Q&A for How to Weld Stainless Steel

To weld steel pieces together, you will need the following materials: steel pieces to be welded; a welding machine suitable for steel welding (such as a MIG, TIG, or stick welder); welding electrodes or wire specifically designed for steel welding (matching the welding process you are using); shielding gas (in the case of MIG welding) or flux (in the case of stick welding); and personal protective equipment, including a welding helmet, gloves, welding jacket, and safety glasses.

Yes, but you may end up with rust on the spot weld. A weld-through primer can help prevent this.

Yes, stick welders work well on stainless steel, but the process throws off a lot of slag. Always wear protective gear, especially over your face and eyes.

It’s easier than welding something like aluminum, but still fairly challenging. Stainless steel warps easily if exposed to too much heat, and also is easily scratched and blemished during the welding process.

The preheating process does not apply to filler metals, only to base metals.

Yes, you can use 308L rods for stainless to stainless, or 309L rods for steel to stainless.

The filler metal you choose will come with its requirements detailed on the packaging.

It is just another way to make a controlled atmosphere for optimal chemistry. It gives the operator real-time control over the welding current (heat) and rate of filler metal addition.

Tig is always your best choice, but a good MIG welder is more than capable of doing stainless. In general you should use 308LSI wire, but your local supply you'll visit to get your tri-mix that you'll need can help you out on wire. Just be sure it's an SI wire, which puddles easier due to higher silicon content. Push the weld, keep a consistent distance from the work, and bump up one setting higher on power than you'd use on steel. Test weld on coupons of the same thickness as your work to practice and get your consistency up. Don't be ashamed to seek outside help to get it done; it's not easy, even for experienced steel MIG welders.

Try to match the chemistry of the metals you are trying to join. Stainless steels are alloys of iron, nickel, and chromium primarily. Trace amounts of other metals are added to impart certain metallurgical properties. If you are welding for critical applications you will be told what filler to use by an engineer. For non-critical applications like ornamental welding, you can select your filler based upon price, aesthetics, etc. Contact your local welding supply company. Tell or show them what you want to weld and they will get you set up.

It's usually stamped, such as with "SS" or "Stainless" when it is. Some silverware is, of course, pure silver. Some eating utensils at restaurants, where cutlery is too frequently stolen or dumped in the trash, is usually just plated aluminum.

Tig, in the hands of a seasoned veteran, is going to leave the least amount of heat tint (which you can lighten by polishing, but it will never go away completely) and lowest incidence of oxidation (rust) later. Stainless steel is definitely a metal to be practiced on before you ever attempt the actual fabrication or repair. Try to get coupons or scrap as close to the actual metal thickness as you can for your practicing.

You can, but it's tricky. Keep the torch over the joint, moving it slightly back and forth to melt the steel. Keep the metal from being exposed to too much oxygen, and add a decent flux.

If the tank is volatile (gas, heating oil, diesel, methanol, ethanol, etc.), empty it properly and flood it with water. Then empty that properly, and repeat until it no longer smells of the substance. Turn it upside down and put an air hose up in it and force purge it overnight. Turn it upright and purge it for another day. When welding, purge He or CO2 into the tank to try and keep any fumes from flashing. Tanks can be very dangerous, pros will tell you they hate them and have bulged one or two before.

It can, but it is guaranteed to rust if exposed to any moisture. Best to just buy a small pack of stainless rod. My local supply sells 5 packs of rods for when you just need a few, try that.

Without special equipment, you will not be able to do so. The easiest method uses a magnet to check if the applied material is magnetic or not. Visual inspection can be done by experienced persons, but other than this, you need to make a chemical analysis.

Brush the weld with a stainless steel wire brush while it is still hot. This will save you a lot of time in the long run. Another mechanical way of cleaning is with Scotchbrite-type abrasives.

Yes. DC stick welding of carbon steel is very similar to stainless steel. Follow the welding rod manufacturer's recommendations for the appropriate settings.

Yes, just choose the correct type of filler. Stainless steel electrodes are available.

It usually isn't worth using unless you're joining copper to steel. For steel to steel joints, you are better off using a stainless steel filler.

Yes. It isn't the preferred method, but it can work. Keep the heat low and work quickly for the best results.

Although most welding processes are typically forgiving, you should always prepare the steel(s) you are joining with the appropriate processes needed to get it all down to clean, bare metal. Fluxless welding rod(s) should also be cleaned. (Acetone works well for rod finish preparation cleaning, but is highly flammable, so use it only within appropriate safety guidelines.) Preheating is not necessary.

Welding stainless steel too hot (either amperage set too high or travelling too slow) can cause the weld to rust on stainless steel; welding too hot literally "cooks" the stainless/anti-rust properties out of the metal, essentially turning it back into regular mild steel (prone to rust) around the weld. You can instantly tell if a weld has been done too hot on stainless steel, as the weld itself will look burnt and there will be a large heat-affected zone (HAZ). Additionally, when stainless steel is welded way too hot, it tends to crystallize on the other side of the weld where there is no argon shielding gas. (Welders sometimes call this "sugar".)

It depends on what grade of stainless steel you are welding -- refer to the graph in Method 1, Step 4. The manufacturer of your item to be welded will usually be able to supply you with technical information, which will usually include the grade of stainless steel used.

It depends on what you would like your finish to look like. Welds can be left with color (uncleaned), they can be ground clean, or they can be brushed, sanded or scoured clean. They can also be chemically cleaned with a specialized paste, usually a type of acid especially designed to clean the welds. This is useful in hard-to-reach spots such as corner welds that cannot be ground well.

If you are referring to the gritty contamination that occurs on the other side of your welds, then this only happens when welding. Known to welders as "sugaring," it occurs mostly with stainless steels where the opposite side of the weld will "sugar up" and develop a grainy black carbon residue/contamination on the other side of the weld where the weld hasn't been protected by the argon shielding gas flow from the TIG torch, or similarly, the slag/fume cloud of stick/flux core welding. To avoid this you can either have backing metal clamped on to physically block out any atmosphere, use purging gas on the other side of the weld or simply weld using a lower heat.

Use stainless steel arc welding electrodes and use a short arc to minimize spatter to get a "neater result". So long as you don't go too hot when arc welding stainless steel, you shouldn't get any carbide precipitation/"sugaring" on either your weld surface or the other side of the stainless steel. If you have access to other welding machines, however, either MIG or TIG processes will give you a much better and neater result for welding stainless steel, especially if you are welding thin stainless steel.