31609奥氏体不锈钢中残留δ铁素体的腐蚀行为

Influence of delta-ferrite on corrosion behavior of S31609 austenitic stainless steel

对含残留δ铁素体的S31609奥氏体不锈钢进行650℃、保温2h的敏化处理,通过金相蚀刻、电子探针和扫描开尔文探针显微镜分析并比较残留δ铁素体和奥氏体晶界处的腐蚀特征。结果表明,随着敏化过程中残留δ铁素体快速分解成稳定的σ相、二次奥氏体(γ_(2))和Cr_(23)C_(6),尽管奥氏体晶界和δ/γ相界处没有明显的Cr/Mo贫化区,但是析出相与邻近基体的电势差始终存在,σ相、γ_(2)和Cr_(23)C_(6)等第二相杂质或颗粒的费米能级相对于基体更低,使得电子更容易从周围基体的费米面跃出,从而使基体在电化学腐蚀中充当阳极,优先发生腐蚀。

The S31609austenitic stainless steel containing residual delta-ferrite was sensitized at 650℃for 2h.The corrosion characteristics of residual delta-ferrite and austenite grain boundary were analyzed and compared by metallographic etching,electron probe microanalyzer and scanning Kelvin probe.The results show that the residual deltaferrite is rapidly decomposed into sigma phase,secondary austenite phase(γ_(2))and Cr_(23)C_(6)during the sensitization process.Although there is no obvious Cr and Mo solute depleted zone at austenite grain boundary andδ/γgrain boundary,the potential difference between the precipitated phase and the adjacent substrate always exists.The Fermi energy of the secondary phase,such as the sigma phase,γ_(2)and Cr_(23)C_(6)is lower than that of the matrix,which makes it easier for electrons to jump from the Fermi surface of the surrounding matrix.As a result,the matrix acts as an anode in the electrochemical corrosion system,and the corrosion occurs preferentially.