How much do you know Duplex Stainless Steels' welding performance?
Today, SSM takes you to learn about it!
It is worth mentioning that the dual-phase steel generally does not undergo post-weld heat treatment.
The weldability of duplex stainless steel combines the advantages of austenitic steel and ferritic steel, and reduces their respective shortcomings.
1) The sensitivity to hot cracking is much smaller than that of austenitic steel.
2) The sensitivity to cold cracks is much smaller than that of general low-alloy high-strength steels.
3) The main problem in the welding of duplex stainless steel is not the weld seam, but the heat-affected zone, because under the action of welding heat cycle, the heat-affected zone is in a rapid cooling non-equilibrium state, and more ferrite is always retained after cooling, thus Increased corrosion tendency and susceptibility to hydrogen-induced cracking (embrittlement).
4) Duplex stainless steel welded joints may precipitate δ phase embrittlement. δ phase is an intermetallic compound of Cr and Fe. Its formation temperature range is 600-1000 ° C. Different steel types have different temperatures for forming δ phase, such as 00Cr18Ni5Mo3Si2 steel At 800-900°C, while duplex stainless steel 00Cr25Ni7Mo3CuN is most sensitive at 800-900°C, 850°C. It takes a certain amount of time to form the δ phase, generally 1-2 min to germinate and 1-2 min to increase and grow the δ phase. Therefore, small heat input should be used for welding, rapid cooling should be used, and lower temperature should be used for stress relief treatment, such as 550-600 ° C is appropriate.
5) Duplex stainless steel contains 50% ferrite, and it also has brittleness at 475°C, but it is not as sensitive as ferritic stainless steel. The ferrite in dual-phase steel will precipitate high chromium α phase when it is kept warm for a long time between 300-525 °C, and it is most sensitive at 475 °C, which makes the dual-phase steel embrittled. Since the α phase precipitates for a long time, it has little effect on general welding, but the working temperature of duplex stainless steel should be limited to not higher than 250 °C.
For the weldment of duplex stainless steel, due to improper process, once the δ phase or the precipitation of α phase causes brittleness at 475°C, it can be eliminated by solution treatment.
The diffusible hydrogen content of duplex stainless steel is less than that of austenitic stainless steel, so when the mass concentration of hydrogen in the welding consumables or in the surrounding environment is high, hydrogen-induced cracking and embrittlement will occur when welding duplex stainless steel.
