Solidification microstructure of high borated stainless steels with rare earth and titanium additions

To study the effects of rare earth (RE) and Ti on the solidification microstructure of high borated stainless steels, 1.6 wt% B stainless steel doped with RE and 2.1 wt% B stainless steel doped with Ti were prepared by ingot casting, respectively. The solidification microstructure of researched steels was characterized in detail. The modification mechanism was clarified based on the heterogeneous nucleation theory and the thermodynamic calculation. The solidification microstructure of 1.6 wt% B and 2.1 wt% B stainless steels was characterized by the continuous and network-like eutectic borides around the matrix grains. It was found that the fine RE compounds could act as the heterogeneous nuclei for both borides and austenite during solidification. Thus, the eutectic borides were more dispersed in the modified steel. Moreover, lots of fine ‘eutectic cells’ were formed in the matrix regions. As a result of the preferential formation of TiB₂ during solidification, the amount of the eutectic borides in the steel modified with Ti was significantly decreased. Besides, the continuity of the eutectic borides network was weakened. In a word, the present work provides a promising method to modify the solidification microstructure for high borated stainless steels.