What are the factors that affect the welding quality of duplex stainless steel?

 　　Effect of nitrogen content: With the increase of N2 partial pressure PN2 in the mixed gas, the mass fraction of nitrogen in the weld seam ω (N) The content of ferrite phase in the weld seam increases rapidly and then changes very little φ ( α) along with ω (N) The increase shows a linear decrease, but φ ( α) The influence of tensile strength and elongation on resistance ω (N) The impact is exactly the opposite. The increase in N content in the weld metal of duplex stainless steel can improve the impact toughness of the joint, which is due to the addition of γ Phase content.

　　Heat input effect: if the heat input is too large during welding, the range of the weld Heat-affected zone will increase, and the metallographic structure will also tend to be coarse and disordered, resulting in embrittlement, which is mainly manifested in the decline of the plastic index of the welded joint. If the welding heat input is too small, it will cause quenching of hard tissue and easy to produce cracks, which is also harmful to the impact toughness of HAZ. In addition, any factors that affect the cooling rate will affect the impact toughness of HAZ, such as plate thickness, joint form, etc.

　　Hydrogen induced cracking: Hydrogen embrittlement in welded joints of duplex stainless steel typically occurs α The sensitivity of hydrogen embrittlement increases with the increase of peak temperature during welding. The changes in its microstructure are: an increase in peak temperature, γ Reduced phase content, α The phase content increases, while the α The amount of Cr2N precipitated at the phase boundary and inside increases, making it highly susceptible to hydrogen embrittlement.

　　Stress corrosion cracking: cracks in base metal and weld metal originate from α/γ Interfacial α On the opposite side, and on the α Phase expansion. Austenite（ γ) Due to its inherent low hydrogen embrittlement sensitivity, it can play a role in blocking crack propagation. Because DSS contains a certain amount of austenite, its stress corrosion cracking tendency is small.