Analysis of the creep crack growth rate for modified 9Cr-1Mo steel using Q* parameter

Abstract

This paper proposes a Q* parameter to analyze the creep crack growth rate (CCGR) for modified 9Cr-1Mo steel. A C* parameter is not reasonable for some practical applications because it has a dual value in the early stage, although the CCGR has been generally evaluated by the C* parameter. The Q* parameter is able to evaluate the CCGR by a simple monotical linear function without a dual value due to the “nose” in the early stage of the CCG curve. The K, C*, and Q* parameters have been used to analyze the CCGR for this steel, and the scattered data among the three parameters were obtained and compared. In the scattered data from the early stage to the acceleration stage, the Q* parameter was found to be superior to the C* parameter, while the K parameter had the largest scatter and there was no systematic trend among each series of tests. It is obvious that the Q* was regarded as an independent parameter, whereas the C* was regarded as a dependent parameter that depends on the creep deformation rate, which is a function of applied load, temperature, specimen shape, and activation energy of deformation, etc.