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

Title & Authors
Effect of W Substitution on the Precipitation Behavior of χ and σ Phase in Super Duplex Stainless Steels
Han, Huyn-Sung; Kim, Seong-Hwi; Kang, Chang-Yong;

Abstract
This study was carried out to investigate the effect of W substitution on the precipitation behavior of $\small{{\chi}}$ and $\small{{\sigma}}$ phases in super duplex stainless steel. The $\small{{\chi}}$ 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 $\small{{\chi}}$ phase increased, and then decreased with the transformation from the $\small{{\chi}}$ phase to the $\small{{\sigma}}$ phase. The $\small{{\sigma}}$ phase was precipitated later than the $\small{{\chi}}$ 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 ($\small{{\gamma}2}$) and $\small{{\sigma}}$ phases by aging treatment. The decomposition of the ferrite phase into the $\small{{\gamma}2}$ and $\small{{\sigma}}$ phases was retarded by W substitution for Mo. The volume fraction of the $\small{{\chi}}$ phase increased and that of the $\small{{\sigma}}$ phase decreased due to W substitution. The $\small{{\chi}}$ and $\small{{\sigma}}$ phases were intermetallic compounds, which had lower nickel concentration, and higher chromium, molybdenum, and tungsten concentrations. The $\small{{\chi}}$ phase has higher molybdenum and tungsten concentrations than those of the $\small{{\sigma}}$ phase. The amounts of chromium and nickel in the $\small{{\chi}}$ and $\small{{\sigma}}$ 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;$\small{{\chi}}$-phase;$\small{{\sigma}}$ phases;aging;
Language
Korean
Cited by
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