Welding Stainless Steel: Understanding the Alloys and Choosing Filler Metal
When a component must withstand corrosion and extreme temperatures — as low as minus 100 degrees Fahrenheit and as high as 1,800 degrees Fahrenheit — manufacturers often turn to stainless steel. While it’s commonly used in manufacturing, welding stainless steel can present some specific challenges. Keeping the heat input low is critical to success in welding the material since it is less conductive to heat.
Understanding the common types
It is also important to select the right alloy and filler metal for stainless steel welding applications, and there are many factors to consider when making these choices. Follow some key best practices to help optimize results.
There are five commonly used grades of stainless steel. Understanding the differences between the types helps ensure the right one is being used.
Across all five types, chromium and nickel are the main alloys in the material to varying degrees. Three of the most common types — austenitic, ferritic and martensitic — are phases of stainless steel. As the material cools, the result will be one of these types or a combination of types, depending on how the metal is cooled and what temperature it reaches during cooling.
The five types all have similar weldability. Because they are all highly alloyed, sluggishness of the weld pool is a common challenge. Using electrodes with boosted silicon content can help address this. The types do vary in strength. If the material classification has an L-grade, such as 308L, this designates a lower carbon level, which can mean slightly lower tensile strength.
Choosing the right filler metal for each type of stainless steel depends on the characteristics of the base material, the properties required for the finished weld and the environment the weld will be exposed to.
Austenitic: This type of stainless steel has chromium content ranging from 16 to 25 percent and nickel content from 8 to 20 percent. Additional alloying elements often include silicon, manganese, nitrogen and molybdenum. Austenitic stainless steels do well in highly corrosive environments and are commonly used for medical equipment and kitchen equipment such as mixers and dishwashers. The most common austenitic steels are 304, 308, 309 and 316. For 304 and 308, a 308 filler metal can be used. For a 309 base material, there are numerous options, including 308, 309 or 316 filler metals. For 316 base materials, it’s recommended to use a 316 filler metal. Pre-heat and post-weld heat requirements aren’t typically an issue with austenitic stainless steels. If there is a need to do post-weld heat treat, avoid the temperature range of 1,200 degrees to 1,650 degrees Fahrenheit, as carbide formation will occur rapidly in this range and cause weld embrittlement.
Ferritic: These stainless steels have a chromium content that can range from 10.5 percent to greater than 25 percent and typically have the best corrosion resistance. With tensile strengths of 55 to 65 ksi, they generally aren’t as strong as austenitic and martensitic stainless steels. Ferritic stainless steels are often found in automotive exhaust systems, chemical processing, and pulp and paper industries. Common grades are 409 and 430, with matching filler metals of 409 and 430. Ferritic base materials are generally limited to service temperatures below 750 degrees Fahrenheit due to the tendency to form embrittling phases. Weld solidification cracking can also be an issue with ferritic base materials, so it’s important to use a filler metal with stabilizing alloys such as titanium or niobium, which help lower solidification cracking susceptibility.
Martensitic: These stainless steels provide a good combination of high tensile strength and corrosion resistance and are commonly used for steam and gas pipes, turbine blades and other applications that may encounter steam and moisture buildup. Keep in mind that materials with high tensile strength tend to have lower ductility. Martensitic stainless steels typically have an 11.5 to 18 percent chromium range and higher levels of carbon and other alloying elements that promote the formation of martensite. Common martensitic stainless steels are 410 and 420, which can be matched with 410 and 420 filler metals with similar characteristics. These alloys are also susceptible to hydrogen-induced cracking. This risk can be reduced by controlling the heat input through proper pre-heat, interpass and post-weld temperature requirements or by reducing the amount of restraint on the weld. A post-weld heat treatment can be used on these types of stainless steels to temper the martensite that is formed, which will impact the hardness, tensile strength and ductility of the weld.
Precipitation hardening (PH): These stainless steels are typically alloyed with various elements and go through heat treatments to obtain their strength and hardness. Some grades of PH stainless steels can have strengths over 200 ksi, making them the strongest type of stainless steel. A common PH stainless steel is 17-4, which is often used in applications where high strength and corrosion resistance are needed. Applications include missile launch tubes, aircraft frames and high-pressure gas bottles. This type can be matched with a 17-4 PH filler metal or 630 filler metal. Because it goes through a controlled cooling to achieve its properties, it’s recommended to bring a 17-4 PH stainless steel up to a solution-treated condition before welding. This temperature is usually within the range of 1,650 to 1,800 degrees Fahrenheit for one to two hours, followed by a quench. Post-weld heat treating can be used to bring the material back to the desired properties after welding. It is recommended to contact the supplier of the PH stainless steel to get recommendations on post-weld heating temperatures and times to achieve the desired properties.
Duplex: These alloys are designed to have a microstructure of 50 percent ferrite and 50 percent austenite in their finished form. Duplex stainless steels have a service temperature range of about minus 40 to 535 degrees Fahrenheit and strengths above 60 ksi, which provide a mix of abrasion and corrosion resistance. They are used in a wide range of applications, including oil and gas pipelines. Duplex filler metals are newer to the market and are growing in use.
Best practices
Proper filler metal selection is one key to successfully welding stainless steel. It’s also important to follow some best practices that can help optimize results.
The less fluid, more sluggish weld pool of stainless steel can cause some issues, especially for welders who aren’t as familiar with the material. If the less fluid weld pool is a concern, choose a filler metal with more silicon in the classification, such as ER308LSi versus a standard ER308L filler metal. Increased silicon levels help with weld pool flow and fluidity.
It’s also important when welding stainless steel to use faster travel speeds, which help keep heat input low. A too-slow travel speed increases heat input, which can burn alloying elements out of the metal and impact end-weld properties like strength, ductility and corrosion resistance. While a travel speed of 3 to 8 inches per minute is typical with other materials, welding stainless steel with flux-cored or metal-cored wires calls for travel speeds of 8 to 11 inches per minute.
Consider the final appearance of the weld, as well. A weld bead using flux-cored or metal-cored wires will have a distinct gold color or rainbow sheen. A TIG weld using filler metal or that is autogenously welded should not have this bead appearance.
Avoid contamination of the weld by using a dedicated stainless steel brush to clean stainless welds. Using the same brush to clean stainless steel and mild steel can cause cross-contamination that can result in rust later. Similarly, don’t use a brush for stainless steel to clean aluminum, or vice versa.
Using proper safety gear and personal protective equipment (PPE) is also important when welding stainless steel. Some filler metals produce higher levels of weld fume than others, so it’s important to have proper ventilation or weld fume source capture in place when using them. In some applications the welder may also want to use a helmet equipped with a respirator.
Success with stainless steel
Matching the appropriate filler metal to the type of stainless steel being used in the application helps ensure that the welds maintain corrosion resistance, toughness and mechanical properties. The proper welding process and filler metal can also help control heat input when welding stainless steel.
Keeping these key considerations and best practices in mind when selecting a filler metal and welding stainless steel can help ensure success and optimize results.
7 Benefits of Stainless Steel
As specialists in fabrication, architectural rigging, cable manufacturing and more we’ve worked with a wide range of materials in residential, commercial and industrial projects. One of our most commonly used materials across all these contexts is stainless steel. Its many unique properties combined, make it an ideal solution for many applications and we thought we’d explore all the different benefits of stainless steel to prove just how useful it really is.
Properties of Stainless Steel
To fully understand the benefits of stainless steel as a material used across a wide range of industries, it’s important to understand more about the properties of stainless steel that make it such an ideal material for use in fabrication, rigging, and cable manufacturing as well as commercial, industrial, and residential projects. Here are seven properties of stainless steel that bring so many benefits:
1. Corrosion Resistance
One of the best and most well-known characteristics of stainless steel is that it is extremely corrosion resistant. When it was first created by Harry Brearley in 1913 it was spoken of as the world’s first ‘rustless steel’. The addition of chromium content was the key component that gave stainless steel this quality and was seen as the major breakthrough in its development. Stainless steel has evolved a great deal since then with many different types/grades available. We typically use 316-grade stainless steel which also contains 3% molybdenum. This further strengthens its resistance to corrosion against industrial acids, alkaline solutions and makes it particularly resilient in high saline environments (i.e. those by the sea). This founding characteristic has made it highly applicable all over the world.
2. Fire and heat resistance
The resilience of stainless steel as a material is a common theme throughout this blog and its resistance to fire and heat is an integral part of that. Stainless steel has this attribute because of its oxidation resistance, even at high temperatures. This enables it to retain its strength under harsh and extreme temperature conditions very effectively. Chromium again plays an important role in this respect and makes stainless steel a great choice with fire resistance and fire prevention in mind. It’s a material that outperforms the likes of galvanised steel and aluminium in this regard.
3. Hygiene
A benefit of stainless steel that might not immediately come to mind, but is particularly true and important, relates to hygiene. Stainless steel is an extremely hygienic material due to the fact that it is extremely easy to clean and sanitise. Its smooth, sheen-like and non-porous surface means that the likes of dirt, grime and bacteria struggle to establish themselves on its exterior. When they do, they can very easily be wiped away. The ease of this cleaning and maintenance makes stainless steel an excellent choice in environments where strong hygiene is vital. This is why professional kitchens are made almost exclusively of stainless steel and why you’ll see it relied on heavily in hospitals, laboratories, factories etc.
4. Impact resistance and strength
Stainless steel is an extremely tough and highly durable material with high impact resistance. Part of the reason for this is that stainless steel has low susceptibility to brittleness at high and low temperatures. Not only does this mean that the material will retain its shape, but it means at its melting point it can be more easily welded, cut, fabricated etc as we do in the manufacture of balustrades for example. Interestingly, it’s also a material that’s commonly used in cryogenic applications given its strength in cold working conditions showing again just how strong a material it is.
5. Aesthetic appearance
Another reason why many turn to stainless steel is somewhat superficial but not less valid and that’s to do with its aesthetic appearance. Ever since its creation, stainless steel has been seen as an elegant, attractive and modern material. Many see it as a material that has a brightness that resonates with a sense of purity. It is also a material that has stood the test of time and if anything, has become more and more popular as a functional and ornamental choice in residences and commercial properties around the world. It is also a material that complements and works well with most other materials, styles and colours.
6. Sustainability
Another benefit that doesn’t get a lot of attention when it comes to stainless steel but one that is very important as a global issue is the fact that it’s a highly sustainable choice. Stainless steel is typically created from about 70% scrap metal meaning its foundations come from that which isn’t being used. Furthermore, it’s 100% recyclable in its original form which means it can be repurposed should it cease to serve its original function. It won’t leach toxic chemicals like some other materials during the recycling process and doing so, reduces the need for mining the rarer elements that play an important role in the creation of stainless steel.
7. Long term value
When you consider the longevity of stainless steel as well as all the other factors mentioned above, the total life cycle cost of the material stacks up well. Its increasing prevalence in our society has increased competition from suppliers meaning pricing has been as competitive as it’s ever been. This, coupled with the fact that the maintenance cost for stainless steel is extremely low, means you’ll get great returns when choosing it as your material of choice. Given we’ve also just mentioned that it’s 100% recyclable means that it is really hard to lose out on stainless steel as a solution.
Some great benefits of stainless steel
Disadvantages of Stainless Steel
The great news about stainless steel is that it has very few disadvantages. One potential downside can be that it is difficult to manufacture stainless steel and this can sometimes lead to higher costs. As we have discussed above, however, the long term value of stainless steel means that any initial outlay pays for itself over time.
Another potential disadvantage is the fact that Stainless steel can also show up dirt and grease in certain environments. When you think about kitchen surfaces or appliances, even the smallest smudge or fingerprint will show up on the surface and whilst they are easy to wipe clean, it can be a battle to keep them clean, especially with a big family.
Overall, however, the advantages of stainless steel far outweigh the disadvantages making it the ideal material for a huge range of applications.
As you can see, there are some great benefits of stainless steel that shouldn’t be overlooked or dismissed. We hope you’ve enjoyed this blog and would be happy to discuss the needs and requirements for your next project and how stainless steel might work as a solid solution for you!