Morphologies of Some Graphites in Ductile Cast Irons

Hara, Takamichi; Kitagawa, Takahiro; Kuroki, Kenta; Saikawa, Seiji; Terayama, Kiyoshi; Ikeno, Susumu; Matsuda, Kenji

doi:10.2320/matertrans.m2014167

Cited by 26 publications

(12 citation statements)

References 8 publications

(4 reference statements)

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“…The SAED patterns in the inner zone are oblong which indicates that graphite got deformed during the casting process. Similar oblong rings to those reported here may be seen in the work by Hara et al [28] The most probable cause for this is when the liquid around the graphite nodules solidified in the metastable system as this is related to a contraction of about 4 to 5 pct. [29] Such a contraction leads to graphite nodules being stressed in compression.…”

Section: Discussionsupporting

confidence: 88%

An Electron Microscopy Study of Graphite Growth in Nodular Cast Irons

Laffont

Jday

Lacaze

2018

Metall Mater Trans A

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Growth of graphite during solidification and high-temperature solid-state transformation has been investigated in samples cut out from a thin-wall casting which solidified partly in the stable (iron-graphite) and partly in the metastable (iron-cementite) systems. Transmission electron microscopy has been used to characterize graphite nodules in as-cast state and in samples having been fully graphitized at various temperatures in the austenite field. Nodules in the as-cast material show a twofold structure characterized by an inner zone where graphite is disoriented and an outer zone where it is well crystallized. In heat-treated samples, graphite nodules consist of well-crystallized sectors radiating from the nucleus. These observations suggest that the disoriented zone appears because of mechanical deformation when the liquid contracts during its solidification in the metastable system. During heat-treatment, the graphite in this zone recrystallizes. In turn, it can be concluded that nodular graphite growth mechanism is the same during solidification and solid-state transformation.

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Section: Discussionsupporting

confidence: 88%

An Electron Microscopy Study of Graphite Growth in Nodular Cast Irons

Laffont

Jday

Lacaze

2018

Metall Mater Trans A

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“…This confirm early TEM work on lamellar graphite [24]. More recent TEM work by Hara et al [25] also concluded that the internal structure of flake graphite consisted of thin layers of graphite platelets arranged in a "mosaic-like" structure, which is the tiled-roof configuration.…”

Section: Graphite Produced Through Liquid-solid Transformationsupporting

confidence: 85%

“…Randomly orientated graphite, with a hexagonal rather than rhombohedral structure, is located in the interplatelet areas. Hara et al [25] concluded that SG has a three-fold internal structure, with and amorphous central region, annular rings of a layered intermediate region, and a mosaic-like (tiled-roof) outer region made of large polygonal crystalline platelets. Recent TEM work by Theuwissen et al [31], argues that both flake and spheroidal graphite consist of blocks stacked upon each other that grow mainly by a 2D nucleation mechanism.…”

Section: Graphite Produced Through Liquid-solid Transformationmentioning

confidence: 99%

Reassessment of Crystal Growth Theory of Graphite in Cast Iron

Stefanescu

Alonso

Larrañaga

et al. 2018

MSF

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The problem of graphite crystallization and growth in cast iron has recently received increased attention. As most of the published literature describe analysis of room temperature graphite, there is a legitimate concern that the crystallization of graphite is concealed by recrystallization and growth in solid state occurring after solidification. To avoid confusion in the interpretation of room temperature graphite morphology, the authors used Field Emission Gun SEM on deep-etched interrupted solidification (quenched) specimens to reveal the morphology of graphite at the very beginning of solidification, when the graphite is in contact with the liquid. Information from related phenomena, such as crystallization of hexagonal structure snowflakes and metamorphic graphite, as well as of diamond cubic structure silicon crystals in aluminum alloys is incorporated in the analysis. Research discussing graphite produced through gas-solid and solid-solid transformations is also examined. Because the faceted growth of graphite is the result of diffusion-limited crystal growth in the presence of anisotropic surface energy and anisotropic attachment kinetics, a variety of solidification morphologies are found. The basic building blocks of the graphite aggregates are hexagonal faceted graphite platelets generated through the growth of graphene layers. As solidification advances, the platelets thicken through layer growth, and then aggregate through mechanisms that may include foliated/tiled-roof crystals and dendrites, curved-circumferential, cone-helix, helical, and columnar or conical sectors growth.

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“…However, the problem of producing vermicular cast iron is difficult to control the vermicular graphite ratio. During the production process, in order to avoid a lot of flake graphite arising from lack modification and too much nodular graphite due to excessive modification, 3) there is a need to quickly and accurately detect the vermicular graphite ratio, and thus adjust the quantity of the vermicular agent in time.…”

Section: Introductionmentioning

confidence: 99%

Influence Factors for the Determination of Vermicular Graphite Ratio in Cast Iron Measured by Ultrasonic Method

et al. 2018

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The ultrasonic method was used to detect vermicular graphite ratio according to the relationship between them. However, there is little report how the factors affect the vermicular graphite ratio detection and ultrasonic velocity measurement. In this paper, using ECHOMETER1076 ultrasonic tester, stylus surface roughness tester and quantitative metallography, the influences of sample two-plane parallelism, probe incident angle, coupling agent type, surface roughness and matrix on the ultrasonic velocity were further studied by experiments and simulation. The parallelism and probe incident angle were found to have important influence on the ultrasonic velocity, increasing more than 4.58 m/s every 0.1°. Contrarily, the influence of coupling agent, surface roughness less than 5 and pearlite percentage were little, and even neglected. So, the parallelism and probe incident angle must be kept as small as possible and the surface roughness is not more than 5. This provide a basis for accurately measuring the ultrasonic velocity and predicting the vermiculate graphite ratio.

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Morphologies of Some Graphites in Ductile Cast Irons

Cited by 26 publications

References 8 publications

An Electron Microscopy Study of Graphite Growth in Nodular Cast Irons

An Electron Microscopy Study of Graphite Growth in Nodular Cast Irons

Reassessment of Crystal Growth Theory of Graphite in Cast Iron

Influence Factors for the Determination of Vermicular Graphite Ratio in Cast Iron Measured by Ultrasonic Method

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