Medium carbon steel sheets of 2.6 mm thick were successfully welded by linear friction welding at various frequencies and applied pressures. The welding temperature decreased with the decreasing frequency, but unexpectedly with the increasing applied pressure. A medium carbon steel joint with no martensitic transformation could be obtained at a welding temperature below the A 1 point under the conditions of low frequency and high applied pressure. Moreover, the welding temperature evolution was found to be correlated with the behaviour of the flash expelling at the welding interface. It was revealed that the welding temperature can be determined as the temperature at which the ultimate tensile strength of the interface material decreased below the applied pressure.

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Synopsis : Linear Friction Welding (LFW) is a solid-state joining process, in which a joint is obtained through the relative motion of two components under a high contact load. The most important factor of this conventional method is to obtain a fresh surface at the interface by expelling the weld interface as flash. In this study, medium carbon steel was welded by LFW at a low frequency, low amplitude and high applied pressure. As a result of the temperature measurements and microstructure observations, the maximum temperature of the weld plane was confirmed to be below the A 1 transformation temperature, and martensitic transformation was prohibited at the weld interface. The key concept of this method are applying a large strain deformation to the interfaces to recrystallize at a lower temperature which is different from the conventional LFW.