Trace Elements and Graphite Shape Degeneracy in Nodular Graphite Cast Irons

Lacaze, Jacques

doi:10.1007/s40962-016-0115-6

Cited by 20 publications

(11 citation statements)

References 44 publications

(31 reference statements)

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“…Based on previous observations [9] and literature review, it has already been pointed out that nuclei may have a rounded shape and be amorphous [6]. In the present study, the rounded nucleus seen in Fig.…”

Section: Discussionsupporting

confidence: 74%

Analysis of Nuclei in a Heavy-Section Nodular Iron Casting

Celis

Domengès²,

Hug

et al. 2018

MSF

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The microstructure of heavy section nodular graphite cast irons often presents a bimodal distribution of nodule size associated with so-called primary and secondary graphite nucleation. It has been found that the nuclei in both types of nodules consist mainly in magnesium sulphide. However, nuclei in primary nodules contain some traces of calcium and are thus related with the inoculation treatment. On the contrary, nuclei in secondary nodules do not contain any element that could be associated to inoculation. It is suggested they form in the late stage of the eutectic reaction as a result of microsegregation build-up in magnesium and sulphur.

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Section: Discussionsupporting

confidence: 74%

Analysis of Nuclei in a Heavy-Section Nodular Iron Casting

Celis

Domengès²,

Hug

et al. 2018

MSF

Self Cite

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“…This subject has recently thoroughly and comprehensively been reviewed, for instance, in References 21,22 and 23. In the present article, it is rather a question of treating and consolidating the subject focusing on chunky graphite. In particular, the studies 6,9,13,19,[21][22][23][24][25][26] especially contribute. Although several theories on the formation and growth of chunky graphite in SGI have been proposed, a universal, unanimously accepted explanation has not yet been established.…”

Section: Formation and Growth Of Chunky Graphitementioning

confidence: 99%

“…The used compilation of concentration limits has been elaborated by Reference 44 and complemented in Reference 59. Lacaze 22 concludes the heavier the trace element atoms are, the lower is their critical concentration limit to avoid detrimental influence on graphite shape.…”

Section: Effect Of Chemical Elementsmentioning

confidence: 99%

Chunky Graphite in Ferritic Spheroidal Graphite Cast Iron: Formation, Prevention, Characterization, Impact on Properties: An Overview

Baer

2019

Inter Metalcast

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Ferritic spheroidal graphite cast iron (SGI) materials have a remarkable technical potential and economic impact in modern industry. These features are closely related to the question of how the cast materials can be produced without structural defects and graphite degenerations such as, for example, chunky graphite. Although the chunky graphite degeneration superficially seems to be well known, its metallurgical background is still controversially discussed, appropriate field-tested nondestructive tools for its quantification in castings are lacking, and the knowledge on its impact on material properties is fairly limited. Addressing this status, the article is providing a current overview on the subject. Existing theories on formation and growth mechanisms of chunky graphite are briefly reviewed. Furthermore, from a metallurgical point of view, causes for the appearance of chunky graphite as well as preventive measures are concisely summarized. Particular attention is paid to the morphology of chunky graphite and how it can be characterized by destructive and nondestructive techniques. Special emphasis was laid on providing a comprehensive overview on the impact of chunky graphite on strength, ductility, fatigue limit, fatigue crack growth rate as well as fracture toughness of ferritic SGI materials based on experimental data. Moreover, conclusions for the assessment of castings affected by chunky graphite are drawn.

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“…5 In addition, past studies have shown that spheroidization is not only caused by the absence of sulfur, but also that the residual magnesium content in iron supports the formation of graphite spheroids during solidification furthermore. 6 If the required magnesium content is reduced due to external influences, it can lead to degeneration of graphite and therefore to the creation of flake graphite. The most common example of an external influence regarding the casting skin is the binding of magnesium at the interface between the molding material and the melt by sulfur or oxygen.…”

Section: Formation Of the Degenerated Graphite Layermentioning

confidence: 99%

Microstructural Adjustment of the Degenerated Graphite Layer in Ductile Iron for Targeted Evaluation on the Fatigue Properties

2020

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Graphite degeneration is the most prominent microstructural defect in the casting skin of ductile iron. Induced by either sulfur or oxygen contained in the molding material, its occurrence can be observed in a large range of iron castings, having substantial negative influences on the mechanical properties, especially fatigue resistance. Previous investigations predominately focused on the influence of the degenerated graphite layer, while accompanying changes of the iron matrix were neglected. The superposition of these effects hinders the evaluation of casting skin defects in state-of-the-art design of ductile iron components. The presented solution utilizes an experimental procedure, which enables the production of specimens with specific, individual microstructural configurations in the casting skin. This approach is based on the application of a modified sand core coating. By adding sulfurizing additives to the coating and adjusting its binder content and viscosity, a predominately homogeneous degenerated layer of 0.5 mm thickness was obtained. Using specific heat treatment steps assured a fully ferritic or pearlitic iron matrix, isolating the degenerated layer as the main microstructural defect. Fatigue testing of these specimens will further enable the numerical evaluation of the fatigue resistance in dependence of the casting skin microstructure.

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Trace Elements and Graphite Shape Degeneracy in Nodular Graphite Cast Irons

Cited by 20 publications

References 44 publications

Analysis of Nuclei in a Heavy-Section Nodular Iron Casting

Analysis of Nuclei in a Heavy-Section Nodular Iron Casting

Chunky Graphite in Ferritic Spheroidal Graphite Cast Iron: Formation, Prevention, Characterization, Impact on Properties: An Overview

Microstructural Adjustment of the Degenerated Graphite Layer in Ductile Iron for Targeted Evaluation on the Fatigue Properties

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