.316 Ln Stainless Steel High-temperature Plasticity And Crack Prediction

As the key material of the nuclear power,316LN austenitic stainless steel isrelated to the safety of nuclear power plant. The organization of316LN is singlephase austenite, we can't improve the organization of316LN by heat treatment,only using the method of forging. In order to ensure the safe operation ofequipment, we need to develop a reasonable forging method, which requires us tohave a full understanding of the performance of the316LN stainless steel. In thispaper, by having some experiments of high temperature tensile on Gleeble^-1500thermal simulation machine, the influence of high temperature plastic of316LNabout temperature,strain rate,the initial grain size,stress triaxiality had beenresearched, and using the method of numerical simulation, we get the criticaldamage value of ductile fracture and empty initiation of316LN austeniticstainless steel, which providing a reference for develop reasonable productionprocess and prevent cracks at the processes of production and using.A tensile experiment of smooth specimen were conducted, the temperaturerange were900℃1250℃and the strain rate were1s^-1,0.5s^-1,0.05s^-1and0.005s^-1,which found that the plasticity of316LN steel get better and better with theincreasing of temperature and strain rate at a given range.The tensile experiment of three different initial grain size:45μm,90μm,220μm were conducted. The temperature were950℃,1050℃and1250℃,thestrain rate were1s^-1,0.5s^-1,0.05s^-1and0.005s^-1, we found that the smaller theinitial grain size of the specimen is,the better the plastic of the specimen is.Stress triaxiality is a parameter of stress state of materials, the bigger thestress triaxiality is, the stress state is more near to tension, the smaller the stresstriaxiality is, the stress state is more near to pressure. In order to analyze theinfluence of stress triaxiality on the high temperature plasticity of316LN steel, atensile experiment of different notch radius were conducted, which the notchradius were0.5mm,1mm,2mm and4mm.We found that the stress triaxiality ofnotched specimens is bigger than smooth specimens and the plastic of notchedspecimens is worse than smooth specimens. At950℃1100℃,the smaller thenotch radius is, the bigger the stress triaxiality is, and the plasticity is worse. Butat the temperature above1100℃, the change of grain size were obvious, the grainsize plays a major role on the material plasticity, the smaller the notch radius is,the better the plastic is.By observing the value of stress triaxiality of material, you can make ajudgment on whether the material easy to generate crack. In this paper, theDeform-2D finite software is used to simulate, we get the distribution law ofstress triaxiality of smooth specimens and notched specimens.