Welding stainless steel can take a bit of getting used to when you’re first starting out. Its properties are different to mild steel; it’s less thermally conductive and more prone to warping. Plus, there’s always the chance it stops being actually stainless.

In general, it can be a more difficult metal to get a good weld on. So, we’ve put together a couple of tips and tricks that will help and have you welding stainless steel like a pro in no time.

1. Keep Your Amperage Down

Stainless steel doesn’t need as much amperage or heat pumped into it as mild steel does. Stainless steel isn’t very thermally conductive, and heat builds up quickly, so to get a good weld, you’ll want to lower your amperage.

As a general rule of thumb, you’ll only need roughly 2/3 of the amperage that you would use on the same joint thickness for mild steel. 

2. Up Your Travel Speed

You want to travel faster on stainless than you would on mild steel. Because stainless steel isn’t very thermally conductive and the heat builds up quickly, you’ll need to move along the weld joint faster to keep everything from overheating, even with a lower amperage.

When TIG welding, that also means getting a puddle going relatively quickly. You want to have a puddle going and start moving, adding filler, within about 2 seconds.

However, you don’t want to go so fast that you don’t get proper fusion or lose control of the weld pool.

3. Use a Foot Control or Torch Potentiometer

A great way to maintain control over your heat input is to use a foot pedal or the amperage dial control on the torch (potentiometer). These can only be used when TIG welding, but the ability to adjust your amps while you’re welding can produce a better weld on your stainless steel.

While you can program in start, peak and finish amps on a TIG welder, having the TIG foot pedal or potentiometer means you can fluctuate your amps at any point during the weld when you feel you need. It can help to minimise distortion or melting through and gives you the best possible weld. 

4. Use the Right Torch & Travel Angle

You want to hold your torch at roughly a 5°-15° angle to the weld and push. The only time you don’t want to be pushing the weld is if you’re working with a filler material that produces slag.

You should pull your weld instead if you’re stick welding or MIG welding flux-cored wire. You still want to hold your torch or the electrode at a 5°-15° angle while you drag.

5. Use a Dedicated Stainless Steel Wire Brush & Clean

Stainless steel is more sensitive than mild steel when it comes to prepping for a weld. That means it needs to be squeaky clean, and you’ll need to use a dedicated stainless steel wire brush.

If you use a brush that’s been previously used on another metal like mild steel, or it’s a mild steel wire brush, it can be transferred onto the stainless steel and cause issues in your weld that reduce its corrosion resistance.

Once you’ve wire-brushed everything, wipe it down with acetone to get rid of any lingering contaminants. Make sure not to use a heavy-duty cleaner when you wipe your material down, as these often leave a residue once they’ve dried that can contaminate your weld.

If you’re TIG welding, give your filler rods a wipe as well.

6. Have a Good Joint Fit Up

To get a good joint fit up, you want to make sure your two pieces of metal are lined up straight along the edge where they meet. There’s no overlap or gap on either end, which can lead to a lack of fusion or burn through.

To make sure everything stays straight and doesn’t move while you tack weld it, you can use clamps to hold it in place. Once the joint has been tacked, you can remove the clamps, and everything should remain where it is.

Proper joint fit up will help to stop your metal from warping, and less heat is needed, whether that’s because it doesn’t need to penetrate through overlapping metal or because you don’t have a gap that requires more metal to fill it in.  

If you’re welding on thicker metal, make sure you bevel your edges when necessary for full penetration through the root.

7. Set a Good Amount of Post-Gas

Whether you’re TIG or MIG welding, if you can set a post flow on your machine, you should. The extra gas flow over the end of the weld will keep it shielded while it cools down and prevent it from cracking or oxidising.

You want the post gas to run long enough that the weld has stopped glowing orange from the heat before it stops. Make sure you don’t move your torch away before it’s done, though.

8. Use Chill Bars or Backing Plates

Clamping copper or aluminium chill bars or backing plates onto your stainless steel pieces is another good way to keep the overall heat input down. Chill bars and backing plates will help draw the heat out of the weld as you go, but you should still keep your travel speed up, even with a chill bar.

Neither copper nor aluminium will stick to your weld afterwards, but copper is a more thermally conductive metal than aluminium. That technically makes it a better backing plate, as it works better to draw more heat out.

When you clamp a chill bar or backing plate in place, try not to leave an air gap. That way, the back of your weld will also be protected from the atmosphere when it penetrates through.

9. Use a Gas Lens on Your TIG Torch

Setting your TIG torch up with a gas lens rather than a standard collet body will give you better, less turbulent gas coverage. The gas lens also allows you to use larger-sized cups, like our SUPER Series gas cups, which will provide you with bigger and better gas coverage.  

A better gas coverage will help keep your weld pool shielded and lets you have your tungsten stick out further, so you can get into tighter spaces or into corners if needed.

Our Arc Torchology T2 TIG Torches come with a gas lens collet body as the default part, so they’re ready to go as is. If you have a standard valve TIG torch or SR TIG torch, you can swap your consumables for a gas lens or get yourself an APEX gas lens kit.

10. Use a Smaller Filler Rod

Depending on the thickness of your workpiece, you can also keep the heat input down by using a smaller filler rod than you would on the same thickness mild steel. Because stainless steel generally requires fewer amps, you can use a smaller filler rod.

Remember that your filler rod has an amperage range that it’s best suited to, so ensure you’re within your parameters and using a tungsten suited to those parameters.

The last thing you want is to use a filler rod that’s too big. You’ll need too much heat to melt it into the joint, and you’ll either burn through or completely cook your weld.

11. Use a Filler Material Designed for the Stainless Steel You’re Welding

Because stainless steel comes in several different types and series, you’ll need to use a filler material that matches to get the best weld and one that won’t crack off later.

For example, the most common type of stainless steel is 304. If you were MIG or TIG welding, you’d use a filler like 316L, reducing the issues you could face and helping your metal retain its non-corrosive qualities.

Stainless can be made to rust, and one of the ways that can be done is by using mismatched filler. The process of welding stainless can cook out the corrosion resistance in the metal, so to stop that from happening, get a compatible filler. The higher the chromium level in the stainless steel, the less likely it is to corrode.

If you’re not sure what kind of stainless steel you’re working with, get yourself some 309L or, if you’re stick welding, some 312L, which are both specifically designed to join dissimilar metals, including mismatched stainless steels and stainless to mild steel.  

12. Back Purge Your Pipes

Purging, or back purging, is the process of shielding the back of your weld from atmospheric contamination (carbide precipitation).

If you don’t purge the back of your weld, especially when working on pipes, the backside will look like it’s covered in granules (known as sugaring) and will often be black. A sugared weld is a bad weld and can eventually crack open.

You can get specific purge caps, or you can use a more DIY option and fold some tin foil over the sides of the pipe, but be sure to leave a vent hole and don’t use glad wrap.

13. Rust Prevention

On top of picking the right filler material, you can do a couple of other things to prevent rust from forming along your stainless welds.

The first thing is to keep your heat input down. Too much heat will burn out the chromium in stainless that gives it its corrosion resistance. Then, make sure you get ample gas coverage along the entire weld and hold your post-gas over the end of the weld for a few seconds while the metal cools.

Once your weld is done, the next thing you can do is clean your weld up and remove any discolouration. Your weld should be silver; any colour on it is still oxidisation, regardless of how minimal. You can clean the weld with a stainless steel wire brush or wire wheel and, if necessary, pickling paste, which will keep it stainless permanently.

Make sure you take the time and use the proper techniques so you can get a nice, shiny silver stainless weld on the end result. Like all welding, the best way to get better at it is to practice, but having the right materials and proper prep also goes a long way to improving your welds.