Strength and Toughness of a Cold Rolled 13Ni-15Co-10Mo Maraging Steel

Abstract

A study was conducted to determine the effect of cold rolling prior to aging on the strength and toughness of an ultrahigh strength 13Ni-15Co-10Mo maraging steel. The smooth tensile strength of cold rolled and aged maraging steel increased continuously with increasing amount of cold reduction. The cold rolled maraging steel exhibited anisotropy in properties: the tensile strength in the transverse direction was higher than in the longitudinal direction, whereas the reduction of area and elongation showed lower values in the transverse direction. The notch tensile strength and plane strain fracture toughness K_IC also increased with increasing amount of cold reduction, taking maximum values at the 60-70% reduction. For example, longitudinal K_IC value increased from 34 MPa·m^1/2 for 0% reduction to 63 MPa·m^1/2 for 70% reduction. The large K_IC increase was attributable to the formation of delamination cracks running parallel to the rolling plane. The K_IC test specimen might behave as the sum of a number of thin plates in the presence of the delamination cracks and each thin plate might fracture under the plane stress condition. From these results, it was concluded that the good combination of the strength and toughness could be obtained at the 60% cold reduction.