Creep rupture tests of 12% Cr heat resisting steel with various heat treatments were carried out, and the application of hardness of creep ruptured specimens for the residual life prediction was investigated.
Creep rupture strength was affected by the heat treatment condition at a short test duration, but the difference of creep rupture strength tended to diminish at a long test duration. The hardness of creep ruptured specimens had the same tendency with the creep rupture strength. In spite of the difference in heat treatments, the relation between the hardness of creep ruptured specimens and the applied stress was liner.
By assuming that the steel fractured when the hardness softened and approached to a critical value which was determined by the applied stress, the equation for calculating the creep rupture time was formulated. It was confirmed that the creep rupture time could be calculated precisely.
