How to Weld Stainless Steel: Methodologies and Tips
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Stainless steel is one of the most popular welding materials to work with. It has applications ranging from DIY home welding to professional industrial welding. This metal has gained popularity because of its strength, heat resistance, and anti-corrosion properties against fluids, gasses, and chemicals. Also, it has easy-to-clean surfaces making it a great option for medical equipment and restaurants.
Since metals have specific properties in terms of materials, the methods used to weld stainless steel are different from the standard mild steel. There are several methods of welding stainless steel including TIG, MIG, and stick welding. These methods offer different advantages and disadvantages, but before you choose one, you need to understand the properties of the different types of stainless steel you are working with.
In this article, we not only explore the different types of stainless steel, but explain the different methodologies of welding it, and also offer tips on the best practices when welding.
Before You Start—Preparations
To be successful in your stainless-steel welding projects, you need to prepare adequately for the process by getting your tools and workspace ready. You don’t just dust off your welder and immediately start welding from anywhere you like. This could potentially lead to the production of unbonded welds, rusting of the metal, and even increase the chances of breakage or cracking of the welds.
1. Identify the Type of Stainless Steel That You Need to Weld
Before you embark on welding stainless steel, it’s necessary to identify the types of stainless steel that you need to weld. This is because welding stainless steel is more expensive (about 5 times more) than regular carbon steel. You should be careful in your identification process to avoid wasting time, effort, and money. Generally, there are three main types of weldable stainless steel, each with unique characteristics.
Austenitic Stainless Steel
This is one of the most widely spread variants of stainless steel for welding because it does not require preheating. You can weld it to temperatures of up to 350 Degrees. Also, you can use a low-heat-input process, which prevents the cracking of the base materials. The best fully austenitic stainless-steel materials that you can weld include 310, 320, and 330 plates of steel that have a 304 grade.
Ferritic Stainless Steel
This is one of the thickest types of stainless steel, mostly used in the automotive industry. The thickness allows welders to do single-pass welding and low heat input. When using this material, ensure that temperatures don’t get too hot because high heat tends to expand the steel, increasing the likelihood of cracking.
This type of steel has low carbon content; hence it does not get hardened by the heat created by welding. For a successful weld using ferritic stainless steel, ensure that the CR level and filler metal match with the base alloy. The standard value for filler materials used to weld this type of stainless steel is 409 or 439. Also, the preheating temperatures should be between 300 and 450ºF.
Martensitic Stainless Steel
This type of steel requires accurate preheating temperatures before welding. Failure to do this, the base material will likely crack during welding. It is a popular option in casting mills where preheating at a range of 400 to 600 degrees Fahrenheit is necessary. Also, martensitic stainless steel requires more cooling time and should be matched with the filler metal.
2. Select Filler Materials Suitable for Your Type of Stainless Steel
The type of filler materials to be used in welding depend entirely on the type of stainless steel you selected for your weld. If the metals you intend to fuse have different qualities, choose the filler material based on compatibility with the base metal. Also, go for one that is less likely to crack due to the heat produced in the welding process. Different types of stainless steel have different filler material recommendations, so it is important you find out the AISI steel grade. If you are not sure about the type of stainless steel you have, 309 works for most of them in many situations.
3. Choose the Type of Joint Design you need to weld
After selecting the type of stainless steel and the filler material suitable for your weld, the next step is selecting the joint design you need to weld. Selecting the right type of joint design will help create a stronger and more durable weld. When selecting a joint design, the factors to consider include welding position, metal thickness, joint accessibility, and final strength required from a weld. Types of joints you can use are the edge joint, top joint, overlap joint, T-joint, and corner joint.
4. Select the Right Tools for the Job
Stainless steel tends to be very sensitive to even the tiniest amount of carbon steel. Hence, you must separate the tools required for each material. If you mix them up, you will likely contaminate the metals creating rust on the surface.
- Power tools: These are energy-powered tools such as an angle grinder with a paddle switch and a metal band saw.
- Consumables: These are tools used to create a welding pool; they include a welding wire, shielding gas, and grinder wheels.
- Clamping, measuring, and marking tools: These tools help with accuracy; they include squaring tools, scribe, welding clamps, and markers.
- Welders: Choose welding machines capable of stainless-steel welding
5. Clean Workspace and Base Metal
Before attempting stainless steel welding, the base metal, welding tools, and your workspace must be free from any metal shavings, adhesives, chemical contaminants, paints, and debris left from previous welding projects. Dust from standard carbon steel lingers in the air and can easily rust or corrode the stainless steel. Welding experts recommend that you do not perform carbon steel and stainless-steel welding from the same workspace.
You can use a wire brush, sandpaper, or grinders to scrub the surface of your base metals to create a clean surface that the weld can stick to. You could also de-grease, pickle, or power brush the base metal to further prepare the surface of the base metal.
After cleaning the base metal, proceed to clean the workspace to remove the debris removed from the base metal. When both the workspace and base metals are clean, begin welding as soon as possible to avoid any dust particles in the air from settling on the surface.
Methodologies for Welding Stainless Steel
There are different techniques that you can utilize to weld stainless steel. Each technique has its pros and cons. So, it’s crucial to understand what type of welding is suitable for different types of stainless steel and the steps involved in each process. This will help choose the best approach. The most popular methods of welding stainless steel are MIG, TIG, and stick welding.
MIG Welding Stainless Steel
MIG welding is a popular welding method for thin-gauge metal plates. In this process, the welding arc produces heat between the metals while continuously feeding filler materials.
Compared to TIG, it is easier and faster, and one does not need to be experienced to fuse stainless steel with other materials using MIG. This method is also slightly similar to stick welding because it uses an electrode that is melted to create a weld instead of using filler metal.
The only difference is that MIG automatically feeds a wire coated with copper into the welding gun. The arc then melts the wire (which acts as a filler) into the base metal. This method does not require a flux because it uses inert gasses for shielding.
Overall, this method creates clean and accurate welds while minimizing post-weld clean-up duties. The only downside is that it creates fragile unions.
- Ready a fume extractor: MIG welding produces dangerous fumes. So, ensure that you set up a fume extractor to have a clean and safe workspace
- Fix ground clamp: Since you are working with electricity, you need to fix the ground to an unpainted surface to prevent possible electrocution.
- Turn the gas on: When welding, oxidation happens, which can have adverse effects on the final product such as warping and cracking. To prevent this, open the valves to release an argon-rich gas for shielding purposes.
- Determine and adjust welding settings: The amount of voltage and the wire speed required for MIG welding is determined by material thickness, wire size, and gas composition. Many welding units offer a chart with the settings information.
- Check the amount of wire left in the welding torch: To do this, pass the filler wire through the machine’s reel and out through the torch’s tip. Ensure that the wire is protruding about a quarter inch. If longer, clip it.
- Weld: Finally turn on the machine, confirm settings and start welding. Always weld at a 30-degree angle to create a welding bend in the joint when the metal melts. Do it at a constant speed to make it uniform throughout the joint.
TIG Welding Stainless Steel
TIG welding is also capable of welding thin stainless steel, approximately up to 6mm. TIG welding on thicker materials is possible too, but hugely uneconomical.
This method is different from MIG because it does not use a consumable electrode that melts into the weld pool. Instead, the arc is created between a non-consumable tungsten electrode and the base metal. The filler metal is added to the weld by hand.
The entire process happens in an atmosphere created by an inert gas selected for the project. The gas acts as a shield from oxidation, the same as in MIG.
TIG is ideal for stainless steel welding because it offers more weld control. The downside to this method is the fact that the process and equipment required for welding are more complicated than MIG and stick welding. The process is also slower and requires a lot of patience.
However, when done correctly, it produces stronger and more durable joints compared to MIG. The chords created by TIG are also high-quality because when using non-consumable electrodes, slag disappears.
- Grind the electrode: The best way to produce clean accurate welds with TIG is by grinding the tungsten rod to a fine point. When welding, the tip assumes a round shape, which causes the arc to be undirected and unfocused. Grind the tip to avoid this.
- Insert correct electrode into the collet: Make sure that the correct electrode corresponds to the alloy you are working with. Normally TIG welders come with the proper electrode, but you should double-check to be sure. Also, the electrode should be ¼ inches from the protective sheath.
- Adjust the settings: TIG welders have different settings including penetrating, amperage, and electricity options. Ensure that these settings are set to the correct parameters and are appropriate for your materials and project.
- Turn the gas on: While TIG welding, you need to protect the weld from oxidation, especially at high temperatures. In stainless steel welding, pure argon and a combination of argon and carbon dioxide are the best for shielding.
- Start the weld: When you begin welding, always ensure that the tungsten electrode is about an inch away from the base metal without the two surfaces touching. Start on the edge while steadily moving inside to avoid warping as well.
Stick Welding Stainless Steel
Stick welding is by far the most widespread technique for welding stainless steel. However, it is not popular because it produces exceptional welds, but it is the cheapest and easy-to-learn welding method.
This method utilizes a special kind of conductible electrode that allows electricity to go through, creating an arc between it and the base metal. Also, a ground wire is connected to the surface of the base metal to complete a circuit.
The electrode used in stick welding is made from consumable filler materials surrounded by flux, thereby creating a convenient tool that completes both welding process requirements. The flux on the electrode also produces a gas that protects the base metals. Moreover, it produces a slag that covers the welded materials when cooling down.
This method is great for fusing large metal sheets and those working on a tight budget. It is, however, not preferred by some professional welders because of its potential to get messy, and it only works on select types of metals such as stainless steel. Therefore, it is not suitable for sensitive and intricate fabrication projects.
Safety Precautions When Welding Stainless Steel
Since welding involves working with molten metal at extremely high temperatures, taking proper safety precautions is crucial. You should wear protective clothing that covers the exposed parts of your body. These include welding gloves, a welding helmet, close-toed shoes, and a welding jacket.
A quality welding helmet will protect your face and neck areas from UV/IR radiation, welding debris, and the brightness from the welding arc. It should also allow you to see the welding process.
Also, ensure that you work in a sufficiently ventilated workspace because some welding processes tend to produce fumes with adverse effects on your health. Alternatively, you can also use a fume hood for further protection.
Stainless steel has definitely proven its importance in the welding industry. It can be fused with other alloys to create strong and durable welds that are heat and corrosion-resistant. If you want to weld stainless steel, you have to consider the quality of the end product.
If you want a budget-friendly method, stick welding is the cheapest option and is easy to learn. If the materials you are welding are not thicker than 6mm, TIG welding is the best fit for that project. MIG welding on the other hand will save you a lot of time if you are working on a tight schedule.
Our article highlights the different types of stainless steel and the different methods of welding stainless steel. We hope that the guide will help you to fully utilize the stainless-steel material when fusing it with other metals to create beautiful, robust, and durable welds.
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