Some New Approaches in the Analysis of High-Temperature Deformation

Creep tests on two heats of a CrMoV steel at 811K (1000°F) are analyzed using a new graphical procedure to solve the equation σ = C(t) H(ε). This enables prediction of both constant load and constant stress creep behavior at different stresses within the range examined which included tests lasting in excess of 10,000 hr. An analytical solution of the equation is also described and used to generate isochronous stress-strain curves. Attempts to predict the response in relaxation and constant strain rate tests where the load is continuously changing are described. Reasonable agreement was obtained in the former type of test using a total strain rule, which assumes a unique relationship between stress, strain and time, when the stress range covered was within the range used in the creep analysis. For constant strain rate testing, where a much broader stress range was involved, it was necessary to use incremental analysis to achieve good agreement between predicted and experimental curves up to about 2 percent strain.