Inclusion Modification and Evolution during Reheating of Ca‐Treated Ti–Al–Mg Deoxidized High‐Strength Low‐Alloy Steels with Two Different Ti/Al Content Ratios

This study investigated the evolution mechanism of inclusion characteristics during reheating and their effects on acicular ferrite nucleation in Ti–Al–Mg deoxidized and calcium‐treated high‐strength low‐alloy steels. The findings indicate that regulating the Ti/Al content ratio in steel may facilitate the formation of dominant TiO x core inclusions rather than dominant Al 2 O 3 , thereby influencing the calcium treatment's effectiveness on inclusion modification. Via reheating, the compositions of Ti 2 O 3 –MgO–Al 2 O 3 core inclusions in high Ti/Al content ratio (5.50) steel change to Ti 2 O 3 –MgO, while (Mn, Ca) S shell with wrapped distribution become MnS and CaO–Al 2 O 3 with short‐arc, mosaic distribution due to their Ostwald aging. This implies that Al and O ions in core inclusions diffuse to surface layer, reacting with the decomposed Ca of CaS, forming more stable CaO–Al 2 O 3 . However, Al 2 O 3 –MgO–CaO core inclusions and MnS shell compositions in steel with low Ti/Al content ratio (0.50) remain almost unchanged during heating. Furthermore, the MnS and CaO–Al 2 O 3 shell precipitates with multiple points in steel with high Ti/Al content ratio are more conducive to acicular ferrites nucleation with more branches, which are attributed to the joint action of the Mn‐depleted mechanism, minimum mismatch mechanism and strain‐induced mechanism, yielding a higher toughness than that at low Ti/Al content ratio.