| It has been reported that SA508 Class 3 RPV steel exhibits dynamic strain aging phenomenon(DSA) at the operating temperature, 288℃. Therefore, DSA effect on the low cycle fatigue behaviors must be necessarily considered for precise life prediction. In this work, the influence of temperature and strain rate on tensile and low cycle fatigue properties of two kinds of steels which was produced by the same steel making method has been investigated. Test temperatures and strain amplitudes at strain rate of 4×10^(-3)/s and 4×10^(-4)/s were varied from room temperature to 400℃ and 0.6 to 1.8%, respectively. Steel with smaller grain and fine carbide size and homogeneous distribution exhibited longer fatigue life and higher mechanical properties. DSA region was considered as the temperature range which appeared inverse strain rate dependence of tensile stress and stress amplitude. Marked secondary strain hardening took place on cyclic stress response curve at DSA temperature, whereas cyclic softening remarkably occurred at different temperatures. As increase of temperature and decrease of strain rate, fatigue life decreased. But DSA resulted in the increase of fatigue life. It was believed that occurrence of secondary crack and surface multicrack improved fatigue crack growth resistance. |
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