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Effect of W Substitution on the Precipitation Behavior of χ and σ Phase in Super Duplex Stainless Steels

슈퍼 2상 스테인리스강에서 χ와 σ상의 석출거동에 미치는 W치환의 영향

Han, Huyn-Sung;Kim, Seong-Hwi;Kang, Chang-Yong
한현성;김성휘;강창룡

  • Received : 2015.12.18
  • Accepted : 2016.03.07
  • Published : 2016.04.27

Abstract

This study was carried out to investigate the effect of W substitution on the precipitation behavior of ${\chi}$ and ${\sigma}$ phases in super duplex stainless steel. The ${\chi}$ phase was precipitated at the interface of ferrite / austenite phases and inside the ferrite phase at the initial stage of aging. With an increase in the aging time, the volume fraction of the ${\chi}$ phase increased, and then decreased with the transformation from the ${\chi}$ phase to the ${\sigma}$ phase. The ${\sigma}$ phase was precipitated later than the ${\chi}$ phase, and the volume fraction of x phase increased with the increase in the aging time. The ferrite phase was decomposed into the new austenite (${\gamma}2$) and ${\sigma}$ phases by aging treatment. The decomposition of the ferrite phase into the ${\gamma}2$ and ${\sigma}$ phases was retarded by W substitution for Mo. The volume fraction of the ${\chi}$ phase increased and that of the ${\sigma}$ phase decreased due to W substitution. The ${\chi}$ and ${\sigma}$ phases were intermetallic compounds, which had lower nickel concentration, and higher chromium, molybdenum, and tungsten concentrations. The ${\chi}$ phase has higher molybdenum and tungsten concentrations than those of the ${\sigma}$ phase. The amounts of chromium and nickel in the ${\chi}$ and ${\sigma}$ phases did not change, but these phases have higher concentrations of molybdenum and tungsten due to W substitution for Mo.

Keywords

super duplex stainless steel;W substitution;${\chi}$-phase;${\sigma}$ phases;aging

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