Simulation Of Void Evolution In Piercing Process Of P91Thick-walled Pipes

P91seamless pipes have excellent performance, with very high high-temperaturecreep strength, tensile strength, and excellent thermal stability and high temperature creepresistance, and they are widely used in various high-temperature boiler tubes. They areusually of very strict quality requirements and high safety and reliability requirements forthey are applied in poor working conditions and have to be under heavy loading. On theother hand, when large steel ingots are produced in the internal metallurgical process, thereinevitably occurs the defect of void, thus seriously affecting the mechanical properties andfatigue properties. The presence of internal void destroys the continuity of the metal. Partof the pipes will be subject to great stress concentration when bearing the load, thusbecoming a source of fatigue and crack, and resulting in a shortening of product life andeven product obsolescence. Therefore, an in-depth understanding of the evolution of thevoid will help to improve the intrinsic quality of the product, and promote the scientific butnot experience-based development of technology.This thesis relies on computer simulation technology, large finite element softwareDeform, and adopts finite element and thermal coupling to make a simulation analysis ofthe void evolution of the P91thick-walled tube in perforation process. It analyzes siteprocess, uses software Solidworks for three-dimensional modeling, implement dataconversion between model and numerical simulation software Deform-3D. It conductsmesh generation of model through finite element software, defines the P91materialproperties, and selects simulation parameters. It adopts hot work die steel H13as the moldmaterial when taking into account the need of mesh generation in heat transfer.In consideration of the temperature field factors, this thesis simulates both cases of theperforation diameters of600mm and350mm, takes into account the two variables ofdifferent pore diameters and different hole positions, selects the key nodes, and focuses onanalyzing temperature field, three-dimensional stress, hydrostatic pressure, effective stress, effective strain and other changes of void in upsetting perforation process. By comparingthe programs, it further reveals the void evolution rule.In the analysis of temperature field changes in upsetting and piercing process, it isfound that the mechanical energy of plastic deformation is converted into heat energy, thusoffsetting most of the heat, but regional temperature of void rises slightly after perforation.After a comparative analysis of the hydrostatic pressure changes under differentperforation diameters, different hole diameters, different hole positions, it shows that aperforation diameter of350mm, hole diameter of100mm, a distance of150mm fromvoid bottom to the top have the maximum hydrostatic pressure values respectively in thecorresponding programs, and it is most likely to appear welding and eliminate the defects.The cloud chart of equivalent stress shows that there emerges around the void with acertain degree of stress concentration, but because of the smaller peak equivalent stress,there will not be too serious consequences. Through the analysis of the void deformationevolution and cloud chart of equivalent strain under point tracking, it is observed that at theupsetting stage, the void begin to have tiny plastic deformation, but the position and shapehave no significant changes at the end. However, in the perforation process, the voidvolume becomes smaller with some welding, but it does not eventually disappear.