Improving strength and ductility of 42CrMo steel by Cr-controlled carbide precipitation and grain refinement

42CrMo steel is widely used in energy infrastructure and critical offshore wind power components. Cr, the primary alloying element, has traditionally been regarded as a means of enhancing strength, often at the expense of ductility. In this study, this conventional trade-off is revisited through a systematic investigation of the effects of varying Cr content on the microstructure and mechanical properties of 42CrMo steels. Increasing the Cr content from 0.6 to 1.2 wt% leads to simultaneous improvements in yield strength (from 915.8 to 1145.3 MPa), ultimate tensile strength (from 1087.7 to 1211.2 MPa), and elongation (from 12.2% to 14.6%), thereby achieving an optimal strength–ductility balance. However, a further increase in Cr content to 1.5 wt% results in a noticeable decline in ductility. These findings reveal a Cr-mediated synergistic mechanism governing carbide evolution, grain structure and strain distribution, providing valuable guidance for the design of high-performance steels.