Fatigue Limit Diagrams of Tufftrided Spheroidal and Flaky Graphite Cast Irons
Hiroshi HOHJO, Akira YAMADA and Katsushi SARUKI
Abstract:On three types of tufftrided spheroidal and flaky graphite cast irons, the fatigue limit diagrams which are used as the basis when estimating the fatigue strength of components were constructed. The major results are shown in below. (1) In the case of smooth specimen of spheroidal graphite cast irons FCD700 and FCD500, the effect of tufftriding could not be correctly estimated because it was influenced in the casting defects. On the other hand, in the case of notched specimen, there was no example of fracture induced by the casting defects, then the improvement of fatigue limit could be correctly estimated. In this case, the fatigue limit of FCD700 was considerably improved with 20%, and that of FCD500 was remarkably improved with 34%. It is considered that the notch reduced the probability with the casting defect which exists in the fracture domain and induced the proper effect of tufftriding. (2) The fatigue limits of tufftrided FCD700 and FCD500 were accurately predicted on basis of 3-parameters, that is to say, the compressive residual stress, Vickers hardness of subsurface pearlitic phase and maximum graphite diameter. (3) In the case of flaky graphite cast iron FC230, the fatigue limits were improved with 17% on smooth specimen, and 14% on notched specimen respectively. The depth of compressive residual stress distribution induced by tufftriding was shallow compared with the size of flaky graphite on both specimen. So there was no great difference on the improvement of fatigue limit between the two types of specimen. (4) The fatigue limit of tufftrided FC230 was accurately estimated from the fatigue limit diagram which was added the compressive residual stress at the distance of flaky graphite length (100ƒÊm) from notch root as mean stress to the fatigue limit diagram of non-tufftrided FC230. Key Words:Spheroidal graphite cast iron, Flaky graphite cast iron, Tufftriding, Fatigue limit diagr