钴元素对Cr18-Ni9奥氏体不锈钢耐蚀性能的影响

Influence of cobalt element on corrosion resistance of Cr18-Ni9 austenitic stainless steel

利用真空感应炉冶炼了不含钴和钴质量分数分别为0.36%、0.55%的3组Cr18-Ni9奥氏体不锈钢,采用65%沸腾硝酸法和电化学动电位再活化法(EPR法)研究了3种不锈钢的晶间腐蚀敏感性;采用电化学试验方法(阳极循环极化曲线法)及化学浸泡法研究了3种试验不锈钢的耐点蚀性能。结果表明:在Cr18-Ni9不锈钢中添加0.36%,0.55%的钴元素,材料的晶间腐蚀速率增大,在稀硫酸介质中的再活化率增大,材料的晶间腐蚀敏感性增大;添加0.36%钴元素对Cr18-Ni9不锈钢的耐点蚀性能影响不大,添加0.55%的钴元素使得Cr18-Ni9不锈钢在氯离子介质中的点蚀形核倾向明显增大,钝化膜的修复能力明显减弱,耐点蚀性能显著下降。腐蚀的电化学特征与其浸泡腐蚀的结果吻合。钴减少了Cr18-Ni9不锈钢中δ铁素体的数量是影响其耐蚀性能的主要原因。

Cr18-Ni9 austenitic stainless steels without and with cobalt of 0, 0. 36% and 0. 55% were smelted by a vacuum induction furnace. Intergranular corrosion sensitivity of the steels was researched by 65% boiling nitric acid method and the electrochemical potentiokinetic reactivation method （ EPR ）. Pitting corrosion resistance of the steels was valuated by electrochemical test method （ the anode circular polarization curve method） and chemical immersion method. The results show that the corrosion rate in 65% boiling nitric acid of the Cr18-Ni9 stainless steels containing 0.36% and 0. 55% cobalt element increases, and the reactivation rate in dilute sulphuric acid medium and intergranular corrosion sensitivity of the stainless steels also increase. The addition of 0. 36% cobalt element has little influence on pitting corrosion resistance of the Cr18-Ni9 austenitic stainless steel, but pitting corrosion tendency increases distinctly of the stainless steel containing 0.55% cobalt. The addition of 0. 55% cobalt reduces the repair ability of the passivation film of the Crl8-Ni9 austenitic stainless steel in chloride ions medium, resulting in the decrease of distinctly. The electrochemical characteristics of local corrosion coincide with the results of immersion corrosion.