Abstract: Effect of different RE contents on inclusions in highly clean bearing steel was studied via adding highly pure rare earth elements. Inclusions in bearing steel were characterized and analyzed with metallographic microscopy, scanning electron microscopy, energy disperse spectroscopy and ImagePro Plus software. The results showed that a suitable amount of RE can not only make inclusions more dispersed and smaller, but also modify irregular shaped Al2O3 and strip MnS into spherical or ellipsoidal rare earth inclusions, both of which improve the quality of highly clean bearing steel. With an increase in the RE amount, inclusions gradually increase in size and their morphology becomes more and more irregular, so the metallurgical quality of highly clean bearing steel has a downward trend. In addition, increasing the RE amount causes the evoluation of main growth mechanism of inclusions from precipitationgrown to aggregationgrown. Considering inclusions modification and bearing steel performance optimization, RE mass fraction in highly clean bearing steel should be controlled around 0.02 % .

Key words: bearing steel, highly pure rare earth, adding amount, inclusion, growth mechanism