Stress Exponent of Steady State Creep Rate and Activation Energy for Creep of Solid Solution Strengthened 25Cr-35Ni Steels

Abstract

Based on the analysis of many creep data obtained previously from strain dip test to estimate the effective stress of the solid solution strengthened 25Cr-35Ni steels, the increases of the stress exponent of the steady state creep rate, n, and the activation energy for creep, Q_c, due to the addition of solute elements were discussed by using the following steady state creep rate equation, namely,
ε_s ∝ (σ_a-σ_f) ^n₀ exp(-Q^*_c/RT),
where σ_f is the friction stress, n₀ the effective stress exponent of the steady state creep rate and Q^*_c the activation energy for creep at constant effective stress.
It was suggested that the values of n and Q_c could be calculated by considering the applied stress and temperature dependence of the friction stress, respectively.
It was found that the calculated values of n and Q_c were in good agreement with those obtained from the creep test.
Then, it was concluded that the change in n with addition of solute elements was mainly attributed to the differences of the effect of various elements on the applied stress dependence of the friction stress and the ratio of the friction stress to the applied stress, while most part of the increase of Q_c was explicable by the temperature dependence of the friction stress.