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Finding a Flux/Wire Combination to Match A572, Weld through Rust
An overhead crane manufacturer solicits the Consumables crew for help choosing a flux/wire combination that closely matches A572.
Q: We manufacture overhead cranes and recently purchased a submerged arc welding (SAW) gantry system to increase throughput and produce more consistent-quality welds. We are welding mostly A36 and some A572-Gr.50 base materials. We would like to have a filler metal that more closely matches the A572. What would be the best wire and flux combination for welding on material that has some light rust or mill scale as we don't have an available blasting process?
A: This is a fairly common application, but to answer your questions, there is one important detail that needs to be addressed.
Will the cranes be operating in cold weather climates such as 0 degrees F or colder? If so, you might require a wire and flux combination that can provide cold weather toughness. If the answer is no, then it shouldn't affect your consumable choice.
Selecting a filler metal strength to match the minimum requirements of the base material depends on the base material combinations you are welding. If all of your components comprise A36 welded to A36 or any other grade of carbon steel, you only need to match to the A36 because it has the lowest strength for this application. A36 has a minimum yield strength (YS) of 36 KSI (36,000 pounds per square inch) and an ultimate tensile strength (UTS) of 58 to 80 KSI. Many of your common SAW consumables start at minimum UTS of 60 to 70 KSI. Typically, the YS of these filler metals will be about 10 to 12 KSI less than the UTS, which still places them above the A36 minimum. If you have some components that are A572 welded to A572 or potentially higher-strength material, then you would want to make sure that your filler metal meets the minimum YS and UTS as designated by the base material requirements.
If we assume that A36 will be the governing material, then a flux and wire combination similar to an F6 or F7 and A0 or A2 and EM12K or EM13K should meet your requirements. However, always check with the appropriate construction code you are building to and any special customer requirements.
The last thing to consider is if your application will require an active or neutral flux. You stated that there is some light rust and mill scale on the base material. In most cases, a neutral flux along with the wire will contain enough deoxidizers to prevent any welding defects that could be caused by the nonprepped weld joint surface conditions. However, if you experience porosity or other welding defects that may be caused by the rust or mill scale, then an active flux should eliminate those issues.
Keep in mind, though, that most of the active fluxes available are limited to single-pass welds up through 1-in. multipass welds. Active fluxes will enhance the manganese pickup in the welding deposit, which can cause cracking.
This article originally appeared in The WELDER magazine.
It is reprinted here with permission of the Fabricators & Manufacturers Association, Intl.