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Carbon Steel Welding Techniques

        Carbon steel is extremely common as a steel because of its strength – indeed, according to the American Iron and Steel Institute (AISI), around 85% of the steel used in the United States is carbon steel. The definition of carbon steel used for technical purposes – and which is also used here, for clarity of instructions – is that this steel is alloyed mainly with carbon, and that it has less than 2% carbon in total; steel with 2% carbon or more is actually iron.

        As the carbon content of steel increases, the following effects take place:
    •    It becomes harder, stronger, and more resistant to the wear and tear of use.
    •    It loses more and more ductility (it becomes more brittle).
    •    Low carbon steel is very easy to weld, while high carbon steel is very difficult to weld and requires the use of special electrodes and welding techniques.
    •    Its melting point goes down the more carbon is alloyed with it.

        Carbon steel is classified into four categories (sometimes more), much like stainless steel is classified into three, depending on its carbon content. These steels are likely to be encountered by you constantly in the course of your welding career, unless you specialize in something like aluminum welding, and most welds will be carried out on mild steel.

    Low-carbon steel or mild steel

        Mild steel is all steel that has a carbon content of between 0.05% and 0.3%, and many of your welding projects are likely to involve mild steel. Practically all sheet metal, for example, is mild steel, so any automotive welding will be carried out on this grade of carbon steel.

        Most pipes, chains, nails, screws, fittings and brackets are made out of mild steel, as are the various hot and cold rolled steel shapes such as angle iron, channel steel, steel pate, and steel bars. Manganese is often alloyed in for the tougher end of mild steel. Mild steel has a melting point of 2,700° Fahrenheit or more, as contrasted to stainless steel’s 2,500° F. This still can’t be hardened by heating, but it will weld readily.

    Medium-carbon steel

        This variety of steel features a carbon content between 0.3% and 0.6% carbon, as well as up to 1.65% manganese. This steel can be tempered with heat, and has a melting point of 2,600° F. Medium-carbon steel is used for more stressful applications than mild steel, including train tracks and rails, train wheels, and railway axles, as well as all kinds of axles, connecting rods, crankshafts, couplings, and assorted lathe-turned parts. From a welding standpoint, medium-carbon steel needs to have its cooling rate accurate controlled.

    High-carbon steel

        These very hard, tough steels are mostly used for vehicle springs, dies, anvils, and high-stress crankshafts. Their melting point is around 2,550° F.  Steel of this type can be tempered, and is a struggle to weld, requiring specialized electrodes, preheating, careful welding, and heat treatment of the weld after the actual welding is completed. Carbon content is 0.6% to 1.25%.

    Very-high-carbon steel

        This steel has a carbon content of 1.25% to 2%, and is a very high-tech steel, treated thermomechanically to built\d up special internal microstructures. It is used almost exclusively as a tool steel, and is welded much like high-carbon steel.