Effect of Prior Austenite Grain Size on Strength and Toughness of an Ultrahigh Strength Maraging Steel

Abstract

The prior austenite (γ) grain sizes have been controlled in the range of 780 μm using cold working recrystallization treatment, and these effects on tensile properties and fracture toughness have been in vestigated for a 2 750 MPa grade 17Ni-20Co-6Mo-1.5Ti maraging steel.
Tensile properties were strongly dependent on the prior γ grain size. Tensile strength and reduction of area mainly exhibited a linear function of the reciprocal of the square root of the prior γ grain size, but the unstable fracture in a low stress level occurred without showing reduction of area when the prior γ grain sizes were coarser than a critical size. Fracture toughness was almost independent of the prior γ grain size and the fracture mode was quasi-cleavage type. Thus, it was concluded that the prior γ grain size had the pronounced influence on crack initiation but no or only a small effect on crack propergation.