Abstract
The effects of different contents of vanadium (V) (0.1, 0.2, and 0.3 wt%) on the microstructure evolution and mechanical properties of 718H steel were investigated. The precipitate was characterized by means of atom probe tomography (APT) and bright-field transmission electron microscopy (TEM). The increase in V content has great benefits for strength, but has an adverse effect on impact toughness. The strength increase can be attributed to the influence of V addition on dislocation density, misorientation gradient, and fine scale MC precipitates. Precipitation strengthening mainly contributes to the V-added steel by analyzing various strengthening mechanisms. However, fine scale MC precipitates can pin dislocation leading to a decrease in its mobility. A large number of immovable dislocations will increase the dislocation accumulation, internal stress and brittle cracking, resulting in a gradual decrease in impact toughness with the V addition. In addition, compared with V-free steel, the dissolved V content in austenite decreases the grain boundary energy and inhibits the diffusion of the C atoms, ultimately reducing the transformation range of pearlite (P).
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