Study On Several Corrosion Issues In Stainless Steel Application

Stainless steels are one of the most widely used eco-friendly materials. However improper fabricating processes and employing conditions will cause various types of corrosion, among which intergranular corrosion is one of the most hazardous forms. While there are still no rapid, quantitative, non-destructive and versatile in situ methods competent for intergranular corrosion sensitivity detection up to now. In recent years as the importance of environment protection are more and more valued, diversified functional stainless steels began to come out, but still there are few reports concerning about corrosion of functional stainless steels in specified environments. This paper is focusing on corrosion problems in application of traditional stainless steel, new functional 304 bright-annealed stainless steel and 430 antibacterial stainless steel developed and manufactured by Taiyuan Iron and Steel Group Co. Ltd.In order to develop intergranular corrosion detection methods, electrochemical tests and SEM are used to study sensitive temperatures of intergranular corrosion, and also the procedure of initiation and development of intergranular corrosion. Electrochemical impedance spectroscopy (EIS) technique is applied to detect intergranular corrosion and equivalent circuit for intergranular corrosion is studied and corresponding parameters are decided accordingly. The relativity between equivalent circuit parameters and intergranular corrosion sensitivity is discussed. The results show that the intergranular corrosion sensitive temperatures between austenitic stainless steel and ferrite stainless steel are different from each other. Therefore in order to avoid unqualified products, the sensitizing heat-treatment system for the intergranular corrosion sensitivity examination should change according to various steel types. During EPR polarization in reactivation region EIS diagrams of both solution-annealed and sensitized 304 stainless steels present feature of double capacitance resistance arc and impedance modulus of sensitized stainless steel is one order of magnitude less than that of solution-annealed one at low frequencies, which shows that intergranular corrosion happens on sensitized stainless steel. Electrochemical equivalent circuit parameters such as Cc and Cd increase with severity of intergranular corrosion of sensitized stainless steel, whereas reverse situation happens to Rt, as is somewhat relative to occurrence and development of intergranular corrosion. The results obtained above provide the knowledge base for...