Welding Stainless Steel

Best practices and tips for safely welding stainless steel to a variety of metal types

Known for its corrosion resistance and outstanding durability, stainless steel can withstand harsh conditions few metals can match. This makes it ideal for a range of industries -- from medical equipment to chemical processing.

However, when working with metal, welding is often required to fabricate complex shapes, construct large structures, or reinforce critical design components.

Does stainless steel still offer advantages after welding and are welds involving stainless steel strong and reliable?

This guide will cover everything from the weldability of stainless steel to the ideal welding methods and filler materials for the various grades and forms of stainless steel on the market.

So, Can You Weld Stainless Steel?

Yes.

Welding stainless steel isn’t much different from welding other metals.

However, when welding stainless, you must control heating and cooling cycles carefully to avoid encouraging grain growth or reducing the strength of the steel.

Exposing stainless to high temperatures -- such as those created when welding -- can cause the chromium in the steel to join with the carbon.

Without this chromium, the chromium oxide layer which provides the characteristic corrosion and stain resistance for which stainless is known cannot replenish itself.

You must also match filler metals with the materials being welded to ensure a strong weld and maintain corrosion resistance of the welded spots.

What Welding Methods Work Best with Stainless?

Most welding methods work well with stainless as long as you take care to consider filler material and temperature requirements of the metals you are joining.

• Tungsten Inert Gas (TIG) Welding or Gas Tungsten Arc Welding (GTAW)

• Resistance Welding

• Spot Welding

• Metal Inert Gas (MIG) Welding or Gas Metal AC Welding (GMAW)

Stick and wire feed welders work well with stainless. However, MIG welding stainless steel and wire feed welders will require gas as flux-cored stainless is not readily available.

TIG is best for thin metals as it uses a lower heat input. This prevents warping and increases corrosion resistance when using alongside a single-sided welding process.

Spot welding is the most economical option but might not offer the same strength as MIG or TIG welding stainless steel.

In most cases, the shape, thickness, families, and grades of steel involved in your project -- as well as the size of the welds required -- will help to highlight which option will work best for you.

For austenitic steels, you will want to complete the weld in multiple passes due the maximum interpass temperatures of most grades.

Should the base metal reach approximately 176C (350F), allow time for the metal to cool before continuing to avoid the risk of degrading corrosion resistance or cracking the metal.

In contrast, martensitic steels often require preheating and must be held in a specific range between approximately 204C (400F) and 315C (600F) while welding due to a minimum interpass temperature.

Failure to do so can cause embrittlement of the metal and premature hardening.

Ferritic steels feature some of the lowest maximum interpass temperatures of stainless steel with limits around 148C (300F).

Higher temperatures may lead to grain growth and strength reduction. High-carbon ferritic steels may also require preheating for optimal results.

Finally, duplex steels often require specialized approaches using high heat inputs and low interpass temperatures due to the differing composition of duplex grades and their combination of austenitic and ferritic properties.

5 Tips to Ensure Safe, Long-Lasting Stainless Steel Welding

While it’s best to adapt your approach to the needs of your project, the following tips will ensure a strong weld and long-lasting results regardless of the stainless you use.

1. Always Clean Stainless Surfaces Prior to Welding

Stainless steel is subject to contamination by high-carbon steels and other metals. When this happens, it significantly reduces the corrosion resistance of the stainless.

Cleaning the surface of your stainless not only helps to reduce contamination risks but will strengthen the weld.

If you’re cleaning the surface using a wire brush, be sure that the brush is only used on stainless steel as any microscopic particles left on the brush from other metals might penetrate the surface of the steel during cleaning leading to problems later.

Specialized pickling treatments and cleaning treatments can provide a brushless method of cleaning stainless that is safe for welding to further reduce contamination risks.

2. Choose a Filler Material Similar to the Metals You Are Welding

Choosing the appropriate filler material is essential to both ensuring a strong weld and maintaining the corrosion resistance of your stainless steel.

When choosing a filler, consider both the grades of steel and any suffixes involved.

For example, you would not want to use a high-carbon stainless steel, such as 316H, as a filler when welding a low-carbon stainless steel, such as 316L.

While exact recommendations vary based on the metals you’re using, you generally want to use a filler that matches or exceeds the grades of the base metal to ensure optimal results.

For duplex steels, you might need to make chemical adjustments to your filler metals -- such as adding nickel -- to account for the balance of austenitic and ferritic properties in the grade of duplex stainless you are welding.

3. Use A Reliable Tool to Track Material Temperatures

Efficient, effective welding of stainless steel is all about controlling temperatures.

Monitoring temperatures throughout the welding process is a simple way to ensure long-lasting results and avoid compromising the qualities of your stainless.

Popular temperature monitoring options include:

• Temperature indicating sticks: These sticks are reliable and proven for tracking temperatures as you weld. However, they are often limited in the range of temperatures they can track. If you’re welding across multiple ranges, you’ll need multiple types of sticks to accurately track temperatures.

• Electronic infrared (IR) thermometers: If you have a line of sight to the base metal, IR thermometers allow you to monitor temperatures accurately and quickly. However, lighting conditions and the finish on the metal might create accuracy concerns.

• Electronic surface temperature probes: Probes are ideal when you can mount them in your welding area. They must touch the surface of the base metal to read temperatures, so keep workspace limitations and placement concerns in mind before proceeding.

4. Watch for Warping on Thinner Stainless Parts

Overheating stainless can impact its corrosion resistance and strength. However, when working with thin stainless steel parts or sheets, there is an additional risk to high temperatures -- warping.

To help minimize warping risks, start with low temps and use tack welds to secure pieces before filling in the weld later.

If you cannot use tack welds to position the base metals, welding in short bursts of 3 to 5 seconds can help to avoid overheating while allowing you to accurately and quickly weld.

5. Always Consider Corrosion Resistance of Welds

If you are not using a corrosion-resistant filler, be sure to treat weld sites to avoid corrosion.

Primer, clear paint, or pickling and passivation treatments can help to improve corrosion resistance and ensure your welds are as durable and long-lasting as the stainless surrounding them.

 As a trusted supplier of stainless steel for industries across Canada for more than 40 years, Unified Alloys is a leading provider of parts, forms, and components. If you’re looking for ways stainless steel might help in your next project, consult with one our expert analysts. From ideal grades for your intended use to welding concerns surrounding stainless steel, we can help to ensure you are using the optimal stainless options available on the market.