316LN不锈钢锻造裂纹分析及工艺控制

【作者】 张义帅；

【导师】 张秀芝；

【作者基本信息】 太原科技大学 ， 材料学， 2011， 硕士

【摘要】 316LN奥氏体不锈钢作为核电主管道用钢的关键材料,具有良好的耐晶间腐蚀性能和力学性能。针对316LN在锻造过程中开裂的现象,本文研究路线从原始铸锭→锻态钢锭→锻造工艺参数,分析316LN锻造开裂的原因。在借助于金相显微镜、SEM、能谱仪分析铸态、锻态组织特征基础之上,通过Gleeble—1500D进行高温拉伸实验,研究316LN的高温塑性以及锻造开裂过程中裂纹萌生机制,为大型锻件的工艺设计和分析提供参考。原始铸锭由于存在着严重的成分偏析、区域偏析现象,因此在锻前必须进行热处理,锻前热处理工艺对后续锻造成型质量保证起着重要的作用。对实际生产过程中锻造开裂的钢锭进行了常温组织分析,钢锭中非金属夹杂主要以脆性氧化铝类夹杂物为主,平均级别2.0级,加大了钢锭在高温锻造过程中开裂的倾向。借助于高温拉伸实验研究了高温拉伸过程中裂纹的萌生及扩展规律,裂纹的萌生主要通过空洞在晶界上形核、长大、积聚来完成。细观损伤力学在预测材料破坏的过程中可以起到很好的作用。通过高温拉断实验研究316LN在高温塑性,1050℃～1250℃在应变速率为0.5S-1时,材料有很好的塑性;断口分析以及断口附近的组织分析表明,高温断裂主要是沿晶断裂;空洞的萌生主要在晶界上,尤其在三叉晶界的交汇处;拉伸过程中再结晶的发生可以有效阻止裂纹的扩展。为了验证316LN在1050℃～1250℃热变形的可行性,进行了缩比工艺实验,通过宏观以及微观分析,试样都没有微裂纹萌生。更多还原

【Abstract】 316LN austenitic stainless steel, as the key materials for the steel pipe in the nuclear power, shows good resistance to intergranular stress corrosion and mechanical. According to the problems that 316LN austenitic stainless steel is easy to crack in forging, this thesis focuses on the causes of 316LN forging cracks with the route from original cast ingot to forging state ingot, and then to forging technology. Based on the analysis of the features of as-cast structure and forging state organization with the help of metallographic microscope, SEM(scanning electron microscope) and ESD(energy disperse spectroscopy), a research has been performed with Gleeble-1500D on the pyroplasticity of 316LN and the mechanism of crack initiation during the forging, which provides references for the process design and analysis of heavy forgings.For the serious segregation in composition and region, the original cast ingot must be through the heat treatment before forging which plays an important role in the quality guarantee of forgings.Having performed the organization analysis in normal temperature to the ingot with cracks formed in the practical manufacturing process, we find, the nonmetallic inclusions in the ingot are mainly brittle aluminum oxide with an average level 2.0, increasing the cracking tendency in the hot forging.Micro-crack initiation is principally accomplished by the nucleation, growth, and coalescence of voids on the grain boundary, with the research of crack initiation and propagation rule in the high tensile by the high tensile experiment. And microscopic damage mechanics is good for forecasting the failure process of materials.The high tensile experiment concerned on the pyroplasticity of 316LN proves that this kind of material has excellent pyroplasticity in 1050℃~1250℃and with the strain rate 0.5s-1. Besides, fracture analysis and fractography show that high-temperature fracture, mainly intergranular fracture. Voids form mainly on the grain boundaries, especially the interchange of grain boundaries. Recrystallization in the drawing process can prevent the extension of cracks effectively.To check the feasibility of hot deformation of 316LN in 1050℃~1250℃, scaled process experiments have been performed. Through the macro-analysis and micro-analysis, samples have no micro-crack initiation.更多还原