Laves phase precipitation behavior and high-temperature strength of W-containing ferritic stainless steels

Small-size Laves phase precipitates have the advantage of providing superior high-temperature properties to ferritic stainless steels. However, the coarsening of precipitates becomes inevitable during long-term service at elevated temperatures, which causes degradation of high-temperature strength and thermal fatigue resistance. In this study, Laves phase precipitation behavior and high-temperature strength is elucidated in W-containing ferritic stainless steels in the temperature range of 800–1100°C. Laves phase preferentially precipitated at the grain boundaries and were uniformly dispersed within the grains after aging. The intragranular Laves phase almost completely vanished and only intergranular precipitates were present after long-term aging, especially at 900–1000°C. The W-containing steels exhibited higher tensile strength than W-free steel, which resulted from the formation of Laves phase at higher temperatures and solid-solution strengthening effect. Nevertheless, the size of Laves phase was increased with the increase of W content, which led to the decrease of precipitation strengthening effect after long-term aging. This change resulted in the apparent reduction of tensile strength with increased aging time, although the W-containing steels continued to exhibit higher tensile strength compared to W-free steel.