In welding carbon steel, you can use carbon dioxide by itself or you can also use a mixture of gases. 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.
You can use carbon dioxide (CO2) gas by itself and the kind of weld that it produces are deep and penetrating. 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. Oxygen is actually an enemy to weld quality, but it is necessary since it helps produce a hotter, smoother arc when added in small amounts. There are three things to consider when choosing this type of welding gas, namely, cost, metal thickness, and weld quality.
If you are just doing MIG welding as a hobby, then cost is not really a big deal. You only go for pure CO2 gas or a high percentage of CO2 gas mixture if cost is a big factor to you.
The role that metal thickness plays in selecting shielding gas is quite a big role. Pure CO2 or a high percentage of CO2/argon gas mixture is used on thinner metals. 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.
When changing the gas type, weld quality is affected. The best choice for deep penetration is CO2. 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 mixture works well and makes globular and spray transfer set easily.
If you use C25 or 25% argon and 25% carbon dioxide, you are using the best all-around welding gas for carbon steel. This mixture works well from thin to thick steel and the machine can be set to produce any transfer type. The weld for this mixture is smooth, and depending on the voltage settings and wire feed speed, the arc can be stiff to soft. With this mixture, you can weld in all positions.
These are the guidelines when choose gases for your MIG welding.