How To TIG Weld Stainless Steel
August 18, 2022TIG welding stainless steel is in many ways easier than welding mild steel if you follow the correct steps. The puddle is slightly more visible and controllable, plus this material provides nice color grading feedback to let you know if you did a good job.
This article will teach you the entire process of TIG welding stainless steel. You’ll learn the challenges, types of stainless, how to set up everything from gas to your TIG machine, and finally, how to put everything into practice to produce high-quality TIG welds on this beautiful metal.
Image source: @mfurick
What’s Challenging About Welding Stainless Steel
Stainless steel is an iron, carbon, nickel, and chromium alloy. So, unlike mild steel (an alloy of iron and carbon), stainless doesn’t corrode thanks to the chromium content.
But, this difference in chemical structure creates specific weldability issues.
For starters, stainless steel retains heat. The melted joint and the heat-affected zone (“HAZ”) do not dissipate heat into the rest of the welded part and air as efficiently as mild steel.
But, here is where things take a turn for the worst. If stainless steel gets heated enough to undergo a carbide precipitation process, it will lose corrosion resistance. This renders the material useless and severely impacts its load-bearing capabilities.
Image source: https://www.ssina.com/education/corrosion/intergranular-corrosion/
The carbide precipitation looks like this: chromium and carbon have a strong affinity for each other but are evenly spaced in the material under normal conditions. However, the chromium and carbon form into a chromium carbide when keeping the stainless steel at temperatures between 800 and 1400°F (426 and 760°C).
As a result, the chromium (what prevents corrosion) is depleted in certain zones because it migrated to combine with carbon. This usually occurs between two grain boundaries, making a perfect spot for intergranular corrosion. Since grain boundaries are missing chromium, corrosion occurs easily, creating a weak spot in the material structure.
Intergranular corrosion grain boundary attack and dropped grains.
Image source: TMR Consulting
Reading the Stainless Steel Welds And Preventing Carbide Precipitation
Luckily for us welders, stainless steel provides a much-needed feedback. Judging by the weld color, you can quickly tell if the weld and HAZ have undergone the carbide precipitation.
- Straw-colored, bright yellow welds are safe and of high-quality
- Light blue colored welds are likely safe
- Dark blue and purple welds have a higher chance of carbide precipitation
- Black welds and HAZ have experienced carbide precipitation and should be reworked
Image source: @ss_custom_welding
To prevent carbide precipitation, you “just” need to keep the stainless steel joint below extreme temperatures, weld fast, and provide appropriate shielding gas coverage. This is easier said than done, and we’ll explain the necessary strategies in the remainder of the article, but let’s first quickly touch on stainless steel types.
Different Stainless Steel Types
Our article discusses the most commonly available and welded stainless steel, 300-series, austenitic type.
The 300-series stainless steel is non-magnetic. That’s how you can always tell if the material is austenitic stainless steel. Just be careful not to mistake it for aluminum, which is also non-magnetic. Aluminum is far lighter, but if you are unsure, grind it a little. Stainless steel will create a stream of sparks, while aluminum doesn’t create sparks.
As for the magnet test, you should also know that some austenitic stainless steels like 304 grade can become magnetic after cold working, while 310 and 316 grades are more likely to remain non-magnet even after cold working (pressing, cutting, bending, etc.).
304 shaft for medical device
Image source: https://turntechprecision.com/clueless-machinist/2020/7/2/difference-between-type-303-and-type-304-stainless-steel-machining
Stainless steel types are:
- Austenitic - 300-series, mainly 304 and 316. It has excellent weldability and is the most widely used stainless steel type.
- Ferritic - 400-series, mainly 430 and 434. It’s magnetic and has lower nickel content. Ferritic stainless is a bit more challenging to weld than austenitic.
- Martensitic - Also 400-series, mainly 420. It has high tensile strength, but it’s less often used.
- Duplex - Family of stainless steels made by mixing austenitic and ferritic stainless steel. It’s often used in pipeline applications because it's very strong and resistant to corrosion.
Image source: https://www.britannica.com/technology/stainless-steel
TIG Setup For Stainless Steel Welding
Now that we’ve discussed the most critical issues with welding stainless and its types let’s explain how to set up everything for TIG welding this material.
Shielding Gas
Using 100% argon for the shielding gas works best in almost all situations. However, adding helium to argon is sometimes needed to improve weld penetration and puddle fluidity. The more helium you add, the higher the heat input. So, unless you know exactly what you are doing, it’s best to stick to straight argon to TIG weld stainless steel.
Polarity
To TIG weld stainless steel, use a DC machine with electrode negative polarity (DCEN). That means you should attach the TIG torch to the negative polarity of the welder and the ground clamp to the positive polarity.
Image source: https://www.britannica.com/technology/stainless-steel
Tungsten Electrode
You can use every tungsten type for stainless steel except pure tungsten, which is meant for aluminum. Red, thoriated tungsten is a very popular choice, but it’s radioactive. If you prefer more safety, consider blue, lanthanated tungsten electrodes.
Tungsten Tip Preparation
Don’t make a taper of more than 2.5 times the electrode diameter. You’ll achieve good penetration, thin beads, and a narrow HAZ by staying below this taper.
Image source: https://yeswelder.com/products/tungsten-electrode-wl20
The table below shows what TIG filler wire to buy for the stainless steel alloys. The most common TIG filler wires are E308/E308L, but you should always strive to use a matching filler material as the welded stainless alloy.
| TIG Filler Wire Type | Welded Stainless Steel Alloys |
| E308 | 301, 302, 304L, 321 |
| E309 | 304, 304L, 309, 309L, it’s also used to weld stainless to carbon steel |
| E316 | 316, 316L |
The filler wire should be thinner than the welded material. If it’s thicker, you’ll need more heat to melt the wire than the base metal. As a result, you’ll overheat the stainless steel before melting the filler material.
Image source: @marylandmoonshinerswelding
Amperage Output
Since stainless steel retains heat well, it requires about 10-20% lower heat input than mild steel. The general rule of thumb for mild steel is that 1 amp of power welds about .001” of steel thickness. So, 200A can weld between 3/16” and 1/4". But, these rules underestimate most welding machines; still, it’s a good starting point. Whatever your stainless steel joint thickness is, convert it to amps and lower the amperage output by about 10-20%.
This may take some trial and error depending on your travel speed, technique, and machine capabilities.
Pre-cleaning Stainless Steel
Stainless steel must be absolutely clean. So if you take one thing out of this guide and apply it, ensure it’s this one.
The welding joint must be cleaned from oils, grease, paints, grime, or anything else before welding. Stainless steel is not a forgiving metal. You must clean the joint perfectly if you want a sound weld.
Using a file to prepare and clean the stainless steel pipe for TIG welding.
Image source: https://welderslab.com/what-are-the-5-basic-types-of-welding-joints
If you buy a fresh stainless steel sheet, it may come with a plastic peel coat. This ensures that the material is ready to weld as soon as you peel the coat and clean it with a solvent wipe.
You should also clean the filler wires you plan to use. Clean a few extra wires just in case, unless you can evaluate precisely how many wires you’ll need to fill the joint.
Additionally, keep the working environment clean from carbon steel dust particles and never cross-contaminate stainless steel with mild steel. Use a stainless steel wire brush and grinding wheels dedicated to stainless steel only. Otherwise, carbon from mild steel will contaminate the stainless steel.
Mechanical weld cleaning offers low procurement costs but requires a great deal of time and effort.
Image source: https://blog.perfectwelding.fronius.com/en/cleaning-stainless-steel-welds/
Techniques For TIG Welding Stainless Steel
Now that your TIG welding equipment is prepared and you’ve cleaned the material, it’s time to discuss how to actually weld the joint. There are many aspects to consider, so let’s break it all down one by one.
Gas Purging
You must have heard about gas purging before. But the question is, do you need to gas purge the stainless steel joint?
If you are welding stainless steel pipes and need excellent weld quality from inside the tube, you must purge the pipe. In most cases, welding stainless pipes requires purging. But, it’s often also necessary to purge the back side of the joint when welding two stainless steel plates side by side with a butt weld configuration.
The image shows the difference between weld quality from inside the pipe if the pipe was purged (on the left) vs. if the tube was welded without a purging gas (right).
Image source: https://www.penflex.com/weld-purging-with-argon-gas/
If you don’t purge the pipes, the oxygen from the inside will weaken the weld. The welded joint is protected from the argon shielding gas coming from the TIG torch cup, but the underside of the weld joint is not protected from the oxygen found inside the pipe.
So, purging the oxygen by releasing the argon gas inside the pipe forces the oxygen outside and leaves a protective argon atmosphere inside the pipe. That way, you are shielding the welding joint from outside and inside.
To purge a pipe, all you have to do is tape both pipe ends shut, poke a hole in one end and stick an argon hose with a diffuser inside, poke another spot on the opposite end for oxygen to be purged, and release the argon gas. This is an elementary DIY purging method. There are more advanced gas purging systems out of this article’s scope.
Image source: https://www.engineerlive.com/content/rapid-purge-pipes
Important note: Use halogen-free, heat-resistant aluminum tape to close pipe endings! Most regular tapes contain halogens like chlorine. If these compounds heat up, they can be absorbed into the welded joint and cause weak, brittle welds.
Copper/Aluminum Backing
If you don’t want to achieve maximum stainless steel weld quality but to create a solid, good enough joint, you can substitute purging with backing. This is especially useful when welding stainless steel plates.
Sometimes it’s just not necessary to achieve a perfect weld from underneath the joint. Purging the joint from beneath takes time, effort, and shielding gas, which is costly.
Instead, you can place a copper or aluminum backing beneath the joint line and clamp it firmly so there is a minimal gap between the backing and stainless steel joint. This is not perfect, so you won’t achieve a clean, silvery weld from beneath the joint. But, in most cases, this will suffice.
Image source: http://weldingstudentofsliet.weebly.com/tig-welding/tig-welding
The copper and aluminum won’t melt as you weld over them because they conduct heat away rapidly, unlike stainless steel. As a result, these materials require more amperage to melt than stainless steel. But, to be sure, use thicker backing parts than the welded stainless steel.
Pre and Post Shielding Gas Flow
It’s a good practice to provide pre-welding shielding gas flow to thoroughly drench the joint before the arc starts melting the base metal. Preflow prevents contamination by pushing atmospheric contaminants out from the joint and creates a safe, argon-rich environment. About one second should be enough for most stainless steel welding jobs. Just make sure the TIG cup is right above the joint.
Post-welding shielding gas flow is even more critical. It prevents oxygen from damaging the weld at the ending phase. You cannot just complete a weld and remove the TIG torch. The super hot stainless steel would oxidize as it comes in contact with air. It’s necessary to keep the shielding gas over the end point of the weld for about one second for every 10A of welded current.
This image demonstrates gas flow rate increases (from left to right). As shielding gas flow rate is increased, the laminar flow column becomes more turbulent, increasing the chances for the weld and/or tungsten to become contaminated. As the flow rate is decreased, the shielding gas column becomes more laminar and less turbulent.
Image source: https://www.canadianmetalworking.com/canadianfabricatingandwelding/article/welding/cover-me-proper-shielding-gas-coverage-is-key-to-gtaw-success
Heat Management
Managing heat when welding stainless steel is crucial. So, let’s discuss all techniques you can use to prevent carbide precipitation from overheating the stainless.
Starting Amps
A low amp start is helpful when welding stainless steel because you’ll give the material more time to heat up slowly. If you input too much heat immediately after starting the arc, there are high chances that you’ll warp the material. Plus, since stainless retains heat too well, you can avoid concentrating heat during the first second or two until you get moving along the joint line.
Stainless Steel’s high coefficient of thermal expansion and low thermal conductivity makes it distort easily when welding.
Image source: http://weldingstudentofsliet.weebly.com/tig-welding/tig-welding
You should set your starting amps depending on the material thickness. But anywhere between 5A and 20A is a good starting point. You’ll quickly learn how to set this setting with some experience. So, practicing on a scrap piece of stainless steel is a good idea.
Foot Pedal Control
The TIG foot pedal will be your best friend when welding stainless steel. Since this material retains heat, it’ll get hotter as you weld. This means that you may need to back off the amperage as you go along the joint.
Foot pedal control lets you set the lowest and highest amperage output. The highest amperage is when you press the pedal all the way, like giving the full throttle to a car. But, when you back off the pedal, the TIG welder will output less amperage. As a result, you can modify heat input in real-time as necessary.
Use TIG pulsed is good for welding stainless steel
Image source: https://vietmfg.com/tig-stainless
But, foot pedal control adds the challenge to TIG welding in general. When performing this welding method, you’ll control the TIG torch with one hand and the filler wire with the other. So, managing the foot pedal simultaneously makes things challenging.
Pulse TIG
Pulsed TIG is another excellent way to control heat input. You can use pulsed welding with or without the foot pedal control. So, you can double down on heat control or just use pulsed TIG on its own if your welder supports this feature.
This function also has a low and high amperage output set, just like using a foot pedal. But, the machine automatically alternates between high and low amperage many times per second. You can pulse as low as 1 pulse per second (“PPS”) or as high as 200 PPS.
Pulsing also lets you tailor the penetration, weld width, and resulting bead aesthetics.
Image source: @stainless_bros
YesWelder offers the following machines with pulsed TIG support:
YesWelder TIG-225P Multi-Process Cold Spot TIG Welder
YesWelder FIRSTESS CT2050 Powerful 7-in-1 Welder & Cutter
DC Pulsed TIG Welding Machine with HF Start
Puddle Size
Try to keep the puddle size equal to the thickness of the base metal. If the puddle becomes larger, you are unnecessarily melting away the material and inputting too much heat. Back off the foot pedal and increase travel speed to resolve this issue.
At the end of the weld, you’ll need to back off the TIG pedal and add filler metal to chill the puddle and avoid crater cracking. Once the arc is turned off, remember to keep the post-flow active, so don’t remove the TIG cup away from the weld.
Travel Speed
You need to move quickly when TIG welding the stainless steel. Otherwise, you’ll concentrate too much heat. As a result, the weld and the HAZ will undergo carbide precipitation, leading to intergranular corrosion and cracking.
If you are uncomfortable with high travel speeds, you can use backing chill bars from aluminum or copper, as we discussed earlier. These two metals conduct heat away rapidly, so they’ll take on themselves a part of the heat you input into the stainless steel. Still, this will only help you so much. You must move the torch quickly to TIG weld stainless steel.
Image source: https://www.researchgate.net/figure/e-Effect-of-travel-speed-on-welding-formation-of-the-butt-joint-a-125-mm-s-b-15_fig4_346872535
Torch Angle
Keep the torch at about a 70-degree angle to the welded joint and a filler metal at about 10 to 25-degree angle to the joint. That’s a typical setup. But, you may have to adjust angles depending on the joint type and accessibility.
Image source: https://www.hobartwelders.com/projects-and-advice/welding-how-to/tig-welding-how-to/how-to-tig-weld
Conclusion
TIG welding stainless steel is relatively simple once you get the hang of everything discussed in this article. It's essential to pre-clean the material, avoid excessive heat build-up, and provide sufficient shielding gas coverage.
It may take some trial and error until you master welding stainless steel. This material is easy to burn, warp, and destroy its corrosion resistance. So, we advise getting as many scrap metal pieces as you can and practicing the whole setup until you gain confidence to weld valuable items like stainless exhausts, vents, frames, fenders, or interior details.