Effect of Cerium on Solidification Structure and Eutectic Precipitates in Electroslag Remelted Cr–W–Co Martensitic Heat-Resistant Steel

The effect of cerium on secondary dendrite arm spacing, Laves phase, eutectic carbides, and the microsegregation of alloying elements in electroslag remelted Cr–W–Co martensitic heat-resistant steels was studied. The number density and size of Ce-containing inclusions in the as-cast ingots with different cerium contents were analyzed. The secondary dendrite arm spacing of remelted ingots decreases from 55 to 34 μm with increasing the cerium content from 0 to 0.03 mass pct. The solidification microstructure of the as-cast ingots is refined by rare earth metal cerium in two ways: (I) the heterogeneous nucleation of primary ferrite (δ-Fe) provided by Ce₂O₂S and Ce₂O₃ inclusions, (II) the growth of dendrites inhibited by the enrichment of alloying elements at the solidification front. The area fraction of Laves phase and eutectic M₂₃C₆ carbides in the as-cast ingots decreases from 0.954 to 0.831 and 0.282 to 0.229 pct, respectively, as the cerium content is increased from 0 to 0.03 mass pct. The decrease in the area fractions are originated from the compression of the growing spaces of Laves phase and eutectic (Cr,Fe,W)₂₃C₆ carbides by both the microstructure refinement and the decrease in the contents of alloying elements Cr and W in the interdendritic regions.