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

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.