Corrosion Resistance Of Stainless Steel For Nuclear Engineering By Laser Melting

Stainless steel is one of the common materials for engineering structure. It is used for shell of fuel component, process piping, steam generator, pumps and valves. Although stainless steel has the advantage of superior corrosion resistance, many corrosion problems ccur when it is used under bad condition, such as stress corrosion, intergranular corrosion, crevice corrosion and pitting. The paper deals with the influencing factors of corrosion effect and analyzes the relationship between its microstructure, chemical composition and corrosion resistance by the following means: Firstly, to treat 1Cr18Ni9Ti austenitic stainless steel base material and welding joint by laser melting using TJ-HL-T5000 CO₂ laser to improve its evenness and increase the corrosion resistance; Secondly, to examine the microstructure of melting layer by such instruments as SEM of JSM-6360V, EDX of OXFORD, and OM of OLYMPUS GX51. Thirdly, to test corrosion resistance of the sample by an electrochemistry analytical instrument of CHI660B. Research results show:(1) The laser melting layers have the better ability of corrosion resistance than the stainless steel substrates relating to their organization. The organization of 1Cr18Ni9Ti austenitic stainless steel substrates is single-phase austenitic cubic crystal. After processed by the laser surface melting the organization of stainless steel substrates change greatly, especially the cubic crystal and super-micro crystalline appear on the surface of the reeking area.(2) On account of the characteristic of welding technology the organization and property of welding joint is not homogeneous. Under bad condition of nuclear engineering, stress corrosion and intergranular corrosion appear in the welding area. The area close to the welding line is the weaker part of the welding joint, laser melting can improve its microstructure and make it finer. So the ability of corrosion resistance of the area close to the welding line improves. Adopting the method of accelerating corrosion experiments by applying tensile stress on the specimen, the tendency of stress corrosion of the area declines. The anodic polarization curves shows that the ability of intergranular corrosion resistance of the stainless steel is stronger after the process of laser melting.The research makes a profitable attempt to improve the corrosion resistance of stainless steel welding joint by laser melting and lays foundation for applying laser melting technology in a much wider field.