A Study On The Cyclic Deformation Behavior And Fatigue Property Of A Wrought 316LN Stainless Steel

Wrought 316LN austenitic stainless steel is widely used in primary circuit in PWR nuclear power plant due to its good mechanical properties as well as good resistance against thermal aging.In this study,low cycle fatigue(LCF)and ratcheting fatigue(RF)were conducted at room temperature and 350~oC using ASTM E606standard samples.Three-point bending stress-cycling tests were conducted from room temperature to 450~oC using small steel beams,which aims at researching the influence of temperature and loading modes on the cyclic deformation behavior of the steel.The conclusions can be reached as follows:(1)As for LCF at room temperature,wrought 316LN steel exhibits a rapid initial hardening,gradual softening and stabilization to failure at high strain/stress amplitude and one stage at low strain/stress amplitude distinguished as continuous gradual softening to failure.(2)As for LCF at 350~oC,the hardening/softening behavior at high strain/stress amplitude is same with that at room temperature,and at low strain/stress amplitude is distinguished as a rapid initial hardening,gradual softening and a second gradual hardening to failure.The hardening degree at 350~oC is much higher than that at room temperature due to dynamic strain aging(DSA).(3)At room temperature and 350~oC,the ratcheting strain increases with the rise of mean stress and stress amplitude,but the RF life increases with mean stress due to mean-stress hardening.And the hardening degree at 350~oC is higher than that at room temperature due to DSA.(4)The SWT model and modified Coffin-Manson model can predict both the LCF life and RF life well.(5)The bending-ratcheting decreases with the rise of temperature from room temperature to 450~oC.The creep-ratcheting tests illustrate that the ratcheting deflection of the material is controlled by creep and it can also indicate that the temperature dependence of ratcheting deflection mainly results from the reduction of visco-plasticity with increasing temperature.The relationship of visco-plasticity and temperature can be interpreted by DSA.