Effect of Ladle Washing Operation on Non-metallic Inclusions in Tire Cord Steel: Laboratory Simulation

In order to simulate ladle exchange in secondary steelmaking, MgO refractory rods with different apparent porosities (2.67 pct and 0.70 pct) were glazed by CaO-Al2O3 system slag (R = w(CaO)/w(SiO2) = 5.5, w(Al2O3) = 30 pct) and CaO-SiO2 system slag (R = 1.0, w(Al2O3) = 2 pct), respectively, and the interaction between the glazed rods and tire cord steel grade LX72A was investigated at 1823 K (1550 degrees C) in laboratory. By using BaO as a tracer of glaze, it was found that ladle glaze is also a source of inclusions in tire cord steel. The direct flush-off of CaO-Al2O3 system glaze and its impact on the rise of the Al content (up to 15 ppm) in liquid steel are not conducive to the plasticity of inclusions. Besides, the structure of the refractory rods influences the effect of glaze evidently. Initial glaze can penetrate into the pores of the refractory, and it can hardly be washed out by the glazes formed in the following heats. Therefore, it is difficult to avoid the negative impact of the penetrated high Al2O3 slag on inclusions. Although dense refractory (apparent porosity 0.70 pct) could restrain slag penetration and weaken the negative effect of high Al2O3 slags, the refractory used in industry is much looser than that in laboratory. In this case, specialized ladles at a suitable age with pure and dense lining are recommended for the refining process of high-end tire cord steel grades.