Can You Weld Stainless Steel to Mild Steel? 

Yes, you can weld stainless steel to mild steel using a compatible filler material, such as 309L or 309LSi stainless steel filler wire. TIG or MIG welding processes are recommended, and proper joint preparation and shielding gas selection are crucial for successful welds and minimizing corrosion.

Fabricators use these two methods when joining different metals. Depending on the purpose, though, welding dissimilar metals, such as stainless steel and mild steel, has its pros and cons.

This is mainly because these two metal alloys differ in terms of corrosion resistance, electrical conductivity, and malleability.

Read on to learn more about welding stainless steel to mild steel. 

How to Weld Stainless Steel to Mild Steel

Stainless and mild steel have varying properties. Still, welding them together is possible, albeit strenuous.

Pre-Welding Preparations

Regardless of the method you’re going to use, ample preparation is necessary to ensure a successful weld. 

So, follow these steps before igniting the torch:

Equipment Required

For a smooth operation, make sure that everything you need is within reach. This may include:

• Defensive gas
• Clamps
• Welders or rods
• Angle grinders
• Copper brush

Wear PPE

For your safety, wear personal protective equipment (PPE) during welding. Here are some of the gears that you may need:

• Hard hat
• Gloves
• Safety glasses
• Overalls and steel-toed boots
• ventilator or mask

Setting Up the Metal Pieces

As soon as all the equipment is in place and the safety gears are on, it’s time to set up the welding materials.

1. Begin by cleaning up the metal pieces with a copper brush. This helps to get rid of debris that may affect the quality of the weld.
2. Alternatively, you may use sandpaper or an angle grinder to remove impurities.
3. Next, arrange the pieces and pin them securely so they don’t shift during welding.
4. Make a tack weld if necessary. 

How to MIG Weld Stainless Steel to Mild Steel

In a metal inert gas (MIG) welding process, the arc welder creates a weld pool using an electric arc. For this reason, this method is also called gas metal arc welding.

I recommend MIG welding for bigger structures or when using thick pieces of metal.

This is how it’s typically done:

1. First, set the welding wire by threading it into your MIG welding machine.
2. Make sure that the wire extends to approximately 0.25 inches from the tip of the torch.
3. Next, set the defensive gas at 2% carbon dioxide and 98% argon. This will help you save energy and strengthen the weld.
4. Then, you may begin welding starting at either end of the joint.
5. Make sure the torch is sharp so that the tip of the flame is in contact with the metals.
6. Move slowly along the joint, maintaining a 30-degree angle.
7. As you move, the surrounding metals then melt into the welding pool and lump together to form beads.
8. When you’re done filling in the entire joint, let everything cool down. Avoid any movement, or else the joint may break.

How to TIG Weld Stainless Steel to Mild Steel

Tungsten inert gas (TIG) welding ‌takes longer than MIG. So, I recommend using it for smaller projects or when welding thin pieces of metal.

This method uses consumable tungsten electrodes to join the metals, hence the name. A TIG welding machine also uses a foot pedal to regulate the heat generated by the torch. 

So, here are the steps in a TIG welding process:

1. Begin by fixing a tungsten electrode rod into the welding torch.
2. Make sure that the rod extends at about 0.25 inches from the tip of the torch.
3. Then, set your welding machine to negative to prevent the tungsten from overheating.
4. Hold the tip of the torch approximately an inch over the joint, keeping an angle of 75 degrees.
5. Ignite the torch and move carefully along the joint. Remember to give the foot pedal enough pressure to heat the torch.
6. Dip the filler rod into the melted metal and move the beads so that they fill the joint.
7. Once you’re done, let the pieces cool down before moving them.

Practical Tips and Reminders

Now that you know how to weld stainless steel to mild steel, let’s go over a few practical tips and reminders that I think are very important to keep in mind. 

Know Your Metals

Here’s a breakdown of their characteristics to help you understand better why stainless and mild steel makes a good match. 

Perhaps this should also explain why they may not be compatible with certain applications.

Properties of Stainless Steel

90% of the stainless steel composition is iron, and the rest is chromium. Other elements that you may find in this mix include molybdenum, nickel, titanium, and copper.

The outcome of this combination is a metal alloy with low weldability and ductility. Still, stainless steel is a favorite material for welding with other metals for its high corrosion resistance.

Don’t get the wrong idea; stainless steel can still rust. It’s made of iron, after all. However, it should take deep scratches and prolonged exposure to moisture until rust develops. So, don’t allow such kind of damage to stainless members to maximize their natural life.

Stainless steel has become a preferred metal in the aerospace and pharmaceutical industries. It’s commonly used as aircraft parts and laboratory equipment because it’s a poor conductor of heat and electricity, non-magnetic, and easy to clean.

Properties of Mild Metal

Mild steel contains less carbon than normal steel, thus the name. The carbon content is typically less than 1%, thus the elevated ductility. You may find other elements in this blend are manganese and silicon, among others. 

Due to the high iron content, mild steel is highly susceptible to oxidation. This is why it usually needs to undergo galvanization, the process where you coat a piece of metal with zinc for surface protection.

The main reason why fabricators use stainless and mild steel together is for economical purposes. In other words, it’s to balance out the other’s features and use them only where they’re needed.

Pick the Right Electrode

The options for electrodes in the market are vast, but the choices for welding stainless and mild steel narrow down to E308, E309, and E310. When choosing the right electrode in this kind of situation, the one with the higher carbon content is better.

The reason for this is that carbon reduces the risk of intergranular corrosion. E309 has the highest carbon content among the aforementioned abovementioned electrodes, making it the most suitable alternative.

The other two will still do the job, plus they’re cheaper than E309. So, you may want to consider these factors in addition to your main objective for welding these two alloys in question.

Choose the Appropriate Rod Diameter

Picking the right rod diameter is more straightforward than choosing the right type of electrode. You’ll probably end up buying the size that’s available in the market that’s closest to the thickness of the metal you’re working with.

Generally, any rod diameter should work with any metal thickness. However, it’ll affect your welding machine’s settings, including temperature and speed.

If you use a rod that’s too big, you’ll likely be using more energy than necessary since it’ll need more heat. When it’s too small, the welding process will take longer.

What to Expect When Welding Stainless Steel to Mild Steel

Combining stainless and mild steel has its pros and cons, but it can be tricky to determine when these attributes may be considered an advantage or a disadvantage.

Economy

Initially, mild steel may seem cheaper than stainless, thanks to the latter’s chrome coating. For this reason, these two alloys are combined to balance out the other’s features.

In other words, you can save on costs by using stainless steel only in areas where it’s needed. Power plants and similar establishments with massive pipelines use this strategy to cut down on costs.

Varying Melting Points

When placed under extreme heat, one metal may melt faster than the other. In the case of stainless and mild steel, you can expect the latter to liquefy faster than the former.

Stainless steel is a poor conductor of heat, and its melting point is between 2,550 to 2,790 degrees Fahrenheit. Meanwhile, mild steel melts at 2,462 to 2,786 degrees Fahrenheit.

So, don’t be surprised if the two metal pieces won’t melt simultaneously. It’s normal and should be expected when welding dissimilar metals.

Varying Expansion Coefficients

Thermal expansion refers to the increase in volume before and after heat acts upon a substance. That said, stainless and mild steel may react differently or expand at different rates during welding.

Poor execution of a welding procedure may cause unnecessary stress to a joint and result in a low-quality joint. A welder can avoid such an issue by making the appropriate temperature adjustments during the operation.

The settings may vary by the kind of metals used, so you may need to do some research before carrying out the project.

Conclusion

Can you weld stainless steel to mild steel? Yes, it’s possible, but it may not be the best option.

While bonding stainless and mild steel is achievable, it may be another case of “just because you could doesn’t mean you should.”

This could vary by objective, so we suggest exploring other options before welding dissimilar metals.

In conclusion, it may be better to stick to welding similar types of steel whenever possible than welding metals of varying properties.