• 산업기술연구
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• 제20권B호
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• pp.3-8
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• 2000

Low cycle fatigue life of spheroidal graphite cast iron is determined by the morphological parameters of internal graphite. The aim of this study is to clarify the effect of the number of nodular grain of spheroidal graphite cast iron on low cycle fatigue life. Two specimens that have identical average nodular grain size by changing nodular grain volume fraction and different number of nodular grain count was tested. In this paper, the parameter governing fatigue life through fatigue test, the number of nodular grain seriously affect fatigue life and nodular grain size is no longer governing parameter of it.

• 한국표면공학회지
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• 제24권1호
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• pp.31-41
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• 1991

The nodular corrosion behavior of Zircaloy-4 alloy was investigated by autoclave test at 50$0^{\circ}C$ under 1500 psi for the specimens quenched into water from $700^{\circ}C$, 80$0^{\circ}C$, 90$0^{\circ}C$, and 105$0^{\circ}C$. It was observed that the corrosion resistance of Zircalloy-4 specimen increased with increase in annealing temperature, and annealing at $\alpha$-region temperatures resulted in nodular corrosion while annealing at the temperature range of $\alpha$+$\beta$ and $\beta$ did not show nodular corrosion. It was also found that the size of nodule formed on the surface of the specimens increased with increase in exposure time in autoclave, but the total number of nodule remained uncha-nged. The corrosion of furnace-cooled specimens progressed mostly in the interior of grains where Fe and Cr alloying elements were largely depleted during the cooling process. However, the grain boundary seemed to act as a barrier to the nodular corrosion. From combining the present results with other works, it is suggested that the nodules nuc-leate in the local region where some of alloying elements are depleted.

• 한국생산제조학회지
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• 제7권5호
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• pp.66-71
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• 1998

It is required the superior materials for the parts of machines or structures, which could be endurable in severe load and environment. According to advancement of casting technology, nodular graphite cast iron is used as suitable for such condition. But nodular graphite cast iron is scattering of fatigue strength and low reliability. Therefore in this study, the effect of matrix structure and number of nodular graphite on the initiation of fatigue crack and fatigue strength. It was found that the material which has relatively high ferrite volume fraction was more easily cracked than other materials and fatigue limit was low. The material which has not found pinhole on the surface, the crack was initiated in graphite went through ferrite and propagated into through graphite, but separated graphite and ferrite grain boundary and combined with other cracks to fro large one.