CO2 vs Argon for MIG Welding Steel

For MIG welding steel, a mix of argon and CO₂ generally delivers the best overall results, combining the clean arc of argon with the deeper penetration and lower cost of CO₂.

But the ideal amounts of argon and CO₂ in the mixture depends on the application – and sometimes pure CO₂ makes more sense.

Here’s a quick overview:

The 75% Argon / 25% CO₂ mix is the most popular choice because it offers the best balance of performance, cost, and versatility for most steel welding applications.

Argon/CO₂ Mixtures: The Best of Both Worlds

The 75% argon/25% CO₂ mixture (often called C25) delivers moderate penetration with relatively low spatter and good arc stability. C25 works well across a wide range of material thicknesses (from 16-gauge sheet metal up to heavy structural plates) and joint designs (from simple butt joints to complex multi-pass fillet welds).   

For thin materials or precision work, a 90/10 Argon/CO₂ mix offers a very smooth arc and minimal spatter production. This low-CO₂-mixture is particularly beneficial when welding sheet metal under 1/8-inch thick, where excessive heat input can cause burn-through or distortion. At the same time, it maintains enough CO₂ for adequate weld penetration.   

For stainless steel applications, tri-mix gases that incorporate helium with argon and CO₂ provide enhanced heat input and flow characteristics. These specialty mixtures optimize corrosion resistance while maintaining structural integrity.

While gas mixtures cost more than pure CO₂ , they allow you to avoid the drawbacks of using pure CO₂ (which we will cover in a bit).      

CO₂: Deep Penetration at Lower Cost

CO₂ provides deeper penetration than argon, which makes it excellent for welding thicker materials. This deeper penetration results from CO₂ partially breaking down in the arc, creating a hotter weld environment with different heat distribution characteristics.

Another major benefit is that pure CO₂ is significantly cheaper than argon-CO₂ gas mixtures – so it’s appealing for high-volume production environments or budget-conscious welders.

Also, CO₂ is good for welding through rust, mill scale, or contaminated surfaces – making it practical for field repairs and less-than-ideal conditions.

But there are drawbacks to using pure CO₂: 

• CO₂ produces significantly more spatter than argon, which calls for additional cleanup time. 
• The arc is less stable and more turbulent, creating a harsher welding experience.
• The finished weld bead tends to be wider with more pronounced ripples when using pure CO₂. 

For many industrial applications where function matters more than appearance, these aesthetic concerns are acceptable compromises for the cost savings.

Choose the Right Gas for Your Projects

Here is a table you can check out now and reference later for help choosing the right gas for your projects:

Tyler O'Brien

Tyler is a results-driven marketing professional specializing in the industrial gases and equipment industry, bringing his 10 years of technical expertise and digital marketing acumen to the complex industrial gas B2B environment.