Microstructures and Mechanical Properties of Friction Welded Steel Tubes

We evaluate the properties of friction welded steel tubes in terms of the relationship between microstructures and mechanical properties. For this work, steel tubes with a diameter of 60.5 mm, which has a thickness of 3.3 and 2.2 mm, was prepared by length of 170 and 70 mm, and friction welding was conducted at a rotation speed of 2,000 rpm and upset time of 5 s, respectively. Applying the friction welding led to the notable grain refinement so that average grain size was refined from 15.1 μm in base material to 4.5 μm in welded zone. These refined grains achieved the significantly enhanced microhardness (20% higher) and a slightly higher tensile strength relative to the base material, respectively. In particular, the tensile tested specimens showed the fracture aspect at the base material zone not at welded zone, which means the soundly welded state.