Effect of Cerium on Solidification Structure and Eutectic Carbides in Electroslag Remelted S136 Tool Steel

The effects of rare earth metal cerium on solidification structure, eutectic carbides and the microsegregation of alloying elements in electroslag remelted S136 tool steel were studied. The secondary dendrite arm spacing of as-cast ingots decrease from 74.61 to 52.44 mu m with increasing the cerium concentration from 0 to 0.075 mass pct. It is only eutectic Cr7C3 carbide that generates as eutectic precipitate during liquid steel solidification. Eutectic Cr7C3 carbides gradually change from blocky to sheet, and their area fractions decrease with the increase in the cerium concentration. The liquidus temperature of S136 tool steel remains consistent with increasing the cerium concentration, whereas the solidus temperature increases slightly. The degree of microsegregation of eutectic M7C3-type carbide-forming elements (C, V, Cr) alleviates with the increase in the cerium concentration from 0 to 0.075 mass pct, which is beneficial to minimizing the precipitation of eutectic carbides. The non-metallic inclusions in the steel with 0, 0.0012 and 0.075 mass pct cerium are MgO<middle dot>Al2O3, CeAlO3 and Ce2O3, respectively, among which only Ce2O3 inclusions serve as the heterogeneous nucleation site of delta-Fe.