Research On Pulse Waveform Control Parameters And Droplet Transfer Characteristics Of GMAW-P Process With WC-Fe Based Powder-cored Wire

In view of the difficulty in controlling the droplet transfer process of WC-Fe based powder-cored refractory wire by GMAW,the GMAW-P deposition process was introduced.Based on the high-speed camera and electric signal synchronous acquisition system,combined with iron-based powder-cored wires with different WC content,the relationship between the pulse waveform control parameters such as pulsing current,pulsing current time,current-rise rate,current-decrease rate and droplet transfer modes,as well as the relationship with welding appearances was mainly studied,trying to obtain the pulse characteristic parameter ranges of droplet transfer in the one drop per pluse condition for powder-cored refractory wires with different tungsten carbide particle content,so as to provide support for the low-cost and high efficient manufacturing of reinforced iron-based composite using powder-cored refractory wires with tungsten carbide particles.Firstly,droplet transfer characteristics were tested by using 45%WC-Fe based powder-cored refractory wire.The range of pulse characteristic parameters of droplet transfer in the one drop per pluse condition was obtained:pulsing current 411-443 A,pulsing current time 4.3-4.7 ms,current-rise rate 409-531 A/ms,current-decrease rate 76-205 A/ms.A large number of powder-cored particles flowing away from the wire end in the hybrid mode of one drop per pluse and multiple drops per pulse were observed.When the droplet was in the one drop per pulse condition,the maximum loss rate of welding wire powder-cored particles in 100 mm welding bead was 1.72%.Then,on the basis of the droplet transfer characteristics of 45%WC-Fe based powder-cored refractory wire,the droplet transfer characteristics of 30%WC-Fe based powder-cored refractory wire were investigated.The range of pulse characteristic parameters of droplet transfer in the one drop per pluse condition was obtained:pulsing current416-441 A,pulsing current time 3.6-4.2 ms,current-rise rate 318-539 A/ms,current-decrease rate 105-311 A/ms.When the droplet was in the one drop per pulse condition,the maximum loss rate of welding wire powder-cored particles in 100 mm welding bead was 1.15%.Then,based on the droplet transfer characteristics of 30%WC-Fe based powder-cored refractory wire,the droplet transfer characteristics of 20%WC-Fe based powder-cored refractory wire were studied.The range of pulse characteristic parameters of droplet transfer in the one drop per pluse condition was obtained:pulsing current 434-460 A,pulsing current time 3.6-3.9 ms,current-rise rate 314-568 A/ms,current-decrease rate 103-315 A/ms.When the droplet was in the one drop per pulse condition,the maximum loss rate of welding wire powder-cored particles in 100 mm welding bead was 0.80%.Finally,the microstructure characteristics of welding beads in the one drop per pulse condition of three kinds of WC-Fe based powder-cored refractory wires were studied.The welding bead microstructure in the one drop per pulse condition of 45%WC-Fe based powder-cored wire was mainly composed of residual tungsten carbide particles,primary faceted dendrites and fishbone-like eutectics（both belonging to M₆C carbides,including Fe₃W₃C and Fe₄W₂C）,interdendritic reticular carbide（containing M₇C₃carbide）and iron-based phase.Primary faceted dendrites were not observed around the tungsten carbide particles in the welding bead in the one drop per pulse condition of 30%WC-Fe based powder-cored wire,instead,a large number of fishbone-like eutectics were observed.The welding bead microstructure of 20%WC-Fe based powder-cored wire was mainly composed of equiaxed crystals,columnar dendrites and interdendrite carbides such as M₇C₃.The average hardness of welding bead in the one drop per pulse condition of 45%WC-Fe based powder-cored wire was up to 740.02 HV.