Study On The Welding Of Cleftiness-shaped Defects In Large-diameter Thick-walled Seamless Tube

Energy is the material foundation for China’s sustainable economic and socialdevelopment, and is the driving force of China’s rise, and is also the congenital conditionsthat human societies depend for survival and development. With the rapid development ofChina’s economic construction, the demands for large-diameter thick-walled stainless steeland high alloy steel seamless pipe are increasing in China’s energy engineeringdepartments such as cracking of petroleum, construction of nuclear power and coal-oil andso on. There will be more excellent market prospects.Due to the special nature of the field of energy engineering plant, it requires that thequality of the pipes have some very good features: high temperature resistance, highpressure resistance and corrosion-resistant and etc. However, some products had beenproduced by making use of traditional method of hot rolling piercing, and then by theprocess of cold rolling (drawn). And to them for quality testing, they were found inner ofthe wall existence of the cleftiness-shaped defects. After research and analysis, we thinkthe defects of the cleftiness-shaped are evolved out of the holes and shrinkages and othercasting defects generated by the original ingot solidification process. Therefore, mind andpurpose of this paper is by setting up reasonable piercing process parameters, according tothe theory of atomic diffusion and recrystallization principle, and taking advantage oftapered roller punch piercing deformation at the same time on the pipe billet to eliminatethe defects of the cleftiness-shaped inside of metal to ensure the continuity of the metallicmaterials, improve product quality, reduce production costs, and energy conservation.Firstly, according to the steel ingot size which used in the actual production, it usedof casting finite element emulation software ProCast that had simulated the steel ingotsolidification process, and analysed the hole shaped defect location, size and morphologybriefly. Secondly, the production of large diameter thick wall stainless steel seamless tubeof an enterprise existing a cone-shaped roll piercer size as the prototype, the geometricmodel had been built by the finite element analysis software Abaqus, and using thesoftware had simulated the rotary piercing to steel pipe in different parameters (size of piercing point, amount of the piercing point protrusion and roll spacing). Then, the stressand strain of the different simulation results have been analysed, and it is concluded thatthe interlayer defects inside of pipe derive from the original casting defects, instead oftearing due to tensile stress or shear stress in the process of perforation. Fourth, using thewelding experiment to judge whether the cleftiness-shaped defects have been eliminatedin the tube internal, and it’s observed and analysed that the welding effect on macroscopicand microscopic. Finally, the experiment was simulated by finite element software Abaquson computer, and the stress-strain state of welded zone also was analysed.