Lesson 7 - Flux Cored Arc Welding Electrodes for Carbon & Low Alloy Steels

7.7.1.1 These electrodes may be used for single or multiple pass welding. The elec- trodes in this group have a rutile (acid) slag that is characterized by a spray-like transfer, little spatter and good weld bead contour that is flat to slightly convex. 7.7.2 EXXT-2 - These electrodes are classified as single pass electrodes because they contain higher amounts of deoxidizers (manganese and silicon) for welding through rust or mill scale. Since the rust or mill scale is iron oxide (FeO), the manganese and silicon will combine with the oxygen in the FeO and float to the slag surface as harmless manganese oxide or silicon dioxide. If no rust or mill scale is present, or if multiple passes are made over the preceding passes, the manganese and silicon will become alloying elements in the weld metal. This can change the mechanical properties drastically, and possibly cause cracking. These electrodes are for welding in the flat and horizontal positions, and the arc characteristics and deposition rates are similar to those of the T-1 types. Running one pass on each side of butt welds can be considered a single pass. There are no chemical composition requirements for the weld metal produced by these electrodes since it would be severely diluted with the base metal on single pass welds. They are, however, required to meet the minimum tensile strength specified in a transverse tensile test as specified in AWS A5.20-95. These electrodes can be used for welding plate with heavy rust and mill scale, and still produce X-ray quality welds. 7.7.3 EXXT-3 - These electrodes require no external shielding gas and are for making high speed, automatic single pass welds on thin material up to 3/16" thickness. Welding current is DC electrode positive (+). They are for use in the flat and horizontal positions, and up to 20° downhill welding. These electrodes are limited to 3/16" metal thickness and single pass welding; otherwise, the welds may become hard and crack sensitive. They have a spray-like metal transfer. 7.7.4 EXXT-4 - These are self-shielded electrodes designed for high deposition rates, and they operate on DC electrode positive (+). The metal transfer is globular and the slag system desulfurizes the weld metal, making it resistant to cracking. Penetration is low, allowing the weld metal to bridge gaps caused by poor fit-up. These electrodes are for single or multipass welding in the flat and horizontal positions. 7.7.5 EXXT-5 - These are gas shielded electrodes for flat and horizontal fillet welds. They have a basic slag system that provides excellent impact properties when compared to the T-1 and T-2 acid slag types. Spatter level is slightly higher than the T-1 and T-2 elec- trodes. Argon-CO₂ gas mixtures are recommended by some manufacturers for the 1/16" diameter sizes, for a spray-like metal transfer and high deposition rates. CO₂shielding gas is usually recommended for 5/64" diameters and up, and the metal transfer is more globu- lar. They may be used for single and multipass welds.

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