Effect of Si on δ‐Ferrite/γ‐Austenite Transformation and M₂₃C₆ Precipitation During Solidification of X10CrAlSi18 Ferritic Heat‐Resistant Stainless Steel

Abstract

Herein, the δ‐ferrite/γ‐austenite transformation and the precipitation behavior of M23C6 carbides in X10CrAlSi18 ferritic heat‐resistant stainless steel (FHSS) with various Si contents at a cooling rate of 100 °C min−1 using confocal scanning laser microscopy (CSLM) are investigated. The findings reveal that γ‐austenite preferentially forms along the δ‐ferrite phase boundaries, and it progressively precipitates into the δ‐ferrite phase as the temperature decreases. The increase in the Si content reduces the δ‐ferrite/γ‐austenite transformation temperature. It also inhibits the martensite transformation in the subsequent cooling process, decreasing the volume fraction of γ‐austenite/martensite. M23C6 carbides are mostly found at the δ‐ferrite and γ‐austenite/martensite phase boundaries. Meanwhile, the nucleation of M23C6 carbides becomes more difficult as the volume fraction of γ‐austenite/martensite decreases. Furthermore, the complex solidification mechanism of the nucleus is addressed.