The effect of trace element Nb on microstructure and wear resistance of 8Cr4Mo4 V bearing steel

The effects of a trace Nb addition (0.016 wt.%) on the phase composition and wear resistance of standard-compliant 8Cr4Mo4V bearing steel were investigated via microstructural characterisation, X-ray diffraction (XRD) analysis, microhardness measurements, and wear performance testing. Results show that the addition of Nb refines the austenite grains in the quenched state microstructure, resulting in a 25.80% reduction in grain size, an increase in the content of lower bainite, and a reduction in retained austenite content. After tempering, the Nb element promotes dispersed precipitation of carbides, and the carbide content increases from 10.02% to 11.86%, while the carbide size decreases. The addition of Nb element to 8Cr4Mo4V steel affects its microstructure, which leads to an increase in the hardness and wear resistance of the steel under the combined effect of solid solution strengthening, fine grain strengthening and precipitation strengthening, resulting in a 40.23% reduction in wear loss.