316LN不锈钢高温塑性与裂纹预测的研究

【作者】 黑志刚；

【导师】 刘建生； 段兴旺；

【作者基本信息】 太原科技大学 ， 材料加工工程， 2012， 硕士

【摘要】 316LN奥氏体不锈钢做为核电主管道的主要材料，直接关系到核电站运行的安全。其组织为单相奥氏体，不能通过热处理来改善组织，只能采用锻造的方法。为了确保设备的安全运行，就需要制定出合理的锻造工艺，这就要求我们对316LN材料的性能有充分的认识。本文通过在Gleeble^-1500热模拟机上进行高温拉伸试验，研究了温度、应变速率、不同初始晶粒大小、应力三维度对316LN奥氏体不锈钢高温塑性的影响，并采用数值模拟的方法得出316LN奥氏体不锈钢发生韧性断裂的临界损伤值和空洞萌生的临界损伤值，为制定合理的生产工艺，预防生产和使用过程中锻件产生裂纹提供参考。在温度为900℃1250℃和1s^-1、0.5s^-1、0.05s^-1、0.005s^-1四种应变速率下，进行了光滑试样的拉伸试验。发现在给定的范围内，随着温度的升高和应变速率的增大，316LN钢的塑性越来越好。对45μm、90μm、220μm三种不同初始晶粒尺寸试样进行了拉伸试验，拉伸的温度为950℃、1050℃、1250℃，应变速率分别为：1s^-1、0.5s^-1、0.05s^-1、0.005s^-1。发现初始晶粒尺寸越小的试样塑性越好。应力三维度为表征材料受力状态的参数，应力三维度越大，应力状态偏于受拉，应力三维度越小，应力状态偏于受压。为了分析应力三维度对316LN钢高温塑性的影响，进行了缺口半径分别为0.5mm、1mm、2mm和4mm缺口试样的拉伸试验。发现缺口试样整体应力三维度大于光滑试样，塑性小于光滑试样。在950℃1100℃，缺口半径越小，应力三维度越大，试样的塑性越差，而1100℃以上温度时，晶粒尺寸变化明显，晶粒大小对材料塑性的影响起主要作用，缺口半径越小的试样，塑性反而越好。通过观察材料应力三维度的大小，就可以对其是否容易产生裂纹作出判断。本文采用Deform-2D有限元软件进行模拟，得出了光滑试样和缺口试样的应力三维度分布规律。更多还原

【Abstract】 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.更多还原