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Abstract
This paper describes the improvement of properties of a high-tensile strength steel joint by an autocompleting friction welding method that was developed by the authors. The base metal was high-tensile strength steel of 800 MPa class. The weld faying surface of the fixed specimen had a 10 mm diameter, and the effect of the thickness and that at the bottom of the grooves (groove bottom thickness) for the insert piece on the joining phenomena and joint properties were investigated. The value of a circumferential shear fracture (CSF value) was defined and calculated by the ratio between the theoretical and the actual generated friction torques. When the CSF value was lower than 1, the insert piece had the CSF before the friction torque reached the initial peak. Also, when the CSF value was larger than 1, the insert piece had the CSF after the friction torque reached the initial peak. When the joint was made at the insert thickness of 5 mm with the CSF value of nearly 1, it had 100% joint efficiency although it had the softened region near the weld interfaces. The joint had cracks at the weld interface when it was made with friction pressures of 36 and 120 MPa. However, the joint had no crack at the weld interface when it was made with a friction pressure of 90 MPa. When the joint was made at the insert thickness of 4 mm with the CSF value of nearly 1, it had also 100% joint efficiency although it had the softened region near the weld interfaces. However, the softened region at the weld interface of the joint with the insert thickness of 4 mm was lower than that with 5 mm. Also, this joint had 90° bend ductility with no crack at the weld interface. In conclusion, it was possible to make a joint with no cracks for high-tensile strength steel by an autocompleting friction welding method.
Acknowledgements
Part of this study was supported by the Japan Society for the Promotion of Science (Grants-in Aid for Young Scientists, Subject No. 20760496). We would like to express our gratitude for this. We would like to thank the Processing Centre of the Engineering Research Department of the Graduate School of Hyogo University for assistance with construction of experimental apparatus used in this study. We are also grateful to Hirakawa Hirosada and Nanba Akihiro of Mechanical Systems Center of the Engineering Research Department of the Graduate School of Hyogo University for their dedicated assistance.
Notes
Presented at the 2009 Welded Structures Symposium, November 2009