TIG welders have specialized in welding of low alloy steels and carbon steel. In general, like every commercial welder will confirm, the TIG welding carbon steel is not difficult. Actually, the things become more complicated and more difficult when the carbon content increases. Here we should also mention the carbon equivalent. This is rather a long formula which takes into account the other elements in the welding process as well, including manganese, silicon, nickel, and copper, chromium, molybdenum, vanadium, which all have a combined effect on the tendency of steels to harden upon quick cooling from an elevated temperature.

The commercial welders, as well as the industrial welders know that a nice example of a familiar material is the 4130 chromoly. This material has approximately 30% carbon, however when the welder plugs in the other elements of the chemical composition, the carbon equivalent is approximately 60%.

This is a big difference and is the reason why the 4130 chromoly over a 125" thick requires being preheated in order to slow the cooling rate and to prevent hardening. The main reason for the preheat is to slow the cooling. The process has benefit for the two sides, as the commercial welders will tell you, the moisture and also the hydrogen are removed, while the thermal shock effect is reduced. Sometimes, the TIG welder uses cast iron as a good example of why the preheat is necessary on carbon steel where the carbon content or carbon equivalent is high enough to cause the hardening.

Sometimes, these TIG welders are using a TIG torch in order to puddle a corner of the manifold. This is done to test the hardenability of the unknown steel. When the welder puddles a corner, then the file will still easily cut the puddled area, while the carbon content will remain low and no problems are likely to occur. In case a file slides over the puddled area as if it was made of glass, then problems are likely to occur unless the welder preheats the materials and takes additional precautions.

The TIG welders are not always in the position to under match the filler metal as the filler metal is often specified on a blueprint or welding code. Sometimes, however the welder is choosing the filer metal. The under matching means that the filler metal is one or two degrees lower than the used base metal.