The 70XX electrodes, E70S-3-6 MIG wires, and E7XT-X flux cored electrodes may be used to weld low and medium carbon steels. When welding low alloys of 1 1/4 Cr 1/2 Mo and 2 1/4 Cr 1 Mo with up to 0.05 percent max carbon, 8018-B2L or 9018-B3L (L Meaning low carbon) are commonly employed. When welding higher carbon steels such as hot-rolled, heat-treated structural shapes and components, a cupro-nickel electrode is required.
When welding low alloy steel, the filler metal should contain at least 75 percent of the material being joined so that it will be strong enough to hold its shape during the welding process. The remaining portion of the filler metal should be allowed to drain off because there is not much strength in a thin bead of metal.
Welding low alloy steel requires careful attention to detail. If the welding procedure is not performed properly, weak spots may develop in the joint that could lead to failure later on. For example, if too much filler metal is used or the welding process is done improperly, voids may form inside the joint where metal atoms could escape during subsequent heating steps. This would leave a non-metallic core in the finished product which would weaken the joint.
Low alloy steel has less than 2.5 percent carbon and greater than 1.25 percent chromium by weight. Medium carbon steel has between 1 and 2.5 percent carbon while low carbon steel has less than 1 percent carbon.
1 CARBON STEEL WELDING Low-carbon mild steel is not only the most often used metal, but it is also the simplest to weld. Although most steel welding today is done with coated electrodes or using one of the consumable-wire arc welding methods, oxy-acetylene welding of steel, particularly at thicknesses of 1/4 in. Or more, is still widely used. The main advantage of gas welding is its ability to create very smooth joints with little or no porosity. The main disadvantage is that gas welding requires a significant amount of skill to achieve good results. There are three main types of gas welding: TIG (tungsten inert gas), MIG (metal inert gas), and FCAW (flame-cutter assisted welding).
2 CARBON STEEL WELDING For heavier gauge material, such as hot-rolled steel up to about 0.5 inch thick, stick welding is used primarily for joining together two straight sections of pipe or tube. This method produces a joint with good strength and corrosion resistance. Stick welding uses a flat piece of metal (the "stick") with a hole through its center that accepts the end of the pipe being joined. The two ends of the pipe are butted against each other with the outside surfaces touching. Next, the welder takes a torch and melts the sticks along their entire length so that they fuse to the inside surface of both pipes. Finally, the pipes are pulled apart by an electric hoist so that they can be lifted into place.
To weld thick metals such as structural steel, many welders utilize E7018 electrodes. E7018 electrodes can also be used on carbon steel, high-carbon, low-alloy, or high-strength steel base metals to produce strong welds with good impact qualities (even in cold weather). The E7018 electrode has a cylindrical shape and is designed for use with transfer arc welding machines. It produces an acicular wire that is suitable for TIG welding.
The E7018 electrode consists of an alloy core surrounded by a coating of zinc and aluminum. The core material is 55 percent nickel, 45 percent copper. The coating protects the metal from contamination by other elements in the welding mixture and provides electrical conductivity. In addition, the coating helps form a solidified pool during welding that ensures complete fusion of the metal being joined.
Welding rods are used in the formation of joints when joining together pieces of metal. They are usually made of brass or stainless steel. The quality of the metal used to make the welding rod affects how well it transfers electricity when exposed to heat from an electric arc. Also important is the type of welding process being used. For example, if an electrode is used instead of a shielded metal arc welder, only those areas of the metal surface not covered by the electrode would be welded.
There are two types of welding rods: filler and consumable.
MIG welding is the most often used method for welding carbon steel. Steel is composed mostly of iron and carbon, with trace quantities of other metals such as manganese, chromium, silicon, vanadium, and nickel. Because low carbon steel has only 0.3 percent carbon, it is extremely easy to weld. Higher carbon steels contain from 1 to 3 percent carbon, which makes them more difficult to weld. However, modern welding methods have made it possible to weld almost any type of steel. Before welding carbon steel, the surface must be cleaned and prepared by removing oxidation and impurities. The joint must also be prepped by grinding and cleaning the surfaces to be joined. Finally, proper shielding should be used when welding carbon steel.
Carbon steel can be hardened by heat treatment. This process changes the composition of the steel without affecting its shape. Two common hardening techniques are carburizing and carbonitriding. In both processes, the metal is exposed to a mixture of CO~and~CO~2~ at high temperatures. This reaction produces a carbide layer that protects the metal against further attack by acids or bases. Carbon steel cannot be hardened simply by painting it with enamel because this material contains little or no carbon. To harden carbon steel, it must be carburized or carbonitrified before being painted.
Carbide tools are used in industrial applications where high levels of wear resistance are required from stainless steel or carbon steel parts.