Welding stainless steel using MIG can be more complicated than TIG welding. The right selection of gases and the right settings for your machine are critical. Once you understand how MIG welding stainless works, you’ll find it pretty straightforward.
Can You Weld Stainless Steel With a MIG Welder?
Yes you can weld stainless steel using inert gas shielded MIG.
Professionals normally use the TIG method for welding stainless steel. However, using a MIG machine to weld stainless steel is still a strong option. The key with stainless steel is protecting the molten weld puddle from oxidation. Otherwise you’ll end up with a brittle weld that will likely fail.
With some MIG welding machines, you can even use a flux core steel wire to weld stainless-steel. But you shouldn’t go gasless.
What Gas Is Needed to MIG Weld Stainless Steel?
You will need three types of gases with your MIG machine to achieve the strongest welds with stainless steel.
First, Helium is the main gas that protects stainless steel. You need 90% of the gas mixture to be Helium.
Next, you need 7.5% Argon gas.
The final 2.5% is Carbon Dioxide gas.
An alternative is to go with 98% Argon and 2% Carbon Dioxide.
You DO NOT want to use straight 100% helium or 100% argon, because the weld arc won’t behave well and you’ll end up with low quality welds.
Combine this mixture with with solid stainless steel wire (308L, 309L or 316L depending on your base metal).
How to MIG Weld Stainless Steel?
Step 1: Put on your PPE
You should wear a pair of leather gloves, full-length pants, and a welding jacket for MIG welding stainless steel.
Put a good welding helmet on with auto-darkening lens.
You should always wear a respirator as well because toxic hexavalent chromium (chromium VI) fumes are produced while welding stainless steel. Chromium VI fumes damage your eyes, skin, nose, throat and pulmonary operation. Most importantly Chromium VI is carcinogenic. Ozone and nitrous oxide are also produced. So wear a respirator when MIG welding stainless!
Step 2: Prepare the working area
Before welding stainless steel then thoroughly clean any dust, paint, oils or other materials from the base metal pieces.
You must have little or no airflow around your work (other than a welding exhaust tube) to ensure the shielding gas isn’t disrupted.
Before starting the welding, make some test welds to make sure the welder is doing what you’re expecting it to do.
If you’re welding a tube or other enclosed area, purging the area with argon prior to welding can significantly increase weld quality. Purging removes the oxidizing agents in the atmosphere that can creep into your weld puddle from the backside.
Step 3: Check your shielding gas blend and regulator
Make sure you have an adequate flow of 90% Helium, 7.5% Argon and 2.5% Carbon Dioxide gas. Or 98% Argon and 2% CO2.
Your gas regulator should be set to flow between 20 to 25 cubic feet per hour for 16 to 20 gauge material. A higher flow rate may work better for heavier stainless. Experiment with different settings because stainless steel welds are sensitive to gas mixture and flow rate — if you see porosity in the weld turn up your gas flow.
Of course, check your welding gun tip and gas cup to make sure it’s clean and there is no blockage from prior weld spatter.
Step 4: Set up your MIG welder with the right wire and voltage
A good place to start is with 308L or 316L stainless steel wire (depending on your base metal). 308L wire is excellent for MIG welding 301, 302, 304, 305 stainless steel (austenitic) base materials.
If you’re MIG welding mild steel to stainless steel, then 309L wire is ideal. 309L is more malleable, which helps eliminate weld cracking from the two metals different cooling rates.
Around 20-22 volts is a good starting range for MIG welding 16 to 20 gauge stainless steel. Of course, this will vary by the type of MIG machine you have, it’s transfer mode and how thick the steel is.
Step 5: MIG weld the stainless steel using the right technique
Here is an excellent video showing how to MIG weld stainless steel:
With stainless steel you can weld forward in a stitching motion, or go straight. A stitching motion will give you better control over the bead. It’s also the best option if you’re a beginner.
When planning your tip movements, consider the HAZ (Heat affected zone). With thinner metals you may need to move quickly in a straight line to prevent burning through or damaging the steel. Thicker metals give you more room to heat the surrounding metal without damage.
Make sure you give stainless steel adequate time to cool and don’t overheat it too much, or it will emit lots of Chromium VI fumes and become brittle.
Stainless steel is very sensitive to the gun tip-to-weld distance. You need to set up your body position and work position correctly to ensure consistent hand movement. Shorts and splatter can significantly affect the strength of a stainless steel weld, so maintaining correct and consistent distance to the weld is necessary.
Welding stainless steel isn’t for beginners, that’s for sure!
Frequently Asked Questions
Here are the most frequently asked questions about welding stainless steel with the MIG welding method:
Is it safe to weld stainless steel?
Yes, but you need to use a self-contained respirator or welding exhaust. Welding stainless steel produces toxic fumes containing hexavalent chromium (Chromium VI), which can be cause damage to skin, eyes, lungs and even cancer. You must ensure adequate ventilation and proper safety measures to weld stainless steel.
Can you weld stainless steel with a MIG welder without gas?
Technically, yes, you can weld two pieces of stainless steel with a gasless MIG welder, but you shouldn’t. You should only use solid steel wire with the proper shielding gas protection while welding stainless steel. Without the right 90% He/7.5% Ar/2.5% CO2 or 98% Ar/2% CO2 gas mixture your welds will oxidize and be full of porosity, making them weak and susceptible to failure.
Do you need a special MIG welder to weld stainless steel?
Inert gas shielded MIG welders rated with sufficient voltage can weld stainless steel just fine. With MIG, you must use the proper shielding gas and wire for the stainless you’re joining. You should not use a flux-cored MIG welder to weld stainless steel. Although it is used in certain controlled manufacturing environments, the flux-cored stainless steel wire is very expensive and your weld tip can be difficult to control (i.e you can’t see the weld puddle through the smoke and fumes).
MIG welding stainless steel, when done correctly with the right shielding gas, wire and machine settings, will give you a solid join. A MIG welder’s ease of use and low cost make it a good option if you’re not ready to invest in a TIG welder.
Good luck on your journey MIG welding stainless steel!