Paul Murphy of Masteel UK and Dr. Sarinova Simandjuntak from the University of Portsmouth, UK recently published a paper in Stainless Steel World looking at the applications of Grade 91 and the challenges of welding it with dissimilar metals.
G91 is a commonly used material in high temperature power plants due to its high temperature creep resistance. In this study, tungsten inert gas (TIG) welding was used to ensure a high quality weld with minimal defects/inclusions.
ASTM/ASME A/SA387 Grade 91 is a modified 9Cr-1Mo steel composed of nitrogen, niobium and vanadium. Although the most common form of Grade 91 material is a plate form, the steel is incorporated into other ASME materials specifications for castings, forgings, fittings, pipes and tubes.
The most common application of ASTM/ASME A/SA387 Grade 91 material is as a high temperature structure material in the fabrication of intermediate heat exchangers, steam generators, secondary piping of a liquid metal reactor that operates at around 550°C, and boiler components used in ultrasupercritical thermal power plants that operate at around 600°C.
The School of Engineering at the University of Portsmouth along with Masteel UK Limited examined the possibility of welding ASTM/ASME A/SA387 Grade 91 material to other steels. A group of researchers and students at the school explored the possibility of a dissimilar metal weld, such as Grade 91 and Duplex/Stainless steel welds. The group studied the process control and parameters in welding that have an impact on the mechanical performances of components of a power plant.
You can read the results in the full article here.