Due to its many advantageous qualities, stainless steel is a popular metal for a wide variety of industrial and consumer products. It resists corrosion from liquids, gases, and chemicals, along with being particularly durable, tough, and visually appealing. Many available stainless steel grades can withstand extremes of hot or cold, which is why it’s popular for oil and other pipelines. As it also resists bacterial growth, it’s often used by restaurants, breweries, and for medical equipment.
Yet welding stainless steel can be tricky, especially for novice welders. Excessive welding heat can warp it, while the metal may also distort when cooling off. Stainless steel is also very unforgiving aesthetically, making every scratch or blemish apparent. For these reasons, it is important to understand stainless steel welding procedure specifications in order to avoid mistakes before engaging in such projects.
Stainless Steel Welding: Procedure Specifications Types, Techniques & Tools
Procedures for welding stainless steel vary markedly. To determine the best stainless steel welding procedure, specifications for working with various types of stainless steel should be considered. Other factors to keep in mind include aesthetic appearance, metal thickness, the skill level of the welder, budgetary restraints, and the time available to complete the project.
The four basic types of stainless steel are:
Austenitic stainless steel offers outstanding corrosion and heat resistance, along with exceptional formability and toughness that ensure it will not harden when exposed to heat treatments. It is used for a variety of industrial applications the aerospace, automotive, medical and other sectors.
Ferritic stainless steel contains over 12 percent chromium, with its chemical composition and molecular grain structure differing from other grades. Unlike other stainless steel alloys, it contains no or very little nickel, and is utilized in consumer products due to the economical processing by which it is made.
Martensitic stainless steel has a chemical makeup that allows it to harden and strengthen through aging and heat treatments. This makes this alloy stronger than other alloys, making it useful for fabricating such things as medical instruments, automated valves, mechanical components and parts for turbines.
Duplex stainless steel combines high resistance to corrosion with excellent mechanical properties. Widely used in many industries, its applications include use as chemical vats and seawater heat exchangers.
Techniques for Welding Stainless Steel
There are three basic methods for welding stainless steel, each with its advantages. Depending on such aspects as metal thickness and chromium content, specific projects will likely use either TIG, resistance or MIG welding.
An abbreviation for “tungsten inert gas” welding, this technique is also known as “gas tungsten arc welding.” Ideal for welding critical joints, it has become the most commonly used method for welding stainless steel. Using argon gas mixed with helium, hydrogen, and nitrogen to protect the tungsten and keep it cool releases less smoke and helps prevent oxidation. TIG welding is often a good fit when aesthetics is the foremost factor.
Also known as spot welding, this process is used to weld seams or spots. The versatility of the tools used in this technique makes it an economical choice for both minor and more extensive projects involving stain-less steel welding. Procedure specifications for resistance welding involve the use of electrical current to melt the metal, binding the edges together. This technique works well with metals that have low melting points, and modifying the manner in which it is carried out helps prevent the metal from distorting.
Short for “metal inert gas,” MIG welding is also known as gas metal arc welding. This semi-automatic process bonds two pieces of stainless steel together using a pulsed power supply. MIG techniques allow welding of hard-to-reach corners, which is especially useful in more complex stainless steel welding projects. MIG welding usually offers a better choice when efficiency and speed are most important to a project.
Due to their versatility, the TIG and MIG procedures for stainless steel welding account for about 90 percent of stainless steel welding, offering high-quality welds with an appealing appearance.
Austenitic Stainless Steel Welding
These stainless steels are the most regularly used for welding because of their toughness and ability to withstand high temperatures. Accounting for some 70 percent of stainless steel made, austenitic stainless steel is used in such things as catalytic converters and exhausts. TIG and MIG welding procedures are often used with these steels, as when they cool to room temperature, they remain unhardened.
Though it does not need treatments either before or after welding, austenitic stainless steel is prone to cracking around the heat-affected zone (HAZ), the area around a weld that does not melt but still undergoes changes in its material properties due to the high temperatures. The risk of cracking is often minimized by using different filler materials in the alloys. Additionally, sigma phase formation can cause austenitic stainless steels to lose their corrosion resistance, ductility, stability, and strength. This can be resolved by utilizing an electrode with 3-5 percent ferrite material while subjected the welded metal to a short burst of the intense heat of about 1652˚F (900˚C).
Ferritic Stainless Steel Welding
Ferritic stainless steels are sensitive to grain growth, in which the molecular structure alters due to high temperatures. These metal alloys display a single-phase structure, meaning they are composed of similarly shaped crystals. When their surfaces have been modified, the molecular structures of these metals destabilize due to this grain growth, increasing the probability of certain types of corrosion. Though not used as frequently as austenitic alloys, ferritic stainless steels work well at high temperatures and exhibit considerable strength, so are also often used in catalytic converters and exhausts.
Their coarse-grained structure, however, sometimes causes cracking and weakness around the thicker sections of the HAZ. To avoid excessive grain growth, the stainless steel should be heated at lower temperatures – 482˚F (250˚C) – and filler material like aluminum, vanadium or zirconium should be added during the welding process. While preheating reduces the cooling rate in the HAZ and reduces residual stresses, it does not restrict grain growth. Because of this, preheating temperatures should remain between 122-482˚F (50-250˚C)
Martensitic Stainless Steel Welding
When comparing martensitic grades of stainless steel to austenitic and ferritic grades, martensitic stainless steel synchronizes with the filler material and has an extremely hard structure at the HAZ. This hardness sometimes leads to hydrogen cracking due to the weld’s hardened part experiencing hydrogen diffusion, which occurs most often when ambient temperatures are near or at normal. This increases as the carbon content grows.
Low hydrogen welding processes like MIG or TIG can minimize this. The pre-welding process needs to reach temperatures between -˚F (200-300˚C), whereas post-welding treatment needs a range between -˚F (650-750 ˚C). This will allow hydrogen to escape from the HAZ. Thin sections up to about a fifth of an inch (5 mm) do not require such treatments before or after the weld.
Duplex Stainless Steel Welding Guide
Austenitic and ferritic stainless steel grades are used to form the dual-phase structure seen in duplex stainless steel. While easy to weld, care should be taken with duplex alloys to ensure a suitable finish and toughness. Duplex stainless steel contains little nitrogen overall, which helps stabilize the alloy in its austenitic phase. To ensure finer welds, shielding gases or filler material should be used. Duplex stainless steels also require no preheating.
Tools for Welding Stainless Steel
With any stainless steel welding procedure, specifications regarding the tools used differ depending on the welder’s preference, type of stainless steel, and other factors. MIG welding in particular requires specific implements.
Tools and materials used for welding stainless steel include:
- Gun liners are simple but important components of welding guns that guide welding wire from wire feeders through the cabling to the contact tip.
- Shielding gases are inert or semi-inert gases used in welding procedures, usually a combination of argon, carbon dioxide and helium.
- Weld cleaning brushes help prepare workpieces in order to make welds more durable, while also being used for cleaning and polishing after MIG or TIG stainless steel welding procedure specifications.
- Welding guns usually come with welding machines, which supplies power to an electrode on the gun to achieve welds.
- Welding machines are devices used to join stainless steel components to produce solid, reliable welds.
- Welding wires are slim metal rods that generate heated arcs in order to fuse stainless steel pieces together.
- Wire feeders pull welding wire from spools, feeding it to the arc, and are generally used for larger or more specialized welding projects.
Stainless Steel Welding by Arthur Harris
Arthur Harris provides capabilities for brazing, soldering, and welding of custom or standard components made from stainless steel or nickel alloys, according to industrial specifications or customer drawings. The company uses cutting-edge equipment that includes laser machining and computer-aided manufacturing (CAM) techniques.
The company also provides customers with the following secondary metal treatments:
- Assembly of electrical or electronic equipment
- Bead blasting
- Mechanical assembly
- Metal finishing
- Powder coating
- Silk screening
To learn more about our services, including drilling, milling, tapping, and turning operations in addition to welding, please contact us at Arthur Harris today!