Influence of the Mo and V Contents on Microstructure and Secondary Hardening of 6Cr6W2MoV Steel

Abstract

The influence of Mo and V contents on the microstructure and secondary hardening of 6Cr6W2MoV steel was studied in this paper, and the process factors and the transformation mechanism of the influence results were discussed by phase equilibrium thermodynamic analysis. The results show that, the microstructure of 6Cr6W2MoV steel is uniform and thin, in which the undissolved carbide size after quenching is 0.23μm. In the heating and cooling process of the annealing, the dissolution and precipitation of M23C6↔M6C carbides transformation can be used to carbides distributing uniform refinement. Adding an overmany Mo content will lead to coarsening of carbide particles due to small amplitude of M23C6↔M6C transformation. Adding an overmany V content will appear a small of the bulk MC carbide on the crystallization, so the heterogeneity of carbides is increasing. The tempering hardness of 6Cr6W2MoV steel is 63.5HRC, and when adding an overmany Mo content the maximal hardness arrives to 65HRC. Adding Mo changes the carbide composing, it is conducive to the variety of carbides precipitation strengthening near intermediate temperature and the tempering hardness increasing. When adding an overmany V content the more MC carbide well occupy more amount of C, the tempering temperature dispersion increases too, so the tempering hardness debases deservedly and the highest hardness only reaches HRC60.5.