1994 年 43 巻 488 号 p. 522-527
The effects of laser treatment on tensile and fatigue properties of spheroidal graphite cast iron were studied by fractographic observations. The laser-treatment was carried out using a 800-500W laser power and at scan speed of 0.5-1.2m/min. The results obtained are as follows;
(1) The typical structure of laser-treated specimen is composed of the melted zone which has cellular dendritic structure, the unmelted (heat affected) zone that contains martensite surrounding graphite nodules, and the ferritic matrix zone.
(2) A sharp drop in hardness occurred at the border between the melted zone (HV800) and the HAZ (HV200).
(3) The tensile test indicated that increasing laser input power lowers the tensile strength.
(4) The tensile fracture surface of the untreated specimen exhibited ductile dimple fracture mode, whereas the laser-treated one revealed dendritic pattern in the melted zone, mixture of quasi-cleavage and small dimple modes in the HAZ and ductile dimple mode in the matrix.
(5) The fatigue life of the laser-treated specimen with melted zone became shorter than that of the untreated one, while the life without the melted zone was longer than that of the untreated one. Lowering the frequency resulted in weakening fatigue strength.
(6) The fatigue fracture surface of the untreated specimen showed no striation pattern. Although the fatigue fracture pattern on the laser-treated specimen was similar to the tensile fracture one, the size and number of graphites on the fatigue fracture surface were less than those on the tensile one.