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On particles and slags in steel casting
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-3671-8087
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hadfield steel is widely accepted as one of the most important steel alloys utilized in industrial applications where high impact strength and wear resistance is required. Like in most metallic alloys used for component casting, the mechanical properties of Hadfield steel are directly connected with the microstructure of the material. It has been reported that Hadfield steel components with fine microstructure can present up to 30% increased strength and reduced risk of porosity formation during solidification when compared with their coarser microstructure counterparts.

In the light-metal alloy and cast-iron industry, one of the most widely used methods for achieving refinement of the microstructure of the material is known as inoculation. As the name implies, inoculation is the practice ofadding selected compounds or alloying elements in a metal melt that have the ability to promote rapid grain nucleation during solidification. Even though it has been proved that inoculation is one of the most efficient methods for the refinement of a wide variety of metallic alloys, it has not yet gained adequate acceptance in the steel casting industry because researchers have not yet been able to identify proper inoculants for steel.

The efficiency of the microstructural refinement when inoculating is influenced by several factors like the type of inoculant used and the processing conditions during melting, deoxidation, casting and heat treatment. Following proper deoxidation methods and application of tailored oxidic slags during melting could significantly promote the precipitation of desired inclusions that can act as potent nucleation sites for grains or as grain growth inhibitors.

In any case, efficient inoculation is influenced by the complex interaction between the inoculant, the oxide slag, and the melt. The way this interaction happens is in many ways dictated by the chemical and thermophysical properties of the substances involved. Therefore, obtaining accurate values of basic thermophysical properties like viscosity and interfacial tension by improving current and utilizing novel measurement methods could significantly help in the effort of identifying and efficiently utilizing potent inoculants for austenitic steels.

Considering the above, this work has a dual objective. The primary aim is to investigate if any of the by-products of deoxidation of Hadfield steel that remain in the material after solidification can act as potent inoculants by examining their qualitative and quantitative characteristics and their influence on the as-cast microstructure of the steel. The secondary aim is to acquire accurate values for oxide slag viscosity and slag-iron interfacial tension at high temperatures using different measurement methods and investigate how thermophysical properties are influenced by thermal and compositional conditions. This type of research is important because not only it can help to identify which substances are potent inoculants for austenitic steels but also pave the way for developing new or improving conventional deoxidation and inoculation processes with the ultimate goal of improving the cast component’s mechanical properties.

The work is divided into 3 different stages. The first stage is dedicated to high-temperature oxide slag viscosity measurements. The viscosity of oxide slags with varying composition is measured in a wide temperature range utilizing the rotational bob and aerodynamic levitation methods. The systematic error is defined, and the compositional and thermodynamic dependence of viscosity is explained. In the second stage, the precipitation of particles in aluminum and titanium deoxidized Hadfield steel is investigated. The characteristics of particles, including type, size, morphology, composition, population, and sequence of precipitation are identified. The results are then compared against thermodynamic equilibrium calculations, a particle growth mathematical model is developed and the precipitation mechanism of each type of particle is described. Finally, in the third stage, the as-cast grain size of samples produced with varying deoxidation procedures is measured and the relationship between particle characteristics and grain size is determined. The particles are ranked according to their refining potency and compared to a ranking based on their disregistry with austenite.

Abstract [sv]

Hadfieldstål är allmänt accepterade som en av de viktigaste stållegeringarna för industriella användning där hög slaghållfasthet och slitstyrka krävs. Liksom i de flesta metalliska legeringar som används för komponentgjutning, är de mekaniska egenskaperna hos Hadfield stål direkt kopplade till materialets mikrostruktur. Det har rapporterats att Hadfieldstålkomponenter med fin mikrostruktur kan visa upp till 30% ökad styrka och minskad risk för porositetsbildandning under stelnandet, jämfört med ett motsvarande material med grövre mikrostruktur.

I lättmetallsindustrin och inom gjutjärnsindustrin är en av de mest använda metoderna för att uppnå rätt sorts och finare mikrostruktur så kallad ympning. Som namnet antyder, är ympning en metod som genom tillsats av särskilda masterlegeringar och föreningar till i en smälta som har förmågan att främja kärnbildningen av korn under stelnandet. Det finns även metoder som kan begränsa korntillväxt under sekundär värmebehandling som även har en kornförfinande effekt. Även om det har bevisats att ympningen är en av de effektivaste metoderna för förfining av en mängd olika metalllegeringar, har den ännu inte fått acceptans inom stålgjutningsindustrin eftersom forskarna ännu inte har kunnat identifiera en lämplig kärnbildare för stål och då särskilt för austenitiska stål.

Effektiviteten vid ympning påverkas av flera faktorer som typ av kärnbildare som används och processbetingelserna vid smältning, desoxidation, gjutning och värmebehandling. Efter en korrekt desoxidation och i kombination med en skräddarsydd oxidisk slagg under smältprocessen skulle kunna främja utskiljning av lämpliga inneslutningar som även kan fungera som potent kärnbildare och som korntillväxthämmare.

I vilket fall som helst påverkas en effektiv inympning av den komplexa interaktionen mellan kärnbildare, oxidslaggen och smältan. Hur denna interaktion sker är på många sätt dikterad av de kemiska och termofysikaliska egenskaperna hos de inblandade ämnena. Därför är fastställandet av korrekta värden hos grundläggande termofysikaliska egenskaper som viskositet och ytspänning viktigt. Detta kan åstadkommas genom att förbättra nuvarande ochatt nyttja nya mätmetoder och därigenom förbättra möjligheten till att identifiera och effektivt utnyttja potenta kärnbildare för austenitiska stål.

Med ovanstående i tank har detta arbete ett dubbelt mål definierat. Det primära syftet är att utreda om någon av de biprodukter som bildas vid desoxidation av Hadfield stål har potential som kärnbildare för ett austenitiskt Hadfieldstål genom att undersöka deras kvalitativa och kvantitativa egenskaper och deras inflytande på den gjutna mikrostrukturen av stålet. Det sekundära syftet är att mäta mer exakta värden för oxidiskaslaggers viskositet och ytspänningen i gränsytan mellan slagg och järn vid höga temperaturer med hjälp av olika mätmetoder och undersöka hur termofysikaliska egenskaper påverkas av temperature och sammansättning hos slaggen. Denna typ av forskning är viktig då den inte bara det kan bidra till att identifiera vilka ämnen är potenta kärnbildare för austenitiska stål utan även kan bereda väg för att utveckla nya och förbättra konventionella desoxidation och ympningsprocesser med det slutliga målet att förbättra den gjutna komponentens mekaniska egenskaper.

Arbetet är uppdelat i 3 olika delar. Den första delen är tillägnad viskositetsmätning av oxidslagger vid hög temperatur. Viskositeten hos enoxidslagg med olika sammansättning har mätts i ett brett temperaturintervall genom en roterande bob viskosimeter och och genom en metod baserad på aerodynamisk levitation. Det systematiska felet definieras och inverkan av sammansättning förklaras genom en strukturell termodynamisk inverkan på viskositeten. I den andra delen studeras utskiljning av partiklar i aluminium- och titan-desoxiderat Hadfieldstål. Egenskaperna hos partiklar, som typ, storlek, morfologi, sammansättning, population (antal) och utskiljningssekvens identifieras. Resultaten jämförs sedan med termodynamiska jämviktberäkningar, en matematisk partikeltillväxt modell utvecklades och utskiljning och tillväxtmekanismen för varje typ av partikel beskrivs. Slutligen, i den tredje delen mäts kornstorleken för de material som framställs med olika deoxidationsförfaranden och förhållandet mellan partikelegenskaper och kornstorlek fastställs. Partiklarna rangordnas enligt deras kärnbildningspotential och jämförs med en rangordning baserad på deras gitters missanpasning med austenit.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering , 2019. , p. 45
Series
JTH Dissertation Series ; 043
Keywords [en]
Hadfield steel, deoxidation, grain size, inoculation, particles, viscosity, slag
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-43605ISBN: 978-91-87289-46-0 (print)OAI: oai:DiVA.org:hj-43605DiVA, id: diva2:1314326
Public defence
2019-05-31, E1405, School of Engineering, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2019-05-08 Created: 2019-05-08 Last updated: 2019-05-08Bibliographically approved
List of papers
1. Measurement of Viscosity of SiO2-CaO-Al2O3 Slag in Wide Temperature Range by Aerodynamic Levitation and Rotating Bob Methods and Sources of Systematic Error
Open this publication in new window or tab >>Measurement of Viscosity of SiO2-CaO-Al2O3 Slag in Wide Temperature Range by Aerodynamic Levitation and Rotating Bob Methods and Sources of Systematic Error
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2018 (English)In: International journal of microgravity science and application, ISSN 0915-3616, Vol. 35, no 2, article id 350204Article in journal (Refereed) Published
Abstract [en]

Viscosity measurements for SiO2-CaO-Al2O3 based ternary slags with low SiO2 content were performed for a wide temperature range utilizing the aerodynamic levitation and rotating bob methods. Aerodynamic levitation was used for temperatures >= 2229 K and the viscosity was calculated by the sample oscillation decay time. The rotating bob method was used for temperatures <= 1898 K and the viscosity was determined by the variation of the torque at different rotation speeds. Fitting curves were created using Mauro’s viscosity equation. The main sources of systematic error were identified to be the sample weight measurement, the resolution of the high-speed camera, the fitting of the linear trend line in the torque against rpm diagrams and the vertical position of the bob. The combined standard uncertainty from all error sources was calculated for both measurement methods.

Place, publisher, year, edition, pages
Japan Society of Microgravity Application, 2018
Keywords
Aerodynamic levitation; Slag; Viscosity; Rotating bob; Gravity
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-41082 (URN)10.15011//jasma.35.350204 (DOI)000431604700004 ()GOA JTH 2018;JTHMaterialIS (Local ID)GOA JTH 2018;JTHMaterialIS (Archive number)GOA JTH 2018;JTHMaterialIS (OAI)
Available from: 2018-08-02 Created: 2018-08-02 Last updated: 2019-05-08Bibliographically approved
2. Viscosity of SiO2–CaO–Al2O3 slag with low silica – Influence of CaO/Al2O3, SiO2/Al2O3 ratio
Open this publication in new window or tab >>Viscosity of SiO2–CaO–Al2O3 slag with low silica – Influence of CaO/Al2O3, SiO2/Al2O3 ratio
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2018 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, no 12, p. 2180-2185Article in journal (Refereed) Published
Abstract [en]

The viscosity of low SiO2 (10–20 mass%)-CaO-Al2O3 slag system was measured in a wide temperature range (1 623–2 800 K) using the rotational bob method and the aerodynamic levitation method. The influence of SiO2/Al2O3 ratio and CaO/Al2O3 ratio on the viscosity was examined. It was concluded that the SiO2/Al2O3 ratio did not affect the degree of polymerization of the aluminosilicate network in the composition range of the present study. An abnormal behaviour of the viscosity was observed at a CaO/Al2O3 ratio of 1.57 which was attributed to the formation of 12CaO·7Al2O3-like clusters. It was concluded that the overall influence on the viscosity could be expressed as the summation of the influence from the aluminosilicate network and the influence from the cluster formation of the primary precipitating solid phase. The temperature dependence of the cluster formation was coupled to the driving force of precipitation of the 12CaO·7Al2O3 phase.

Place, publisher, year, edition, pages
Iron and Steel Institute of Japan, 2018
Keywords
Driving force, Low silica slag, Slag, Suspension, Viscosity, Alumina, Aluminosilicates, Aluminum oxide, Slags, Suspensions (fluids), Temperature distribution, Abnormal behaviours, Aerodynamic levitation, Cluster formations, Composition ranges, Degree of polymerization, Driving forces, Temperature dependence, Wide temperature ranges, Silica
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-42436 (URN)10.2355/isijinternational.ISIJINT-2018-381 (DOI)000454672900003 ()2-s2.0-85058967730 (Scopus ID)JTHMaterialIS (Local ID)JTHMaterialIS (Archive number)JTHMaterialIS (OAI)
Funder
Swedish National Space Board, 117/15
Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-05-08Bibliographically approved
3. Particles precipitation in Ti and Al deoxidized Hadfield steels
Open this publication in new window or tab >>Particles precipitation in Ti and Al deoxidized Hadfield steels
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2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 10, p. 1344-1355Article in journal (Refereed) Published
Abstract [en]

The characteristics and precipitation mechanism of particles in titanium and aluminum treated Hadfield steel casted during pilot scale experiments have been studied. Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were utilized for the particle analysis and characterization. Additionally, thermodynamic equilibrium calculations were performed using Thermo-Calc software. Aluminum oxides, titanium carbon nitrides, titanium carbides and manganese sulfides were the main types of particles found. The order of precipitation during solidification and chemical composition range of each type of particle was determined. Aluminum Oxides were found to act as nucleation sites fortitanium carbon nitrides. Thermodynamic equilibrium calculation for particles characteristics were in good agreement with the experimental findings. Titanium carbides were found to form during initial stages of the Ferro-titanium additions dissolution.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Hadfield steel; particles; Titanium; Aluminum; Deoxidation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-29401 (URN)10.1002/srin.201500400 (DOI)000387017200011 ()2-s2.0-84959496093 (Scopus ID)
Projects
InDeGrainS
Funder
Knowledge Foundation, 20130149
Available from: 2016-02-15 Created: 2016-02-15 Last updated: 2019-05-08Bibliographically approved
4. A particle population analysis in Ti- and Al-deoxidized Hadfield steels
Open this publication in new window or tab >>A particle population analysis in Ti- and Al-deoxidized Hadfield steels
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2018 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 31, no 3, p. 125-134Article in journal (Refereed) Published
Abstract [en]

A quantitative analysis of the amount, size and number of particles that precipitate in situ in titanium- and aluminium-treated Hadfield steel cast during pilot-scale experiments has been performed. SEM with EDS and automated particle analysis abilities was utilized for the analysis. Additionally, Thermo-Calc was used for thermodynamic calculations and Magma 5 for solidification and cooling simulations. Predicted particles sizes calculated with a model based on the Ostwald ripening mechanism were compared with the experimental data. The effect of solute availability, cooling rate and deoxidation practice on the particle population characteristics was determined. It was concluded that the amount, size and number of precipitating particles in Hadfield steel castings is possible to be controlled according to certain requirements by a careful selection of proper additives in proper amounts and also by the optimization of the casting process in aspects of deoxidation timing and control of the cooling rate of the castings.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
Hadfield steel, particles population, deoxidation, casting, titanium, aluminum, inclusion control, particle growth
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-37418 (URN)10.1080/13640461.2017.1379262 (DOI)000437344000001 ()2-s2.0-85019740665 (Scopus ID)
Available from: 2017-09-27 Created: 2017-09-27 Last updated: 2019-05-08Bibliographically approved
5. The Influence of Deoxidation Practice on the As-Cast Grain Size of Austenitic Manganese Steels
Open this publication in new window or tab >>The Influence of Deoxidation Practice on the As-Cast Grain Size of Austenitic Manganese Steels
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2017 (English)In: Metals, ISSN 2075-4701, Vol. 7, no 6, article id 186Article in journal (Refereed) Published
Abstract [en]

The effect of in-situ precipitating particles on the grain size of Al-Ti-treated and untreated Hadfield steel cast in a pilot scale environment was studied. Hadfield steel was melted in an induction furnace and cast in Y-Block samples. Light Optical Microscopy (LOM) and the intercept method were utilized for the grain size measurements. Additionally, Thermo-Calc Software TCFE7 Steels/Fe-alloys database version 7 was used for thermodynamic equilibrium calculations of the mole fraction of particles. The planar disregistry values between the austenite and the precipitating particles were calculated. It was observed that increasing oxide content in samples with low Ti(CN) content resulted in a finer microstructure, while increasing the Ti(CN) content under similar oxide content levels led to a coarser microstructure. The potency of each type of particle to nucleate austenitic grains was determined. Spinel (MnAl2O4, MgAl2O4) particles were characterized as the most potent, followed by olivine (Mn2SiO4), corundum (Al2O3, TiO2), and finally Ti(CN), the least potent particle.

Place, publisher, year, edition, pages
MDPI, 2017
Keywords
Hadfield steel, grain size, austenite, deoxidation, particles, aluminum, titanium, oxides, titanium nitrides
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35598 (URN)10.3390/met7060186 (DOI)000404056600003 ()2-s2.0-85019680224 (Scopus ID)GOA JTH 2017 (Local ID)GOA JTH 2017 (Archive number)GOA JTH 2017 (OAI)
Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2019-06-07Bibliographically approved

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