Thermal Deformation Control of Multiphase Composite Inclusions in Bearing Steel Treated by Ce‐Mg Combined Treatment

This study comparatively investigated the thermal deformation behavior of composite inclusions in Ce‐Mg combined treated GCr15 bearing steels with different Ce/Mg content ratios (1.8, 2.8). The results indicate that the typical inclusions in experimental steels are spherical, multiphase, core‐shell composite inclusions, their shells consist mainly of Ce 2 S 3 inclusions, whereas their cores exhibit significant differences in size, shape, and phase distribution. The inclusion cores in low Ce/Mg steel are composed of several Mg‐containing inclusions (MgS, MgO) with varying sizes and diverse morphologies, while these in high Ce/Mg steel consist of multiple fine Mg‐containing inclusions interconnected with the Ce 2 S 3 inclusions in an alternating pattern. The deformation index of the inclusions in hot‐compressed specimens decreased as the Ce/Mg content ratio increased, owing to the alternating hard (Mg‐containing inclusions) and soft (Ce 2 S 3 ) phases that form a rigid internal framework and restrict inclusion deformation. Moreover, the Ce 2 S 3 shells exhibit favorable cooperative deformability with steel matrix, mitigating the residual stress accumulation around the multiphase composite inclusions after thermal deformation. Consequently, precise control of Ce/Mg ratio tailors the component proportions and spatial distribution in core‐shell inclusions, regulating deformability of inclusions to make them deform in coordination with steel matrix and mitigating the detrimental effects of residual inclusions on steel performance.