High Temperature Properties and Constitutive Equations for 1 Cr-1/2 Mo Steel

This paper presents the tensile, creep, rupture, and fatigue properties of 1 Cr-1/2 Mo steel. Tensile tests were conducted over a temperature range of 70–1150 F (21 to 621 C). Creep-rupture tests were run for the stress range of 10–56 ksi (69 to 386 MPa) at temperatures of 850 to 1150 F (454 to 621 C) and the strain-controlled fatigue tests were run to 145,000 cycles at room temperature. Results of the tensile tests are presented as stress-strain curves and as constitutive equations. The parameters in the equations were obtained by a nonlinear least-squares technique assuming an origin offset power law formulation of true stress as a function of true strain. The creep analysis resulted in a creep constitutive equation, isochronous stress-strain curves, and correlations between rupture time, time to onset of tertiary creep, and minimum creep rate. The constitutive equation is a two-term rational polynomial with a steady-state term which describes primary plus secondary creep. Isochronous stress-strain curves were developed from the creep equation and extrapolated to 100,000 hr. Over the measured range, the isochronous curves showed excellent agreement with the actual data. In absolute strength level, both the rupture stress and minimum creep rate data show that this particular heat of material lies in the upper part of the scatter band for 1 Cr-1/2 Mo steel. The room temperature cyclic stress-strain curves show the alloy strain softens in the low strain region and strain hardens in the high-strain region. The fatigue behavior is typified by a linear relationship between both elastic and plastic strain range and cycles to failure on a log-log basis. The fatigue results conform reasonably well to predictions from Manson’s method of universal slopes.