Life Prediction and Stress Evolvement for Low Cycle Fatigue in PWR Primary Pipe Material

The low cycle fatigue (LCF) behavior of primary pipe material Z3CN20.09M cast stainless stell (CASS) was studied at room temperature (RT) and elevated temperature of 350 degrees C by conducting total axial stain controlled tests in air with strain amplitude in the range +/-0.175% to +/-0.8%. Based on the test results, the cyclic stress response of material was analyzed, and a dynamic strain aging (DSA) phenomena was discovered at 350 degrees C. Besides, the evaluation of elastic modulus during cyclic tests was studied, and the effect of elastic modulus on parameters of low cycle fatigue was investigated based on the Manson-Coffin model. It is shown that elastic modulus for Z3CN20.09M decreases constantly during the whole fatigue life, but fluctuates more frequently at elevated temperature. Both the static and dynamic elastic modulus result in a same life trend in low cycle fatigue, but the elastic modulus affects the precision of fatigue life prediction to some extent when the fatigue life exceeded 10(5).