Effect of Notch Root Radius on the Determination of Toughness in Ultrahigh Strength Steel Friction Welds

摘要

The plain strain fracture toughness and Charpy impact energy of friction welds in ultrahigh strength AISI 4340 steel were determined. Fracture toughness values for the weld zone were found to exceed those of the base metal. This is believed to be due to the larger prior austenite grain size in the weld zone resultant from the weld thermal cycle. Charpy impact energy data for the weld zone, however, were approximately 50 percent lower than those of the base metal. This was due to the adverse reorientation of sulfide inclusions in the weld zone resulting from the forging stage of the welding cycle. Discrepancies between fracture toughness and Charpy impact test data can be attributed to notch root radius effects. The use of both sharp notch and rounded notch toughness tests are recommended for the determination of weld joint ductility in ultrahigh strength steels.