Effects of Nitrogen-Added Double Shielding Gas and Solution Treatment on Duplex Stainless Steel Weld Microstructure of Deep-Penetration Tungsten Inert Gas Welding

Duplex stainless steel possesses excellent performances when the austenite/ferrite phase ratio is close to 1:1. In this study, a double-layered shielding gas welding method was employed to compare the welding efficiencies and the weld microstructures of the ASTM A240 duplex stainless steel under different shielding gas conditions. The experimental results showed that the welding efficiencies could be improved effectively by adding a small amount of active gas in the shielding gas. The addition of nitrogen in the shielding gas could greatly increase the amount of the austenite phase, and thus a recovery of the austenite/ferrite phase ratio in the weld was achieved. The effects of the solution treatment temperature and the time on the weld microstructures were also studied by using different solution treatment conditions. The results showed that proper solution treatment could improve the austenite phase proportion in the ASTM A240 duplex stainless steel welds. With the increase in the solution temperature and the time, the austenite content was raised obviously, the grain became fine, and the two phases tended to be uniformly distributed.