The influence of martensite volume fraction and microstructure morphology on the fracture toughness of DP1180 steel

Abstract This study evaluates the influence of microstructural morphology and phase proportion on the fracture toughness of DP1180 steel processed through different quenching routes, with comparisons made against fully martensitic structures. Analysis of fracture toughness data reveals that, at comparable martensite volume fractions, the lamellar microstructure demonstrates significantly superior fracture toughness with only marginal deterioration in tensile properties compared to the blocky/island-type microstructure. This enhancement is ascribed to the anisotropic nature of lath martensite in impeding microvoid nucleation, growth, and coalescence. Crack propagation necessitates traversing intact martensite laths, effectively suppressing interfacial decohesion at ferrite/martensite boundaries. The fully martensitic condition exhibits substantially higher fracture toughness than all dual-phase variants, further emphasizing the beneficial role of lath martensite in enhancing crack resistance.