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Best Methods for Welding Stainless Steel

Date: 08-05-2023
TIG Welding Stainless Steel MIG Welding

Best Methods for Welding Stainless Steel - Alphaweld Insights

Stainless steel is corrosion-resistant and has excellent aesthetics, making it a perfect material for many applications, from pipelines to medical equipment and the food and beverage industry. However, welding this material can often pose a challenge, even for experienced welders.

Why is Welding Stainless Steel So Challenging?

Stainless steel retains heat, unlike mild steel, so it’s easy to warp, distort, or even burn through this metal, especially when welding thin sheets. To make matters worse, stainless steel can lose its corrosion resistance if it remains at elevated temperatures for too long. High heat causes its chromium molecules to drift towards carbon to form chromium carbides, which leaves certain zones depleted of chromium, making the material susceptible to intergranular corrosion and weak spots in the structure.

Heat input control is paramount for successful stainless steel welding, but so is cleanliness. Stainless steel is highly susceptible to contamination. So you must use a dedicated stainless steel wire brush and/or grinding wheels and other tools for this material only to ensure you prevent contamination with carbon steel and other contaminants.

Which Welding Process is the Best for Welding Stainless Steel?

Selecting the best process for welding stainless steel depends on the required finish quality, material thickness, involved costs, and your welding skills.

You can weld stainless steel with MIG, Flux-cored, TIG, and MMA arc welding processes, and various other methods like friction and laser welding. But most jobs are straightforward and require either MIG or TIG welding to join stainless steel, so we will primarily focus on these two processes.

MIG Welding Stainless Steel

MIG welding stainless steel can produce good-looking welds, but it’s not as aesthetically pleasing compared to the TIG welding method. However, MIG welding requires less skill, provides far faster travel speed, and you can weld thick joints with ease. 

You’ll achieve the best results using a pulsed MIG arc output. For example, welders like the Weldmax 225C with the pulsed MIG support create an arc that alternates between high and low amperage output, allowing you to weld with a high deposition rate but with minimal heat input. As a result, you’ll create strong welds with minimal distortion and no corrosion resistance loss.

Avoid using the standard 75/25 Ar/CO2 shielding gas for mild steel to weld stainless steel. Instead, use an argon gas mixed with 1-2% oxygen or a Tri-mix of 90% helium, 7.5% argon, and 2.5% carbon dioxide for optimal results.

Try to use a matching filler metal with the alloy you are welding when selecting your MIG wire for stainless steel. But if the exact match filler is unavailable, you can use a wire with a higher alloy content. The most commonly used filler wires for MIG welding stainless steel are:

• 316LSi Stainless Steel MIG wire - High silicon levels improve arc stability and edge wetting. Best used with an argon +2% oxygen shielding gas for 316/316L stainless steel alloys.

• 309LSi Stainless Steel MIG wire - Low carbon stainless steel filler metal for 304L and 309 types of stainless steel. But it can also be used to join carbon steel with stainless steel.

TIG Welding Stainless Steel

TIG welding stainless steel produces the best results — welds look clean, and you have the highest control over the heat input. However, TIG welding works best for joining thinner sections, it requires a skilled operator, and welding is far slower compared to MIG.

You should use a DC TIG welding current to weld stainless steel with a high-frequency (HF) arc start. Unlike scratch or lift TIG, HF arc is initiated between the tungsten electrode and the welded joint without touching the material, which reduces the chances of contaminating sensitive metals like stainless steel. 

We recommend the Kemppi Minarc TIG/MMA Evo 200 for DC TIG welding stainless steel. It features an HF arc start, but most importantly, it includes the pulsed DC TIG welding function. Pulsed welding works even better with TIG than with the MIG welding process, so you can weld thin joints without fear of burn-through or excessive distortion. In addition, the Kemppi Minarc supports low amp output of just 5A and upslope/downslope settings, allowing you to weld the thinnest stock, corners, and edges with high chances of success. 

It’s best to use pure argon when TIG welding stainless steel. However, you can use an argon-helium mixture to successfully join thicker sections because helium increases arc heat and penetration. 

Look for thoriated, ceriated, or lanthanated electrodes when choosing tungsten electrodes for TIG welding stainless steel. Ceriated electrodes are best used with lower amperages, while lanthanited tungsten tolerates higher amperage outputs well. The thoriated tungsten is the most commonly used TIG welding electrode and offers the best of both worlds, but it is radioactive, so exercise caution when grinding the electrode’s tip. 

Need Help Choosing Your Welding Equipment for Stainless Steel?

If you need guidance selecting the welding power source, filler metals, electrodes, or welding accessories suitable for working with stainless steel, the experts at Alphaweld are here for you. To speak with an expert, give us a call on (08) 9456 8000 or get in touch and we’ll gladly assist.