On the crystallization of graphite from liquid iron–carbon–silicon melts

Stefanescu, Doru M.; Alonso, G.; Larrañaga, P.; Fuente, E. de la; Súarez, Ramón

doi:10.1016/j.actamat.2016.01.047

Cited by 74 publications

(80 citation statements)

References 19 publications

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“…The boundaries of particular radial sectors were observed on the surface of the graphite spheroid exposed after the pure G/M debonding (Figure a,b). Similar features were also detected in Qing, Richards, and van Aken (), Stefanescu, Alonso, Larranaga, de la Fuente, and Suarez (), and Theuwissen, Lacaze, and Laffont (). In the equatorial area, some traces of the superficial destruction of the spheroid structure in the form of parallel shifted graphene layers, were revealed in the radial sectors (Figure c,d).…”

Section: Resultssupporting

confidence: 70%

Microscopic approach to micromechanism of damage in spheroidal cast iron

Warmuzek

Polkowska

Gazda

2020

Microscopy Res & Technique

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In this work, the observations of the fracture surface after standard tensile tests of several kinds of spheroidal cast irons, ferritic and austempered ductile irons, have been carried out by means of scanning electron microscopy. The local crack path in the area of graphite (G)/matrix (M) interface has been analyzed as affected by a matrix phase composition and the austempering treatment parameters. The obtained results allowed identifying some determination factors for debonding mode at the G/M interface and their role in a final damage mechanism. Some microstructural details in the microregions composed of graphite and matrix showed that the G-M debonding mode in the separation area of the G/M interface seems to be controlled by macroscopic properties of the alloy and by the morphology of G/M interface. On the other hand, the internal destruction of graphite nodule has been mainly determined by a structure and anisotropy of graphite crystal lattice. K E Y W O R D S characterization, electron microscopy, fracture behavior, iron alloys

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Section: Resultssupporting

confidence: 70%

Microscopic approach to micromechanism of damage in spheroidal cast iron

Warmuzek

Polkowska

Gazda

2020

Microscopy Res & Technique

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“…To explain spheroidal growth, Amini and Abbaschian suggested a roughening transition at the graphite liquid interface which would have no reason for giving sectors as observed. Stefanescu et al [13] proposed graphite spheroids build-up as so-called tad-pole dendrites. These dendrites emanate from the centre of the spheroids and are made of plate-like growth blocks stack upon each other, though not filling the space as does graphite in spheroids.…”

Section: Introductionmentioning

confidence: 99%

A 2-D nucleation-growth model of spheroidal graphite

2017

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a b s t r a c tAnalysis of recent experimental investigations, in particular by transmission electron microscopy, suggests spheroidal graphite grows by 2-D nucleation of new graphite layers at the outer surface of the nodules. These layers spread over the surface along the prismatic direction of graphite which is the energetically preferred growth direction of graphite when the apparent growth direction of the nodules is along the basal direction of graphite. 2-D nucleation-growth models first developed for precipitation of pure substances are then adapted to graphite growth from the liquid in spheroidal graphite cast irons. Lateral extension of the new graphite layers is controlled by carbon diffusion in the liquid. This allows describing quantitatively previous experimental results giving strong support to this approach. IntroductionGraphite spheroids in spheroidal graphite cast iron are known to consist of piling up of graphite layers having their c axis oriented parallel to the spheroid radius. To accommodate for the change in orientation in the tangential direction, the spheroids appear to be divided in adjacent sectors which are easily observed by optical microscopy as illustrated in Fig. 1. The change in orientation of the c axis at the boundary between two sectors may amount from 10 to several tens of degrees, while the orientation changes within sectors are more limited [1,2].It has long been recognized that graphite layers within spheroids are arranged in growth blocks which are elongated along the prismatic a direction of the graphite structure [3]. This would imply that graphite grows along the prismatic (tangential) direction during spheroidal growth even though the overall (apparent) growth direction is the radial one. Two types of models have been suggested in the past to account for this tangential growth: i) those based on screw dislocations [4] or cone-helix growth [5e7]; and ii) those based on the continuous growth of a graphite layer folding around the spheroid [8,9]. In the first type, tangential growth proceeds around screw dislocations or cones emanating from the spheroid's centre (Fig. 2-a), giving features that would agree with the observation of sectors. However, transmission electron microscopy (TEM) observations have shown that the orientation of the c axis along a sector tilts at random and in either ways [10] which implies that continuous growth around a screw dislocation did not occur. The second type of models (Fig. 2-b) would hardly explain the formation of sectors as already stressed by Gruzleski [9]. However, a slight modification where nucleation of new layers proceeds at the step between two neighbouring sectors which was suggested by Double and Hellawell [11] would (Fig. 2-c).There has been a renewed interest these last years for investigating the growth mechanism of spheroidal graphite [12e14]. Qing et al. [14] report observation of defects and dislocations in graphite, but do not seem to have observed long range ordered arrangements of these defects that would support the ...

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“…The precise graphite particle form is strongly influenced by interface energy and by modification of growth sites due to adsorption of active elements (e.g., S, O, N) at the growth front of the precipitating particles . Graphite inclusions strongly influence the mechanical properties, specifically there is an inverse correlation between the graphite content and the strength of gray cast iron.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, for form I (lamellar graphite), five different distributions, named A to E and eight size classes are designated by Arabic numbers that range from the mm‐scale down to the sub‐μm scale. The most common distributions of lamellar graphite are coarse lamellar type A or arrangements type D and E. Type E is a very fine distribution of graphite within the interdendritic spaces of the ferrite dendrite, and it is often referred to as undercooled graphite …”

Section: Introductionmentioning

confidence: 99%

Foams of Gray Cast Iron as Efficient Energy Absorption Structures: A Feasibility Study

et al. 2019

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Gray cast iron foams are produced using a reticulated polyurethane by using a modified investment casting process. To evaluate the attributes of the produced micro-geometries, foam segments and single struts are investigated by light and electron microscopy in 2D, and synchrotron micro-computed tomography in 3D. Mechanical properties are determined by macro/micromechanical testing and nanoindentation. In the microstructure of the gray cast iron struts, both flake-like coarse type A and locally fine undercooled type D graphite particles are observed. The distribution of the two graphite types is heterogeneous and is the likely cause for the large scatter of the mechanical properties of the single struts. The high graphite content and the resulting brittle behavior of the struts lead to strong serrations in the stressstrain curve of the foams with a negative effect on energy absorption. We found a relatively low energy absorption efficiency of below 50% as compared to 75% in 316L austenitic steel struts. The small specimen size results in scale effects which strongly influence the mechanical properties of the foams. Further improvement in the fabrication of gray cast iron foams is needed to tailor graphite distributions and optimize performance of cast iron-based foams.

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On the crystallization of graphite from liquid iron–carbon–silicon melts

Cited by 74 publications

References 19 publications

Microscopic approach to micromechanism of damage in spheroidal cast iron

Microscopic approach to micromechanism of damage in spheroidal cast iron

A 2-D nucleation-growth model of spheroidal graphite

Foams of Gray Cast Iron as Efficient Energy Absorption Structures: A Feasibility Study

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