Duplex stainless steel pitting problem

Pitting resistance is an important characteristic of duplex stainless steel, which is closely related to its chemical composition and microstructure. Pitting usually occurs at the α/γ interface, so it is considered to occur in the γ* phase between the γ and α phases. This means that the Cr content in the gamma * phase is lower than in the gamma phase. The composition of the γ* phase is different from that of the γ phase because the Cr and Mo contents in the γ* phase are lower than the Cr and Mo contents in the initial γ phase. The further study shows that the pitting potential of steels with lower N content is more sensitive to the cooling rate. Therefore, when welding duplex stainless steel with low N content, the control requirements for cooling speed are more stringent. In the process of duplex stainless steel welding, reasonable control of welding line energy is the key to obtain high quality duplex stainless steel joints. Because the line energy is too small, the cooling rate of weld metal and heat affected zone is too fast, and the austenite can not be precipitated in time, thus increasing the ferritic phase content in the tissue. If the linear energy is too large, although enough austenite can be formed in the tissue, it will also cause the ferrite grain growth in the heat affected zone and the precipitation of harmful phase equal to σ. In general, Shieded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW), Flux-Cored WireArc Welding, Welding methods such as FCAW and Plasma Arc Welding (PAW) can be used to weld duplex stainless steel, and generally do not require preheating measures before welding, and do not require heat treatment after welding.