We evaluate the properties of friction welded STK400 steel tube in terms of the relationship between microstructures and mechanical properties. Friction welding is conducted at a rotation speed of 1,600 rpm and upset time of 3-7 sec for different thicknesses of STK 400 tubes. To analyse the grain boundary characteristic distributions(GBCDs) in the welded zone, electron backscattering diffraction(EBSD) method is introduced. The results show that a decrease in welding time (3 sec.) creates a notable increase grain refinement so that the average grain size decreases from 15.1 μm in the base material to 4.5 μm in the welded zone. These refined grains achieve significantly enhanced microhardness and a slightly higher yield and higher tensile strengths than those of the base material. In particular, all the tensile tested specimens experience a fracture aspect at the base material zone but not at the welded zone, which means a soundly welded state for all conditions

Abstract
 1. 서 론
 2. 실험 방법
 3. 결과 및 고찰
 4. 결 론
 References

• 김경우(조선대학교 용접·접합과학공학과) | Gyeong-Woo Kim (Dept. of Welding and Joining Science Engineering, Chosun University)
• 송국현(조선대학교 용접·접합과학공학과) | Kuk-Hyun Song (Dept. of Welding and Joining Science Engineering, Chosun University) Corresponding author