Study On Droplet Transfer Of CMP+P Welding Process In SAF2507 Super Duplex Stainless Steel

SAF2507 super duplex stainless steel has the characteristics of austenitic stainless steel and ferritic stainless steel.It has excellent corrosion resistance,especially local corrosion resistance.It has been widely used in petrochemical,ocean,coal and electricity,building and other industries.In order to explore the droplet transfer characteristics of CMT + P welding process in SAF2507 Super Duplex Stainless Steel,the high-speed photography system and electrical signal acquisition system were used to observe and study the CMT and CMT+P(cold metal transfer + pulse)droplet transfer process of SAF2507,and the process parameters of CMT+P were optimized.The study of droplet transfer characteristics can provide technical support and theoretical basis for the practical welding operation of SAF2507 duplex stainless steel in industry.Firstly,the droplet transfer characteristics of CMT bead weld under different WFS were observed and studied.The results show that there is a short circuit prophase in the CMT current waveform;the length of the base value phase and the short circuit phase will affect the length of the CMT period amd the heat input;when the WFS becomes larger,the waveform and the droplet transfer image will become extremely unstable,so it is not feasible to improve the heat input by improving the WFS;when WFS < 5m /min,the transfer form of the whole process is the typical form of CMT short circuit transfer.When WFS is more than 5 m/min,a mixed form of the projected transfer and the short circuit transfer,the form of the sub-projected transfer,and a mixed form of the sub-projected transfer and the short circuit transfer will appear in the form of droplet transfer.Then the droplet transfer characteristics of CMT+P bead weld under different WFS were observed and studied.The results show that there is no obvious peak phase in the CMT phase of the current waveform,and the actual short circuit phase current is higher than the base phase current,and there is a preheating phase.The shape,size and transfer form of droplet,wave state of molten pool,the distance of the workpiece to the end of the welding wire,the explosion of droplet,spatter and so on can be reflected in the actual voltage waveform.The voltage waveform diagram can be used to guide the analysis of the droplet transfer behavior.With the increase of WFS,the CMT phase presents a stable CMT short circuit transfer,while in the pulse phase,the complex forms of the projected transfer,the sub-projected transfer and spray transfer will appear.The heat input of the pulse phase is much larger than the CMT phase,so the pulse phase plays a major role.Finally,based on the feature points of WFS=5m/min,the single factor test method is adopted to optimize the characteristic parameters.The results show that the pulse peak current is 270 A and the pulse base current is 50 A,which is the best process parameter,and the heat input can be controlled by adjusting the number of pulses.