The welding of stainless steel is substantially different from welding other materials. The difference begins with the unique chemical composition of stainless steel.
What is stainless steel?
Like other steels, stainless steel is an alloy of iron and carbon. What makes stainless steel different, though, is its inclusion of at least 10.5% chromium, an element that makes the resulting alloy corrosion resistant. Kloeckner Metals supplies stainless steel in various formats, including stainless steel sheet, stainless steel plate, stainless steel tube, and stainless steel bar.
Stainless steel comes in five types, but just three of these typically show up in fabrication shops — austenitic stainless steel, martensitic stainless steel, and ferritic stainless steel. The most common is austenitic. Martensitic stainless steel goes in hard-facing applications. And ferritic steel, the cheapest option, gets used most in consumer products.
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Each of these types of steel is categorized based on its microstructure, which influences its ductility and strength. The microstructure of steel depends on its chemical composition. For example, austenitic steel contains 16-26% chromium (Cr) and 8-22% nickel (Ni). Martensitic steel has a Cr content in the range 11-28%. Ferritic steel runs 12-18% Cr. As a result, the material welded to each type of steel must match that steel’s composition.
What makes welding stainless steel tricky?
Stainless steel welding is more complicated than carbon steel welding.
First, stainless steel effectively retains heat causing it to warp when exposed to the high temperatures that welding creates. Stainless steel can also warp or crack during the cooling process after it has been heated by a welder. Even when a piece of stainless steel doesn’t crack or warp after a bad welding session, it will nearly always show scratches and blemishes.
Each kind of stainless steel presents a distinct challenge to welders. Austenitic steel may crack if given a high heat input or if you make a concave or flat weld. Martensitic steel can crack if not properly preheated. And with its low maximum interpass temperature of 300, ferritic steel will lose strength unless it’s heated with a low heat input.
The key to successfully welding stainless steel lies in getting the right filler material. The filler material grade needs to match the base material’s grade to get a good weld.
Materials and equipment you need to weld stainless steel
Why does stainless steel welding require specialized equipment, and what are the must-have tools and materials for welding stainless steel?
Stainless steel can be stick welded, shielded metal arc welded (MIG), or gas tungsten arc welded (TIG). The best choice depends on what you’re trying to accomplish since each process yields a different outcome.
You can weld stainless steel with a stick, but you probably shouldn’t. Other, better options are out there.
A MIG welding machine creates the most solid, reliable welds with stainless steel. It’s an especially good choice if you are welding something thick. TIG welding machines can be the right option for thinner materials and for welds that require beauty and precision. Still, TIG is a tough weld unless you have the experience and the time to do it properly. An inexperienced TIG welder can leave unfortunate marks or blemishes on stainless steel.
Although producing a less fine weld, a MIG machine is generally your best option for welding stainless steel. Choose a machine that comes with a welding gun and a sample welding wire. Most machines have a gun, but you can upgrade yours if you’re looking for something that will produce a more precise weld. You’ll also want to pick up some welding gun tips to replace yours when they wear out.
To protect your welding gun, you can purchase a liner. This is a great add-on because it allows you to switch between different types of metal wire quickly and efficiently. You don’t need a welding wire feeder unless you are a professional welder or you plan on doing a lot of welding. As for the wire itself, you must use the appropriate stainless steel welding wire, which is usually .030 inches in diameter but .035-inch to .045-inch wire could be right for thicker pieces.
Since you need to check the temperature when welding stainless steel to avoid performance problems, you’ll want to have a temperature-tracking device on hand. You can go with a traditional stick, but remember that it’s range is limited. Other options include electronic infrared thermometer and an electronic surface temperature probe.
You’ll also need a shielding gas. Inert gasses are not recommended, so you probably want a mixture of 7.5% argon, 90% helium, and 2.5% carbon dioxide. Finally, you will need to add a brush for metal scraping and cleaning. This tool can help you prepare your workspace and ultimately help you achieve a more durable weld.
Preparing to weld
What are the things to take care of when preparing to weld? How does it differ for the various types of steel?
Use your metal brush to eliminate any dust, dirt, oil, grease, or water from your workstation. You can also help prevent warping and cracking by clamping a piece of brass or copper behind your welding seam. This trick can help absorb heat and keep your stainless steel cool enough.
Keep a separate set of tools for welding stainless steel. Once your tools touch carbon steel, they will get carbon residue on them. That residue will transfer to stainless steel during a weld, and it can cause the product to rust eventually.
Other tips to take into account while welding stainless steel
How can you ensure best results when actually welding?
- If TIG welding, go with a DCEN or DC electrode negative setting and a current with a ratio of 1 amp for every 1/1000-inch thickness of the metal.
- If MIG welding, use the push technique. This approach lets you see what you are doing more clearly and produces less beading. Only use the pull technique when you need deeper penetration.
- Hold your welding gun at a 90-degree angle with a travel angle of 5 -15 degrees. For T-joints and lap joints, try a greater angle of about 45-70 degrees.
- Keep your work area clean, safe, and well ventilated.
Although welding stainless steel is a little more complicated than other welds, it can be done. You can even weld stainless steel to mild steel. Using the right equipment, managing your temperature, and getting the right filler material can produce a strong, durable weld.
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