In this study,the effect of core bar inserted into weld faying part to obtain an ideal pipe joint with nongenerating inner flash via friction welding is described.A steel pipe with inner and outer diameters corresponding to 8.0 mm and 13.5 mm was used,and the weld faying surface was machined to a groove shape of a flat (butt) type.The core bar of various materials was inserted in the weld faying part of the pipes,and those pipes were welded with a friction speed of 27.5 s-1 and friction pressure of 30 MPa.The core bars did not decrease inner flash when joints were fabricated with a core bar of some metallic materials with melting points below that of steel;thus,they were melted during the welding process.The joint with an alumina core bar did not decrease inner flash and was crushed by generating an inner flash.However,a commercially pure tungsten (CP-W) core bar was successfully achieved for decreasing the inner flash.Additionally,all joints with a CP-W core bar did not exhibit the tensile strength of the base metal and a fracture in the base metal,when they were fabricated during the same time,the friction torque reached the initial peak.The joint exhibited a fracture in the base metal when it was fabricated with a CP-W core bar and a taper groove shape that was proposed in the previous study.Furthermore,the core bars were easily removed from the joints;thus the joint with almost no inner flash was successfully obtained.To reduce the inner flash of pipe joints,they should be fabricated with a CP-W core bar inserted into the weld faying part with a taper groove shape.