MIG Welding Stainless Steel

You can utilize a number of different techniques to join stainless steel. MIG welding is one of the most versatile welding techniques. But can you use MIG to weld stainless steel?

This article will cover the basics of MIG welding stainless steel, the best shielding gas, welding wire, and how the process differs from other types of welding.

Can You MIG Weld Stainless Steel?

MIG Welding Stainless Steel
You certainly can weld Stainless Steel with a MIG welder and to great effect. MIG welding stainless steel when performed correctly produces extremely strong welds with high productivity rates. It is important to note that the process for welding stainless steel with a MIG machine is different than as you would weld on mild steel, please read on to learn more about how to MIG weld stainless steel and the processes that are involved.

Shielding Gas for Welding Stainless Steel

As with most MIG welding processes, a shielding gas is required to protect the weld from exterior atmospheric contaminants which would otherwise affect the weld’s integrity. Most effective and often utilized is a combination of carbon dioxide and argon, however, it is possible to weld with other gases. Two of the most common questions we hear from our readers are the following.

Can I MIG Weld Stainless Steel with 100% Argon Gas?

A question valid and put simply yes, you can MIG weld stainless steel with pure argon gas but it’s complicated. 100% argon will certainly protect a weld from atmospheric contaminants (which would negatively affect your weld), therefore it is functional as a shielding gas. However, this is where functionality stops.

MIG welding with pure argon becomes a problem for stainless steel as it has an effect on the final weld quality and overall welding performance.

The electrical connection between the steel and welding machine (also known as the arc) is interrupted when using a 100 percent argon gas mix. In other words, the arc stability is overall very low. When welding with arc instability the produced weld will appear inconsistent with defects such as undercut and weld penetration that is at half of what it should be. The weld will also sit on the surface of the joint and although the joint will indeed fuse together, it will not be a passable weld by industry standard.

To add, the thermal conductivity of the weld is impacted by using pure argon making for a less fluid weld pool.

This is less than optimal for welding because generally, the purpose of welding is to create a strong and permanent bond between steel parts.  That means by using 100 percent argon gas the purpose of welding is defeated.

Using MIG with 100 percent argon gas on stainless is not something I recommend unless you have absolutely no other option. This is especially so when you are welding together a structure or product which requires longevity and strength and/or could injure a person or damage property if the weld is broken.

Can I Weld with 75/25 of Argon/CO2?

A common occurrence for many welders based at home is that they will predominantly weld mild steel on a day-to-day basis, and then one day they come across a piece of stainless-steel work with only 75/25 gas to work with. The question is, in the situation described (or in any given moment) can we use 75/25 successfully when welding stainless steel?

The answer is yes and to quite a good effect. When MIG welding stainless with 75/25 Argon/CO2, all the key aspects of a good weld remain unaffected; the penetration is normal, undercut does not prove to be a big problem and arc stability is stable. We recommend using 75/25 gas on stainless over using 100% argon.

However, 75/25 shielding gas does not come without its kinks. Whenever welding with a MIG, weld splatter is produced, and this is especially so with 75/25 gas. The problem with splatter and stainless steel is that it can affect aesthetically important projects and it is sometimes difficult to remove. Splatter sticks to metal and where the weld aesthetics is truly crucial, it is best to avoid splatter and the marks it makes. A simple solution is to apply anti-splatter spray prior to welding or even better, invest in an advanced MIG machine that has an anti-splatter setting.

With 75/25 the final weld also appears a little dull and colorless. While it does not affect any structural aspects of the weld, it can be important again where aesthetics are deemed crucial. Aside from this, 75/25 is perfectly fine to weld stainless steel with and is one of our most recommendable options.

Best Gases for MIG Welding Stainless

Following are the most effective shielding gases for stainless steel MIG welding.

  • Argon and Carbon Dioxide (CO2) combinations such as 75/25, 90/10, 95/5, or 98/2.
  • Tri-Mix Gas: This contains 90% Helium, 7.5% Argon, and 2% CO2 and works great for increasing thermal conductivity performance.

Welding Wire

Best Wire for MIG Welding Stainless Steel

Always select a specially designed Stainless Steel MIG wire. Wire labeled as “ER308L” is a safe choice and is most commonly used. Do not use Mild Steel MIG wire as it will immediately contaminate your weld and produce rust in the future.

When selecting wire thickness, this will completely depend on the project at hand, for larger projects with thicker material go for wire with a greater thickness (up to 0.35 – 0.45 inch). With most other projects of smaller to medium sizes, a wire with a thickness of 0.30 inches will work perfectly.

MIG Welding Stainless Steel with Flux Core Wire

MIG welding with flux core wire (otherwise known as Gasless MIG), is to be considered an entirely separate process to MIG welding with different wires. The use of flux core wire removes one’s necessity for external shielding gas; this is because when the wire’s flux coating is subjected to heat, it releases its own gas and therefore the weld pool is safely protected from external atmospheric contaminants.

Flux core wires in general have become increasingly popular over the past few years. This is because many people working on metal projects at home do not want to be purchase or rent welding gas bottles.

So, what is the result when using flux-cored wire on stainless steel?

Firstly, it is important to note that stainless steel is a difficult material to work with and weld. This is because it absorbs heat very quickly and is temperamental to change. When we match this together with flux core wire, the final result is not all that great. Welding with flux core wire is generally reserved for MIG welding jobs that are deemed as unimportant, are located outdoors, or when there is no other option available.

The operator of a flux core MIG must use a drag (pull) technique, much like stick welding. You will notice that the weld will be accompanied by slag, which needs to be chipped away after welding. The final weld result will appear bland and weak-looking weld which, again, is not what a finished stainless-steel weld joint should really look like.

With so many obstacles at hand, it is very easy to produce defective welds when using MIG flux core on stainless steel. Avoid these problems by familiarizing your machine well and practicing on stainless steel to understand the travel/wire speeds and heat settings required.

How to MIG Weld Stainless Steel?

Follow our easy step-by-step guide on how to successfully weld stainless steel with a MIG welding machine.

1. Gather the equipment required

This includes your MIG welder (complete with your welding gun, earth clamp, and spare parts such as nozzle tips) welding helmet, leather gloves, and fireproof covered clothing.

2. Select your consumables

A spool of stainless-steel welding wire, Argon/CO2 mix, or Trimix shielding gas. We have discussed how to select which wire will better suit your job but if you are still unsure 0.30-inch stainless steel wire is a safe bet.

3. Prepare your weld joint

This is a crucial step. If you try to weld over the top of grease, oil, rust, or paint then your welding will be difficult, and the weld is going to end up low quality. Use an angle grinder with a flap disc to remove rust, paint, and stubborn dirt. Clean your weld surface with a cleaning product such as weld thinner. Spray your joint with an anti-splatter solution to prevent a big post-weld cleanup process.

4. Set up your welder and gas flow to your required settings

Check everything is in order and operational. To set your welder settings correctly, this will again depend on the size of the material you are about to weld. I recommend performing some test runs on some scrap stainless of the same thickness and adjusting your settings accordingly.

5. Start Welding

As with all welding processes, stainless MIG welding requires focus and good technique.

When starting to weld, try not to rush into the weld. By allowing a second for the weld pool to build up at the beginning and maintaining this size, you will produce a more even weld.

Welding Angle

The ideal angle at which you are to hold your weld gun should be around 5 – 15 degrees. A more horizontal angle will lack in penetration and produce more splatter while a more vertical angle will create a weld that looks like a blob.

Welding Speed

Take your time to be mindful of your weld pool when moving so as to not move too slowly or quickly; a slow weld will over-penetrate the stainless and look big while a fast weld will appear narrow and stringy.

When concluding the weld, do not stop immediately or pull your nozzle away from the workpiece. The best way to stop a MIG weld on stainless steel is to utilize a “downslope” setting which most welding machines will have; this is where the arc slowly decreases in temperature allowing the weld pool to cool gradually.

As I said earlier, stainless is particularly subjective to heat and a downslope setting will help a lot with the sensitive characteristics of the stainless. Also, by leaving your MIG nozzle near the stainless for an extra 1 – 2 seconds you will allow the shielding gas to continue to protect the pool until it has completely cooled down. Removing your MIG nozzle too quickly will increase the chances of contamination from lack of shielding gas.

Tips for MIG Welding Stainless

  • Do not forget how sensitive stainless steel is to high temperatures. MIG welding is hot, so if welding for a long time on stainless steel and you are concerned about the stainless warping before you begin welding, tack the stainless to a workbench or brace. When finished welding, allow your workpiece to cool down completely and then remove the tacks or brace. Your stainless project will retain its original dimensions much better than if welding without the supports.
  • Use anti-splatter spray! Splatter is particularly noticeable on stainless steel. By applying the anti-splatter spray, you will save a lot of time cleaning up the mess after welding.
  • Think about using pulse settings if you have them. Pulse setting changes the weld pool temperature rapidly between a higher temperature and cooler temperature when welding. This is extremely useful when MIG welding stainless steel as it allows for better heat management and often results in a prettier-looking weld.
  • Practice before committing. Welding stainless with any type of welding process is not easy. Take time to master your skills on scrap metal of different thicknesses and in different positions so as to know the stainless steel and its characteristics better and the personality of your own individual welder.