You need to do a weld repair on stainless steel.
And all you have to hand is your MIG welder and some normal MIG wire. – Mild steel MIG wire.
It’s all you’ve got in your workshop right now.
You need to get this done.
And you don’t have time to hunt around or wait while you order up some stainless steel wire and have that delivered.
So can you weld stainless steel with normal MIG wire?
Yes you can.
But … stainless steel is steel with Chromium and Nickel added to make it shiny and rust resistant. Normal MIG wire is low carbon steel and will rust.
You welding stainless steel with normal MIG wire puts steel that will rust into your weld joint. And you risk a weld that is weak and will crack over time.
When Could You Weld Stainless With Mild Steel Wire?
Using normal solid MIG wire isn’t recommended for welding stainless steel. But there are some times when you may choose to do it anyway.
1. When it’s a small job and barely worth welding.
If the weld is a short bead length. A quick job and you just need something that will hold for now. Then sure go ahead. It’s worth picking your shielding gas mix carefully so that you don’t have a disaster right from the start.
More on that later.
2. When you don’t care what your weld looks like.
Welding stainless steel with normal MIG wire isn’t going to be pretty. But if the weld is where no one will see it. Or you don’t care what it looks like, then again go ahead.
3. When you don’t care that your weld will rust.
The low carbon steel in the mild steel filler wire will rust when left unprotected. And it’s not just on the outside. You’ll have mild steel embedded into the weld joint along with your stainless steel. If you’re looking for the weld to last a bit of time. Then paint over your weld joint to protect it as soon as you can.
4. When you don’t care about your weld’s holding strength.
Stainless steel can suffer from something called Intergranular corrosion (weld decay). Particularly thin gauges of stainless steel.
And when you’re welding up stainless steel with mild steel welding wire. You increase the risk of your weld cracking and breaking.
When the weld has to hold or its safety critical. – Weld it right.
5. When the weld isn’t safety critical.
A for instance is type 316 stainless steel. You’ll find 316 stainless in the food and drink industry, restaurants and kitchens.
This type of steel is highly corrosion resistant and has Molybdenum added. It’s added to resist the acids in food. And it’s a steel that doesn’t give a metallic taste to the food.
It’s not the kind of steel you should think of welding with normal MIG wire. Because even the smallest amount of porosity and rust in a joint is a place where microbes can grow. And threaten the safety of the food.
6. When it’s your own personal stuff
You have your own personal barbeque grill. And you don’t mind scrubbing off any rust before you use.
Is where you’re welding where the food will sit?
Normal mild steel MIG wire will give your food a certain metallic something in the taste.
But if it’s only for you, you may not mind.
Or you could search around to find a good food grade protective coating for your weld. And when you heat up your weld – say in a cooking pot. Then the protective coating may not be heat resistant as well.
Otherwise you then face the prospect of scrubbing any rust off before you use your mended pot. And putting up with the taste enhancement!
Or perhaps it’s a small fix on a part around your yard. It doesn’t hold any particular weight. And it doesn’t have to be pretty. And if it fails at some point you won’t care much.
How Do You Go About Welding Stainless Steel With Mild Steel Wire?
So you’re going to do it.
Because it’s a small job. No one cares what it looks like.
It’s not safety critical and you’re not expecting the weld to hold for a long time.
So how to go about it.
1. Choose The Right Shielding Gas.
You’re using mild steel MIG wire to weld with but you’ll still have molten stainless steel at the weld point. And it needs protection from the air while you weld.
The best gas to use … and its the most expensive … it Tri Mix Gas. (90% Helium, 7.5% Argon, 2.5% Carbon Dioxide).
But you might not get a small cylinder in your area. Or want to spend time getting it. Or run to the cost of the gas.
The next best is a gas with a high Argon mix. 98% Argon and 2% Oxygen.
You can weld successfully with a 3 – 5% Oxygen in your Argon mix. And you can also weld well with a 98% Argon and 2% Carbon Dioxide mix.
What’s not recommended is C25 – 75% Argon and 25% Carbon Dioxide or 100% Carbon Dioxide. Because neither of these gasses will shield your stainless steel.
And you will get a poor performing weld.
2. Do You Have A MIG Welder That Will Weld Stainless Steel?
And by that you’ll need a welder that can output 130 Amps. Stainless steel is sluggish to weld. And you’ll want to set your welder at the lowest Amp setting you can yet still weld. Too high an Amp setting and your risk warping your stainless steel and the dreaded weld decay.
For this you’ll need to play around with your Amp settings and wire feed speed.
And if you’re prepared to weld stainless steel the normal way.
Then the best way to weld stainless steel is to use stainless steel MIG wire.
Or stainless steel flux core wire. You can use gasless or the type that needs a shielding gas.
You’ll use welding wire that matches the type of stainless steel you’re welding.
And the right shielding gas for the wire you’re using.
Or none if you’re using gasless stainless steel flux core wire.
But when that’s not what you’ve got.
Then yes you can weld stainless with normal MIG wire. Mild steel MIG wire when you’re in a pinch.
About Bill Byers
I started welding at 27 and now have over 20 years on the job experience. I MIG, TIG and flux core weld. Even done a bit of Blacksmithing in my time.
I enjoy helping novice welders find their feet.
In my spare time you’ll find me enjoying a game of football.
And on the odd weekend paying a round of golf badly. Just duck when you see a golf club in my hand.