Secondary pressured system was adopted to promote the directive friction welding feasibility of 45~# steel hollow rods with the outer and inner diameters of 42 and 26 mm respectively. The results showed that the welding heat input was increased with the increasing friction time and rotation speed. Welding heat input could not be increased effectively by increasing the upsetting force and the secondary pressured friction force at short friction time and low rotation speed. Thus,massive deformations cannot be...