Multidimensional characterization and evaluation model of inclusions in LF-RH double-refined ultra-clean bearing steel

This study presents a systematic investigation into the evolution of non-metallic inclusions during the industrial continuous casting production of high-carbon chromium bearing steel. Conventional 2D characterization techniques and X-ray-based Micro-CT were employed to compare the number, type, size, and spatial distribution of inclusions throughout the LF-RH double-refining process. The results show that Al 2 O 3 and MgO·Al 2 O 3 are the dominant inclusion types formed during melting and refining, with MgO·Al 2 O 3 exhibiting a strong thermodynamic tendency for formation. Due to differences in the resolution of the two characterization methods and variations in inclusion characteristics among the samples, inclusions with an equivalent diameter larger than 5 μm show better consistency between the results obtained from the two techniques. This finding revises the assumption that X-ray-based CT techniques inherently yield larger equivalent inclusion diameters. The spatial distribution and morphological characteristics of inclusions are identified as key influencing factors. In ultra-clean bearing steel characterized by non-uniform inclusion distribution and predominantly spherical oxide inclusions, when only inclusions larger than the critical equivalent diameter of 5 μm are considered, the equivalent diameters obtained from 3D characterization are significantly smaller than those derived from 2D methods. This study provides vital industrial data for the future development of precise multidimensional characterization of inclusions in ultra-clean special steels. It also supports the establishment of a reliable 2D-3D conversion model that incorporates characteristic parameters.