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Hernando, Juan CarlosORCID iD iconorcid.org/0000-0002-6339-4292
Publications (10 of 13) Show all publications
Xu, C. L., Andriollo, T., Zhang, Y. B., Hernando, J. C., Hattel, J. & Tiedje, N. (2020). Micromechanical impact of solidification regions in ductile iron revealed via a 3D strain partitioning analysis method. Scripta Materialia, 178, 463-467
Open this publication in new window or tab >>Micromechanical impact of solidification regions in ductile iron revealed via a 3D strain partitioning analysis method
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2020 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 178, p. 463-467Article in journal (Refereed) Published
Abstract [en]

Strain partitioning between first-to-solidify (FTS) and last-to-solidify (LTS) regions upon tensile loading of ductile iron was investigated by combining in-situ X-ray tomography with digital volume correlation and postmortem metallographic examinations. The results indicate that the plastic shear bands form mainly by linking graphite particles contained in the same FTS region. A special distance function is introduced to show that this is due to the lower strength of the FTS regions compared to the LTS regions, but also to the higher stress concentration associated with the particles. The methodology is general and therefore extendable to material systems containing similar microstructural heterogeneities.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Cast iron, Digital volume correlation, Micromechanics, Solidification microstructure, Strain distribution, Ductility, Solidification, Strain measurement, Digital volume correlations, Distance functions, Graphite particles, Metallographic examination, Microstructural heterogeneity, Solidification microstructures, Strain distributions, Strain partitioning
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-47215 (URN)10.1016/j.scriptamat.2019.12.018 (DOI)000510947200093 ()2-s2.0-85076825424 (Scopus ID)PP JTH 2020 embargo 24;JTHMaterialIS (Local ID)PP JTH 2020 embargo 24;JTHMaterialIS (Archive number)PP JTH 2020 embargo 24;JTHMaterialIS (OAI)
Available from: 2020-01-02 Created: 2020-01-02 Last updated: 2020-02-20Bibliographically approved
Hernando, J. C., Elfsberg, J., Ghassemali, E., Dahle, A. & Diószegi, A. (2020). The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys. International Journal of metalcasting
Open this publication in new window or tab >>The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys
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2020 (English)In: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193Article in journal (Refereed) Epub ahead of print
Abstract [en]

This work investigates the role of primary austenite morphology on the eutectic and eutectoid microstructures and the ultimate tensile strength (UTS) in a hypoeutectic compacted graphite iron (CGI) alloy. The morphology of primary austenite is modified by isothermal coarsening experiments in which holding times up to 60 min are applied to the solid–liquid region after coherency. The cooling conditions for the subsequent eutectic and eutectoid reactions are similar. Miniaturized tensile tests are performed to evaluate the UTS. The morphological characteristics related to the surface area of primary austenite, the modulus of primary austenite, Mγ, and the hydraulic diameter of the interdendritic region, DHydID, increase with the cube root of coarsening time. The eutectic and eutectoid microstructures are not significantly affected by the morphology of primary austenite, thus indicating that the morphology of the interdendritic regions does not control the nucleation frequency and growth of eutectic cells or graphite. UTS decreases linearly with the increasing coarseness of primary austenite for similar eutectic and eutectoid microstructures, demonstrating the strong influence of primary austenite morphology on the UTS in hypoeutectic CGI alloys.

Place, publisher, year, edition, pages
Springer, 2020
Keywords
cast iron, compacted graphite iron, CGI, solidification, dendrites, primary austenite, UTS
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-47569 (URN)10.1007/s40962-020-00410-9 (DOI)2-s2.0-85078435803 (Scopus ID)
Funder
Vinnova, 2013-03303Knowledge Foundation, 2018-0033
Note

This paper is an invited submission to IJMC selected from presentations at the 2nd Carl Loper 2019 Cast Iron Symposium held September 30 to October 1, 2019, in Bilbao, Spain.

Available from: 2020-01-28 Created: 2020-01-28 Last updated: 2020-02-05
Hernando, J. C., Elfsberg, J., Dahle, A. & Diószegi, A. (2019). Evolution of primary austenite and its influence on eutectic microstructures during coarsening of Fe-C-Si alloys. Materialia, 7, Article ID 100391.
Open this publication in new window or tab >>Evolution of primary austenite and its influence on eutectic microstructures during coarsening of Fe-C-Si alloys
2019 (English)In: Materialia, ISSN 2589-1529, Vol. 7, article id 100391Article in journal (Refereed) Published
Abstract [en]

The evolution of primary austenite morphology during isothermal coarsening has been studied in the three main Fe–C–Si alloys used in industry, LGI, CGI, and SGI. The dendritic microstructure increases length scale during coarsening accompanied by fragmentation and coalescence of austenite crystals. The morphological parameters, SDAS, Mγ, DhydID, and Dγ show a linear relation with the cube root of coarsening time, t1/3, with similar rates for the three different Fe–C–Si alloys. The eutectic microstructures after coarsening of primary austenite in CGI and SGI alloys are not significantly affected by the surface area of primary austenite and the size of the interdendritic regions. Fraction, nodularity, shape distribution of graphite particles and the number of nodules and eutectic cells are similar when studied as a function of coarsening time. These results suggest that the nucleation frequency in CGI and SGI, and the growth of eutectic microstructures in CGI, are not significantly influenced by the morphology of primary austenite.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Solidification; Coarsening; Dendrites; Austenite; Eutectic; EBSD; CGI; SGI
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-43552 (URN)10.1016/j.mtla.2019.100391 (DOI)2-s2.0-85068795536 (Scopus ID)PP JTH 2019 embargo 24 (Local ID)PP JTH 2019 embargo 24 (Archive number)PP JTH 2019 embargo 24 (OAI)
Funder
VinnovaKnowledge Foundation
Note

Included in thesis in manuscript form with the title "Evolution of primary austenite and its influence on eutectic microstructures during coarsening of Fe-C-Si alloys".

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-02Bibliographically approved
Ghassemali, E., Hernando, J. C., Stefanescu, D. M., Diószegi, A., Jarfors, A. E. .., Dluhoš, J. & Petrenec, M. (2019). Revisiting the graphite nodule in ductile iron. Scripta Materialia, 161, 66-69
Open this publication in new window or tab >>Revisiting the graphite nodule in ductile iron
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2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 161, p. 66-69Article in journal (Refereed) Published
Abstract [en]

The growth mechanism of graphite nodules in ductile iron was experimentally investigated using high-resolution 3D tomography of an individual graphite nodule in a near-eutectic ductile iron. The dual beam scanning electron microscopy (FIB-SEM) technique was used for this purpose. Iron particles elongated in the radial direction were observed inside a graphite nodule. Some micro-voids were detected inside the nodule, mostly located at the end of the iron particles. These observations were compared with established theories about the growth of graphite nodules and iron entrapment/engulfment in between the graphite sectors during solidification of ductile iron. 

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
3D reconstruction, FIB, Growth mechanism, Solidification, Ductility, Graphite, Iron, Scanning electron microscopy, 3-d tomographies, Graphite nodules, Growth mechanisms, High resolution, Iron Particles, Micro voids, Radial direction, Cast iron
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-41986 (URN)10.1016/j.scriptamat.2018.10.018 (DOI)000450375500015 ()2-s2.0-85055115924 (Scopus ID);JTHMaterialIS (Local ID);JTHMaterialIS (Archive number);JTHMaterialIS (OAI)
Available from: 2018-11-07 Created: 2018-11-07 Last updated: 2020-01-20Bibliographically approved
Hernando, J. C., Elfsberg, J., Ghassemali, E., Dahle, A. & Diószegi, A. (2019). The effect of coarsening of primary austenite on the ultimate tensile strength of hypoeutectic compacted graphite Fe-C-Si alloys. Scripta Materialia, 168, 33-37
Open this publication in new window or tab >>The effect of coarsening of primary austenite on the ultimate tensile strength of hypoeutectic compacted graphite Fe-C-Si alloys
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2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 168, p. 33-37Article in journal (Refereed) Published
Abstract [en]

The effect of primary austenite morphology on the ultimate tensile strength (UTS) of hypoeutectic compacted graphite Fe-C-Si alloys (CGI) is studied by isothermal coarsening experiments. Secondary dendrite arm spacing (SDAS) and the morphological characteristics related to the surface area of primary austenite, M γ and D ID Hyd , increase with the cube root of coarsening time. UTS decreases linearly with increasing coarseness of primary austenite. The eutectic and eutectoid microstructures are unaffected by the primary austenite morphology. These observations demonstrate the strong influence of primary austenite morphology on the mechanical properties of hypoeutectic CGI alloys.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Coarsening, Compacted graphite iron, Dendrites, Mechanical properties, UTS, Austenite, Dendrites (metallography), Graphite, Morphology, Ostwald ripening, Silicon alloys, Tensile strength, Morphological characteristic, Primary austenite, Secondary dendrite arm spacing, Si alloys, Surface area, Ultimate tensile strength, Iron alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-43550 (URN)10.1016/j.scriptamat.2019.04.010 (DOI)000470798400008 ()2-s2.0-85064563538 (Scopus ID)PP JTH 2019 embargo 24 (Local ID)PP JTH 2019 embargo 24 (Archive number)PP JTH 2019 embargo 24 (OAI)
Funder
Vinnova, 2013-03303; 2013-04720Knowledge Foundation, 2018-0033
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-08-06Bibliographically approved
Hernando, J. C. (2019). The role of primary austenite morphology in cast iron. (Doctoral dissertation). Jönköping: Jönköping University, School of Engineering
Open this publication in new window or tab >>The role of primary austenite morphology in cast iron
2019 (English)Doctoral 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. Urged by strict environmental regulations on emissions, these components constantly need to combine higher demands on performance with lighter designs. As a result, cast iron industry continuously faces new challenges related to solidification of new alloys, component designs and casting processes.

Complex shapes, variations in the thickness of the casting and the molding material strongly influence the solidification time for a component, thus varying its microstructural coarseness and hence showing different properties depending on the local shape of the casting.

This work increases our understanding of the morphological evolution of primary austenite occurring during isothermal coarsening at the semi-solid state. New experimental techniques have been developed to show that primary austenite coarsens according to the Ostwald ripening model in lamellar (LGI), compacted (CGI)and spheroidal (SGI) graphite iron. Significant morphological changes occur after long coarsening times, including dendrite fragmentation and coalescence. The quantitative characterization of the morphological changes during coarsening is accurately described by morphological parameters, i.e., Mγ, DIDHyd and DγNN.

Subsequently, the impact of primary austenite morphology on the eutectic microstructures in CGI and SGI has been investigated. It was observed that the eutectic microstructures are not significantly affected by the surface area of primary austenite and the size of the interdendritic regions. Fraction, nodularity, shape distribution of graphite particles and the number of nodules and eutectic cells are similar as a function of coarsening time. These results suggest that the nucleation frequency and growth of eutectic microstructures are not significantly influenced by the morphology of primary austenite.

Furthermore, miniaturized tensile tests demonstrated that the UTS in CGI is directly related to the primary austenite morphology. The UTS decreases with the increasing coarseness of primary austenite, showing an inverse linear relation to Mγ, DIDHyd and DγNN. These results demonstrate the strong impact of primary austenite morphology on UTS when the eutectic and eutectoid microstructures are similar, emphasizing the importance of incorporating the morphology of primary austenite in our models.

Abstract [sv]

Fordonsindustrins produktportfölj innehåller en mängd olika gjutjärnskomponenter med komplicerad geometri, exempelvis komponenter till lastbilsmotorer. Skärpt lagstiftning beträffande olika miljöpåverkande utsläpp har höjt kraven på sådana komponenter vad gäller både mekaniska egenskaper och vikt. Gjutjärnsgjuterierna måste ständigt hantera nya utmaningar beträffande stelning av ny legeringar, komponentkonstruktion och gjutprocesser.

Den lokala stelningstiden kommer att variera med varierande tjocklek på såväl gjutstycke som formmaterial vilket ger stora variationer i mikrostrukturens grovlek. Denna mikrostrukturvariation leder till väsentliga skillnader i mekaniska egenskaper inom ett gjutstycke med komplex geometri.

I detta arbete studeras hur den primära austenitens morfologi förändras under så kallad isoterm förgrovning i gjutjärn i delvis stelnat tillstånd. Nyutvecklade experimentella metoder har använts för att visa att austeniten i gjutjärn med lamellärgrafit (LGI), vermikulär/kompakt grafit (CGI) samt sfärisk grafit (SGI) förgrovas i enlighet med Ostwalds modell för förgrovning. Austenitmorfologin förändras högstavsevärt efter långa hålltider vid relevanta temperaturer för förgrovning, även genom dendritfragmentering och koalescens. Morfologiförändringarna kankvantifieras tämligen väl med morfologiparametrarna Mγ, DIDHyd och DγNN.

Vidare har den primära austenitens påverkan på den eutektiska mikrostrukturen i CGI och SGI studerats. En observation var att den eutektiska mikrostrukturen inte påverkas av ytarean av den primära austeniten eller av storleken av de interdendritiska områdena. Fraktionen grafit, nodulariteten, grafitens formfördelning, antalet noduler samt antalet eutektiska celler påverkas på likartat sätt av förgrovningsprocessen. Detta antyder att kärnbildningsfrekvensen och tillväxten av eutektisk struktur inte påverkas i någon större utsträckning av den primära austenitens morfologi.

Dragprovning av stavar i miniatyrformat visade att dragbrottgränsen (UTS) hos CGI är direkt beroende av den primära austenitens morfologi. UTS är linjärt avtagande med ökande Mγ, DIDHyd och DγNN vilket visar att den primära austenitens morfologi har en stark påverkan på gjutjärns mekaniska egenskaper. Alltså bör de modeller som används för att prediktera gjutjärns egenskaper innehålla den primära austenitens morfologi.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2019. p. 74
Series
JTH Dissertation Series ; 040
Keywords
Solidification, Cast Iron, Primary Austenite, Microstructure Evolution, Coarsening, LGI, CGI, SGI, UTS, stelning, gjutjärn, primär austenit, mikrostrukturbildning, förgrovning, LGI, CGI, SGI, UTS
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-43553 (URN)978-91-87289-42-2 (ISBN)
Public defence
2019-05-21, E1405, School of Engineering, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-04-29Bibliographically approved
Hernando, J. C. (2018). Artistic Entries from the 2017 International Metallographic Contest. Metallography, Microstructure, and Analysis, 7(1), 91-92
Open this publication in new window or tab >>Artistic Entries from the 2017 International Metallographic Contest
2018 (English)In: Metallography, Microstructure, and Analysis, ISSN 2192-9262, Vol. 7, no 1, p. 91-92Article in journal (Other (popular science, discussion, etc.)) Published
Place, publisher, year, edition, pages
Springer, 2018
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-38730 (URN)10.1007/s13632-017-0417-y (DOI)
Note

"Showcasing the best work of metallographers and microstructural analysts from all around the world, the International Metallographic Contest is an important venue for recognizing the technical achievements of the metallographic community."

Available from: 2018-02-02 Created: 2018-02-02 Last updated: 2019-02-14Bibliographically approved
Hernando, J. C. & Diószegi, A. (2018). On the primary solidification of compacted graphite iron: Microstructure evolution during isothermal coarsening. Materials Science Forum, 925, 90-97
Open this publication in new window or tab >>On the primary solidification of compacted graphite iron: Microstructure evolution during isothermal coarsening
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 925, p. 90-97Article in journal (Refereed) Published
Abstract [en]

It is widely accepted that in most commercial hypoeutectic alloys, both static mechanicalproperties and feeding characteristics during solidification, are extremely linked to the coarseness ofthe primary phase. It is therefore of critical importance to provide tools to control and predict thecoarsening process of the dendritic phase present in hypoeutectic melts. The characterization of theprimary phase, a product of the primary solidification, has traditionally been neglected whencompared to the eutectic solidification characterization in cast iron investigations. This workpresents the morphological evolution of the primary austenite present in a hypoeutectic compactedgraphite cast iron (CGI) under isothermal conditions. To that purpose, a base spheroidal graphitecast iron (SGI) material with high Mg content is re-melted in a controlled atmosphere and reversedinto a CGI melt by controlling the Mg fading. An experimental isothermal profile is applied to thesolidification process of the experimental alloy to promote an isothermal coarsening process of theprimary austenite dendrite network during solid and liquid coexistence. Through interruptedsolidification experiments, the primary austenite is preserved and observed at room temperature. Byapplication of stereological relations, the primary phase and its isothermal coarsening process arecharacterized as a function of the coarsening time applied. The microstructural evolution observedin the primary austenite in CGI and the measured morphological parameters show a similar trend tothat observed for lamellar graphite cast iron (LGI) in previous investigations. The modulus of theprimary austenite, Mγ, and the nearest distance between the centre of gravity of neighbouringaustenite particles, Dγ, followed a linear relation with the cube root of coarsening time.

Place, publisher, year, edition, pages
Trans Tech Publications, 2018
Keywords
Primary austenite, Microstructure evolution, Dendritic coarsening, Compacted Graphite Iron, CGI
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-40548 (URN)10.4028/www.scientific.net/MSF.925.90 (DOI)XYZ ()2-s2.0-85050029582 (Scopus ID)
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2019-04-29Bibliographically approved
Domeij, B., Hernando, J. C. & Diószegi, A. (2018). Size distribution of graphite nodules in hypereutectic cast irons of varying nodularity. Metallurgical and materials transactions. B, process metallurgy and materials processing science, 49(5), 2487-2504
Open this publication in new window or tab >>Size distribution of graphite nodules in hypereutectic cast irons of varying nodularity
2018 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 49, no 5, p. 2487-2504Article in journal (Refereed) Published
Abstract [en]

An SGI was machined into 400 g cylindrical pieces and remelted in an electrical resistance furnace protected by Ar gas to produce materials ranging from SGI to CGI. The graphite morphology was controlled by varying the holding time at 1723 K (1450 °C) between 10 and 60 minutes. The discrete sectional size distribution of nodules by number density was measured on cross sections of the specimens and translated to volumetric distribution by volume fraction. Subpopulations of nodules were distinguished by fitting Gaussian distribution functions to the measured distribution. Primary and eutectic graphite, were found to account for most of the volume of nodular graphite in all cases. For holding times of 40 minutes and greater, corresponding to nodularity roughly below 40 pct, the primary subpopulation was very small and difficult to distinguish, leaving eutectic nodules as the dominant subpopulation. The mode and standard deviation of the two subpopulations were roughly independent of nodularity. Moreover, the nodular and vermicular graphite were segregated in the microstructure. In conclusion, the results suggest that the parallel development of the vermicular eutectic had small influence on the size distribution of eutectic graphite nodules.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35530 (URN)10.1007/s11663-018-1274-z (DOI)000444765500033 ()2-s2.0-85048767236 (Scopus ID)HOA JTH 2018 (Local ID)HOA JTH 2018 (Archive number)HOA JTH 2018 (OAI)
Note

Included in licentiate thesis by Björn Domeij (2017), On the solidification of compacted and spheroidal graphite irons, as manuscript.

Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2019-05-13Bibliographically approved
Hernando, J. C., Ghassemali, E. & Diószegi, A. (2017). The morphological evolution of primary austenite during isothermal coarsening. Materials Characterization, 131, 492-499
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, 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
Keywords
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)000411535600054 ()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: 2019-04-29Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6339-4292

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