By using S35C/S35C friction welded tubular butt joints fabricated under five different friction welding processes, a series of tests were conducted to determine the effect of welding conditions on joint performance. At first, the hardness measurement revealed that, though the extent of heat affected zone was different from each other depending on the welding condition, no noticeable difference was observed in the maximum hardness value at the weld interface of joint. Then, the results of monotonic tensile tests indicated that the joint efficiencies of four joints were sufficiently high excepting only one joint fabricated under the lowest friction pressure condition. But the above-mentioned results did not necessarily reflect on the fatigue strength of the joints, and their fatigue strength behaviors could be subdivided into two groups as follows: Two types of joints showed lower fatigue strength than that of the base material and appeared to have no fatigue limit in the range of this experiment; and in contrast, the fatigue strength of the other three types of joints well exceeded that of the base material and showed a tendency to have a fatigue limit. Such fatigue strength behaviors seemed to be correlated closely to the magnitude of forging pressure in the friction welding process.
