首页|Cerium refinement of grains and primary carbides during solidification of Cr4Mo4V bearing steel
Cerium refinement of grains and primary carbides during solidification of Cr4Mo4V bearing steel
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The effect of cerium(Ce)on the solidification microstructure of Cr4Mo4V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt％)of Ce addition,the coarse columnar grains in as-cast microstructure transform into equiaxed ones,and the average diameter is reduced from 56 to 27 μm.The network-like and bulky primary MC and M2C carbides at the interdendritic regions become disconnected and refined,and their volume percentage decreases from 4.15 vol％to 2.1 vol％.Ce-inclusions acting as heterogeneous nucleation agents of prior-austenite grains and Ce atoms segregating at grain boundaries,both contribute to the refinement of grains.Thermody-namic calculations reveal that primary carbides are precipitated after γ-austenite forms near the end of the solidification process.The modification of primary carbides in size and amount is mainly attributed to the isolated remaining melt separated by refined γ-austenite grains in which the nucleation of carbides is promoted,while the growth is restrained owing to the less segregation of alloying elements.
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