Control Of Oxygen Content And Non-metallic Inclusions In Continuous Casting Bearing Steels

High carbon bearing steel with 1.0% C, 1.5% Cr is an important special steel grade, which represents technology level of high quality clean steels. Oxygen content in bearing steel is a major index to judge its quality because oxide inclusions greatly affect the fatigue life of bearing steel. Therefore one of the bottleneck problems to produce high-quality bearing steel is how to reduce oxygen content and get rid of the harmful inclusions.In this subject, the capacities of various typical refining slags that are used to deoxidate, desulphurize and control spot inclusions are analyzed, which is the theoretical basis to choose proper refining slag. Meanwhile the thermodynamic calculations about the formation of some main type inclusions were carried out. The results of calculation and comparison showed that slag system of CaO-Al₂O₃ with high basicity could reduce SiO₂ content in slag, and then it would keep dissolved oxygen content lower in molten steel. And it was very difficult to control the formation of TiN inclusions by reducing nitrogen content in bearing steel, so the titanium content has to be reduced in order to reduce TiN inclusions in molten steel. On the conditions of calculation of this subject, if dissolved aluminum content in steel was in the range of 0.01% - 0.04%, microcontent of magnesium in bearing steel could lead to the formation of MgO·Al₂O₃ spinel. Therefore, it was possible to make attempts to modify inclusions by treating with magnesium, aiming at elminating the negative influence of calcium aluminate on bearing steel.Based on the thermodynamic calculation, the experiments with different refining slags have been carried out to compare its effect on oxygen content and character of inclusions in bearing steel, and to investigate the modification results to inclusions by treating with magnesium aluminum alloy. The experimental results showed that slag system of CaO-Al₂O₃ with high basicity has a good effect on reducing oxygen content in bearing steel, and the composition of inclusions in molten steel was mostly Al₂O₃-MgO-CaO after treating with it. Another conclusion was that the type of inclusions in steel was single after treating with magnesium aluminum alloy; and the inclusions were mostly...