Strength-ductility-toughness balance in flash-tempered martensitic steel: Role of dislocation-precipitate interactions

Abstract

Flash tempering has emerged as a sustainable and energy-efficient method for optimizing the mechanical properties of martensitic steels. This work investigates the temperature-dependent substructural evolution and mechanical properties of a high‑carbon low-alloy martensitic steel subjected to flash tempering. Results show that dislocation density decreases sharply with increasing tempering temperature, stabilizing at a high level (∼10¹⁵ m⁻²). Meanwhile, carbides evolve from dense intragranular η-carbides at lower temperatures (439 °C) to a mixture of η and θ-carbides, and finally to predominantly θ-carbides at higher temperatures (524 °C). Optimal mechanical properties are achieved at 473 °C, with an ultimate tensile strength of 2077 MPa, total elongation of 15.1 %, and fracture toughness of 49.3 MPa·m^1/2. This balance is attributed to the synergistic effects of partially recovered dislocations, finely dispersed η-carbides, and intergranular θ-carbides, which collectively enhance ductility and toughness while sustaining ultra-high strength. These findings underscore the critical role of dislocation-precipitate interactions in tuning the microstructure and mechanical properties of flash-tempered martensitic steels.