High-temperature evolution and deformation behavior of residual modified Al2O3 inclusions in Si-killed and Ce-treated GCr15 bearing steel

Cerium treatment was used to modify residual Al 2 O 3 inclusions in Si-killed GCr15 bearing steel, and high-temperature evolution and deformation behavior of these residual inclusions were studied to assess their harmfulness. The results indicated cerium treatment can modify Al 2 O 3 , SiO 2 and MnS inclusions in as-cast Ce-free steel (S0) into finer, near-spherical Ce–S–Al–O composite inclusions in Ce-treated steel (S1, 0.017 wt% Ce). During isothermal heating at 1473 K for 120 min, these initially glassy Ce–S–Al–O composite inclusions in as cast S1 steel evolved into Ce 2 S 3 (core)–Al 2 O 3 (shell) multiphase composite inclusions by crystallization, which is attributed to first precipitation of the thermodynamically more stable Ce 2 S 3 at the core of the inclusions and to outward diffusion of aluminum and oxygen atoms due to the repulsive effect of Ce 2 S 3 crystals, froming an Al 2 O 3 shell layer with crescent moon shape on the inclusion surface. Gleeble hot-compression simulations revealed that the deformation index (ν) of inclusions in Ce-treated steel S1 (average ν ≈ 0.36) is significantly lower than that in Ce-free steel S0 (average ν ≈ 0.67), mainly because of the higher toughness of Ce 2 S 3 (core) compared to MnS in S0 steel and the restraining deformation effect of the rigid Al 2 O 3 shell of the dual phase inclusions in S1 steel. The coordination deformation of Ce 2 S 3 (core)–Al 2 O 3 (shell) composite inclusions in steel significantly reduced stress brittleness of Al 2 O 3 shell like single polygonal Al 2 O 3 inclusions during hot-deformation process, the fatigue performance of the tested steel still needs to be further verified.