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Simulation of the Soaking and Gas Jet Cooling in a Continuous Annealing Line using Dilatometry
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 2, 158-167 p.Article in journal (Refereed) Published
Abstract [en]

The present study concerns the simulation of a continuous annealing line (CAL), using dilatometry. Simulations of CAL have been performed on four commercial steel grades with different chemical compositions in order to investigate how the alloying elements C, Mn, Si and B affect the microstructure and hardness of dual phase (DP) and martensitic steels. Three annealing cycles corresponding to those used in a CAL have been applied. When annealing intercritically, as is the case in DP-steel production, the materials do not reach equilibrium during soaking. Mn and C increase the austenite content and consequently the hardness of the materials. Higher levels of Si (0.4 wt %) are required to retard the formation of new ferrite during cooling in the gas jet section, prior to quenching. 6 increases hardenability effectively when annealing in the austenite region but is not as efficient during intercritical annealing, which implies that boron restrains ferrite nucleation rather than impeding ferrite growth. Results from DICTRA calculations show that it is possible to simulate the phase transformations during soaking, gasjet cooling and quenching.

Place, publisher, year, edition, pages
2010. Vol. 81, no 2, 158-167 p.
Keyword [en]
dilatometry, simulation, continuous annealing, high strength steels
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-24971DOI: 10.1002/srin.200900097ISI: 000275142400009Scopus ID: 2-s2.0-77949483612OAI: oai:DiVA.org:kth-24971DiVA: diva2:354764
Note
QC 2010104Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2011-03-16Bibliographically approved
In thesis
1. Structure and mechanical properties of dual phase steels: An experimental and theoretical analysis
Open this publication in new window or tab >>Structure and mechanical properties of dual phase steels: An experimental and theoretical analysis
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The key to the understanding of the mechanical behavior of dual phase (DP) steels is to a large extent to be found in the microstructure. The microstructure is in its turn a result of the chemical composition and the process parameters during its production. In this thesis the connection between microstructure and mechanical properties is studied, with focus on the microstructure development during annealing in a continuous annealing line. In-line trials as well as the lab simulations have been carried out in order to investigate the impact of alloying elements and process parameters on the microstructure. Further, a dislocation model has been developed in order to analyze the work hardening behavior of DP steels during plastic deformation.

From the in-line trials it was concluded that there is an inheritance from the hot rolling process both on the microstructure and properties of the cold rolled and annealed product. Despite large cold rolling reductions, recrystallization and phase transformations, the final dual phase steel is still effected by process parameters far back in the production chain, such as the coiling temperature following the hot rolling.

Lab simulations showed that the microstructure and consequently the mechanical properties are impacted not only by the chemical composition of the steel but also by a large number of process parameters such as soaking temperature, cooling rate prior to quenching, quench and temper annealing temperature.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2010
Keyword
Dual phase steels, continuous annealing, dilatometry, microstructure, mechanical properties, process parameters, dislocation model, plastic deformation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24869 (URN)
Public defence
2010-10-27, Nya konferensrummet, Brinellvägen 23, Stockholm, 16:20 (English)
Opponent
Supervisors
Note
QC 20101004Available from: 2010-10-04 Created: 2010-09-28 Last updated: 2010-10-06Bibliographically approved
2. Simulation of Phase Transformations and coarsening: Computational tools for alloy development
Open this publication in new window or tab >>Simulation of Phase Transformations and coarsening: Computational tools for alloy development
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The final properties of an alloy are highly interlaced with its microstructure. It is therefore essential to control the evolution of the microstructure of the material during the fabrication process. Nowadays, materials design involves an increasing part of computational design to complement the traditional experimental trial and error approach. Such simulations of the process can decrease the number of material prototypes and shorten the development time for new alloys.

In this thesis several microstructure models, aimed for process design, have been suggested. The ambition has been to develop physically based models that are capable to represent the evolution of hundreds of grain or particle sizes, where the models should be possible to run on a standard computer with simulation times less than one day. To achieve this goal, simplified approaches have been suggested, which are accurate enough for the growth rate of grains and particles. The microstructure models have all in common that size distributions of grains or particles are simulated with mean-field approaches. Several of the models also utilize composition and temperature dependent thermodynamic and kinetic properties continually throughout the simulations. These properties have been calculated with programming interfaces to Thermo-Calc and DICTRA together with appropriate thermodynamic and kinetic databases. The materials that have been considered in the present thesis are low alloyed steels, aluminium alloys and cemented carbides. The models are however generic in the sense that all materials can be handled if appropriate thermodynamic, kinetic and property databases exist for the alloy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. iv, 40 p.
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31454 (URN)978-91-7415-891-5 (ISBN)
Public defence
2011-03-25, F3, Lindstedtsvägen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20110316Available from: 2011-03-16 Created: 2011-03-16 Last updated: 2011-03-16Bibliographically approved

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