Ratcheting boundary of 316LN austenitic stainless steel under thermal aging

Previous studies,including ASME and RCC-MR standards,did not consider the influence of environmental factors on the ratcheting boundary of the material,and only a unified ratcheting boundary was proposed.In this paper,thermal aging was taken into consideration,and the effect of thermal aging time on the ratcheting boundary of 316 LN austenitic stainless steel was characterized by the efficiency diagram rule.The results show that,when the secondary ratio U is small,there is no significant difference in ratcheting boundary between the original material and the thermal aged material.When the secondary ratio U is large,the ratcheting boundary of the material presents a slight upward trend with the increase of thermal aging time.Compared with ASME and RCC-MR standards,it is found that RCC-MR is conservative.Based on the evolution of the efficiency index V with the number of cycles,it is more conservative and reasonable to choose the stage when the efficiency index V develops into a constant.