Study On Welding Manufacturing Process And Joint Properties Of 16MnDR Nuclear Vessel

With the development and utilization of nuclear energy,the nuclear power industry has been developing on a large scale and the nuclear fuel is the energy source for nuclear power generation.Once the nuclear fuel transport tank leaks during longdistance transportation,it will cause unpredictable losses.Meanwhile,in the use of nuclear energy a certain amount of nuclear waste will be produced,which needs to be sealed at low temperature,so,a large number of high-strength thick-walled storage tanks will be used.Because the connection of materials is mainly realized on welding,so,the quality of welded joints becomes one of the main problems of large-scale production of tanks,it is necessary to develop efficient and high-quality welding methods to realize the welding of low-temperature storage and transportable tanks.At present,most of the welding process of thick-walled storage and transportable tanks adopts the traditional welding process,which combines groove backing welding with filling and covering welding.Therefore,the process also determines potential problems such as low welding manufacturing efficiency,poor quality stability and low reliability of welded seam,which directly affect the service safety of mid-to-high-end equipment and the safe and sustainable development of certain industries in the country.Research and develop a new advanced welding processes and equipment to replace traditional welding methods to achieve high-quality plates efficient and reliable connection is a prerequisite for improving the manufacturing level of the above-mentioned mid-tohigh-end industries.This article has carried out TIG deep penetration welding method,filling and covering welding process,and welding joint microstructure and mechanical properties of 16 MnDR mid-thickness plates under actual working conditions.Aiming to improve welding efficiency and automation,and solve the problem that the mechanical properties of welded joints are not up to standard.In order to analyze the forming mechanism of the root weld and the reason for improving penetration during the backing welding process,the dynamic behavior of the arc and pool was collected with the help of a high-speed camera,and the temperature field of pool was monitored in the help of an infrared camera.From the perspectives of arc morphology,pool flow and pool heat transfer,the reason for one side welding with back formation and the mechanism of improving penetration are analyzed.On the basis of root bead,the process of filling and covering welding procedure is designed.By the submerged arc welding process experiment,the best welding parameters were finally obtained.During the welding process,the general rule of weld forming under different parameters was obtained through the selection of welding materials,the control of heat input and the selection of interlayer temperature.Confocal laser microscope and scanning electron microscope(SEM)were used to analyze the microstructure and element distribution of the weld,combining with the microstructure of the weld and the morphology of the fracture,explained the reasons for the change of the mechanical properties of the weld under different process parameters.Related research results show that the dual-frequency modulated pulsed TIG arc has higher energy and better stiffness,which ensures the stability of the molten hole during the backing welding process.The reason for dual-frequency modulation pulse TIG welding method can realize one side welding with back formation is the flow of liquid metal to the back and bottom of the pool.The modulation effect of highfrequency pulse makes more heat transfer to the bottom of the pool to improve the penetration.Through the design of the submerged arc welding process,the welding of the mid-thickness plates is finally realized.The analysis of the structure and mechanical properties of the welded joints shows that there are fine acicular ferrite structures(AF)generated in the two wire systems.It is of great help to the improvement of the mechanical properties of the joint,but the pearlite(P)of the bottom layer and the ferrite side-plate(FSP)of the cover layer will have an adverse effect on the mechanical properties.