Effects of Aging Conditions and Strain Rate on Rupture Elongation of 13Ni-15Co-10Mo-0.2Ti (280kg/mm²-Grade) Maraging Steels

Abstract

Tensile strength and elongation have been measured in aged 13Ni-15Co-10Mo-0.2Ti, 14Ni-10Co-10Mo and 14Ni-15Co-7Mo maraging steels. The temperature range in aging has been varied from 450°C to 575°C for the 13Ni-15Co-10Mo-0.2Ti steel, and from 425°C to 475°C for the 14Ni-10Co-10Mo and 14Ni-15Co-7Mo steels. A cross head speed in a tensile test has been ranged from 1mm/min to 0.005mm/min. The effect of strain rate on tensile elongation has been investigated in relation to aging temperature and time.
In tensile tests of the maraging steels in which fine coherent precipitates are considered to be formed, it is observed that tensile elongation is decreased with decreasing a strain rate. The elongation decrease in a low strain rate is also observed in tensile tests of the 13Ni-15Co-10Mo-0.2Ti steel in which coarse precipitates are contained by over-aging. It is considered that the elongation decrease in a low strain rate is attributed to both stress concentrations resulting from plastic deformation characteristics of the aged maraging steels and hydrogen diffused to regions having intense stress concentrations.