Competition between martensite recovery and nanoscale (V,Mo)C precipitation governs the strength–toughness synergy of V-alloyed martensitic mining chain steel

Achieving strength–toughness synergy in tempered martensitic steels is challenging because martensite recovery improves deformation compatibility while reducing dislocation strengthening. This study investigates how martensite recovery and carbide precipitation compete during tempering of a V-alloyed 23MnNiMoCr54 mining chain steel. Specimens were tempered at 400–650 °C and examined by tensile, hardness, and instrumented Charpy testing, multiscale electron microscopy, electron backscatter diffraction, and X-ray diffraction, together with a semi-quantitative strengthening analysis. Strength, hardness, and total instrumented absorbed energy evolved non-monotonically. Across 400–650 °C, the dislocation density decreased from 4.316 × 10 15 to 1.359 × 10 15 m −2 , while the microstrain decreased from 0.429% to 0.241%. From 400 to 550 °C, precipitation strengthening only partly compensated for recovery-induced softening, and a coarser precipitate-size distribution at 500–550 °C coincided with a tempering-associated toughness trough. Between 550 and 600 °C, the mean precipitate diameter decreased from 27.9 to 20.2 nm, while the yield strength increased from 1186 to 1234 MPa, indicating precipitation-assisted secondary hardening. The 600 °C condition combined a yield strength of 1234 MPa, hardness of 40.7 HRC, elongation of 14.0%, and total instrumented absorbed energy of 104.8 J. At 650 °C, continued recovery dominated and reduced the yield strength to 1110 MPa despite the persistence of a fine precipitate population, indicating over-tempering. These results indicate that the useful tempering window is governed by a competition between martensite recovery and nanoscale (V,Mo)C precipitation, providing a mechanistic basis for strength–toughness synergy in precipitation-strengthened martensitic steels.