Tailoring Microstructure and Strength Contribution in a Mo–Nb–Ti Tempering Steel via Controlled Coiling and Tempering Temperatures

A 700 MPa grade Mo–Nb–Ti tempered steel was developed utilizing a low‐alloyed design and a direct‐tempering after rolling process. The distinct effects of coiling temperature (CT) and subsequent tempering temperature (TT) on microstructural evolution and strengthening mechanisms were systematically examined. The results indicate that coiling at 500°C and tempering at 650°C yields a yield strength of 785.37 MPa and a tensile strength of 890.74 MPa. The elongation reaches 23.05%, resulting in a product of strength and elongation of 20.53 GPa▪%. As the CT increases from 450°C to 600°C and the TT rises from 550°C to 700°C, strength initially increases and then decreases, while elongation remains approximately 20%. Furthermore, quantitative analysis of strength contributions at varying coiling and TTs revealed that the primary variations in the strength of tempered steel arise from three mechanisms: grain refinement strengthening, dislocation strengthening, and precipitation strengthening. Among these mechanisms, dislocation and precipitation strengthening are the most significant. Low‐temperature coiling promotes the retention of a high density of dislocations, which serve as preferential nucleation sites for carbide precipitation during the subsequent tempering process. Following high‐temperature tempering, the carbides display a fine‐uniform‐dispersed distribution. This microstructure effectively mitigates the precipitation insufficiency associated with low‐temperature coiling and provides a substantial precipitation strengthening effect.