Solid reactions between CaO–Al2O3 and Si–Ti-containing steel at 1273 K

Solid reactions between Si–Ti-containing steel and calcium aluminates with various CaO/Al2O3 ratios at 1273 K were studied. Particle precipitation zones (PPZs) were observed and analyzed for the composition and thickness. After heating at 1273 K for 10 h, 30 h, and 50 h, the composition of precipitated particles was Ca–Ti–O and TiOx in diffusion couples with a slag phase of CaO·Al2O3 (CA). The precipitates changed into mainly Ca–Si–O when the slag phase was 3CaO·Al2O3 (C3A) or 12CaO·7Al2O3 (C12A7). Elements of calcium and oxygen diffused from the slag phase to the steel phase were proved not to be from the decomposition of calcium aluminates, but ion diffusion under concentration gradients. The thickness of the PPZ increased from 1.5 μm to 14.8 μm with the increase of CaO/Al2O3 ratio of the slag phase and the heating time. The dissolved oxygen at the slag-steel interface calculated by the dynamic model demonstrated that the oxygen delivery capacity of calcium aluminates increased with their CaO/Al2O3 ratios. The evolution path of Ca–Ti–O to Ca–Si–O calculated by FactSage primely explained the precipitation variance of diffusion couples with various slag phases.