Corrosion of the Austenitic Stainless Steel Weld Joint
Welding joints are one of the most commonly used methods in engineering and fabrication projects to join two or more metal components together to assemble a final product. The selection of the correct welding process and welding materials is integral in ensuring the joint’s integrity. Among the most common metals used in welding applications are the austenitic stainless steels. Their corrosion resistance makes them ideal for many applications, as their properties remain intact even when exposed to corrosive environments. However, their susceptibility to corrosion at the weld joint means that welders must be extra cautious in ensuring that the weld joint is adequately protected against corrosive elements.
The austenitic stainless steel (AS) weld joint can be potentially vulnerable to corrosion due to the difference in metal compositions between the base metal and the filler metal used in the welding process. This is especially true with weld joints constructed from materials from different metal families. For instance, a stainless steel weld joint made from an austenitic stainless steel base metal, combined with a high-nickel martensitic filler metal, will be highly susceptible to localized corrosion at the joint. In addition, the dissimilar metals in the weld joint can create a galvanic cell, leading to accelerated corrosion, particularly when the joint is exposed to chloride environments.
The solution for this corrosion issue lies in proper welding and fabrication techniques. The selection of the right type and grade of weld filler metal is critical in preventing corrosion at the weld joint. The weld filler metal should be coordinated with the base metal to ensure that they are as similar in composition as possible to eliminate the risk of galvanic corrosion. In addition, the selection of an appropriate welding process is also important. In the case of austenitic stainless steel weld joints, gas metal arc welding (GMAW) is the preferred welding process due to its ability to create a high-quality weld that is less susceptible to corrosion.
To protect the weld joint from corrosion, proper shielding gases should also be selected when welding austenitic stainless steel components. Inert gases, such as argon and helium, should be used, as these will protect the joint from oxygen and other corrodents. In addition, the selection of post-weld cleaning processes such as passivation and pickling are also of importance in protecting the weld joint from corrosion. These processes are used to remove surface contaminants and oxides from the weld joint, thus reducing its susceptibility to corrosion.
In conclusion, understanding the susceptibility of the austenitic stainless steel weld joint to corrosion is critical for ensuring its integrity when used in fabrication projects. Careful selection of the base and filler metals, welding processes, and post-weld treatments are essential to prevent corrosion of the weld joint. With the right selection and implementation of these mechanisms, weld joints made from austenitic stainless steels can provide durable and reliable connections even in harsh environments.
