Choosing the Right Gas for MIG Welding Carbon Steel
When carbon steel is welded, a mixture of gases is used with the exception of carbon dioxide, which is used by itself. There are some gases that are mixed in order to do MIG welding and these gases include carbon dioxide (CO2), argon (Ar), and oxygen (O) which is the least common among them.
The deepest penetrating weld can be produced using carbon dioxide (CO2) alone. However, when one welds using CO2 gas, the appearance of the weld is rough, and it produces more smoke than other shielding gases.
Argon and CO2 gas mixtures are most commonly used. 90% or more argon, 5% or more carbon dioxide, and 5% or less oxygen are the components of the gas mixture for welding. When oxygen is added in small amount while welding, it produces a hotter, smoother arc which makes oxygen necessary for welding even though it adversely affects the quality of the weld. Cost, metal thickness, and weld quality are the three things to consider when choosing this type of welding gas.
The cost is not a big deal if you are just MIG welding as a hobby. You should go with CO2 or a high percentage of CO2 gas mixture if cost is a big factor.
Metal thickness plays a big role when choosing shielding gas. Common for thinner metals are pure CO2 or a high percentage CO2/argon mixture. In welding thin metals, you use a short circuit metal transfer and this is why it is best to use pure CO2 or a high percentage CO2/argon mixture. For thicker metals and globular or spray transfer types, the best choices contain 75 % or more argon, and the rest CO2 and 5% or less oxygen.
The quality of the weld is affected if your change the gas type. CO2 is the best choice for deep penetration. If you want a smooth weld, the you need to add argon to the mixture, or use a mixture with high percentage of argon gas mixed for a smoother weld. This works well and makes globular and spray transfer easier to set.
Ultimately, the best all-around welding gas for carbon steel is C25 or 25% carbon dioxide and 75% argon. With this mixture, you can weld thin to thick steel and the machine can be set to produce any transfer type. It has a smooth weld, and the arc can be stiff to soft depending on the voltage settings and wire feed speed. With this mixture, you can weld in all positions.
Although carbon dioxide can be purely used for welding carbon steel, sometimes it is best to use a mixture of argon and carbon dioxide to get a good results on your welding project.