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A dislocation model for the stress-strain behavior of dual phase steels
2008 (English)In: IDDRG 2008 International Conference, 2008Conference paper, Published paper (Refereed)
Abstract [en]

The Bergström dislocation model is used to study the influence of coiling temperature after hot rolling on the mechanical properties of the cold rolled SSAB-grade Docol 800DP. Further, the anisotropy-effect for this type of steel, caused for instance by banding, is investigated. The physical dislocation model is based on the assumption that the work hardening behaviour is controlled by the creation, the immobilisation and the remobilisation of dislocations and it is demonstrated that all these processes are strongly influenced by the amount of hard martensite particles in DP-steels. The true strain to necking is a widely used tool for estimating the stretch formability of DP-steels. A detailed discussion regarding the influence of for instance friction stress, rate of dislocation remobilisation and mean free path of dislocation motion is presented. It is also indicated that the best stretch formability of DP-steel is obtained by minimising the quotient between the rate of work hardening at smaller strains with that at larger strains, close to the strain at necking.

Place, publisher, year, edition, pages
2008.
Keyword [en]
Strain hardening, Dislocation model, Dual-phase steel, Formability
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-24978OAI: oai:DiVA.org:kth-24978DiVA: diva2:354776
Note
QC 20101004Available from: 2010-10-04 Created: 2010-10-04 Last updated: 2010-10-04Bibliographically 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

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