Effect of Sulphur Concentration on Precipitation Behaviors of MnS-containing Inclusions in GCr15 Bearing Steels after LF Refining

摘要

The precipitation behavior and mechanism of MnS-containing inclusions in GCr15 bearing steels were analyzed. The results show when the optical basicity of the refining slag is 0.776, the minimum sulphur concentration is 0.0020 mass% in the present samples. MgO·Al_(2)O_(3) (MA) and CaO–MgO–Al_(2)O_(3) (CMA) inclusions are easy to become nucleation cores for MnS precipitating. MnS-containing inclusions are main MnS, MA and CMA encapsulated with MnS, and a little amount of MnS compounded with TiN. It is the concentration of sulphur in the steel and the composition of oxide cores that influences the precipitation behavior of MnS-containing inclusions. The thickness of MnS on CMA type inclusions is about 2.5–4.5 times larger than that on MA type inclusions even if the precipitation ratio of MnS is lower. MnS can precipitate on CMA type inclusions when the mole percent of CaO in the inclusions is less than 33 mole% (0.33), and the thickness of MnS precipitation is decreased with the increase of CaO concentration. However, MnS can’t precipitate on CMA inclusions when the mole percent of CaO exceeds 38 mole% (0.38) and CMA type inclusions without MnS precipitating are almost in liquid region.