ISIJ International · 1995 · 110 citations · 0 references
Natural SciencesMaterials EngineeringMaterials ScienceMechanical Behavior Of MaterialsMetallurgyStructural MaterialsAlloysDuctilityFracture MechanicsFracture ToughnessStrain HardeningStrengthening MechanismsDuctile FractureEmbrittlementGrain BoundariesMartensitic MicrostructureMartensitic SteelsSteel MicrostructureSteelsStrain Hardening Rate
This study examines how low‑temperature‑tempered martensitic steels achieve ultrahigh strengths and how carbon content influences ductility and toughness, and discusses strategies to harness high‑strength high‑carbon variants while mitigating quench embrittlement. The high strengths of LTT martensitic steels arise from strain hardening by a transition carbide/dislocation substructure, while increasing carbon raises strain hardening and reduces ductility, and high‑carbon steels suffer quench embrittlement from phosphorus segregation and cementite at grain boundaries, limiting toughness and fatigue resistance.
This paper describes the microstructure, deformation, and fracture of low-temperature-tempered (LTT) martensitic steels. The microstructural reasons for the ability of these steels to achieve ultrahigh strengths and the factors controlling ductility and toughness are described for low-carbon, medium-carbon, and high-carbon LTT martensitic steels. The key strengthening mechanism of LTT martensitic steels is the strain hardening provided by the transition carbide/dislocation substructure of the martensite crystals. In low- and medium-carbon steels, LTT microstructures fail by ductile fracture mechanisms, and ductility decreases as strain hardening rates increase with increasing carbon content. In high-carbon LTT steels, quench embrittlement associated with phosphorus segragation and cementite formation at austenite grain boundaries limits toughness and fatigue resistance. Approaches which permit the application of the high strengths of high-carbon LTT steels and minimize the effects of quench embrittlement are discussed.