Abstract
The authors have been systematically studying stress relaxation properties for typical heat resisting materials which are used in high temperature plants. In this study, the influences of test temperature and total strain on the long-term stress relaxation behavior for a 1Cr-Mo-V turbine rotor steel and a 2.25Cr-1Mo pressure vessel steel and the relationship between stress relaxation properties and creep properties were investigated, and a simple prediction method of residual stress was proposed.
The residual stress at shorter times in stress relaxation curves for 1Cr-Mo-V steel showed the same dependence on temperature as that at longer times. The dependence of residual stress on temperature for 2.25Cr-1Mo steel was fairly small at longer times. The influence of total strain on residual stress for 1Cr-Mo-V and 2.25Cr-1Mo steels was small. It was found that the relaxed stress ratio at a specified time in stress relaxation tests was related with the rupture time in creep test at the same stress as the initial stress in the stress relaxation test, and the relationship between the relaxed stress ratio and the rupture time was nearly independent of test temperature, total strain and materials. A simple prediction method of residual stress in stress relaxation tests was proposed on the basis of the diagram of relaxed stress ratio versus rupture time obtained. The predicted residual stress from the proposed method agreed well with the observed one.
