The effect of Mg and Ca treatment on the behavior and the particle size of inclusions in bearing steels were studied by industrial experiments and thermodynamic calculations. The results showed that the excess addition of Mg wires is not conducive to control the total oxygen content in bearing steel because of the secondary oxidation. The irregular and clustered Al2O3 inclusions are the dominant in the aluminium killed bearing steels. The different quantity Mg wires were added, which can change the irregular and clustered Al2O3 inclusions into the spherical MgO or MgO·Al2O3 inclusions. When the Ca addition is insufficient, the Al2O3 and MgO·Al2O3 inclusions could not completely change into the spherical CaO-MgOAl2O3 system inclusions. By the three-dimensional morphologies analyze, Al2O3 inclusions are easy to gather and the size of clustered Al2O3 inclusions is large. By the Mg or Ca treatment, the size of Al2O3 inclusions can be reduced, but the large size CaO inclusions are brought into steel after the Ca treatment.
Al 2 O 3 and high Al 2 O 3 content composite oxides are the main types of inclusions in aluminium killed bearing steel, and these also have the most significant impact on rolling contact fatigue (RCF) life. The calculation results in the phase diagram by using the FactSage showed that the activity of Al 2 O 3 reached the minimum with the slag composition in a low melting point area at a MgO content less than 5%; a basicity of 5 to 8 and a ratio of CaO/Al 2 O 3 of 1?5 to 2?0 in slag. This slag was most effective in improving the absorption ability of slag for inclusions in bearing steel. By using the experimental slag, the total oxygen could be reduced to 7-10 ppm at Hangzhou Iron and Steel Group Company (HIRGC).
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