Stainless steel is an excellent material to work with – it has many uses in the oil industry, in restaurants, in chemical processing, in medical equipment, and so much more. Since it’s so widely used, any welder worth his salt should know how to weld stainless steel.
Unfortunately, stainless steel is difficult to weld, especially if you’re a novice welder. It resists heat quite well, so you’ll need a bit more heat than typical steel; but, if you apply too much heat, it can get warped or distorted. It’ll also show every blemish you inflict on it. Discolored stainless steel isn’t just unsightly, it also means that it’s lost some of its chrome content and is more vulnerable to corrosion. Make no mistake, stainless steel is an unforgiving material, especially for inexperienced welders.
That’s why I’ve written this guide for you. The more you know about how to weld stainless steel, the easier it’ll be for you when you get to the task. I’ll take you through what you need to know. What welding processes are best, what kind of steel there is, and a few tips to keep in mind when you’re working stainless steel.
Best Welding Processes For Stainless Steel Welding
There are three welding processes you can choose from when you’re dealing with stainless steel.
- TIG Welding is precise, high-quality, and long-lasting, and it’s the most common welding process typically applied to stainless steel. It’s my personal preference out of the three. The low heat output means TIG Welding a good choice for thin pieces of stainless steel, and the resulting weld is clean and precise. The downsides are that you need to be a skilled welder, and even for good welders, it’s a slow process.
- MIG Welding is fast, cheap, and efficient, but it won’t look as good as a TIG weld. If appearance is not a relevant concern for that job, then I highly recommend a MIG weld over a TIG weld. It’s better at handling thicker workpieces than TIG. Also, most repair or maintenance jobs on stainless steel generally call for MIG welding, as the equipment is simple and easy to transport.
- SMAW Welding, or stick welding, is a portable and low-cost option. My first stainless steel jobs were all stick welds until I got better at TIG welding. It doesn’t need much equipment, not even any shielding gas. All it needs is a compatible power source and a stainless steel SMAW electrode. It’s the cheapest of the three options, but it’s also not as fast or efficient as MIG welding, and there tends to be a lot of slag and spatter that needs cleaning afterward.
Families Of Stainless Steel
There are three types or ‘families’ of stainless steel that you may be working with. Not all three families are made equal, and what works for one might not necessarily work for another family of stainless. Working temperature is a big difference, and there’s also filler. Not matching your filler to the right family of stainless steel means that the welding point might not be as strong as the surrounding material.
- Austenitic stainless steel is the type you’ll see most often. It has more chromium compared to the other types and thus is more resistant to corrosion. It’s usually non-magnetic, though cold working may turn some austenitic steels magnetic. All stainless steel with a grade number in the 300 range is austenitic, and you’ll most commonly see 304 and 316 ‘marine grade’ steels.
- Martensitic stainless steel is the least common in typical use. It’s got the least corrosion resistance of the three types, but it’s also the strongest of the three, and it’s magnetic. You’ll see it in applications needing strength or a good edge. Most cutlery and medical tools use martensitic steel. They’re in the 400 series of grade numbers. You’ll usually see 420 ‘surgical steel’ and 410 grades.
- Ferritic stainless steel is between the above two for rarity. It’s the cheapest of the three, and it’s magnetic. It’s usually used when appearance isn’t a factor. Like martensitic steel, ferritic steel grade numbers are in the 400 series, the most common ones being grades 409 and 430.
I touched on this last section, and it’s worth going a little further into filler here. Normally, it’s the project’s design engineer who specifies the filler, so you don’t typically need to worry about that. But it’s also helpful to know about what fillers should go with a material. An extra eye looking at the process helps catch errors before they become unfixable.
I could write a whole article about what fillers go with what types of stainless steel, and what to use if the product has to deal with a corrosive environment, and so on. The most important thing to do is to match the composition. You want a filler that’s as close as possible to the workpiece’s metal composition. Always check the labels and read closely when you’re out buying filler wire so that you know where it can be used and for what applications.
Related to that, don’t forget to check corrosion resistance. If you’ve got a corrosion-resistant filler, then you’re fine. If not, you’ll need to treat your weld site to protect it from corrosion. There are lots of options available here, depending on what your workpiece is supposed to do.
The heat you need to apply a proper weld differs based on the type of steel you’re working with. If you go too low or too high, depending on the steel, bad things happen to your workpiece.
If you’re working on an austenitic steel, you’ll have to keep the temperature relatively low to avoid cracking or stripping the chromium oxide. If your workpiece reaches 176 C (350 F), let it cool down before proceeding.
Martensitic steel is a different animal. The relevant temperature range is 204 C to 315 C (400 F to 600 F). You’ll need to pre-heat it to the minimum, otherwise, it turns brittle and may harden prematurely.
Ferritic steel has an even lower maximum temperature. Stay below 148 C (300 F) with ferritic steels, otherwise you’ll get a weaker workpiece and grain growth in the steel.
This is one more reason it’s important to know what kind of stainless steel you’re working with. You don’t want to use the wrong amount of heat, or you’ll end up either damaging the steel or having no effect on your workpiece. Always check the grade number to be sure.
Since it’s important to keep an eye on your workpiece’s temperature, it pays to know what methods are available to do that. Each has its pros and cons, and I use several at once to be on the safe side.
- Thermometers are the classic, of course. You’ve got your choice of contact versus infrared. Between the two, it’s better to go with contact. Infrared thermometers have issues with reflective surfaces, and you may not get an accurate reading if your workpiece is highly polished. Next to that downside, contact thermometers are well worth any hassle you may have to deal with. Always bring a contact thermometer if you’re welding stainless steel.
- Temperature crayons are well known among welders. Each crayon is rated for a specific temperature. If you mark a surface with one, apply heat, and the mark melted, your heat was too high. While you can use them to keep you in a given temperature range, their quick-and-dirty nature means that they’re not usable for temperature control, and you’ll need another instrument to find out exactly how hot you’re running.
- Thermocouple probes are my instrument of choice for temperature measurement. The probe connects to a thermometer unit that displays the temperature. The probe itself might have a handle for easier use, while some models let you fix the probe to the workpiece. This lets you monitor the temperature on the fly, which helps a lot in controlling heat.
Avoid Carbon Steel Contamination
If you work with both carbon steel and stainless steel, I advise having entirely separate toolsets for both. Stainless is very sensitive to carbon steel, and even trace amounts of carbon steel that gets onto stainless steel will cause rust. In a pinch, you can give your tools a thorough cleaning before you start, but it’s better to just have a separate stainless steel set so you don’t have to worry about that. For the same reason, I keep my carbon steel and stainless steel work areas entirely separate so that carbon steel dust doesn’t get onto the stainless.
Stainless steel does take some care and attention to work with, but don’t let that scare you from learning how to weld stainless steel. It’s well worth the effort you put into it, and once you’re comfortable with it, more jobs are open to you. Get comfortable with your tools, know what family of stainless steel you’re working with, and always keep an eye on your heat. Keep those in mind, and you’ll be fine with stainless steel welding, no matter what type it is.