Improved methodology for calculating initial loading strains in high-temperature creep deformation

摘要

For a design application of Alloy 617, the isochronous stress-strain curves (ISSC) should be constructed at a specified temperature. The ISSCs can be constructed using Young's modulus, average tensile hardening rule, and creep strain laws. To develop the ISSCs, it is necessary to determine the total strain composed of the elastic, plastic, and creep strains. To determine the total strain, the RCC-MR code and Blackburn's methods are described in detail. In addition, to practically determine the tensile elastic and plastic strain components of Alloy 617, a new method is proposed and applied in addition to these two methods. Results show that in the elastic regime, these three methods were identical in the tensile curves, and in the plastic regime, the Blackburn's equation was higher in the stress-strain curves than the RCC-MR code. Two methods revealed some differences in the analyzed curves, but a new method seemed to be better because it lay midway between the two methods. However, in spite of this difference in the plastic regime, it is suggested that these three methods can be utilized to calculate the elastic and plastic strain of Alloy 617. The reason for this is that the creep stress conditions, which are generally tested at 800°C, 850°C, 900°C, and 950°C of Alloy 617, correspond to a lower elastic regime rather than the plastic regime.