질소 보호 가스 첨가가 하이퍼 듀플렉스 스테인리스 밀봉용접재의 마모부식 저항성에 미치는 영향

Abstract

Duplex stainless steels with nearly equal fraction of the ferrite(α) phase and austenite(γ) phase have beenincreasingly used for various applications such as power plants, desalination facilities due to their highresistance to corrosion, good weldability, and excellent mechanical properties. Hyper duplex stainless steel(HDSS) is defined as the future duplex stainless steel with a pitting resistance equivalent (PRE=wt.%Cr+3.3(wt.%Mo+0.5wt.%W)+30wt.%N) of above 50. However, when HDSS is welded with gas tungstenarc (GTA), incorporation of nitrogen in the Ar shielding gas are very important because the volume fractionof α-phase and γ-phase is changed and harmful secondary phases can be formed in the welded zone. Inother words, the balance of corrosion resistance between two phases and reduction of Cr2N are the keypoints of this study. The primary results of this study are as follows. The addition of N2 to the Ar shieldinggas provides phase balance under weld-cooling conditions and increases the transformation temperature ofthe α-phase to γ-phase, increasing the fraction of γ-phase as well as decreasing the precipitation of Cr2N. In the anodic polarization test, the addition of nitrogen gas in the Ar shielding gas improved values ofthe electrochemical parameters, compared to the Pure Ar. Also, in the erosion-corrosion test, the HDSSwelded with shielding gas containing N2 decreased the weight loss, compared to HDSS welded with theAr pure gas. This result showed the resistance of erosion-corrosion was increased due to increasing thefraction of γ-phase and the stability of passive film according to the addition N2 gas to the Ar shieldinggas. As a result, the addition of nitrogen gas to the shielding gas improved the resistance of erosion-corrosion.