.316 Ln, Stainless Steel Forging Crack Analysis And Process Control

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.