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http://dx.doi.org/10.3740/MRSK.2016.26.4.200

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

Han, Huyn-Sung (Busan Campus of Korea Polytechnic)
Kim, Seong-Hwi (Department of Metallurgical Engineering, Pukyong National University)
Kang, Chang-Yong (Department of Metallurgical Engineering, Pukyong National University)
Publication Information
Korean Journal of Materials Research / v.26, no.4, 2016 , pp. 200-206 More about this Journal
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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