To weld stainless steel, a shielding gas mixture of argon and carbon dioxide (CO2) is typically used, such as a 98% argon/2% CO2 or 90% argon/10% CO2 mix. This combination offers optimal weld quality, corrosion resistance, and minimal spatter while working with stainless steel in TIG and MIG processes.
In this article, I will explain why argon and argon-based welding gases are the most popular welding gases, and how to weld stainless steel using the proper gas mixture.
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Why is Argon The Standard Welding Gas?
Argon is an inert gas with a versatile thermal conductivity range. It also remains very stable even with the presence of reactive gases like oxygen or helium.
Most welding gas mixtures use argon as a base, as it regulates reactive additive gases like carbon dioxide and helium to minimize oxidation rates or stabilize combustibility.
Argon can work in both low-temperature welding methods like gas tungsten arc welding (GTAW) and high-temperature settings such as gas metal arc welding (GMAW) and flux-cored arc welding (FCAW).
Due to its inert nature, it serves primarily as a shielding gas to protect your weld pool from contaminants, such as free-ranging oxygen that might induce oxidation that causes rust and weakening of weld joints.
Gas Blend to Weld Stainless Steel
Argon in its pure form can maintain arcs and retain heat even in low temperatures. However, mixed gas blends are preferable when welding stainless steel.
Additive gases like carbon dioxide, oxygen, or helium are usually added to increase heating capacity, increase welding speed, or improve corrosion resistance.
Argon mixed with 2–5% carbon dioxide is considered the standard gas blend for conventional welding since it works on narrow and wide-surfaced metals.
This gas ratio can create both narrow spray transfers and wider globular transfers and produce consistent arcs. Carbon dioxide also improves welding speed and travel time by up to 25%.
90–98% argon mixed with oxygen improves corrosion resistance, but oxygen should remain below concentrations of 10% to prevent oxidation. It’s also good for keeping the molten weld in its liquid state longer.
A gas blend of argon with up to 35% helium is a good option if you want to fuse metals quickly. Helium concentrations of up to 85% improve short-circuiting, enabling you to weld more in a shorter time on low voltage.
Hydrogen (up to 10% maximum) mixed with argon is good for welding austenitic stainless steel using gas metal arc welding (GMAW) and flux-cored arc welding (FCAW) methods.
When using the gas tungsten arc method (GTAW), up to 50% hydrogen can be added, which improves welding speed by up to 50–100%. Hydrogen should only be used on austenitic steel alloys, however.
How to Weld Stainless Steel
Here are the steps you should follow to weld stainless steel:
1. Inspect Your Stainless Steel Surfaces
Inspect the surfaces of the stainless steel parts you will weld for any dents, cracks, or bent parts. You may also clean the parts first to eliminate any grease or oily surfaces.
Smoothen out and clean any disfigured or dirty areas first to improve weld fusion and fitting and avoid accidents.
2. Pick the Correct Filler Wire
You should choose a compatible steel filler wire for the stainless steel you will weld. This can be a difficult task that requires sufficient knowledge about steel alloy mixtures. It becomes more complicated when working with mixed, dissimilar, or unknown metals.
As a rule of thumb, you should choose a stainless filler wire of the same material as your stainless steel parts, or at least in the same grade.
You should choose a 316L filler wire to match your 316L austenitic steel (same material), and a 308 filler wire or a stick electrode when welding austenitic stainless steel in the 300 series (similar grade).
3. Choose the Appropriate Welding Gas Mix
You should also be knowledgeable about how various gases interact with metal during welding. Choose the right argon-based gas mixture depending on how fast you want to work, and the arc type you want to achieve (spray transfer, globular transfer, short-circuiting).
Keep in mind that certain additive gases might not work well with some stainless steel types. For example, hydrogen and nitrogen should only be used on austenitic and semi-austenitic alloys such as duplex and precipitation-hardening stainless steel.
4. Check Your Welding Machine’s Amperage and Voltage
Finally, select the appropriate amperage and voltage settings. This will depend largely on metal thickness and time constraints.
A thicker material will require a higher welding current and voltage from your welding machine. However, welding gas ratios can affect arc formation and either decrease or increase amperage and voltage settings accordingly.
For example, using pure argon might take longer and require higher welding current (amperage) and voltage than with the same settings with an argon-carbon dioxide mix.
Choosing the right welding gas depends on the type of stainless steel you will use.
In general, argon-based gas mixtures enable you to weld stainless steel efficiently with the right settings.