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Overcoming Stainless Steel Welding Challenges



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Services & Tech >> Overcoming Stainless Steel Welding Challenges
How to overcome welding challenges of stainless-steel parts fabrication
When a component must withstand corrosion and extreme temperatures—as low as -100 F and as high as 1800 F—manufacturers often turn to stainless steel. While commonly used in manufacturing, stainless steel can present welding challenges. Keeping heat input low plays a critical role, since stainless steel is less conductive to heat steel. This, along with selecting the filler metal and following proven best practices, is critical for optimal weld results.
Understanding Types
Understanding the differences between the five used grades of stainless steel helps to ensure selection of the right grade. Across all five grades, chromium and nickel represent the main alloy materials to varying degrees. Three of the most common types: austenitic, ferritic and martensitic. 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.
As for weldability, all stainless-steel alloys share a common challenge: sluggishness of the weld pool. Using electrodes with boosted silicon content can help address this.
Strength varies across the alloys. 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 welds and the environment to which the welds will be exposed.
The five types of stainless steel:
1. Austenitic alloys have chromium content from 16 to 25 percent, and nickel from 8 to 20 percent. Additional alloying elements 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.
2. Ferritic alloys have a chromium-content range of 10.5 percent to greater than 25 percent, and 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, and find use in automotive exhaust systems, chemical processing, and the pulp and paper industries.
3. Martensitic alloys, commonly used for steam and gas pipes, turbine blades and other applications that may encounter steam and moisture buildup, provide a good combination of high tensile strength and corrosion resistance.
4. Precipitation-hardening stainless steels go through heattreatments to obtain their strength and hardness. Grades of PH stainless steels can have strengths of more than 200 ksi, making them the strongest types of stainless steel.
5. Duplex alloys, designed to have a microstructure of 50-percent ferrite and 50-percent austenite in their finished form, have a service temperature range of about -40 to 535 F and strengths above 60 ksi, which provide a mix of abrasion and corrosion resistance.
Best Practices
In addition to proper filler-metal selection, successful stainless-steel welding requires following these best practices:
1. Increase silicon levels to help with weld, pool flow and fluidity. The more sluggish weld pool of stainless steel in the filler metal, due to less fluid, can cause some issues, especially for welders not familiar with the material. If the less-fluid weld pool causes 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.
2. Use faster travel speeds to help keep heat input low. Slow travel speed increases heat input, which can burn alloying elements out of the metal and impact weld properties including strength, ductility and corrosion resistance. While a travel speed of 3 to 8 in./min. is typical with other materials, welding stainless steel with flux-cored or metal-cored wires calls for travel speeds of 8 to 11 in./min. Consider, too, the final appearance of the weld.
3. Avoid contamination of the weld 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 and result in rust.
4. Use proper safety systems and protective gear. 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.
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