Low cycle fatigue resistance of SA533 pressure vessel steels

Abstract

Low cycle fatigue (LCF) tests were conducted on SA533 steels with different levels of sulphur content at room temperature and 300 °C. The fatigue limit shows little or no dependence on sulphur content, but significantly depends on testing temperature. At 300 °C, the fatigue limit is at 0.2% strain amplitude, slightly higher than the 0.1% strain amplitude obtained at room temperature. The fatigue limit of SA533 steel subjected to LCF tests at 300 °C was improved by the combined effects of dynamic strain aging (DSA) and grain size reduction. DSA and grain size reduction increase the steel strength and, accordingly, improve the LCF limit at 300 °C. But, concurrently, the carbide/nitride precipitates in SA533 steel lead to a decrease in steel strength. Grain size reduction and precipitation compete with each other. Grain size reduction is dominant and the net effect is reflected in the increase in hardness value. Fatigue life could be predicted either by means of the strain-life equation or the SWT (Smith, Watson and Topper) parameter for specimens under low cycle fatigue conditions. The strain-life equation for SA533 steel in air is independent of the sulphur content, but significantly dependent on the testing temperature.