Mild steels offer numerous advantages - from easy weldability to the ability to bend and shape the material - making them suitable for a wide range of welding applications. With so many mild steel options available, how can a company decide which one?vulmetalis it the right choice for a specific application?
What is mild steel?
Base materials considered mild steels typically have little or no alloying elements. Mild steel has a carbon limit of 0.25% and is also called low carbon steel. Two common mild steels used in many manufacturing and manufacturing applications are ASTM A36 and AISI 1018.
The properties of mild steel vary by material type, but in general mild steel has lower tensile and yield stresses than low-alloy steel. Tensile strengths are typically 70 kilopounds per square inch (ksi) or lower, while yield stress can be as low as 30 ksi.
Due to the lower tensile strength and yield point, the material is not so hard that it can be bent or rolled into different shapes. In applications where higher yield and tensile strengths are required, the material can be made in thicker, heavier sections to compensate for the lower strengths.
In general, mild steels offer very good weldability, and the lack of additional alloying elements in mild steels also makes them a cost-effective option for many welding applications.
Filler metal options
Mild steel filler metals are generally designed to outperform the base materials with higher tensile and yield stresses.
Standard filler metals in mild steelIt is known to provide good weldability. Mild steel filler metals for wire welding are available in solid, metal-filled and cored wire options for production and fabrication.
Sturdy wires
Solid wires are versatile for many applications because they can be used at very low or very high currents. When welding thicker materials with solid wire, it is recommended to use a spray transfer process;for thinner materialsa transfer process with a short circuit works best. Solid wires provide good travel speeds and a good weld bead, along with deep penetration ability when welding tighter joints or corners due to a narrower penetration profile. Common mild steel filler metals in solid wire include American Welding Society (AWS) classifications such as ER70S-3 and ER70S-6.
Solid wires are often used in automotive and robotic welding applications. Because solid wires have high column strength and are often copper-clad, they are slightly stiffer than other wires and provide good penetration. But keep in mind that solid wires can have a higher heat input than metal wires, so the deep, floating arc of solid wires can sometimes result in over-penetration or burnout.
Also keep in mind that solid wires do not wet well on surfaces with mill scale. Because solid wire has fewer deoxidizers added to it, it does not handle surface contaminants as well as other filler metals, requiring welders to use slower travel speeds on materials with mill scale or rust.
Metal wires
Almost any mild steel welding application that uses solid wire can use a metal wire. Where solid wires have a narrower, finger-like penetration profile, metal wires have a wider, wider penetration profile that is not as deep. As a result, metal wires become wet and adhere better to the side walls. They can generally be used at lower heat inputs while producing the same pearly appearance. The wider penetration profile and extra cushioning can also make wire placement more forgiving.
Because metal wires have a powdered core, they can be formulated with more deoxidizers than solid wires. This allows them to handle mill scale and dirty base materials better and at higher travel speeds. Their greater deposition rates result in higher productivity. Although metal wires are typically more expensive than solid wire, the productivity gains can provide a quick return on investment. Because of these factors, metal wires are often recommended when completing welds 6 inches or longer and for operations that attempt to increase travel speed. One of the most common metal core options for mild steel applications is E70C-6M.
Gas shielded cables with flux core
When welding mild steel, there are two commonly used gas shielded flux cored wire options: the E70T-1 for flat and horizontal welds and the E71T-1 for all position welds.
E70T-1 filler metals offer comparable or higher deposition rates than metal wires and are suitable for thick, heavy welds that require a lot of weld metal. These wires are also good options for materials with heavy mill scale or rust and can provide a good beaded appearance and faster travel speeds even on these materials.
Because it can be more difficult to make large non-bonded welds with metal wires and solid wires, the flat and horizontal cored wires are good for these applications because the slag helps hold the weld bead in place as it cools. However, the slag needs more time to clean after welding.
When the application does not allow welding in a flat or horizontal position, E71T-1 flux wires provide an all-position option. These wires are suitable for vertical up or overhead welding and offer higher travel speeds and a much flatter weld profile. Like the E70T-1 filler metals, wires at all positions generate slag that must be cleaned up after welding. It is recommended to use a pulling technique for wires that generate slag and a push technique for wires that do not generate slag.
Tips for choosing mild steel filler metals
When choosing the right filler metal for mild steel welding, there are some additional factors to consider.
The condition of the base material is an important factor when choosing a filler metal. Some mild steels A36 and 1018 are available in hot or cold rolled condition. A hot-rolled mild steel can result in mill scale on the material surface, making it more difficult to weld correctly. Mild steel that has been cold rolled has a neat finish, but sometimes has a light oil on the surface.
If the base material shows light mill scale or rust, it is advisable to remove it. If that is not possible, choose a metal or flux wire, which usually gives better results in these situations. For parts that are cold rolled or have a light oil on the surface, solid wire filler metals such as ER70S-6 are acceptable.
The joint design to be welded is also a factor. A narrow V-groove weldment may require deeper penetration in a tighter location and would be best suited for a solid wire. All-position cored wires do not provide the deep, finger-like penetration that solid wires provide and would be better suited for welding shallower joint designs.
Mild steel materials offer advantages in weldability and flexibility in many welding applications. Understanding the characteristics of the mild steel base material type, the objectives of the welding application and the design of the weld joint – and matching it with a suitable mild steel filler metal – helps improve productivity, throughput and weld quality.
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