Microstructure refinement and mechanical properties improvement by developing IAF on inclusions in Ti-Al complex deoxidized HSLA steel

The present study focused on microstructure refinement in Ti-Al complex deoxidized low alloy structural steel by developing IAF on inclusions. The goal was to establish more determined relation between Ti, Al in steel and the produced microstructures. In steel sample with Ti and Al contents of 0.0035% and 0.0004%, respectively, IAF was well developed by inclusions characterized by TiOx-MnO oxide cores enwrapped by (MnO-SiO2-Al2O3)-MnS or (MnO-SiO2)-MnS surface layers. With the rise of Ti and Al contents, IAF volume decreased greatly because of different inclusion chemistry, TiOx + MnS, TiOx-Al2O3 or Al2O3, which inhibit the formation of IAF. Thermodynamic calculations were carried out for optimal Ti and Al contents in steel to target inclusions with proper chemistry for nucleating IAF. These laboratorial findings were successfully applied and reproducibly observed in pilot trials. It was indicated that low temperature impact toughness at 0 °C and − 20 °C of the produced medium plate was effectively improved despite lower Ti contents than common process, which was very meaningful in saving the cost of high Ti content steels.