Strength enhancement of autocompleting medium and high carbon steels friction welded joints

An autocompleting friction welding method, which was developed by the authors, is to weld with using a rotating insert piece set between fixed workpieces. The conditions to enhance the strength of the welded joint in an autocompleting friction welding method which involves a rotating insert between the fixed workpieces were determined. The weld faying surface of the fixed specimen had a 10 mm diameter. When MCS joint was made at an insert thickness of 4 mm through a friction pressure of 36 MPa, it did not achieve 100% joint efficiency because the weld interfaces were not completely joined. MCS joint had 100% joint efficiency and fractured on the MCS base metal although the crack was generated at the weld interface, when that was made at an inner groove diameter of 11 mm with the bottom of the grooves for the insert piece (groove bottom thickness) of 0.9 mm or more through a friction pressure of 90 MPa. To obtain a joint with no cracks, MCS joint was made with an inner groove diameter of 12 mm at a friction pressure of 90 MPa. When the groove bottom thickness was 0.75 mm, MCS joint had 100% joint efficiency and the MCS base metal fracture with no crack at the weld interface. When HCS joint was made with an inner groove diameter of 11 mm at friction pressures of 90 and 150 MPa, it did not achieve 100% joint efficiency because the weld interfaces were not joined completely. The weld interfaces of HCS joint at a friction pressure of 120 MPa were completely joined although it did not achieve 100% joint efficiency. To improve the joint efficiency, HCS joint was made with an insert thickness of 5 mm, a groove bottom thickness of 0.64 mm, and an inner groove diameter of 12 mm with a friction pressure of 120 MPa. HCS joint had 100% joint efficiency and fractured on the HCS base metal with no crack at the weld interface.