Effect of Mo Concentration on the Microstructure Evolution and Properties of High Boron Cast Steel

The microstructure evolution, mechanical properties, and tribological properties of high boron cast steel (HBCS) with various Mo concentrations are investigated. The results indicate that Mo addition can significantly modify the microstructure and enhance the comprehensive properties. With the increase of Mo concentration, borides change from the original fish-bone Fe-rich and Cr-rich M₂B to dendritic Fe-rich M₂B, blocky and cluster-like Cr-rich M₂B, and grainy Mo-rich M₂B. The hardness of HBCS increases gradually with the increase of Mo content due to the solid solution strengthening and the refinement of M₂B. It can be found that all the samples exhibit quasi-cleavage, but the impact toughness increases firstly and reaches the maximum value when the concentration of Mo is 2.10 wt.%, which is the result of the dispersive distribution of M₂B rather than the original fish-bone M₂B. Subsequently, the impact toughness begins to decrease as the concentration of Mo further increases because of the extensive formation of grainy Mo-rich M₂B at the grain boundary. Meanwhile, the wear results reveal that the average friction coefficient and wear ratio decrease with the increase of Mo content, and the wear mechanism changes from abrasive wear and adhesive wear to abrasive wear when the concentration of Mo exceeds 2.10 wt.%.