自動車用高張力鋼板における穴抜き工具刃先摩耗が穴抜き部材疲労強度に及ぼす影響

抄録

The effect of tool wear on the fatigue strength of pierced steel sheets has been investigated through a plane bending test, in which three kinds of high-strength steel were used as specimens. The tools for this study sustained wear after 10,000 piercing shots on commercial JIS-S45C steel. The results show that the tool wear possibly reduces the fatigue strength of the pierced steel sheets. The possibility of such deterioration depends on the type of material. The holes pierced on the ferrite-pearlite or precipitation-strengthened steel do not induce the reduction in fatigue strength by the tool wear. Nevertheless, the holes on the ferrite-martensite steel induce deterioration, probably caused by residual stress. The tool wear induces tensile residual stress around the burr side of the holes; this residual stress probably accelerates the propagation of fatigue cracks. The tool wear hardly affects the roughness and hardness of the pierced surface, which are other factors related to fatigue strength.