Welding of Austenitic Stainless Steel and Low Carbon or Low Alloy Steel
Introduction
Austenitic stainless steel is a popular and widely used material, particularly in the oil and gas industries. It is a kind of stainless steel with a high percentage of nickel, chromium and molybdenum, and it is often used in applications where corrosion resistance is required. Low carbon or low alloy steel is also a common material in the industry, which is used for a variety of applications due to its different properties. These two materials are not generally welded together due to differences in their properties and welding characteristics.
Classification and Properties of Austenitic Stainless Steel
Austenitic stainless steel is a type of steel which is based on the 300 series. The name “austenitic” is derived from its origin, which is the name of its inventor, the British metallurgist Sir Robert Austen. The stainless steels in this series have a minimum chromium content of 18%, and they also contain other elements such as nickel, molybdenum and nitrogen. The most common austenitic stainless steels are 304, 316, 317 and 321 with their key element contents being 18Cr-8Ni-2Mo, 18Cr-10Ni-2Mo, 18Cr-12Ni-3Mo and 18Cr-9Ni-3Mo respectively. The main characteristics of this material are its high ductility, excellent corrosion resistance and good strength.
Classification and Properties of Low Carbon or Low Alloy Steel
Low carbon or low alloy steel is basically carbon steel which has a low content of either carbon or alloying elements, or both. The main alloying elements used in low alloy steels are chromium, nickel, molybdenum, vanadium, and silicon. The material is classified as either low carbon or low alloy steel depending on its composition. Low carbon steels (LCs) contain a maximum carbon content of 0.30% and are commonly used for applications where strength and toughness are not priority. Low alloy steels (LAs) contain a higher quantity of alloying elements, usually up to 5%. They have better physical and mechanical properties than LCs and also offer better corrosion resistance, making them suitable for corrosive environments.
Welding of Austenitic Stainless Steel and Low Carbon or Low Alloy Steel
Despite their similarities, austenitic stainless steel and low carbon or low alloy steel have different welding characteristics due to their different composition and properties. Austenitic stainless steel is slightly different to ferritic stainless steel because of its higher alloys content and hence they are usually welded differently.
Low carbon or low alloy steel can be welded to austenitic stainless steel using a variety of methods such as MIG, TIG, shielded metal arc welding (SMAW), flux cored arc welding (FCAW). The most suitable process for the application should be chosen based on the type of alloy being used, the size and shape of the components, and the welding position.
The most commonly used method for welding these two materials is the gas metal arc welding (GMAW) process. This is because it is more reliable than other welding processes and it can also achieve a good weld joint with minimal post-welding clean-up. However, it is important to ensure that the weld joint is well prepared before welding. As with all stainless steel welding, it is essential to use the correct filler metal and welding parameters. This will help to reduce the risks of weld cracking due to the thermal stresses induced by welding.
Conclusion
The welding of austenitic stainless steel and low carbon or low alloy steel is possible but it poses some challenges due to the differences in their properties and welding characteristics. The most suitable welding method should be chosen based on the type of alloy being used, the size and shape of the components and the welding position. It is important to ensure that the weld joint is well prepared before welding and the correct filler metal and welding parameters are used. These steps will help to reduce the risks of weld cracking due to the thermal stresses induced by welding.
