During submerged arc welding production, the slag removal performance of flux directly affects welding efficiency and weld quality. Difficult slag removal is mainly manifested as the firm adhesion of slag crust to the weld bead surface. Slag sticking at weld toes and groove corners is hard to clear. It not only increases grinding workload but also brings risks of slag inclusion during multi layer and multi pass welding. The slag removal result is jointly determined by molten slag physical properties, slag system composition, crystallization state and welding process.
The difference in thermal expansion coefficient between molten slag and weld metal is the basic factor for slag removal. The closer the two values are, the smaller the interfacial peeling stress during cooling, and the harder it's for the slag crust to fall off. Excessively high viscosity of molten slag and a wide solidification range also lead to poor spreading of molten slag inside the groove and produce interlocked slag adhesion.
The chemical composition of the flux slag system acts as the decisive factor. When the oxidizing property of molten slag is relatively high, spinel phases tend to form and firmly combine with the oxide layer on the weld bead surface. Excessively high SiO2 content forms a continuous glass phase and increases the tendency of slag sticking. CaF2, Al2O3 and TiO2 require precise proportioning. Imbalanced proportions will change the viscosity and crystallization behavior of molten slag and worsen slag removal performance.
The crystallization morphology of molten slag is equally critical. Welding heat input changes the microscopic crystallization. Oriented rod shaped crystals help crack and peel off the slag crust. Fine acicular crystals improve the toughness of the slag crust and make it hard to detach. This point deserves special attention for basic fluxes.
On the premise that the flux is qualified, process issues such as improper heat input, small groove angle, base metal rust and insufficient flux drying will also aggravate slag sticking. When slag removal problems occur on site, we shouldn't simply attribute the issue to unqualified flux. Instead, troubleshoot layer by layer from slag system design, molten slag phase, crystallization state and welding process. Combined with specific working conditions, optimize flux selection and process parameters to steadily improve slag removal performance.
