플럭스코어드와이어를 이용한 슈퍼오스테나이트스테인리스강 용접부 내식성에 미치는 합금원소의 영향

Abstract

In this work, the effects of Cr, Mo, and N contents on the pitting resistance of weld metal which is produced by a trial iron-based flux cored wire were investigated. The results were interpreted in terms of the microsegregation of the elements and formation of intermetallic compounds. It was found that the effects of Cr and Mo contents on the pitting resistance of weld metal depends strongly on the amount of sigma phase formed in the weld metal. When the amount of the phase is smaller than 1%, critical pitting temperature (CPT) increased with an increase of Cr and Mo contents because of higher pitting resistance equivalent number (PREN). However, when the amount of the phase is larger than 1%, an increase of Cr and Mo contents and thus higher PREN decreased CPT. These results indicate that PREN should be controlled so that the weld metal has about 1% of sigma phase. In this work, 22%Cr-5.5%Mo or 25%Cr-4%Mo showed the highest CPT of 65oC. An increase of N content improved the passive film properties and suppressed the formation of sigma phase further, and thus increased the pitting resistance of weld metal. The highest CPT of 80oC was obtained in 25%Cr-5.5%Mo-0.5%N composition which was produced when 98%Ar+2%N shielding gas was used. A trial iron-based flux cored wire that produces the optimum composition, 25%Cr-5.5%Mo-0.5%N, showed, in addition to the high pitting resistance, high solidification cracking resistance and good arc stability as well, indicating that the trial wire can be used as an alternative wire to the expensive Ni-based wire.