The intent of this report is to describe the development of a creep model for use in producing isochronous curves for grade 91. The basis for the other component of strain, the plasticity or “hot tensile” curve, has been described elsewhere. Values of creep strain are needed over a wide range of conditions. At some temperatures, stresses, and times, the creep strain is dominated by the primary component; at other conditions tertiary creep is important. The model must in some cases be predictive of conditions for which there are no available data, specifically estimating creep strains at very low stresscs, high temperatures, and long times.
