Research On Welding Process And Solid Solution Treatment Of Ultra-low Carbon Duplex Stainless Steel

Due to the composition of ferrite(α) and austenite(γ) phase in microstructure, duplex stainless steels(DSS) have combined the merits of ferritic stainless steel and austenitic stainless steel. Duplex stainless steel is widely used in pulp and paper industry, oil and gas industry, chemical, chemical transportation, pharmaceutical and construction and other industries by its excellent advantages. The overall performance of the duplex stainless steel depends mainly on two phase proportion within the welding joint. So when the welding duplex stainless steel, the key task is to control the welding of ferrite and austenite phase transformation, makes the phase ratio is close to 1:1, at the same time, no harmful phase precipitation. But during the practical application, Welding thermal cycle is bound to affect the weld structure, makes the weld microstructure of duplex stainless steel complicated. On the one hand the two phase proportion and tissue morphology is more complex. On the one hand there are a lot of other secondary harmful phases such as σ, nitride, carbide and so on in the joint.To determine the welding characteristics of the ultra-low carbon duplex stainless steel, the 00Cr22Ni5Mo3 N duplex stainless steel was selected as the research object in this paper. The 00Cr22Ni5Mo3 N duplex stainless steel was welded by using Shielded metal arc welding and gas tungsten arc welding process. The microstructure, mechanical properties and anti-corrosion properties of welded joint specimens under different welding input by changing the argon arc welding welding current are tested. According the duplex stainless steel TTT curve, the samples are treated under different solution treatment temperatures. The influence of different solid solution treatment on the structure, mechanical and corrosion resistant property of cast duplex stainless steel is investigated.Test and analysis results indicate that the joint microstructure and mechanical properties 00Cr22Ni5Mo3 N duplex stainless steel are greatly influenced by welding heat input. The excellent weld structure and mechanical properties can be obtained under 1.2kJ·mm-1 heat input. The influence of too low and too high heat input make the two phase ratio in the joint change, Then that will affected the performance of mircostructure and properties in the joints. Besides, as the rise of the solution heat treatment temperature, the coarse austenite is divided by the ferrite and uniformly distributed on the ferrite matrix In the experiment, the microstructure can be obviously refined after solid solution treatment of 1050℃. the welded joints of 00Cr22Ni5Mo3 N duplex stainless steel is optimal solid solution treatment at 1050℃ water quench after 1h, at that moment, the welded joint to eliminate the sigma phase and can keep good ratio, excellent corrosion properties.