The effect of heat treatment on recrystallized microstructure, precipitation and ductility of hot-rolled Fe-Cr-Al-REM ferritic stainless steel sheets

This study presents research works about the effects of heat treatment on recrystallized equiaxed grain size, precipitation, room temperature (RT) toughness and ductile to brittle transition temperature (DBTT) of Fe-Cr-Al-REM ferritic stainless steel (FSS) hot-rolled sheet. Results showed that the recrystallization of hot-rolled Fe-Cr-Al-REM FSS sheet could be completed after annealing treatment at 750 °C for 15 min with the equiaxed grain diameter of approximately 50 μm. Inappropriate annealing treatment would inevitably leads to the unexpected grain coarsening. On the other hand, a great deal of needle-like or spot-like fine aluminum-lanthanum compound Al11La3 precipitates were observed in the ferrite matrix after 1 h aging treatment at 750 °C. The microstructure observation results associated with the impact test definitely illustrated that the Al11La3 precipitates was the reason for the brittle crack in the as-casted ingot and as-forged slab. The real DBTT of the annealed Fe-Cr-Al-REM FSS sheet with average grain size of about 50 μm was −4 °C. Meanwhile, the DBTT of the hot-rolled Fe-Cr-Al-REM stainless steel sheet was evidently increased as the recrystallized grain size increased.