Phase reconstruction of Al ₂ O ₃ –C–Al–Si–TiO ₂ system at elevated temperatures in nitrogen

Abstract The Al 2 O 3 –C refractories with low‐carbon content (w(C) ≤ 5%) are very crucial for the ultra–low‐carbon steelmaking. However, the properties of the Al 2 O 3 –C refractories like slag erosion resistance and thermal shock resistance deteriorated sharply if the content of graphite is reduced to below 5 wt%. To solve this problem, Al, Si, and TiO 2 are used as additives to reconstruct a novel Al 2 O 3 –C refractory at elevated temperatures in nitrogen. The results indicate that Al 4 SiC 4 , (Al 2 OC) 1– x (AlN) x and TiC 0.3 N 0.7 phases were obtained in the matrix when the Al 2 O 3 –C refractories with Al/Si/TiO 2 ratio of 9:2:2 were calcined above 1425°C. Benefiting from these new phases, the Al 2 O 3 –C refractory reconstructed at 1425°C exhibits excellent mechanical strength and thermal shock resistance; its cold modulus of rupture, cold crushing strength, and hot modulus of rupture are 20, 122, and 31 MPa, respectively, and its residual strength ratio after three times of air cooling at 1100°C reaches 75%. The thermodynamic calculations illustrated that the formation of flaky Al 4 SiC 4 was the result of Si(l), Al(l), and C(s) through liquid–solid reaction. The novel Al 2 O 3 –C refractory prepared in this work has great application prospects in the field of ultra–low‐carbon steelmaking.