| P91 steel(9 Cr1 Mo,V,Nb)is a new type heat-resistant martensite steel which always serves under harsh environment that local crack is usually inevitable.With the advantages of lower cost,higher reparative rate and simple operation,repair welding has become the first choice to repair heat-resistant steel tube defects.However,the welding residual stress which caused by local repair welding has always been the prominent problem to the safety service.Therefore,in order to improve the success of repair welding procedures and ensure structure performance of each repair welded part,the welding residual stress must be analyzed comprehensively and systematically.The traditional residual stress testing methods can only measure the residual stress distribution on the surface of the work-piece which making the residual stress analysis is not accurate enough,but numerical simulation can quickly determine the distribution of residual stress under different welding parameters.By means of numerical simulation,the factors that affect the distribution of residual stress could be fully understood and so as to provide the basis for establishing reasonable welding procedures and predicting welding residual stress.In this paper,two kinds of filler materials are employed in repairing welding of 60 mm thick P91 steel.Based on thermal elastic-plastic theory,using finite element analysis software ANSYS,a 3D numerical model of P91 steel multilayer repair welding is established and residual stress is calculated.The analysis of characteristics of residual stress distribution is also been done.The study results show that simulation results have a good agreement with experimental results,demonstrating the reliability and rationality of FE model.For homogeneous repair welding,in the process of welding,due to the heat treatment of the pre order welding beads,the peak value of the longitudinal stress on the surface of each weld layer decreases gradually.When the welding is finished,the welding beads and its vicinity show a high longitudinal residual tensile stress with peak value 532 MPa which is higher than the yield stress of base material at room temperature.The longitudinal residual tensile stress is reduced to compressive stress quickly with the increase distance to the welding center.The large transverse tensile stress is located at the first weld bead in the last welding layer and the peak value is 444 MPa.The maximum Von Mises stress zone is located at the start/end of arc and beyond the yield stress of base material at room temperature.The value of residual stress along the thickness is relatively small and could be ignored.In the Groove profile area,the longitudinal residual stress increases along the thickness direction and the peak value appears 5-7mm down to the upper surface of weld beads.The latter weld bead side stress is larger than that of the first weld beads side in the weld groove profile and the value is 589 MPa.For heterogeneity repair welding,there is a large longitudinal tensile stress in the weld and its vicinity after the last weld bead was finished,and the peak value is 482 MPa.The tensile stress is reduced to compressive stress rapidly with the increase of distance from the weld center.The large transverse tensile stress is located on the two sides of the upper surface of the weld beads area,peak value is 333 MPa.The maximum Von Mises stress zone is located on the upper surface of the weld zone,and the peak value is 470 MPa which is less than yield stress of base metal.In the Groove profile area,the longitudinal residual stress decreases first and then increases with the increase of the thickness of the weld beads,and the peak value lies at the root of weld beads with peak value 424 MPa.Under real service conditions,the residual stress has a larger decline.In the Groove profile area,the longitudinal residual stress increases with the increase of the thickness of the weld and the larger stress region is located in the middle of all the weld. |
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