Formation and Evolution of Oxide Inclusions in Titanium-Stabilized 18Cr Stainless Steel

摘要

During Ti-stabilized stainless steelmaking process, oxide inclusions in steel generally cause the clogging of submerged entry nozzle and surface defects of cold-rolled products. Therefore, the evolution mechanism of oxide inclusions in Ti-stabilized 18Cr stainless steel was investigated by industrial experiments. The characteristics of inclusions in specimens were analyzed by scanning electron microscopy and energy dispersive spectroscopy. After Al deoxidation, the main inclusions were irregular MgO–Al_(2)O_(3) spinel. After calcium treatment, MgO–Al_(2)O_(3) inclusions were modified to be spherical multilayer CaO–MgO–Al_(2)O_(3) inclusions consisting of spinel crystal embedded in CaO–Al_(2)O_(3) liquid matrix. Thermodynamic calculation indicated that several ppm Ca could significantly expand the liquid oxides phase in Mg–Al–O phase diagram. After Ti addition, multilayer CaO–MgO–Al_(2)O_(3)–TiO_(x) inclusions were formed. The compositions of steel were located close to Al_(2)O_(3)–TiO_(x) liquid oxide phase, which would help to reduce oxide inclusions and increase titanium yield. Titanium addition has modified spinel inclusions to multilayer MgO–Al_(2)O_(3)–Ti_(3)O_(5) inclusions containing solid spinel inner layer and MgO–Al_(2)O_(3)–Ti_(3)O_(5) liquid oxide outer layer. As for improving the cleanliness of molten steel, the contents of magnesium, aluminum, and titanium could be considered simultaneously to liquefy oxide inclusions during Ti-stabilized stainless steelmaking process.