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The morphological evolution of primary austenite during isothermal coarsening
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-6339-4292
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-7527-719X
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-3024-9005
2017 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 131, p. 492-499Article in journal (Refereed) Published
Abstract [en]

The morphological evolution of primary austenite in an industrial hypoeutectic lamellar cast iron was studied under isothermal conditions for coarsening times varying from 0 min to 96 h. The dendritic austenite structure formed during the primary solidification suffered major morphological changes during the isothermal coarsening process. After a sufficient coarsening time, dendrite fragmentation, globularization, and coalescence of austenite were studied using electron backscatter diffraction (EBSD) technique. This study confirmed that the secondary dendrite arm spacing (SDAS) is an inappropriate length scale to describe the primary austenite coarsening process for longer times. The application of shape independent quantitative parameters confirmed the reduction of the total interfacial area during microstructural coarsening. The modulus of the primary austenite, Mγ, which represents the volume-surface ratio for the austenite phase, and the spatial distribution of the austenite particles, measured as the nearest distance between the center of gravity of neighboring particles, Dγ, followed a linear relation with the cube root of coarsening time during the whole coarsening process. The mean curvature of the austenite interface, characterized through stereological relations, showed a linear relation to Mγ and Dγ, allowing the quantitative characterization and modeling of the complete coarsening process of primary austenite.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 131, p. 492-499
Keywords [en]
Dendrite fragmentation, Dendritic coarsening, EBSD, Microstructure evolution, Primary austenite, Austenite, Cast iron, Isotherms, Microstructure, Dendrite fragmentations, Electron backscatter diffraction technique, Micro-structure evolutions, Microstructural coarsening, Quantitative characterization, Secondary dendrite arm spacing, Coarsening
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-36890DOI: 10.1016/j.matchar.2017.07.030ISI: 000411535600054Scopus ID: 2-s2.0-85026387205OAI: oai:DiVA.org:hj-36890DiVA, id: diva2:1133573
Note

Included in licentiate thesis in submitted form.

Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2018-09-19Bibliographically approved
In thesis
1. Morphological characterization of primary austenite in cast iron
Open this publication in new window or tab >>Morphological characterization of primary austenite in cast iron
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Automotive industry products portfolio includes a wide variety of complex‐shaped cast iron products, such as truck engine components, that need to withstand a constant trend of higher demands, especially urged by stricter environmental regulations on emissions. Combined with this continued demand on properties improvement, cast iron industry faces a process problem related to the lack of understanding of solidification and mechanisms behind defect formation.

Casting products are highly affected by the product design and the manufacturing method itself, which governs the final microstructure and hence the final mechanical properties. Wall thickness of the moulding material strongly influences the solidification time, varying the microstructural coarseness, resulting in a component with different properties depending on the local shape of the casting.

The main objective of this work is the characterization of the primary austenite microstructure and its coarsening process, which has been poorly documented in cast iron literature, to allow the prediction and control of these microstructural features present in the casting.

The microstructural evolution of the primary austenite in hypoeutectic lamellar graphite iron (LGI) is studied under isothermal coarsening conditions. The dendritic microstructure suffered major morphological changes that included dendrite fragmentation, globularization, and coalescence. Empirical relations based on morphological parameters are introduced to predict the microstructural evolution of primary austenite. A novel technique for colour‐etching and semi‐automatic image analysis for the characterization of quenched dendritic microstructures in cast iron is presented. A new experimental technique for production of graphitic iron with varying nodularity is presented as a solution to control the production of compacted (CGI) and spheroidal graphite iron (SGI) under laboratory conditions. The nodularity evolution is controlled as a function of the holding time and the residual Mg, allowing the study of the primary solidification and primary microstructures of hypoeutectic CGI and SGI in future investigations.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2017. p. 50
Series
JTH Dissertation Series ; 23
Keywords
Lamellar Graphite Iron, Solidification, Primary Austenite, Microstructure Evolution, Dendritic coarsening, Compacted Graphite Iron, Magnesium Fading, Nodularity
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35585 (URN)9789187289248 (ISBN)
Supervisors
Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-08-16Bibliographically approved

Open Access in DiVA

The full text will be freely available from 2019-07-18 00:00
Available from 2019-07-18 00:00

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Hernando, Juan CarlosGhassemali, EhsanDiószegi, Attila

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