In this study, X-ray radiographic tests of friction-welded AISI 4340-AISI 2205 steels were investigated. AISI 4340 tempered steel and AISI 2205 duplex stainless steel, each of 12 mm diameter, were used to fabricate the joints. The friction-welding tests were carried out using a direct-drive-type friction-welding machine for different parameters. After this process, the radiographic tests of the welded joints were examined by X-ray diffraction. The experimental results indicated that the AISI 4340 tempered steel could be joined to the AISI 2205 duplex stainless steel using the friction-welding technique and for achieving a weld with sufficient strength. The result of the radiographic tests indicated that by increasing the rotation speed, the friction pressure and the forging pressure, the amount of flash increased for all the specimens. In contrast, when increasing the friction time the amount of flash decreased. The best properties for steels AISI 4340-2205 were observed for the specimens welded at a rotation speed of 2200 min(-1), a friction pressure of 40 MPa, a forging pressure of 80 MPa, a friction time of 6 s and a forging time of 3 s.