The influences of N 2 content in shielding gas on microstructure and impact toughness of different zones in cold metal transfer and pulse (CMT-P) hybrid welded joint of duplex stainless steel (DSS) were systematically studied. The results showed that the N 2 -supplemented in shielding gas significantly facilitated austenite formation (weld root: 39.9%→41.2%, weld filler: 40.5%→43.7%, and heat affected zone (HAZ): 36.4%→39.6%). However, when the N 2 content in the shielding gas exceeded 4%, there was no significant change in austenite content because of reaching the solubility limit of N atoms. In addition, γ 2 precipitated both in the weld root and HAZ but not in the weld filler, which cannot be inhibited by N 2 addition in the shielding gas. Besides, a great number of Cr 2 N and dislocations in addition to γ 2 formed in the HAZ, and the content of Cr 2 N and dislocation significantly increased with the increase of N 2 content in the shielding gas. Furthermore, the HAZ exhibited the lowest toughness in comparison with other zones. In addition, with the increase of N 2 content in the shielding gas from 0% to 6%, the toughness increased first and then decreased, and reached the maximum when 4% N 2 added to the shielding gas as (weld root: 122.0 J/cm 2 , weld filler: 135.0 J/cm 2 , and HAZ: 91.8 J/cm 2 ). According to detailed microstructure analysis and toughness level, Ar+4% N 2 was recommended as the shielding gas to join DSS by using CMT-P welding technique.
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Zhang et al. (2023) studied this question.
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