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Morphological characterization of primary austenite in cast iron
Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0002-6339-4292
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. , 50 p.
Series
JTH Dissertation Series, 23
Keyword [en]
Lamellar Graphite Iron, Solidification, Primary Austenite, Microstructure Evolution, Dendritic coarsening, Compacted Graphite Iron, Magnesium Fading, Nodularity
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-35585ISBN: 9789187289248 OAI: oai:DiVA.org:hj-35585DiVA: diva2:1097238
Supervisors
Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-08-16Bibliographically approved
List of papers
1. An overview of isothermal coarsening in hypoeutectic lamellar cast iron
Open this publication in new window or tab >>An overview of isothermal coarsening in hypoeutectic lamellar cast iron
2015 (English)In: Advances in the science and engineering of casting solidification: An MPMD symposium honoring Doru Michael Stefanescu / [ed] Laurentiu Nastac, Baicheng Liu, Hasse Fredriksson, Jacques Lacaze, Chun-Pyo Hong, Adrian Catalina, Andreas Buhrig-Polaczek, Daan M. Maijer, Charles Andrew Monroe, Adrian Sabau, Roxana Ruxanda, Alan A. Luo, Subhayu Sen, Attila Diószegi, Hoboken, New Jersey: John Wiley & Sons, 2015, 295-302 p.Conference paper, Published paper (Refereed)
Abstract [en]

A complete qualitative characterization of the isothermal coarsening process in hypoeutectic lamellar cast iron is presented for the first time in this work. Interrupted solidification experiments were used to study the evolution of the dendritic austenite network under long term isothermal conditions. Cylindrical samples were re-melted and isothermally coarsened for times from 2 minutes to 6 days at 1175°C after dendritic coherence was reached. Micrographs from horizontal and vertical sections of the coarsened samples are presented. Complete fragmentation of the dendrite network and further rearrangement of the solid phase are reported as new behaviors in the coarsening process in lamellar cast iron. A linear increase in secondary dendrite arm spacing in agreement with the literature is observed in the first several samples confirming qualitative observations. A new model is proposed which describes the entire coarsening process observed in this investigation.

Place, publisher, year, edition, pages
Hoboken, New Jersey: John Wiley & Sons, 2015
Keyword
Lamellar Cast Iron; Coarsening; Ripening; Dendrite Morphology; Solidification
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-27639 (URN)10.1002/9781119093367.ch35 (DOI)2-s2.0-84931418627 (Scopus ID)9781119082385 (ISBN)9781119093367 (ISBN)
External cooperation:
Conference
The honorary symposium "Advances in the Science and Engineering of Casting Solidification" (TMS2015, Orlando, Florida, March 15-19, 2015) held in honor of Professor Doru Michael Stefanescu, Emeritus Professor, Ohio State University and the University of Alabama, USA.
Available from: 2015-07-28 Created: 2015-07-28 Last updated: 2017-05-22Bibliographically approved
2. The morphological evolution of primary austenite during isothermal coarsening
Open this publication in new window or tab >>The morphological evolution of primary austenite during isothermal coarsening
2017 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 131, 492-499 p.Article 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
Keyword
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:nbn:se:hj:diva-36890 (URN)10.1016/j.matchar.2017.07.030 (DOI)XYZ ()2-s2.0-85026387205 (Scopus ID)
Note

Included in licentiate thesis in submitted form.

Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-08-16Bibliographically approved
3. Quantification of dendritic austenite after interrupted solidification in a hypoeutectic lamellar graphite iron
Open this publication in new window or tab >>Quantification of dendritic austenite after interrupted solidification in a hypoeutectic lamellar graphite iron
2016 (English)In: Metallography, Microstructure, and Analysis, ISSN 2192-9270, Vol. 5, no 1, 28-42 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an unconventional etching technique to reveal the microstructure in a hypoeutectic lamellar graphite iron that has been quenched after isothermal heat treatment in the proeutectic semi-solid temperature region. A technique for quantifying the dendrite microstructure using the aforementioned etching technique involving a combination of a raster graphics editor and an image analysis software is outlined. The agreement between this quantification technique with regard to volume fraction and surface area per unit volume of the dendritic austenite and corresponding point counting and line intercept techniques is analyzed. The etching technique was found useful but sporadic tinting of martensite was problematic. Some measurements showed significant systematic disagreement which correlated with the coarseness of the measured dendrites. Most systematic disagreement is attributed to difficulties in defining the dendrite boundary in the analogues and much of the random disagreement to easily identified discrepancies between the analogue and the micrograph.

Place, publisher, year, edition, pages
New York: Springer, 2016
Keyword
Cast iron, Quantitative metallography, Color metallography, Microstructure
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-28880 (URN)10.1007/s13632-015-0250-0 (DOI)000377604200007 ()2-s2.0-84960404906 (Scopus ID)
Projects
Spofic II
Funder
VINNOVA, 2013-04720
Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2017-07-03Bibliographically approved
4. Influence of Ti and Mo additions on the isothermal coarsening process of primary austenite in Lamellar Graphite Iron
Open this publication in new window or tab >>Influence of Ti and Mo additions on the isothermal coarsening process of primary austenite in Lamellar Graphite Iron
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35581 (URN)
Note

Abstract accepted for presentation at the 5th Decennial International Conference on Solidification Processing, Old Windsor, UK, 25th‐28th July 2017.

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-05-22
5. New experimental technique for nodularity and Mg fading control in compacted graphite iron production on laboratory scale
Open this publication in new window or tab >>New experimental technique for nodularity and Mg fading control in compacted graphite iron production on laboratory scale
Show others...
2017 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940Article in journal (Refereed) Epub ahead of print
Abstract [en]

The narrow production window for compacted graphite iron material (CGI) drastically reduces the possibilities to produce it in small batches outside an industrial environment. This fact hinders laboratory-scale investigations on CGI solidification. This work presents a solution to that issue by introducing an experimental technique to produce graphitic cast iron of the main three families. Samples of a base hypereutectic spheroidal graphite iron (SGI) were re-melted in a resistance furnace under Ar atmosphere. Varying the holding time at 1723 K (1450 °C), graphitic irons ranging from spheroidal to lamellar were produced. Characterization of the graphite morphology evolution, in terms of nodularity as a function of holding time, is presented. The nodularity decay for the SGI region suggests a linear correlation with the holding time. In the CGI region, nodularity deterioration shows a slower rate, concluding with the sudden appearance of lamellar graphite. The fading process of magnesium, showing agreement with previous researchers, is described by means of empirical relations as a function of holding time and nodularity. The results on nodularity fade and number of nodules per unit area fade suggest that both phenomena occur simultaneously during the fading process of magnesium.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35584 (URN)10.1007/s11661-017-4315-3 (DOI)
Note

Included in licentiate thesis in submitted manuscript version with title "New experimental technique for nodularity and Mg fading control in CGI production on laboratory scale".

Available from: 2017-09-15 Created: 2017-05-22 Last updated: 2017-09-15

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