FEM Analysis and Experimental Verification of the Integral Forging Process for AP1000 Primary Coolant Pipe
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ANALOGOUS to the main artery, the primary coolant pipe is one of the most important mechanical components in an AP1000 nuclear power plant.[1] This large special-shaped pipe, made of 316LN austenitic stainless steel, must have high geometrical precision and superior mechanical properties to be employed in, and withstand, severe working conditions.[2–4] Because the pipe has a large size with quite complicated shape and the material is difficult to deform, it requires deformation to the approximate final geometry through a complex three-dimensional integral forging technology.[5] In addition, owing to the heterogeneous distributions of the temperature and stress during the forging process, some defects that can negatively affect the performance of the pipe, like cracks, flow instabilities, and mixed-grain structures, are more likely to occur. To achieve excellent service properties, it is essential to control the defects development during forging. Therefore, predicting and preventing these forging defects has SHENGLONG WANG, MINGXIAN ZHANG, HUANCHUN WU, Ph.D. Students, are with the State Key Laboratory for Advanced Metals and Materials, University of Science & Technology Beijing, Beijing, 100083, P.R. China. XIAOYI YU, Manager, is with THM Company Ltd., Yantai, 264000, P.R. China. BIN YANG, Professor, is with the State Key Laboratory for Advanced Metals and Materials, University of Science & Technology Beijing, and also with the Collaborative Innovation Center of Steel Technology, University of Science & Technology Beijing. Contact e-mail: [email protected] Manuscript submitted September 2, 2015. Article published online August 8, 2016 5114—VOLUME 47A, OCTOBER 2016
become one of the most important subjects in this field.[6–10] Until now, many researchers have carried out work focusing on the analysis of defects in large forgings. For example, Zhang et al.[11] studied the defects during the upsetting of 42CrMo steel billet by Deform-3D. They found that cracks and other forging defects prefer to form around the edge angles, between the center part and regions near the head surface, or around the side edge of the billet, owing to the large stress risers, the existence of friction, and uneven temperature distributions. Chen and Lin[12] investigated the evolution mechanisms of voids during a drawing-out process both numerically and experimentally. They proposed a ‘‘two stage’’ theory for the closure process of voids, and suggested that the changes of the void aspect ratio are greatly affected by the initial aspect ratio and position of voids, but only slightly by the void size. Weron´ski et al.[13] found that coarse grain structures in forgings may result from low strains, and then used FEM to study the magnitude of the strain on the coarse grain structural defects of an aluminum alloy bar after upsetting. Moon et al.[14–16] presented an upper-bound method to analyze the formation of process-induced, side-surface cracks in an axisymmetric forging with a double ram action, and FEM and plasticine modeling were conducted fo
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