18Cr-12Ni系鋼のクリープ破断強度におよぼす溶体化温度の影響

Abstract

Low and high carbon 18 Cr-12 Ni steels were solution treated at various temperatures and the creep rupture test was conducted at 600 and 700°C. These steels were employed since they were considered to give a fundamental aspect of the effects of heat treatments on creep rupture strength.The creep rupture life at the test temperature of 600°C showed a maximum at a certain solution temperature. This solution temperature, for shorter life tests (i. e., higher stress tests), was that which gave incomplete solution of carbide, and for longer life tests (i. e., lower stress tests), was that which gave just complete solution of carbide.At the test temperature of 700°C, however, appeared no maximum in the rupture life as a function of solution temperature.The above experimental facts on creep rupture life (tr) can be analysed by considering the effects of solution temperature on creep rate (ε) and rupture elongation (εr), since, apporoximately, tr is εr devided by ε.The rupture life maximum at 600°C stems from the fact that ε comes to the lowest value at a certain solution temperature and above the temperture no material change occurs ε in while εr continues to decrease as the solution temperature is raised.The result at 700°C that no maximum appeares in life can be explained by that the intergranular cracking at 700°C is of cavity type which is independent of grain size and hence εr as well as ε, does not change above the solution temperature that gives just complete solution of carbide.