The Effects of Processing Parameters on the Microstructural Evolution and Mechanical Properties of Inertia Friction Welded 21Cr-6Ni-9Mn

摘要

Tubular specimens of the nitrogen-strengthened alloy 21Cr- 6Ni-9Mn were instrumented with thermocouples and inertia welded using a wide range of axial forces and kinetic energies. It was determined that a linear relationship exists between upset and kinetic energy for a given axial force. Furthermore, the peak temperatures are inversely related to the applied axial force. Microstructural characterization was performed using optical and electron microscopy techniques. Ferrite was observed locally at the weld interface, and it was determined that the width of the ferrite zone could vary widely depending on the process parameters. Electron backscattered diffraction analysis revealed that the ferrite and austenite at the weld interface exhibit the Kurdjumov-Sachs orientation relationship, and suggests that a very large amount of ferrite is present during the welding process that subsequently transforms to austenite during cooling. The fracture toughness of inertia welds thermally charged in gaseous hydrogen was also measured. It was found that the hydrogen-assisted fracture susceptibility of the inertia welds was greater than that of the base metal, but less than that of 21Cr-6Ni-9Mn gas tungsten arc welds.