贫铬区演化对奥氏体不锈钢晶间腐蚀影响

Effect of Cr-depleted zone evolution on intergranular corrosion of austenitic stainless steel

采用电化学动电位再活化(EPR)法测定了950℃固溶处理的304不锈钢敏化温度-时间-敏化(TTS)曲线,观察了敏化处理的晶间腐蚀组织形貌。建立了一维304奥氏体不锈钢敏化的物理模型,模拟了敏化过程中晶界区域富铬碳化物沉淀析出长大、相界面的溶质热力学、相界迁移动力学和基体中溶质Cr、Ni浓度分布。结果表明:贫铬区中的Cr浓度变化和有效贫铬区宽度两个参量能体现晶界腐蚀的程度,这与敏化处理的晶间腐蚀形貌观察一致;溶质Ni富集及扩散不仅改变贫铬区中溶质Fe、Cr浓度分布,而且改变富铬碳化物成分组成以及其长大速率。敏化处理时贫铬区中溶质碳化学势先升高后缓慢下降,溶质铬化学势变化与之相反;基于相界面迁移一致性的富铬碳化物长大基本符合Zener抛物线增长趋势。

Temperature-time-sensitization(TTS) curves of he 304 austenitic stainless steel were studied by means of electrochemical potentiodynamic reactivation(EPR) after solid-solution treatment at 950 ℃,the corresponding micro intergranular corrosion morphology was observed. The physical model was established based on the solutes thermodynamics,solutes flow equation in phase interface and solutes diffusion equation in the bulk,the one dimensional sensitization process of 304 austenitic stainless steel was simulated. The results show that the intergranular corrosion is determined by Cr solute concentration profiles in Cr-depleted zone,and influenced by the width of effective Cr-depleted zone,the change combination of two parameters agrees with experimental results; Ni-enriched concentration and its diffusion will change Fe,Cr solutes concentration profiles in Cr-depleted zone and(CrFe) C(6/23) carbide components and carbide precipitation growth rate. The carbon chemical potential in the bulk near the phase interface increases in initial sensitization stage then decreased slowly,the Cr chemical potential changes oppositely. Based on the phase interface migration consistency,(CrFe) C(6/23) carbide interfacial migration agrees with Zener parabolic growth trend.