Theoretical Prediction And Control Of Welding Deformation Induced By Laser Beam Welding In Large And Thick Austenitic Stainless Steel Structures

Austenitic stainless steel,which has good corrosion resistance and excellent integrated mechanical properties,is normally used to manufacture key structures in the nuclear power plant.Welding is an important process for connecting these metal structures,and is also a common means of retrofitting and maintaining nuclear power equipment.The characteristic of non-uniform heating of the welding process results in inevitable generation of residual stress and deformation on work pieces after welding.The main cause of stress corrosion cracking occurs during weld residual stress-induced service.For thick welded structures,correcting residual deformation is not only technically difficult,but also significantly increases manufacturing costs and lead times.For this reason,predicting residual stress and deformation on welded structures with numerical simulation techniques and during manufacturing period rising the relevant control measures have very significant meanings for cost reduction of nuclear power construction,extension of the durable years of equipment and maintenance of safe operation of the nuclear power plant.As fundamental research,a thermal-elastic finite element simulation method of thermodynamic sequential coupling,which is based on the software-MSC.Marc,has been developed.Based on this calculation method,deep weld temperature field and stress deformation caused by laser penetration welding on thick plates and the influence of different heat source models such as mobile heat source,variable length heat source and instantaneous heat source is explored.After the relationship between heat source simplicity and calculation accuracy is compared,the residual deformation of welded irradiated sample holders is simulated with the thermal-elastic finite element simulation method.Besides,the influence of deformation mechanism on such thick structures after welding and processing techniques such as weld heat input,weld sequence,confinement conditions,pre-welding anti-deformation is discussed and the experimental measurement result are compared with simulation result in order to verify the efficiency of the calculation method.In the end,a special anti-deformation technique called elastic anti-deformation method is raised,which can be used to control welding deformation of thick structures,and its principle and function are discussed,as well.As the research result shows,firstly,simplifying heat source can extremely increase the calculation efficiency and high calculation precision for longitudinal bending deformation of structures can also be achieved.However,as heat source simplification increases,the calculation precision of angle deformation is decreasing.For this reason,the use of simplified heat source models can be considered for welding deformation calculation of welded structures which is mainly with longitudinal bending deformation.Secondly,main deformation of welded irradiated sample holder is longitudinal bending deformation and the experimental measurement result basically matches prediction result with finite element method,which verifies the efficiency of used calculation method.Reducing welding heat input and pre-welding anti-deformation can effectively control longitudinal bending deformation of welded work pieces and anti-deformation works best,while weld sequence and confinement conditions have little impact on deformation.Finally,based on the fundamental mechanics principles,the elastic anti-deformation method is developed and applied to deformation control of irradiated sample holders after welding,which has achieved good results.However,which remains attention,the application of elastic anti-deformation requires satisfaction of certain conditions,which are significant increase in bending stiffness after structural welding and the use of external tooling to maintain the elastic deformation of the work pieces during the entire welding process.The method of simplifying heat source is used in this study to simulate welding deformation of thick plates,which will provide a basis for study of efficient calculation methods for the residual deformation of thick welded structures.The research on the deformation mechanism of irradiated sample holders and the influence of technique factors on welding deformation will provide theoretical guidance for the relevant technical personnel to develop reasonable technique measures to control welding residual deformation of thick structures.