Effect of Oxide Inclusions Modification During Electroslag Remelting on Primary Carbides and Toughness of a High-Carbon 17 mass% Cr Tool Steel

摘要

The effect of oxide inclusions modification during electroslag remelting (ESR) process on nitrides and primary carbides in as-cast and annealed 8Cr17MoV tool steel was investigated. Impact toughness testing and fractography were performed. Primary carbides M7C3 were found to be dominant precipitates in as-cast ingot, besides a very small fraction of M23C6-type carbides. Al2O3 and MgO center dot Al2O3 inclusions promoted the formation of (Ti,V)N and primary carbides through serving as preferred nucleation sites, whereas heterogeneous nucleation of (Ti,V)N and primary carbides was avoided by modifying Al2O3 and MgO center dot Al2O3 inclusions to calcium aluminates. Oxide inclusions modification only refined the dimensions and distribution of carbides, but did not change the types and compositions of carbides. The improvement in the dimensions and distribution of carbides increased significantly the impact toughness of annealed steel. Large secondary carbides precipitated near retained primary carbides in annealed steel, which lowered greatly the impact toughness of 8Cr17MoV steel. Suppressing the formation of large primary carbides in as-cast ingot was favorable to preventing large secondary carbides formation after annealing, which improved greatly the impact energies of annealed steel accordingly.