| The concept of green energy conservation,environmental protection and sustainable development has become the leader of the development of manufacturing industry in today's society.Stainless steel pipe has many advantages,such as good corrosion resistance,smooth inner wall,small resistance,and durability.It has become the most ideal pipe for use,and has the trend of gradually replacing nonferrous metal pipes in all walks of life.Therefore,in-depth study of stainless steel connection technology will be conducive to the development of pipe products in China has a strong advantage.In this paper,a high speed high frequency induction welding technology was used to weld 316 austenitic stainless steel pipe with wall thickness of 0.3mm.The macroscopic morphology,weld microstructure,weld formation,mechanical properties and corrosion resistance of welded pipe joints under different high frequency induction welding parameters were studied.X-ray diffraction(XRD),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)were used to analyze the defect mechanism,fracture mechanism and corrosion mechanism of stainless steel welded joints.The main conclusions of this paper are as follows:(1)The grains in the weld zone of the high-frequency induction welded joint are fine,and the microstructure of the weld is mainly austenite and ?-ferrite.In order to ensure the good weld formability of thin-walled 316 austenitic stainless steel,the burrs formed on both sides of the weld should be continuous and consistent,and the heat input should be matched with the extrusion amount.When the heat input increases,the extrusion amount should be reduced,and when the extrusion amount increases,the heat input should be reduced.When the force applied during welding reaches or exceeds the elastic limit of the strip,the plastic deformation of the steel strip occurs,and the welding power increases and the width of the fusion line decreases.The smaller the opening angle is,the more serious the hump defect is.With the increasing opening angle,the hump defect tends to decrease until a continuous defect-free burr is formed.A molten metal flow model is proposed to analyze the formation mechanism of hump defect.Moreover,keeping the strip dry and clean at the welding point during welding can effectively avoid splashing.(2)The hardness of the welded joint is represented by the highest hardness value in the weld zone,and at the same time there is a tendency that the hardness decreases with the increase of heat input.The welding speed is 40m/min,the extrusion amount is 0.36mm,the heat input is 49.5KJ/m high-frequency welding technology,the tensile strength of the welded joint reaches 1074.6MPa,and the fracture position is mostly the heat-affected zone;80m/min,opening angle 6 °,with a heat input of 18.8KJ/m welding parameters,the tensile strength of the joint reached 921.79MPa,and the fracture location was mostly the weld zone.There are a large number of tearing dimples on the fracture surface of the former,and the fracture mode is a microporous aggregation fracture;the fracture surface of the latter can be observed locally after magnification,and there are tearing dimples on the other surface fractures.The fracture type is ductile fracture.There are many characteristics without obvious brittle fracture characteristics.The flattening performance test of the entire pipe was performed on the welded samples,and there was no cracking at the weld,indicating that the high-frequency induction welded stainless steel pipe had good plasticity.(3)Different degrees of corrosion occurred in each area of the welded joint,and a large number of corrosion pits were formed microscopically.Heat affected zone corrosion is the most serious,there are deep corrosion pits;Secondly,the weld zone presents large and deep corrosion morphology: the lightest corrosion degree is the base metal,forming large and shallow corrosion pits;The corrosion pit depth trend is that the heat affected zone is greater than the weld is greater than the base metal.With the change of solution pH3?5,the corrosion degree of different regions of the joint decreased.With the change of time,the corrosion rate showed a weight loss trend of first increase and then decrease.With the change of pH1?3?5,the corrosion rate showed a continuous decreasing weight loss trend.When the material is placed in an environment containing active anions such as chloride ions and oxidants,the anions are easily adsorbed on the sensitive parts of the stainless steel surface,so that the passive film of the material is corroded and destroyed,resulting in pitting holes.The metal in the hole has a low potential and becomes an anode,and the surface is in a passivated state with a high potential and becomes a cathode;therefore,a potential difference between the inside and outside of the hole will form a primitive cell reaction,and eventually pitting pits will be formed. |
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