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Low-Density Steels: Complex Metallurgy for Automotive Applications
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-9010-525X
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-5031-919X
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2014 (English)In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 66, no 9, 1747-1758 p.Article in journal (Refereed) Published
Abstract [en]

The current aim in the development of third-generation steels for lightweighting automotive applications is to increase strength keeping at least the same formability as current steel concepts. In this philosophy, an optimal concept would be one that brings, in addition, a lower density. For this purpose, low-density steels have been designed with important aluminum additions obtaining density reductions of 8-10% or higher in comparison with low-carbon steels. At the levels required for lightweighting, aluminum introduces complex phenomena in steels. Here, some of the effects of aluminum in phase stability, CALPHAD-type modeling, and microstructure development are described, the latter in relation with mechanical properties. Finally, the potential of two families of lightweight steels for automotive applications is assessed by comparison with a steel currently present in automotive structures.

Place, publisher, year, edition, pages
2014. Vol. 66, no 9, 1747-1758 p.
Keyword [en]
Al-C System, Mechanical-Properties, Phase-Equilibria, Spinodal Decomposition, Thermodynamic Calculation, Ternary Alloys, Fe System, Aluminum, Carbide, Ferrite
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-154385DOI: 10.1007/s11837-014-1084-yISI: 000341916100032ScopusID: 2-s2.0-84920253175OAI: diva2:756970

QC 20141020

Available from: 2014-10-20 Created: 2014-10-20 Last updated: 2015-05-06Bibliographically approved
In thesis
1. Thermodynamic investigation of systems related to TWIP steels
Open this publication in new window or tab >>Thermodynamic investigation of systems related to TWIP steels
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The world is facing serious challenges regarding environmental issues. Carbon dioxide levels increase every day. In an attempt to decrease carbon emissions the automotive industry searches for lighter, stronger materials. TWinning Induced Plasticity (TWIP) steels show an impressive combination of strength and ductility. The possibility of adding high amounts of aluminum that decreases the density while maintaining the mechanical properties makes this type of steel very interesting for use in automotive applications. The only thing keeping the TWIP steels from being used in the automotive industry is that the Yield Strength (YS) is too low. The TWIP steels usually have a YS around 400 MPa. For them to be useful in automotive applications YS around 600-700 MPa is necessary. One of the most promising ways of improving the YS is by precipitation hardening. This work has been performed within a European Research Fund for Coal and Steel (RFCS) project called Precipitation in High Manganese steels (PrecHiMn). As the name of the project suggests, the goal of this project has been to study the precipitation in TWIP steels. The precipitation hardening is achieved through the addition of carbide and carbonitride formers such as Nb, Ti and V. In order to build advanced models to simulate precipitation it is important to have a good understanding of the thermodynamics of systems related to TWIP steels.

The goal of this work has been to study the thermodynamic properties of systems related to TWIP steels, more specifically the system forming the matrix phases of TWIP steels. Therefore the Al-C-Fe-Mn system has been studied as well as the Al-Ti-V system. Complete thermodynamic descriptions that reproduce the experimental data well have been produced including descriptions of order-disorder transformations.

Abstract [sv]

Varlden star infor stora utmaningar nar det galler miljofragor. Koldioxidnivaerna okar varje dag. I ett forsok att minska koldioxidutslappen soker bilindustrinefter lattare och starkare material. TWinning Induced Plasticity (TWIP)stal uppvisar en imponerande kombination av hallfasthet och duktilitet. Mojlighetenatt tillsatta hoga halter av aluminium som minskar densiteten med bibehallnamekaniska egenskaper gor denna typ av stal mycket intressanta for anvandning ifordonstillampningar. Det enda som hindrar TWIP stal fran att anvandas inomfordonsindustrin ar att strackgransen ar for lag. TWIP stal har vanligtvis enstrackgrans runt 400 MPa. For att de ska vara anvandbara i biltillampningarkravs en strackrans omkring 600-700 MPa. Ett av de mest lovande satten attforbattra strackgransen ar genom utskiljningshardning. Detta arbete har utfortsinom en europeisk forskningsfond for kol och stal (RFCS) projekt kallat Precipitationin High Manganese steels (PrecHiMn). Som namnet pa projektetantyder, har malet med projektet varit att studera utskiljning i TWIP stal.Utskiljningshardning uppnas genom tillsats av karbid- och karbonitridbildaresasom Nb, Ti och V. For att bygga avancerade modeller for simulering av utskiljningar det viktigt att ha en god forstaelse for termodynamiken i systemrelaterade till TWIP stal.Malet med detta arbete har varit att studera de termodynamiska egenskapernahos system med anknytning till TWIP stal. Mer specikt har systemetsom bildar matrisfaserna i TWIP stal. Drfr har Al-C-Fe-Mn-systemet studeratsliksom Al-Ti-V-systemet. Fullstandiga termodynamiska beskrivningar somaterger experimentella data val har producerats inklusive beskrivningar av ordningsomvandlingar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. v, 48 p.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-166224 (URN)978-91-7595-516-2 (ISBN)
Public defence
2015-05-22, B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)

QC 20150506

Available from: 2015-05-06 Created: 2015-05-05 Last updated: 2015-05-06Bibliographically approved

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Lindahl, BonnieSelleby, Malin
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