While several types of materials are available for structural steel applications, A913 high-strength low-alloy (HSLA) steel offers some distinct advantages to structural steel fabricators. For instance, in populated urban areas, real estate is at a premium, so buildings are designed to have as much usable square footage as possible. A913 allows fabricators to use less material but still gain the strength needed to create a sound structure capable of carrying large loads over long spans. A913 steel also works well in hospitals and stadiums, where the design requires a lot of open space.
These benefits are prompting some fabricators to transition to A913 steel from A572 and A992 steel. The latter rely on the addition of micro-alloys and higher carbon content to achieve strength, while A913 steel achieves its strength from the quench and self-tempering process. During this process, a water spray is applied to the hot-rolled steel to rapidly cool it, resulting in a thin martensitic surface. Heat in the core expands to the surface to temper it, reducing hardness and improving toughness.
A913 steel also has a much lower carbon content that increases its overall toughness and improves weldability, along with having low amounts of sulfur and phosphorus. The low level of these impurities is important, as high levels reduce toughness and ductility and make steel more brittle, leading to potential cracking, especially in welded applications.
Unlike some structural steel, A913 steel is not available in plate, but rather in special shapes such as wide flange beams, or W-beams, that can be used for columns and beams in structural steel applications. They provide the main columns that rise from the center of a building, with other structures attached to them on each floor.
Offering better benefits
While A572 and A992 are considered HSLA steel, A913 steel offers benefits over the two in terms of improving productivity namely because it requires little to no preheating prior to welding. Under the American Welding Society (AWS) D1.1 code, A913 steel is considered a prequalified base material that lessens or eliminates those preheating requirements due to the lower carbon equivalency content.
For A913 Grade 65 steel, for example, no preheating is required (regardless of thickness) provided that the base material is at a minimum temperature of 32 degrees F and it is being welded with a filler metal with an H8 designation. The H8 designation indicates that there are 8 ml of diffusible hydrogen (or less) per 100 grams of weldment.
In addition to saving time and costs by lessening or eliminating preheating, fabricators can maximize labor by focusing on welding instead. A913 steel also creates a safer environment by minimizing the use of open flames for torches and reduces costs associated with the purchase of the torches and the propane to fuel them.
Additional cost savings can be found due to the higher strength-to-weight ratio of A913 steel grades. Because the material is stronger, it can be used in thinner sections that are lighter, ultimately resulting in the need to purchase less steel. It is estimated that A913 Grade 65 steel reduces the weight for columns by 15 to 20 percent and up to 35 percent for trusses when compared with A992 steel. And even though A913 steel can be more expensive than other HSLA steel, it can still reduce costs when considering other factors.
For instance, A913 steel can reduce transportation and fuel costs as more material can be moved to the jobsite in fewer trips. Also, the material does not require the heaviest model of handling equipment to put sections into place. That is a benefit to contractors because tower cranes with greater lifting and payload capacity are a significant expense on the jobsite.
Additionally, there is an environmental benefit to using A913 steel. Along with requiring less transportation and fuel, using less steel reduces the carbon footprint on structural steel fabrication projects.
Ultimately, using thinner sections of A913 steel requires less time to weld, less labor and less filler metal – all of which reduces costs on the jobsite.
Choosing a filler metal
Depending on the grade and the welding specifications, various filler metals can be used for welding A913 steel. For example, A913 Grade 80 steel is prequalified for welding with an SMAW process utilizing a 100-ksi tensile strength electrode with an H4 designation. For lower grades, such as A913 Grade 50 steel, an AWS E71T-1 gas-shielded wire or E71T-8 self-shielded flux-cored wire may be used.
However, some of these products on the market can have limitations, such as problems consistently meeting mechanical requirements for Grade 65 and higher. Other issues include low deposition rates and trouble balancing travel speed and weld puddle control. Hobart is addressing these challenges by providing fabricators with two new filler metals: Fabshield FE80 and FE81 self-shielded flux-cored wires designed for field welding A913 Grade 65 steel specifically.
These wires are out-of-the-box solutions that ensure consistently robust mechanical properties, something that can be difficult to achieve with other wires. They offer the weldability common with lower strength wires while also meeting the higher strength requirements for welding A913 Grade 65 steel. This weldability means operators experience a smoother arc and good weld puddle control. Also, the wires have a wide controllable operating range, which allows operators to adjust their parameters to weld faster or slower, depending on their skill set.
The Fabshield FE80 wire is for flat and horizontal welding and recommended for groove welds on column-to-column connections (column splices). The wire has an AWS classification of E80T6-G-H8, so it provides 80-ksi tensile strength and is available in 3/32 in. diameter. It operates between 330 and 475 amps and 23V to 27V at a wire feed speed of 160 to 300 ipm and a contact-to-work distance of 1.75 in. The wire provides between 10 and 20 lbs. per hour of deposition or the amount of weld metal filling the joint within that time frame.
The Fabshield FE81 wire provides 80-ksi tensile strength but is usable in all positions for welding moment connections and truss connections. It has an AWS classification of E81T8-G-H8 and is available in 5/64 in. diameter. It operates between 200 and 340 amps and 18V to 24V at a wire feed speed of 100 to 280 ipm, offering deposition rates ranging from 4 to 9 lbs. per hour.
Hobart collaborated with ironworkers and other industry professionals to develop these new wires with the aim of addressing challenges with welding A913 Grade 65 steel in field erection, seismic applications and high-rise construction. In addition to reducing or eliminating bottlenecks, the wires provide sound welds capable of passing ultrasonic inspection and reducing rework. Overall, they are designed to help operators meet productivity expectations and project deadlines.
From new welding tech to filler metals that help fabricators reach productivity goals, our welding archive is filled with helpful articles.
