Precipitation Behavior and Elemental Distribution of MC Carbides in High Carbon and Vanadium High-Speed Steel

摘要

Precipitation behavior and elemental distribution of MC carbides in high carbon and vanadium high-speed steel were analyzed through the thermodynamic calculations and experimental measurements. The results illustrated that the primary MC carbide always nucleated from the fine inclusions or particles as the heterogeneous nuclei and was followed by the occurrence of eutectic reaction (L ->gamma + MC). 2D lumpy (primary) and stripe-like (eutectic) MC carbides were mainly formed inside the grains, the former was mainly in hexahedral shape with four-leaf grass-shaped surface and few in complex polyhedral shape with short branches, while the latter was mainly in clustered coral-like morphologies. High cooling rate can effectively refine the size and reduce the quantity of primary MC, it can also promote the uniform precipitation of fine eutectic MC. The primary MC precipitated preferentially contained more N, C, V, and less Cr, Mo, W with a better uniformity of elemental distribution when compared with that in eutectic MC. For the latter, its composition (mainly V) changed obviously which was mainly affected by the carbide's quantity, distribution characteristic, and the actual solute concentration during the solidification process. Generally, the more quantity and much denser distribution of the eutectic MC branches, the less contents of C and V in the eutectic MC branches. Based on the 2D and 3D morphologies of MC carbides, the primary MC showed good symmetry and the eutectic MC showed an obvious directionality of its branch from grain interior to grain boundary. It provided an effective reference for further research on the growth mechanism of carbides.

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