Effect of Lanthanum and Cerium on Inclusions in GCr15 Bearing Steel

To investigate the effect of La-Ce on inclusions in GCr15 bearing steel and its modification mechanism, relevant industrial tests were carried out. The results show that the typical inclusions in GCr15 bearing steel were long strip MnS and irregular Al2O3. At 1600 °C, with increasing La-Ce content, the transformation sequence of inclusions was Al2O3 → REAlO3 → RE2O3 → RE2O2S → RE2O2S + RExSy (RE was La-Ce). The formation of RExSy and RE2O2S was the fundamental reason for reduction in the quantity and size of MnS, and the spheroidization of inclusions was caused by REAlO3 and RE2O3 formed by La-Ce replacing Al in Al2O3. Considering the production cost and modification effect, the addition amount of La-Ce in the steel must reach at least 90 ppm to effectively improve the morphologies of all the inclusions thermodynamically, and the content of S could be remarkably reduced when the addition amount reached 120 ppm.