Investigation On The Process And Arc Stability Of Laser-MAG Hybrid Surfacing With Stainless Steel Flux-cored Wire

With the sustainable development of continuous casting technology and equipment,hollow and small-size casting rollers is increasingly applied in metallurgical industry.Traditional MAG surfacing process cannot meet the surfacing repair demand of hollow and small-size casting rollers for its characteristics including large dilution rate,low deposition efficiency,high heat input,and poor weld appearance.In view of this,laser-MAG arc hybrid surfacing process with stainless steel self-shielded flux cored filler wire is chosen to repair hollow and small-size continuous casting rollers in this dissertation,which focused on acquired surfacing layer with small ratio of weld reinforcement to width,low dilution rate,low porosity susceptibility and achieved high efficiency and stability surfacing for hollow and small-size casting rollers.In addition,the problems of weld appearance,arc stability,droplet force and transition are systematically studied.Specific research contents are as follows:Laser-MAG arc hybrid surfacing process was optimized andcompared with MAG.Results indicated that the laser-MAG arc hybrid surfacing stainless steel self-shielded flux cored wire reduced 14% in welding joint formation,20% in fusion ratio,28% in width of HAZ and increased 2% in hardness.The martensitic structure in weld zone became was apparent and HAZ grain size was more uniform and finer.The laser-MAG arc hybrid stability analysis results shown that addition of laser not only increased melting speed of filler wire,changed the melting state of wire tip,obviously reduced MAG arc drift rate,but also changed MAG arc space from flat cylinder towards circular cone,made arc length double.Their synthetic effects increased droplet transition frequency,stabilized droplet placement,reduced droplet short circuit transition probability and 22% current variation coefficients in comparison with MAG.For laser-MAG hybrid arc welding,the droplet transition along axis mode significantly improved the arc stability and solved the problem of arc instability and stagnation of the self-shielded flux cored wire welding material.The droplet transfer mode and force was analysised model of laser-MAG arc hybrid surfacing stainless steel self-shielded flux cored wire was established.The droplet transition was divided into left off-axis,right off-axis and along-axis transition.The mechanism of the influence of laser addition on the force of selfshielded flux-cored wire welding droplets was revealed.The laser controls the magnitude and direction of the electromagnetic contraction force,the plasma flow force,the aerodynamic force by changing the angle between the direction of electromagnetic contraction force(the direction of arc axis)and the axis of wire,the angle between droplet center and wire axis and the heating temperature of droplet,and then affect droplet transition.Results indicated that the transition along axis(droplet cancroids and arc axis return to the wire axis)not only significantly reduced the critical diameter of droplet transition,but also increased transition frequency,is the best transition mode in the laser-MAG arc hybrid surfacing with stainless steel self-shielded flux cored filler wire.Through the regression analysis of the effect of composition and content of mineral in the flux core on slag detachability coefficient,spatter loss coefficient,weld appearance,arc stability,the influence and mechanism of the various mineral components and its contents on surfacing weldability was investigated.In addition,the effect of interaction among any three components in mineral composition on the performance of the surfacing process is clarified.Based on the welding performance comparative analysis and experimental verification with the similar foreign filler wire,the influence of oxide composition and content on welding spatter was revealed.Results shown that the types of splash depended on oxide components and content in the core,which included the repulsive transition small particle splashing,short circuit transitional electric explosion splashing and arc bridge coexisting transition liquid bridge splashing.The spatter lose rate of the last type of splashing is minimal.The force mathematical model of radial and axial force between the surface tension and the radius of liquid bridge necking cross section was established,based on the model the surface tension control scope for bursting of arc bridge coexisting transition bridge was deducted.Through adjusting the oxide components and content in the core,the surface tension of droplet can be changed,the splash can be effectively reduced in the arc-bridge coexisting transition mode.