Effect of strain rate on tensile deformation and fracture behaviour of 18%Ni 300 maraging steel sheet

Abstract

Deformation and fracture under uniaxial tensile loading at room temperature were investigated for 18%Ni 300 maraging steel sheet in the strain rate range 1·67×10⁻⁵ to 1·67× 10⁻¹s⁻¹. The steel showed an increase in flow stress with strain rate and the increase in yield strength (YS) was more pronounced compared with the tensile strength (TS), resulting in a corresponding decrease of TS/YS ratio. Both the level of deformation and the deformation zone were also reduced by the increasing strain rate. Fractographic analysis indicated that the increasing strain rate induced, to some extent, plane strain constraint in the sheet resulting in increasing fracture angle, decreasing ductility/fracture strain, and increasing dimple size. With increasing strain rate the work hardening rate dσ/dɛ and strain hardening coefficient (n value) of the steel also decreased; hence, correlations were found between dσ/dɛ, TS/YS ratio, and n value. The decrease of these three parameters caused strain localisation as confirmed by the presence of intergranular dimples and intergranular shear. Also, the dimple density decreased as the strain rate was increased.

MST/729