How to Weld Duplex Stainless Steel

Heat Input and Interpass Temperatures

By far, the most common error seen when welding duplex stainless steel is utilizing an improper heat input and interpass temperature. Duplex stainless steels require relatively high heat input and low interpass temperatures when welding to obtain the proper phase balance in the weld metal.  Insufficient time at temperature can result in high ferrite and insufficient austenite. Conversely too much time at temperature can result in high austenite, an increased chance of forming nitrides and sigma phase in the base metal. These changes will decrease the corrosion resistance and toughness.

Quality Checks

It is essential to perform quality checks after welding to ensure proper phase balance. Therefore, when developing a welding procedure, it is critical to test corrosion resistance, impact toughness, and ferrite/austenite mix in the weld qualification to ensure that the final production weld yields good results and is fit for service. Often it is unfeasible to test a production weld thoroughly. As this is the case, it is common to utilize a ferritscope to test the ferrite content of a production weld to roughly determine any weld-related problems. Typically, incorrect ferrite levels will be the first indication of a problem. If a problem is found, further testing should be performed.  The ferritiscope is not a substitute for the more accurate microscopic methods.  Rather it is meant only as a QC check.  If there are inconsistencies, a destructive test and a microscopic investigation may be necessary.