Conquering Stainless Steel: A Quick Guide for the Gas MIG Welder
Last updated ago
6 min read
By 
Welding Buddy Experts
Published 
July 20, 2021

Conquering Stainless Steel: A Quick Guide for the Gas MIG Welder

Last updated ago
6 min read
By 
Welding Buddy Experts
Published 
July 20, 2021

So you have a sheet of beautiful and shiny metal on your work table. You know you’ve never welded one like it before. Most of the base metals you’ve worked (and practiced) with, you know for sure. But this one is different.

You think it’s stainless steel.

Now you’re overthinking. How do you know for sure it’s stainless steel? Are you going to use a gas MIG welder, gasless MIG, TIG, or perhaps an oxy torch? Is it even weldable? These are the thoughts running through your head as you inspect the metal from all angles, thinking about how great it would be as a component for your next project.

Here’s what you need to know about the hundred-year-old rustless metal invention before you pull that trigger on the welding gun.

Know Your Stainless Steel

To weld stainless steel, you have to get familiar with its different types. Stainless steel has three common types. Knowing how to identify them would help you decide how to approach welding them.

Austenitic Stainless Steel

This type of stainless steel belongs in the 300 series and has a chromium and nickel composition. The series 304 is the most commonly used stainless steel. Among its typical uses are cooking tools, tubing, and paneling for architectural purposes.

In general, welding austenitic stainless steel is easy with or without a filler rod using any welding process.

Martensitic Stainless Steel

Martensitic stainless steel is the strongest type of stainless steel, all under the 400 series. It is commonly used for medical tools and equipment as well as mechanical valves.

Most martensitic stainless steel grades aren’t suitable for welding because of their high carbon content and propensity to form martensite crystalline. If you’re working with martensitic stainless steel, check whether its grade is at least 410 as it is the least challenging to weld in the series.

Ferritic Stainless Steel

The ferritic type has high chromium and low carbon content, with little to no nickel in its composition. This type is commonly used for kitchen utensils, cooking equipment, and automotive exhaust parts. It has a high thermal conductivity, which means it spreads the heat to the surface area, making it challenging to get a good weld puddle going.

The Challenges of Welding Stainless Steel

Using stainless steel as a material for welding is advantageous to any project you aim to provide with durability. But welding stainless steel, as with any other metal, comes with its challenges. Know what they are so that you can navigate them when you start welding.

Hot Cracking

This issue normally occurs when you’re welding austenitic stainless steel with high cooling rates or even eutectics that have certain impurities, such as alloy elements. Hot cracking creates an insufficiency of liquid weld metal to fill spaces in between the base metal, so the immediate solution to it is the use of adequate amounts of filler metal and heat it at the right temperature.

Preservation of Corrosion Resistance

When you weld stainless steel, the high temperatures caused by the heat transfer from the arc to the base metal heavily alters the surface that gives it its utmost ability to resist corrosion. You can solve this by removing any rust that has already formed, as well as impurities and heat tints around the bead and the heat-affected zones.

Warpage

Warping happens to low-conductivity and high-expansion stainless steel, especially when welding steel sheets in fabrication. When heat transfers to the base metal, the heat expands to the surface while the arc is firing. When it cools, the base metal contracts and warping happens to cope with the stresses of contraction.

Depending on how thick your stainless steel is, you can use different solutions, such as hammering. Still, it’s better to recognize the type of stainless steel you’re welding before you begin so that you can prevent overwelding the base material by doing intermittent welding or keeping your passes few.

Carbide Precipitation

Carbide precipitation happens when the carbon and chrome react to the atmosphere and get drawn out of the base metal. It usually occurs when there isn’t enough argon, when the temperature is higher than 800 degrees Fahrenheit, and when your torch travels too slowly when doing a pass.

You can address these challenges better when you’re using either a flux-cored or MIG welding process, as both of them use filler metal wires and gas shields from the get-go. But which process should you perform?

Gasless vs. Gas MIG Welder: Which Welds Steel Better?

Let’s look at the two preferable types of welding for stainless steel: the gasless kind and the one with gas. Several factors make either weld process great.

Flux-Cored

This welding process is sometimes called “gasless MIG” because the process doesn’t need a gas tank to operate. However, the flux-core isn’t gasless. Instead, the shielding gas is integrated around the flux-cored wire, effectively shielding the arc while melting the wire.

Pros

  • Convenient to use (no gas settings)
  • Used for dirty, textured, and thick stainless steel
  • Suitable for use outdoors

Cons

  • Restricted; flux-core is only capable of flat welds.
  • Vertical wires are hard to source.
  • It generates a substantial amount of slag.

Metal Inert Gas

Metal inert gas (MIG) welding is what is commonly called “gas MIG welding.” This type of welding process needs a gas mixture fed to the welding torch to protect the arc from elements in the air. It is most commonly used when welding stainless steel because it offers more control over the shielding gas, an important factor for welding stainless steel.

Pros

  • Produces clean welds
  • Meant for smooth, clean, and thin metals
  • Does not require shipping or sanding and produces less spatter
  • Flexible; allows vertical or overhead positioning for welding

Cons

  • MIG wires (if you use a mild steel wire) cause the stainless steel to rust.
  • Only suitable indoors

MIG Welding Gas Setting for Stainless Steel

Gas MIG welding steel can be a delicate process depending on the type of steel you’re working on. The shielding gas has to have an adequate amount of pressure to prevent undesirable results such as carbide precipitation.

We’re giving you the recommended setting for the austenitic stainless steel as this is the most commonly welded steel by both hobbyists and pros.

MIG Welding Gas Pressure

Gas pressure is measured in psi. Normally, your MIG welder regulates this. Even if that’s the case, you have to monitor your pressure regulator and make sure it’s right around 3 to 8 psi. Unlike the oxyacetylene welding process, the MIG process requires a much lower gas pressure.

MIG Welding Gas Flow Setting

The gas flow from the cylinder to the torch tip, especially for MIG welding, is measured in CFH, a standard measurement of how much volume of gas is released to the tip of the torch. Getting this right is important as this determines the quality of your stainless steel weld. It also depends on the diameter of your welding gun’s nozzle.

To achieve a laminar flow, set your CFH to the following:

Hobby/Professional

  • Set 18–22 CFH for ⅜-inch diameter.
  • Set 22–27 CFH for ½-inch diameter.

Industrial

  • Set 30–40 CFH for ¾-inch diameter.
  • Set 30–35 CFH for ⅝-inch diameter.

Gas Mixture for Stainless Steel

The gas mixture also determines the quality of the final weld and is crucial in preventing carbide precipitation. The ideal setup for welding stainless steel is as follows:

  • Helium 90%
  • Argon 7.5%
  • Carbon Dioxide 2.5%

As a caveat, we don’t recommend using 100% argon. It significantly reduces the bead quality and makes your final weld look rough because the molten metal pool stiffens due to the unstable arc caused by low-ionizing argon.

Final Thoughts

Welding stainless steel can be a daunting task at first. As you work the stainless steel, you have to balance the temperature applied to the base metal depending on the steel’s thermal conductivity. You also have to select the optimum gas flow and get the right mixture of shielding gases to make high-quality welds.

Despite the challenges, welding stainless steel can be a fun experience that would test your MIG welding skill. Getting acquainted with the common types of stainless steel is a must so that you’ll know how to treat it and whether you should or shouldn’t weld it.

The information we provided should get you started on getting better at welding stainless steel. Now go ahead and practice.

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