Question

what two shielding gases can be used on steel?
(select all that apply.)

75% argon / 25% carbon dioxide
100% helium
100% carbon dioxide
100% argon

Explanation:

Identify the requirements for shielding steel

Using the Steel Shielding Gases knowledge point, we evaluate which gases are suitable for welding carbon steel. Carbon steel requires shielding gases that provide arc stability, adequate penetration, and prevent porosity. Pure inert gases like \(100\%\) Argon or \(100\%\) Helium are not typically used alone for carbon steel because they cause poor bead profile, lack of fusion at the edges, and an unstable arc.

Evaluate the given options

Using the Steel Shielding Gases knowledge point:

• \(75\%\) Argon / \(25\%\) Carbon Dioxide (C25): This is the industry standard mixture for short-circuit gas metal arc welding (GMAW) on carbon steel, providing excellent arc control and minimal spatter.
• \(100\%\) Helium: Typically reserved for non-ferrous metals like aluminum or copper.
• \(100\%\) Carbon Dioxide (\(\text{CO}_2\)): This is a common, economical shielding gas used for welding steel, offering deep penetration but more spatter.
• \(100\%\) Argon: Used for non-ferrous metals or GTAW, but causes poor wetting and undercutting when used alone on steel with GMAW.

Answer:

• [x] 75% Argon / 25% Carbon Dioxide (Correct answer)
• [ ] 100% Helium
• [x] 100% Carbon Dioxide (Correct answer)
• [ ] 100% Argon