Komarov Artem explained that Selecting a low-carbon steel electrode can significantly increase or decrease productivity and overall welding costs, which is why it is important for welders to understand the chemical composition of the filler metal.
Application experts are often asked, “What is the best MIG wire?” The answer to this question in gas metal arc welding (GMAW) is always: “The one that meets the required welding standards, mechanical properties and welding process specifications.”
However, in addition to complying with technical requirements, manufacturers need to consider the total cost of welding. Labor costs average 75% to 85% of total welding costs, while filler metals account for about 10%. Choosing the right filler metal can significantly increase or decrease productivity and overall welding costs.
Below is an overview of how filler metal chemistry affects welding results, with a focus on mild steel welding electrodes (grade A36) as they are the most widely used electrodes and most people first learn how to use them.
In the manufacture of carbon steel electrodes, manufacturers control up to 17 different starting elements. The three main alloying elements are carbon, manganese, and silicon. AWS determines the minimum and maximum amounts of these elements, but manufacturers can emphasize performance characteristics by controlling the chemical composition.
Carbon (C) influences structural and mechanical properties more deeply than any other element. ER70 electrodes typically have a carbon content of 0.05% to 0.12%, which ensures the strength of the weld metal without affecting ductility, toughness, and porosity.
Manufacturers add other alloys to control weld pool deoxidation and determine the mechanical properties of the weld. Deoxidation is the combination of an element with oxygen from the weld pool, resulting in the formation of islands of slag or silica on the weld surface. Removing oxygen from the puddle eliminates it as a cause of weld metal porosity.
Silicon (Si) is the most common deoxidizing element; depending on the intended use, the electrodes typically contain between 0.45% and 1% alloy. In this percentage, silicon has a very good deoxidizing ability. Increasing the silicon content will increase the strength of the weld with a slight decrease in ductility and toughness. However, the weld metal may become susceptible to cracking at more than 1-1.2% silicon. The alloy also affects the fluidity of the puddle.
Manganese (Mn) is also a common deoxidizer and hardener. Manganese makes up 1% to 2% of mild steel electrodes. An increase in the manganese content increases the strength of the weld metal to a greater extent than silicon. Manganese also reduces the sensitivity of the weld metal to hot cracking.
Aluminum (Al), titanium (Ti) and zirconium (Zr) are very strong deoxidizers. These elements are sometimes added in very small doses, usually no more than 0.2% combined. Some increased strength is achieved in this range.
AWS categorizes carbon steel electrodes based on factors such as tensile strength and chemical composition.
Other elements such as nickel (Ni), chromium (Cr), and molybdenum (Mo) are often added to improve mechanical or corrosion-resistant properties. In small quantities, they can be used in carbon steel wire to increase the strength and toughness of the deposit.
GMAW electrodes for mild steel are usually designated with the letter S (indicating that it is a solid electrode) and either a numerical designation (from 2 to 7) or the letter G. The most widely used electrodes are S-3 and S-6.
Electrodes with low hydrogen content reduce the likelihood of hydrogen cracking, especially in materials with more rigid mechanical properties. The designation H4R indicates less than 4 ml of diffusible hydrogen per 100 g of weld bead.
The information bulletins indicate the chemical composition of the filler metal. The chemistry of the ER70S-6 electrode used for welding non-alloyed steels such as conventional structural steels, for pressure vessels and shipbuilding, as well as for fine-grained carbon-manganese steels, is shown.
G (or GS) electrodes are general classification electrodes that have no composition, mechanical properties, or test requirements, but their properties may meet or exceed those of AWS-classified electrodes. They are intended for single pass applications only, which may include special applications such as welding galvanized steel.
Electrodes without classification often indicate a special application. For example, “easy grind” electrodes are fully deoxidized and are designed to weld over moderate levels of rust and paint found in auto body repair. Welded metal grinds more easily than most commercial electrodes, making post-weld cleaning quick and easy.
Manufacturers can emphasize different characteristics of electrodes by controlling chemical composition, chemical composition tolerances, electrode coating and manufacturing process.
As a result, even though electrodes from different manufacturers have the same designation, their characteristics can vary greatly. Some common examples include:
Consistent Chemistry. — Major manufacturers and robotic welders prioritize consistent and predictable batch-to-batch performance.
Arc Stability. — Spatter and porosity are some of the main causes of grinding, rework, quality issues and unplanned downtime. Arc instability is the main reason for this, especially when GMAW is shorted. The use of electrodes with the same chemical composition contributes to the stability of the arc, which in turn reduces the overall cost of welding.
Galvanized Steel. — Wire manufacturers offer chemistries designed for specific applications. For example, when welding galvanized steel, zinc fumes are produced which can affect arc stability, increase spatter, and cause porosity. By controlling the microalloying elements, they can reduce zinc fumes problems and improve results.
Low Silica Islands — This wire chemistry allows manufacturers to enjoy the fluidity of the S-6 electrode, but with reduced silica island formation, and islands that form are easily removed.
Shielding gas and chemistry
Shielding gases for GMAW determine the method of metal transfer and penetration depth. In short, mixtures of argon and CO2 are the most common shielding gases for mild steel electrodes. A high argon mixture (75 to 90% argon, the rest is CO2 or CO2 and oxygen) provides good mechanical performance and produces less smoke and less spatter, making the operator more attractive.
However, mixtures with a high argon content are more expensive. CO2 is the least expensive gas and provides the widest penetration profile and best cleaning performance. The trade-off is slightly lower mechanical test results, more welding fumes, a harder arc, and more spatter.
CO2 and oxygen are sometimes useful as they contribute to arc stability and good fusion between the weld pool and base material. Oxygen is much more oxidizing than CO2. Therefore, the addition of oxygen to argon is typically less than 10% by volume, while 100% CO2 can be used for GMAW shorting. When using oxidizing gases, the electrodes must contain strong deoxidizing elements to suppress porosity.
Generally, when welding with argon and 1-3% oxygen or low CO2 argon mixtures, the weld metal chemistry will not differ much from the wire electrode analysis. However, when using 100% CO2 and oxygen in the shield gas, silicon, manganese, and other deoxidizing elements can be expected to decrease while nickel, chromium, molybdenum, and carbon remain constant. Note that very low carbon electrodes (between 0.04% and 0.06%) will produce higher carbon weld metal when using 100% CO2.
In many carbon steel applications, the base material has a light layer of dross, light rust, or pickling oil, which can affect weld quality if not removed prior to welding. In this case, it is ideal to use a high argon electrode, such as 90% argon/10% CO2 for GMAW sputtering or 80-85% argon with CO2 as balance for GMAW short circuit. Electrode deoxidizers, in combination with 10-20% CO2, should provide adequate cleaning action and provide a weld with good appearance, good permeability and smooth transitions at the end of the weld.
Filler metal manufacturers are constantly updating the chemistry and packaging according to customer requests to help them solve application and welding problems. Using a modern compound can help manufacturers eliminate many of the common causes of non-productive time associated with spatter, porosity, silica islands, contact tip wear and weld quality. In an era when manufacturers are struggling to find more people, the path to increasing productivity requires that all possible measures be taken to ensure the efficiency of welding by existing operators, including the selection of the optimal filler metal, Artem Komarov noted.