Choosing the Right Gas for MIG Welding Carbon Steel
In welding carbon steel, you can use carbon dioxide by itself or you can also use a mixture of gases. The mixture of gases used in MIG (Metal Inert Gas) welding include carbon dioxide (CO2), argon (Ar), and Oxygen (O), although oxygen is the least common of the gases.
Carbon Dioxide or CO2 gas by itself works well and produces the deepest penetrating weld. The reason why carbon dioxide is not really the best option although it produces deep weld is that the final result appears rough, and during welding there is a lot of smoke produced compared to using the other shielding cases.
Argon and CO2 gas mixtures are most commonly used. This mixture contains 90% or more Argon, 5% or more carbon dioxide, and 5% or less oxygen. 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. If you will use this welding gas mixture, then you need to consider three things 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. However, if cost is a big factor then you should go with CO2 or a high percentage of CO2 gas mixture.
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. The reason for this is that on thin metals you typically weld using a short circuit metal transfer. If you are welding thicker metals and globular or spray transfer, then it is best to use a mixture of 75% or more argon, the rest CO2 and 5% or less oxygen.
When changing the gas type, weld quality is affected. For deep penetration, use 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.
Ultimately, the best all-around welding gas for carbon steel is C25 or 25% carbon dioxide and 75% argon. This mixture works well from thin to thick steel and the machine can be set to produce any transfer type. With this mixture, ou can have an arc that can be stiff to soft depending on the voltage setting and wire feed, and the weld for this mixture is smooth. You can weld in all positions with this mixture.
If you are doing MIG welding as a hobby or as part of your job, then you should be aware of the different types of gases and gas mixtures that can be used for any welding project.