炭素鋼同種摩擦圧接継手の腐食疲労強度について

抄録

Friction welded butt joints have come into wider use as structural members and machine elements such as propellor shaft and engine value of automobile structure, cutting tool, motor shaft and so forth. Friction welded butt joints have opposite aspects in their mechanical properties : Low absorbed energy in Charpy impact test and high joint efficiency under both monotonic tensile and fatigue load conditions. Furthermore, recent study on the fracture toughness of the joint revealed that the joint possessed sufficiently high toughness value for practical applications despite of its low Charpy impact energy. But, it is also clarified that the scatter of fatigue distribution of the joint is larger than that of the parent material. Therefore, it is an important problem to clarify main factors controlling the fatigue strength and fatigue life distribution from the viewpoint of reliability design engineering. And, the corrosion fatigue behavior of the joint is also an urgent problem to be solved, because some of the joint elements are practically used in corrosive environments.
In order to clarify the corrosion fatigue behavior of the friction welded butt joint composed of similar carbon steel, JIS S25C/JIS S25C, a series of rotating bending fatigue tests was carried out in ordinary atmospheric environment and in artificial seawater. Results of the study indicated that the fatigue strength of the joint at 10⁷ stress cycles in artificial seawater was almost the same as that of the base material, and the evaluation of fatigue life distribution on Weibull probability paper showed that, in artificial seawater, the scatter of fatigue life distribution for the joint is smaller that that for the base metal. Above mentioned corrosion fatigue characteristics of the joint can be discussed reasonably on the bases of the corrosion pits generated on the notch root area of the joint specimen.