氮对不锈钢抗点腐蚀性能作用分析

Analysis of Anti - pitting - corrosion Performance of N2 in Stainless Steel

石化装置与设备多使用一般不锈钢,但往往遭受点腐蚀的困扰。近年国外已开发出高含氮的不锈钢,不仅提高了耐腐蚀性与强度,而且可替代部分镍,具有一定的经济效益。该文综述了高含氮不锈钢腐蚀特征的评价方法,根据ASTMG48标准方法,测得临界点腐蚀温度(CPT)和临界缝隙腐蚀温度(CCT),CPT和CCT与耐点腐蚀当量(PRE)有关。一般PRE=Cr+3.3Mo+16～30 N时,说明氮对不锈钢抗点腐蚀性能具有很大作用。氮主要是通过生成氨或NH4+以及生成硝酸根离子或促进表面膜稳定等方法来改善和提高不锈钢的抗点腐蚀性能。同时也分析了其它元素对不锈钢抗点腐蚀性能的影响,铬与钼是非常有利的元素、钨和铜是有利的元素、锰和硫是很不利的元素、镍是否是不利元素有不同观点,倾向是不利的元素。最后对200系列Cr-Mn-Ni-N不锈钢、双相不锈钢以及超奥氏体不锈钢等各种高含氮不锈钢的应用作了展望与分析。

As stainless steel is mnormally selected for the equipment in petrochemical plants,the equipment is subject to pitting corrosion.In the last several years,a high nitrogen steel has been developed abroad,which not only improves the steel’s pitting corrosion resistance and strength but also replaces some nickels,which is more economical.The evaluation methods of properties of high nitrogen stainless steel are introduced.Based upon ASTMG48,the tested critical pitting corrosion temperature（CPT） and crevice corrosion temperature（CCT） are related to pitting corrosion resistance equivalent（PRE）.When PRE = Cr ＋ 3.3Mo ＋ 16 ～ 30 N,it is indicated that nitrogen has played a very important role in improvement of pitting corrosion resistance of stainless steel.The improvement of pitting corrosion resistance of stainless steel is the result of formation of NH4＋ and nitrate radical ions and stabilization of surface film,etc.The impacts of other elements on pitting corrosion resistance of stainless steel are also studied.Cr ad Mo have a very good impact.W and Cu have a positive impact.Mn,sulfur and Ni have a negative impact.The high-N stainless steels such as 200 series Mn-Ni—N stainless steel,deplex steel and super austenitic stainless steel,etc are studied.