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Dendritic morphology and ultimate tensile strength of pearlitic lamellar graphite iron
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The continued development, of cylinder blocks and cylinder heads for heavy truck engines that are made of lamellar graphite iron (LGI) is focused on achieving high ultimate tensile strength (UTS) whilst conforming to environmental regulations. The purpose of this work is to further improve the tensile strength as well as the predictive engineering tools for optimization of LGI aimed to enhance the efforts for producing lighter and sustainable components without sacrificing performance.

Varying the carbon content and solidification rate greatly influences the amount and the coarseness of the microstructure phases resulting in large variations of material properties. The experimental data set provided in this work covers a comprehensive range of microstructure and the UTS values aimed to be used in a holistic model for UTS prediction.

In pearlitic LGI the primary austenite dendritic network reinforces the material while the distance between the pearlite grains defines the maximum continuous defect size. The novel parameter of Hydraulic Diameter of the Inter-dendritic Phase (DIPHyd) has been introduced in this work to express the amount and the coarseness of the space between the pearlite grains that have been solidified as primary austenite dendrites. The DIPHyd has proven to be the generic parameter that defines the maximum continuous defect size in the material, and hence it has been applied in modified Griffith and Hall-Petch models for prediction of UTS.

Microstructure models have been developed for prediction of the key microstructure parameters that define the strength of LGI. These models have been combined with the modified Griffith and Hall-Petch equations and incorporated into casting simulation software to enable the strength prediction for pearlitic LGI alloys with various carbon contents. The results show that the developed models can be successfully applied, along with the simulation tools across a wide range of carbon content from eutectic to hypoeutectic composition, for the alloys solidified at various cooling rates typical for both thin and thick walled complex shaped iron castings.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering , 2019. , p. 47
Series
JTH Dissertation Series ; 38
Keywords [en]
Lamellar graphite iron, Primary austenite dendrite, Ultimate tensile strength, Microstructure model
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-43228ISBN: 978-91-87289-40-8 (print)OAI: oai:DiVA.org:hj-43228DiVA, id: diva2:1293214
Public defence
2019-01-16, 10:30 (English)
Opponent
Supervisors
Available from: 2019-03-08 Created: 2019-03-04 Last updated: 2019-03-08Bibliographically approved
List of papers
1. Effects of Carbon Content on the Ultimate Tensile Strength in Gray Cast Iron
Open this publication in new window or tab >>Effects of Carbon Content on the Ultimate Tensile Strength in Gray Cast Iron
2010 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 649, p. 511-516Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Switzerland: Trans Tech Publication, 2010
Identifiers
urn:nbn:se:hj:diva-10800 (URN)10.4028/www.scientific.net/MSF.649.511 (DOI)
Available from: 2009-11-03 Created: 2009-11-03 Last updated: 2019-03-08Bibliographically approved
2. Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 2 – The influence of carbon composition
Open this publication in new window or tab >>Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 2 – The influence of carbon composition
2014 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 790-791, p. 211-216Article in journal (Refereed) Published
Abstract [en]

Investigation of dynamic coarsening in lamellar cast iron is extended over a wide interval ranging from hypoeutectic to eutectic composition. The dendrite morphology is defined on as-cast samples produced under various cooling rates. The as-cast morphology is considered being close to the one at the end of solidification. The obtained relations describing the coarsening process as a function of local solidification time and fraction austenite are compared to results obtained from interrupted solidification experiments. By using the Modulus of primary dendrite (MPD) and the Hydraulic diameter of the interdendritic space (DHyd IP) become possible to characterize the coarseness of a wide range of lamellar cast irons solidified under various cooling rates. 

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-25447 (URN)10.4028/www.scientific.net/MSF.790-791.211 (DOI)2-s2.0-84901397357 (Scopus ID)
Conference
6th International Conference on Solidification and Gravity; Miskolc, Lillafured; Hungary; 2 September 2013 through 5 September 2013
Available from: 2014-12-30 Created: 2014-12-30 Last updated: 2019-03-08Bibliographically approved
3. Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 1 – Investigation based on interrupted solidification
Open this publication in new window or tab >>Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 1 – Investigation based on interrupted solidification
2014 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 790-791, p. 205-210Article in journal (Refereed) Published
Abstract [en]

Dynamic coarsening of austenite dendrite in lamellar cast iron has been studied for a hypoeutectic alloy. The common morphological parameter to characterize dynamic coarsening, secondary dendrite arm space has been replaced by the Modulus of primary dendrite (MPD) and the Hydraulic diameter of the interdendritic space (DHydIP) to interpret the dynamic coarsening with respect to the local solidification time. The obtained results demonstrate the coarsening process of both the solid and liquid phase. The interdendritic space is increasing as the contact time between the solid and liquid phase increases. The ratio between the DHydIP/MPD is strongly dependent on the precipitated fraction primary austenite indicating clearly the morphology variation during coarsening. The interrupted solidification method demonstrate that the observed coarsening process is not only a combination of the increasing fraction precipitated solid phase and the rearrangement of the solid - liquid interphase curvature but the volume change due to density variation is also contribute to the coarsening process.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-25446 (URN)10.4028/www.scientific.net/MSF.790-791.205 (DOI)2-s2.0-84901420606 (Scopus ID)
Conference
6th International Conference on Solidification and Gravity; Miskolc, Lillafured; Hungary; 2 September 2013 through 5 September 2013
Available from: 2014-12-30 Created: 2014-12-30 Last updated: 2019-03-08Bibliographically approved
4. A generic model to predict the ultimate tensile strength in pearlitic lamellar graphite iron
Open this publication in new window or tab >>A generic model to predict the ultimate tensile strength in pearlitic lamellar graphite iron
2014 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 618, p. 161-167Article in journal (Refereed) Published
Abstract [en]

Varying the carbon contents, chemical composition and solidification rate greatly influences the microstructural morphology in lamellar graphite iron resulting in large variations in material properties. Traditionally, ultimate tensile strength (UTS) is used as the main property for the characterisation of lamellar graphite iron alloys under static loads. The main models found in the literature for predicting UTS of pearlitic lamellar graphite iron are based on either regression analysis on experimental data or on modified Griffith or Hall-Petch equation.

In pearlitic lamellar graphite iron the primary austenite transformed to pearlite reinforces the bulk material while the graphite flakes which are embedded in an iron matrix reduce the strength of the material. Nevertheless a dominant parameter which can be used to define the tensile strength is the characteristic distance between the pearlite grains defined as the maximum continuous defect size in the bulk material, which in this work is expressed by the newly introduced parameter the Diameter of Interdendritic Space. The model presented here covers the whole spectrum of carbon content from eutectic to hypoeutectic composition, solidified at different cooling rates typical for both thin and thick walled complex shaped castings.

Keywords
Lamellar graphite iron; Tensile properties; Primary austenite; Carbon content; Cooling rate
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-25448 (URN)10.1016/j.msea.2014.08.061 (DOI)000344439500020 ()2-s2.0-84907512331 (Scopus ID)
Available from: 2014-12-30 Created: 2014-12-30 Last updated: 2019-03-08Bibliographically approved
5. Strength prediction of lamellar graphite iron: From Griffith’s to hall-petch modified equation
Open this publication in new window or tab >>Strength prediction of lamellar graphite iron: From Griffith’s to hall-petch modified equation
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 925, p. 272-279Article in journal (Refereed) Published
Abstract [en]

Traditionally, ultimate tensile strength (UTS) is used as the main property for the characterization of lamellar graphite iron (LGI) alloys under static loads. The main models found in the literature for predicting UTS of pearlitic lamellar graphite iron are based on either regression analysis on experimental data or on modified Griffith or Hall-Petch equation. In pearlitic lamellar graphite iron the primary austenite dendritic network, transformed to pearlite, reinforces the bulk material while the distance between those pearlite grains, defines the maximum continuous defect size in the bulk material. Recently the novel parameter of the Diameter of Interdendritic Space has been used to express the flow length in a modified Griffith equation for the prediction of the UTS in LGI. Nevertheless this model neglects the strengthening effect of the pearlite lamellar spacing within the perlite grains. A model based on modified Hall-Petch equation was developed in this work. The model considers the effect of both microstructure parameters and covers a broad spectrum of microstructure sizes typical for complex shape castings with various wall thicknesses. 

Place, publisher, year, edition, pages
Trans Tech Publications, 2018
Keywords
Lamellar graphite iron, Pearlite spacing, Primary austenite, Tensile strength, Austenite, Forecasting, Graphite, Materials handling equipment, Microstructure, Pearlite, Regression analysis, Graphite iron, Interdendritic space, Micro-structure parameters, Strength prediction, Strengthening effect, Ultimate tensile strength, Cast iron
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-41295 (URN)10.4028/www.scientific.net/MSF.925.272 (DOI)XYZ ()2-s2.0-85050010996 (Scopus ID)9783035710557 (ISBN)
Conference
11th International Symposium on the Science and Processing of Cast Iron, SPCI-XI 2017, Jönköping, Sweden, 4-7 September 2017
Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2019-03-08Bibliographically approved
6. Strength prediction for pearlitic lamellar graphite iron: Model validation
Open this publication in new window or tab >>Strength prediction for pearlitic lamellar graphite iron: Model validation
2018 (English)In: Metals, ISSN 2075-4701, Vol. 8, no 9, article id 684Article in journal (Refereed) Published
Abstract [en]

The present work provides validation of the ultimate tensile strength computational models, based on full-scale lamellar graphite iron casting process simulation, against previously obtained experimental data. Microstructure models have been combined with modified Griffith and Hall–Petch equations, and incorporated into casting simulation software, to enable the strength prediction for four pearlitic lamellar cast iron alloys with various carbon contents. The results show that the developed models can be successfully applied within the strength prediction methodology along with the simulation tools, for a wide range of carbon contents and for different solidification rates typical for both thin-and thick-walled complex-shaped iron castings. 

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
Gravity casting process simulation, Lamellar graphite iron, Primary austenite, Ultimate tensile strength
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-41729 (URN)10.3390/met8090684 (DOI)000448144400031 ()2-s2.0-85053238597 (Scopus ID)
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2019-03-08Bibliographically approved

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