In general, the goal when welding austenitic stainless steel is to reach a maximum ferrite number between 3 and 7 however, special applications may call for higher ferrite numbers to achieve the best results. The amount of ferrite present isĭetermined largely by the chemistry of the material. This number quantifies the amount of ferrite versus austenite in the material’s structure, providing an indication of its ability to resist cracking, and in some cases the number indicates its corrosion resistance. Engineers and designers often refer to a property in stainless steels known as the ferrite number. With the introduction of ferrite into the weld by way of chromium and nickel, is important, because it helps refine the grain structure of the weld and make it more crack-resistant. The addition of silicon helps maintain weld pool fluidity and stabilize the amount of austenite in the weld. Molybdenum also offers good high-temperature performance, while nickel helps increase weld strength. For example, chromium helps ensure corrosion resistance, as does molybdenum. In such a case, a 309L-gradeĪll of these filler metals contain alloys that contribute to the weld’s integrity. It’s also not uncommon to join an austenitic stainless steel tube or pipe to a carbon steel component. In the case of 304L austenitic stainless steel tube and pipe, the proper filler metal match is one with an American Welding Society (AWS) 308 or 308L designation, while a 316L filler metal is the appropriate choice for welding 316 austenitic stainless steels. The intended service conditions dictate the tube or pipe alloy to be used, which in The process of making this match, however, is somewhat easier with austenitic stainless steel than with many other materials. Like filler metals for welding other materials, those for austenitic stainless steel must match the base material’s chemical and mechanical properties. Having the right filler metal and controlling the material’s temperature, the heat input and postweld cooling, can help prevent cracking, as well as minimize the risk of losing corrosion resistance during the welding process. This material is particularly susceptible to this defect due to its rather large grain structure. Hot cracking - a defect that occurs immediately after welding - is the biggest potential problem when welding austenitic stainless steel tube and pipe. Why Is Choosing the Right Filler Metal So Important? It requires special attention to achieve optimal results, and it requires the right filler metal. Like any other application, welding austenitic stainless steel tube and pipe presents specific challenges. The material also provides good toughness, particularly at low temperatures. In addition to corrosion resistance, austenitic stainless steel offers good mechanical properties, including yield strengths from 30,000 to 40,000 pounds per square inch (PSI) and tensile strengths from 70,000 to 80,000 PSI. Austenitic stainless steel systems also are used to comply with the sanitary standards required for many food-processing applications. The corrosion resistance comes mainly from their chromium content which, combined with other elements, provides ideal protection against corrosive elements in industries such as pharmaceutical, energy,Īnd chemical processing. Known for its exceptional corrosion resistance, austenitic stainless steel, the 300 series, has become a staple in tube and pipe applications, with 304L and 316 grades being the most prevalent.
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