Which shielding gas produces a much hotter weld bead and is not recommended for high-strength steel?

Which shielding gas produces a much hotter weld bead and is not recommended for high-strength steel?

• A. CO2
• B. Argon
• C. Helium
• D. Air

Answer: (A)

CO2 as a shielding gas tends to make the arc hotter and drive deeper penetration, which increases the heat input into the weld. That extra heat expands the heat-affected zone and can soften or embrittle the microstructure in high-strength steels, raising the risk of cracking and reducing toughness. For high-strength steels, you usually want more controlled heat input and a stable arc, which is why CO2 is generally not recommended. Other gases or gas mixes with argon or helium provide smoother, less aggressive heat profiles, and inert, moisture-free shielding helps maintain weld quality.

CO2 as a shielding gas tends to make the arc hotter and drive deeper penetration, which increases the heat input into the weld. That extra heat expands the heat-affected zone and can soften or embrittle the microstructure in high-strength steels, raising the risk of cracking and reducing toughness. For high-strength steels, you usually want more controlled heat input and a stable arc, which is why CO2 is generally not recommended. Other gases or gas mixes with argon or helium provide smoother, less aggressive heat profiles, and inert, moisture-free shielding helps maintain weld quality.