Effects of nitrogen in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel welding joint
By Zhang, Zhiqiang; Jing, Hongyang; Xu, Lianyong; Han, Yongdian; Zhao, Lei; Zhou, Chao
Published in Applied Surface Science
2017
Abstract
Abstract The effects of nitrogen addition in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel (DSS) welds were studied. N2-supplemented shielding gas facilitated the primary austenite formation, suppressed the Cr2N precipitation in weld root, and increased the microhardnesses of weld metal. Furthermore, N2-supplemented shielding gas increased pitting resistance equivalent number (PREN) of austenite, but which decreased slightly {PREN} of ferrite. The modified double loop electrochemical potentiokinetic reactivation in 2 M {H2SO4} + 1 M {HCl} was an effective method to study the localized corrosion of the different zones in the {DSS} welds. The adding 2% {N2} to pure Ar shielding gas improved the localized corrosion resistance in the {DSS} welds, which was due to compensation for nitrogen loss and promoting nitrogen further solution in the austenite phases, suppression of the Cr2N precipitation in the weld root, and increase of primary austenite content with higher {PREN} than the ferrite and secondary austenite. Secondary austenite are prone to selective corrosion because of lower {PREN} compared with ferrite and primary austenite. Cr2N precipitation in the pure Ar shielding weld root and heat affected zone caused the pitting corrosion within the ferrite and the intergranular corrosion at the ferrite boundary. In addition, sigma and {M23C6} precipitation resulted in the intergranular corrosion at the ferrite boundary.