Abstract
In this paper, we explore the effect of a long solidification time (12 h) on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI). For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried out on specimens extracted from the same casting. The obtained results are compared with those of similar materials published in the technical literature. Moreover, the discussion is complemented with metallurgical and fractographic analyses. It has been found that the long solidification time, representative of conditions arising in heavy-section castings, leads to an overgrowth of the graphite nodules and a partial degeneration into chunky graphite. With respect to minimum values prescribed for thick-walled (t > 60 mm) EN-GJS-400-15, the reduction in tensile strength and total elongation is equal to 20% and 75%, respectively. The rotating bending fatigue limit is reduced by 30% with respect to the standard EN-1563, reporting the results of fatigue tests employing laboratory samples extracted from thin-walled castings. Conversely, the resistance to fatigue crack growth is even superior and the fracture toughness comparable to that of conventional DCI.
Highlights
Low production cost and excellent castability make ductile cast iron (DCI) the preferred material choice when low-to-moderately stressed mechanical components of complicated shape and large dimensions must be manufactured
The fatigue life is exclusively thought of as the propagation of cracks up to a critical size leading to structural collapse or functionality loss. They require a detailed characterization of the fracture toughness and the fatigue crack growth resistance of the castings in order to assess the critical crack size and the time to propagation to this critical value. We address this latter issue by investigating the crack growth resistance of a DCI produced under very slow cooling conditions, representative of the microstructural conditions arising in thick walled castings
It can be noted that about 1/3 of the graphite has degenerated into chunky graphite and that the remaining fraction of spheroidal graphite has overgrown to very large nodules with a mean diameter of about
Summary
Low production cost and excellent castability make ductile cast iron (DCI) the preferred material choice when low-to-moderately stressed mechanical components of complicated shape and large dimensions must be manufactured. The formation of the austenitic shell is delayed at low cooling rates In this situation, liquid channels separate the austenitic grains and allow a longer contact time of the spherical graphite with the melt. Mourujärvi et al [40] analyzed the performance of a normalized DCI EN-GJS-800 containing different quantities of chunky graphite through rotating bending fatigue tests. We address this latter issue by investigating the crack growth resistance of a DCI produced under very slow cooling conditions, representative of the microstructural conditions arising in thick walled castings For this purpose, static tensile, fatigue and fracture mechanics tests are performed to quantify the resistance to fatigue crack initiation and propagation as well as the fracture toughness.
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