Low Cycle Fatigue of Carbon Steel in High Temperature Pure Water Environment

Abstract

An environmental fatigue test machine was developed and axial strain controlled fatigue tests could be conducted in the pressurized high temperature pure water using it. The fatigue life of carbon steel in the environment was investigated.
Results obtained are summarized as follows;
(1) In 250°C pure water containing 8 ppm dissolved oxygen, the fatigue life of carbon steel degraded markedly with decrease in strain rate in the comparatively large strain amplitude (above 0.25%). However, in the small strain amplitude, there was no degradation in fatigue life.
(2) The environmental fatigue degradation was significant in the temperature range of 250°C to 290°C and in the dissolved oxygen contents above 0.2 ppm.
(3) It was supposed that the conspicuous environmental fatigue degradation was caused by the combination effects of SCC and dynamic strain aging.
(4) The prediction method of fatigue life of carbon steel in high temperature water was proposed with considering strain rate.
(5) The environmental correction factor K_en was proposed to correct the design fatigue strength of carbon steel in high temperature water.