Creep and Relaxation Properties of 9-12

摘要

The sizing of bolted joints at elevated temperatures in steam turbines relies on the results of strees relaxation tests. It is often observed that relaxation strength is not directly poprotional to the creep ruptures strength. Structural changes occurring during creep exposure have an immediate influence onthe creep rates as they modify the strengthening and/or degradation level at each moment of the creep exposure. These changes have an important influence on the creep rupture strength as well, but can be detected after some delay. The significant and immediate influence on the relaxation strength is also evident. Therefore, sometimes the creep curves are used to estiamte or to predict the relaxation resistance of the steel, but only the firt and the second stage of the creep curve should be taken into account.