Dependence of corrosion fatigue behaviour of friction‐welded butt joints on friction welding procedure

Abstract

Although friction-welded butt joints are seeing more widespread applications as machine components and structural members, a valid method for evaluation of the joint performance, especially under operating load conditions, has not yet been established. The reliability of this type of joint is supported only by available empirical knowledge. To clarify the fatigue behaviour of joints, the authors have run a series of fatigue tests of several types of friction-welded butt joints in air and have shown that the fatigue strengths of the joints are higher than that of the base metal but that the fatigue lives show heavy scatter. Evaluation of the corrosion fatigue behaviour of frictionwelded butt joints is also a matter of urgency, because some joints have practical applications in corrosive environments.The main purpose of this study is to determine the relationship between the fibre flow conditions near the weld interface of joints and their corrosion fatigue resistance. A series of experiments was run with four frictionwelded butt joint specimens composed of JIS S25C similar carbon structural steel fabricated under different welding conditions. This study covers the following four phases:(1) dependence of the fibre flow conditions on the friction welding procedure; (2) the corrosion response of the four types of joint fabricated by different friction welding procedures; (3) fatigue strength behaviour of the joints with corrosion pits in air; (4) corrosion fatigue resistance of the joints under no-load immersion conditions in artificial sea water.The results of the study show that the corrosion fatigue resistance of the joints is well correlated with the fibre flow conditions. Many deep corrosion pits are formed in the surface area intersecting the fibre flow, and the notch effect of the corrosion pits causes loss of fatigue strength. In other words, joint specimens without this surface area intersecting the fibre flow exhibit superior corrosion fatigue performance.