Not Your Father’s Gas-Shielded Flux-Cored Electrodes
FCAW-G consumables have steadily evolved into application-specific productivity workhorses
by Tom Myers, The Lincoln Electric Company
These new specifications demand the need for low-alloy FCAW-G electrodes which produce welds with increased tensile and yield strengths (compared to carbon steel electrodes) for welding these higher-strength steels. Other applications require electrodes which produce welds with improved impact properties. Generally, electrodes needed to produce welds with low temperature toughness of at least 20 ft•lbf (27 J) at a test temperature of 0⁰F (-18⁰C) or -20⁰F (-29⁰C). Some applications now require these same absorbed energy values at temperatures of -40⁰F (-40⁰C) or even lower.
Similarly, operator demand for just the "right" application-specific, flux-cored electrode has steadily increased over the past five to ten years, to keep up with a growing desire for increased weld productivity, performance and quality, not to mention aesthetics.
Because of this increased specification of new materials, combined with demands for more customized, more efficient electrodes, manufacturers have been returning to the proverbial R&D drawing boards to develop new gas-shielded flux-cored consumables. No longer does the one-size-fits-all approach to electrode design work for many FCAW-G applications. This consumable category has come a long way. In short, they aren’t your father’s gas shielded flux-cored electrodes anymore.
Fundamentals and Advantages of FCAW Electrodes
Flux-cored electrodes were originally developed as a higher productivity extension of shielded metal arc welding (SMAW) electrodes. They are, in fact, like a SMAW electrode turned inside out. They are a steel tube (i.e. outer steel sheath) with flux inside the tube or at the electrode’s core, hence the name, “flux core.” Because of this design, the electrode can be wound onto a coil or spool, and with the use of a wire feeder and welding gun, fed continuously into the weld joint.
Flux-cored electrodes fall into two fundamentally different categories: self-shielded, flux-cored electrodes (FCAW-S) and gas-shielded, flux-cored electrodes (FCAW-G).
The FCAW process also has a higher operating factor than the SMAW process (where operating factor (%) equals arc time divided by total fabrication time). It’s also easier to use. It operates at higher current levels, which yields higher deposition rates and resulting higher productivity. Finally, FCAW electrodes have higher electrode efficiency than SMAW electrodes. This means that more of the purchased pounds (kg) of electrode end up as deposited weld metal and less is lost through stubs.
FCAW electrodes, with their slag systems, also have inherent advantages over slag-less processes, such as gas metal arc welding (GMAW). The fast-freezing slag system of all-position classified FCAW electrodes allows for better out-of-position welding capability, including vertical and overhead, as the slag helps hold the molten metal against gravity. FCAW electrodes produce higher deposition rates when welding out of position than GMAW consumables do. In addition, many in-position classified FCAW electrodes have good penetration characteristics, making them ideal for thicker sections of steel plate.Concerns with One-Size-Fits-All Electrodes
The traditional multipurpose approach towards FCAW-G electrodes has proven to be increasingly ineffective over the years. While the use of a one-size-fits-all electrode for a wide range of applications can deliver adequate arc performance, the reach for a single electrode to perform well in every application is just too broad. As a result, the arc is never optimized.
Some industries, such as shipbuilding / barge building, have increasingly pushed the deposition rate capabilities of all position FCAW-G electrodes. Generally when welding in position or with gravity, welders can utilize faster wire feed speed procedures to produce higher deposition rates than they can when welding out of position or against gravity. However, because of remote welding locations and limited access to their welding equipment, welders often cannot easily turn up their procedures when they transition from out of position to in position welding. Therefore they need one set of welding procedures for FCAW-G electrodes which produce maximum deposition rates for out of position welding and still produce high deposition rates for in position welding. Many of the original one-size-fits-all FCAW-G electrodes could only be pushed so far before the slag system would not support the additional molten weld metal. Therefore, new FCAW-G electrodes were needed with a different type of slag system. These high deposition or “HD” electrodes have very fast freezing slag systems which better support higher wire feed speed welding procedures.
Furthermore, operator appeal of low-alloy FCAW-G electrodes also has improved. A welder can weld with a carbon steel FCAW-G electrode or a low-alloy FCAW-G electrode and not really see a difference in arc performance. This results from the fact that manufacturers have succeeded in coming up with a standard slag system for families of electrodes. Individual electrodes can be modified for different applications by tweaking the alloy formulation in the electrode’s core so that welders and fabricators will see similar operating characteristics, no matter the application. Application Specific FCAW Electrodes
Today, manufacturers of FCAW electrodes offer broad product lines, with many electrodes designed for specific applications and industries. Examples of more specialized electrodes include the following:
FCAW-G electrodes designed for use with one specific type of shielding gas. (i.e., UltraCore® 71C, UltraCore® 71A85)
FCAW-G electrodes designed for higher-strength steels (i.e. 80 ksi, 90 ksi and 100 ksi minimum tensile strength). (i.e., UltraCore® 81Ni1A75-H, Outershield® 91K2-H, Outershield® 690-H)
"HD" type FCAW-G electrodes designed for high-deposition, out-of-position capability. (i.e., UltraCore® HD-C, UltraCore® HD-M)
FCAW-G electrodes designed for exceptionally high deposition rates in the flat and horizontal positions. (i.e., UltraCore® 70C, UltraCore® 75C)
FCAW-G electrodes designed for improved low temperature toughness properties. (i.e., UltraCore® 712A80, UltraCore® 81Ni2A75-H)
"SR" type FCAW-G electrodes designed for stress-relieved applications. (i.e., UltraCore® SR-12)
FCAW-G electrodes designed for pipe welding applications. (i.e., Pipeliner® 81M, Pipeliner® 101M, Pipeliner® 111M)
FCAW-G electrodes designed for chromium-molybdenum (Cr-Mo) steels. (i.e., Cormet 1, Cormet 2)
Again, gone are the days of FCAW-G electrodes simply being of the “one-size-fits-all” variety. Today, welders have a broad choice of electrodes that have been designed for a variety of specific applications and industries, expanding the range of use, as well as overall quality and productivity. With improved operating characteristics and performance, these enhanced, highly efficient products are truly not our father’s flux-cored electrodes anymore.
Tom Myers is a Senior Applications Engineer at Lincoln Electric in Cleveland, Ohio.