| Austenitic stainless steel is widely used in the field of nuclear power valves because of its excellent corrosion resistance and good mechanical properties.Austenitic stainless steel material used in this research is Z2CND18-12 NS,which corresponds to the standard RCC-M M3301 "CLASS 1,2 AND 3 AUSTENITIC STAINLESS STEEL FORGINGS AND DROP FORGINGS”.this kind of austenitic stainless steel valves are widely used in our country have been built or under construction in a number of nuclear power units,such as the Red River,Guangdong Nuclear Power Ningde,Yangjiang,Fangchenggang and other projects,in Fuqing,Fang Jiashan,Changjiang and other projects.The sealing lip welding structure of the valve body has the advantages of compact structure,safety and stability.The valve has no leakage in the welding of body cover lip,can run without regular maintenance of small disintegration,irradiation opportunity of the human body,so the body cover sealing lip welding structure of the valve in the domestic and foreign nuclear power plant has been used.Nuclear grade austenitic stainless steel valve cover on the valve sealing lip welding quality and the valve is in the process of nuclear power operation in safe operation plays a very important role in the actual product welding process in lip weld thickness is not standard,the weld porosity and weld root appeared issues such as cracks and weld formation seriously affect the weld quality and operation safety of the valve body cover lip welding at.In this paper,through the simulation of the actual welding structure of austenitic stainless steel lip products,in different welding current(80A,75 A,70A),different welding speeds(0.3rad/min,0.4 rad/min,0.6 0.5rad/min,rad/min),and different body cover with gap(0.02 mm,0.05 mm,0.10mm)a total of 21 seven sets of welding in the simulation,simulation of all 84 experimental specimens,using optical microscope,scanning electron microscope and other test equipment to observe and analyze experimental samples,to find a group to meet the requirements of lip weld thickness(1.0mm-1.5mm)of the best welding current and welding speed,analysis of different process parameters of lower welding root crack,at the same time to find the cause of the formation of cracks at welding lip.The results are as follows:(1)when the welding current is 70 A and the welding speed is 0.6 rad/min,the thickness of the lip welding is obtained according to the standard;(2)the root crack of lip welding is formed by the joint action of welding heat input and weld clearance.In this experiment,when the large heat input welding 1019.1J/mm welding,welding root gap exists in the lip,lip welding root have cracks,there is no gap in the lip welding root,lip welding roots do not have cracks;when the small welding heat input welding 445.9J/mm,regardless of whether there is gap welding root lip,lip there is no root welding crack;(3)lip welding root crack in the larger welding heat input(1019.1J/mm)under the condition of welding stress and welding lip root gap caused by the existence of stress concentration,the interaction of the two factors of formation and expansion. |
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