Microstructural Evolution in 18Cr-Al-Si Ferritic Heat-Resistant Stainless Steel During Solidification Process With Different Al Content

Aimed at clarifying δ-ferrite/γ-austenite transformation of 18Cr-Al-Si ferritic heat-resistant stainless steel (FHSS) with various Al content, high temperature confocal scanning laser microscopy (CSLM) was used for in-situ observation of microstuctual evolution during solidification. The results demonstrated that δ→γ transformation was observed in 18Cr-Al-Si FHSS with different Al content during the solidification process. With the increase of Al content, the amount of γ-austenite phase in the solidified structure gradually increased, and part of the martensite was transformed inside the γ-austenite grains. M23C6 carbides were precipitated at the phase boundaries between the δ-ferrite phase and γ-austenite/martensite phase. The hardness of δ-ferrite phase and γ-austenite/martensite phase increased and decreased with the increment of Al content, respectively. In addition, the solidification mechanism of the complex nucleus was also discussed.