Control of Ultra Low Titanium in Ultra Low Carbon Al-Si Killed Steel

Titanium is the impurity in some special steel grades. The existence of titanium decreases the grain size, depresses the yield strength, and results in the low quality of these steels in various properties. Thus, titanium should be removed to the minimum. Based on the industrial production of ultra low carbon Al-Si killed steel, the physical-chemical behavior of titanium was investigated in vacuum degassing refining (RH) process with and without desulfurization. The influences of titanium content in hot metal, ladle slag composition, and ladle slag quantity, etc, on titanium content of refined liquid steel were discussed. The results showed that the partition ratio of titanium between ladle slag and liquid steel is in inverse proportion to the 4/3 square of aluminum content. The maximum partition ratio of titanium between top slag and liquid steel can be obtained by adjusting an optimum slag composition including contents of FeOx and A12O3 and the slag basicity, and the suitable range of them should be controlled higher than 6%, less than 20%, and within 1. 5 to 3. 0, respectively. Moreover, desulfurization refining by RH decreases the partition ratio of titanium between ladle slag and liquid steel significantly. To ensure the titanium content stably less than 15 × 10−6 in a 300 t ladle, the titanium content in hot metal must be less than 500 × 10−6 and the thickness of basic oxygen furnace (BOF) slag carrying over must be less than 50 mm.