Can You Weld Stainless Steel To Mild Steel With Flux Core Wire Title Image

There you are staring down at your two pieces. One stainless steel the other mild steel.

You want to weld them together.  And luckily you have a welder.

But you’ve heard that welding stainless steel needs gas.

And you can’t or don’t want to weld with gas.

And now you’re wondering.

Imagine you could weld join stainless steel and mild steel without gas.

Is it even possible to use flux core wire to weld them?

And not have the bother of a tank of gas.

Can You Weld Stainless Steel With Mild Steel Flux Core Wire?

Yes you can.

And the flux core welding wire to use is type 309L stainless steel flux core welding wire.

And you can find 309L flux core stainless steel wire that needs no tank of compressed gas to protect your weld.

But there are some things for you to bear in mind.

Before You Weld Stainless Steel To Mild Steel With Flux Core Wire

This type of flux core welding like any welding  – it needs you to prepare the join.

And this means you have to have a clean joint.

Both your stainless steel and mild steel has to be absolutely clean where you plan to weld them together.

Keep this in mind if you’re repair welding a car exhaust .

Oil, grease, general dirt or carbon from an exhaust are all weld contaminates. And will cause porosity in your weld and a weak weld joint.

A good scrub with soap and water. A good dry off. Followed by some Acetone can help.

As will grinding the surface of your weld by using flap discs that are the right type for the metals you’re welding.

You’ll find some articles on the site to help you go about the cleaning of your metals.

Acetone For Welding, Clean the Oil and Grease on 3 Metals

Flap Discs For Metal, for Welding Prep and Smooth That Weld

What’s The Best Flux Core Welding Wire To Use For Flux Core Welding Stainless Steel To Mild Steel?

When you’re flux core welding stainless steel to mild steel. The best wire to use is stainless steel flux core wire.

Look for 309L stainless steel flux core wire.


The L means it’s low carbon. 

When you’re welding stainless steel. It’s important you keep the amount of carbon around the weld joint low. 

Because carbon messes with stainless steel structure and can cause something called weld decay.

The last thing you want.

As it causes damage to your stainless steel.

309L is ideal to join your stainless steel to mild steel because this welding wire is made to weld both metals.

You can weld a wide range of stainless steels, from 300 series stainless steels.  All the way up to series 309 stainless steel. And join stainless to mild steel.

Question Mark Icon

Where Can You Buy 309L Stainless Steel Welding Wire?

One welding wire that’s easy to get your hands on is on Ebay. And on Amazon is the Blue Demon 309LFC.

It’s stainless steel welding wire. And it’s flux core.

This means the compounds in the middle of the wire melt as you weld. And they form a gas to protect your weld from the surrounding air.

And so you need no separate tank of compressed gas to weld with it. Brilliant when you’re a hobby welder and you don’t want to be bothered with gas.

What you will need is a welder that will produce enough amperage to weld the wire with.

You’ll find this means 130 Amp to 150 Amp output from your welder.

It’s a stainless steel flux core wire that has great buyer feedback.

And a few days after you’ve ordered it you can weld up your mild steel and stainless steel parts.

You can find it on Amazon using the picture and text links below.

*Disclosure: This document contains affiliate links. And at no extra cost to you this site earns a commissions through these links should you decide to buy.

You can buy it in 0.035 inch and 0.045 inch diameter sizes, depending on the thickness of the metals you’re welding. And the capacity and welding output of your flux core welder.

Or for the welding output of your MIG welder that will weld with flux core wire.

Some downsides on this welding wire.

You can only weld in flat and horizontal welding positions. So if your stainless steel and mild steel joint is somewhere above your weld position. Or vertical, you’ll either have to get the parts out. Or choose another wire.

Some Other Things To Know About Joining Your Stainless Steel To Mild Steel

Mild steel and stainless steel are just two types of steel.

Sounds obvious but stick with me.

Stainless steel is special because it’s used where its shiny look is exactly what’s wanted. Or where you need resistance to rusting or staining or attack from acidic liquids.

Mild steel in contrast will rust when your leave it exposed to air and water.

And this is a point worth thinking about when you join the two metals.

Their properties are different.

Using type 309L stainless steel flux core wire will help keep the stainless steel side stainless.

But you will need to think about protection for your join as it will have mild steel mixed in.

Find yourself a anti rust primer and top protection for your mild steel.

YouTube Video On Welding With Flux Core Stainless Steel Wire

In this 9 minute 28 second video you can see what it’s like to weld with stainless steel flux core wire. 

Bob uses 308 stainless steel flux core wire but the principals are the same.


Stainless Steel FCAW without Gas

Video Credit :

Last Words

When you’re needing to join mild steel to stainless steel flux core. Use stainless steel based flux core wire.

And the wire to choose that’s made for the job is 309L flux core stainless steel welding wire.

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