Mo와 W이 29%Cr 페라이트 스테인리스강의 이차상 석출에 따른 국부부식 및 취화에 미치는 영향

Abstract

Influences of molybdenum (Mo) substitution by tungsten (W) on the formation kinetics of secondary phases and the associated localized corrosion and embrittlement of Fe-29Cr-4Mo, Fe-29Cr-4W, and Fe-29Cr-8W ferritic stainless steels were investigated. Fine χ phase formed first in grain boundaries in an early stage of aging. and it was gradually substituted by IT phase with further aging. The precipitation rate of δ phase appears to be determined by both the diffusion rates of Wand Mo for the formation of the δ phase as well as by the affinity of χ phase, as a competitor, for the elements. Due to the high affinity of χ phase for W with a slow diffusion rate, the nucleation of δ phase was significantly delayed in Fe-29Cr-4W and Fe-29Cr-8W alloys compared with that in Fe-29Cr-4Mo alloy. In addition, the deterioration of ductility and localized corrosion resistance by the precipitation of secondary phases was significantly retarded in Fe-29Cr-4W alloy compared with that in Fe-29Cr-4Mo alloy, due to the delayed precipitation of secondary phases in Fe-29Cr-4W alloy. In particular, retardation of degradation in localized corrosion resistance by the formation of δ phase, which induced significant depletion of Cr and W (or Mo) around the phase, was prominent in the W-containing alloys. The W-containing alloys exhibited effective delay of δ phase formation.