25Cr-7Ni-2Mo-4W 슈퍼 2상 스테인리스강의 충격인성에 미치는 χ상의 영향

Abstract

This study was carried out to investigate the precipitation behavior of the <TEX>${\chi}$</TEX> phase and the impact toughness of 25%Cr-7%Ni-2%Mo-4%W super duplex stainless steel. The <TEX>${\chi}$</TEX> phase was precipitated in the early stage of aging, and with the increasing aging time. However, after reaching a maximum value, the number decreased as a result of the gradual transformation of the <TEX>${\chi}$</TEX> phase into the <TEX>${\sigma}$</TEX>-phase. It was proved that the <TEX>${\chi}$</TEX> phase was an intermetallic compound, which represented a lower nickel concentration, higher chromium and molybdenum concentrations, and very higher tungsten concentration compared to the matrix phases. It also showed higher molybdenum and tungsten concentrations than the <TEX>${\sigma}$</TEX> phase. The decomposition of the ferrite phase into the <TEX>${\gamma}_2$</TEX> and <TEX>${\sigma}$</TEX> phases was retarded by W substitution for Mo. Thus, the number of <TEX>${\chi}$</TEX> phases increased. The impact value was decreased by the substitution of W for Mo. The impact toughness rapidly decreased with time when the <TEX>${\chi}$</TEX> phase began to precipitate in the initial stage of aging. The impact toughness was, therefore, greatly influenced for the precipitation of the <TEX>${\chi}$</TEX> phase.