Conventional and Multiscale Modeling of Microstructure Evolution During Laminar Cooling of DP Steel Strips
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THE aim of modern thermomechanical processing technologies is to achieve both high strength and ductility of the steel product. The combination of desired properties can be achieved by optimizing the chemical composition of the steel and/or by suitable thermomechanical processing. As a rule, the development of fine microstructure is a prerequisite for obtaining high strength combined with good ductility in majority of constructional steels, specifically in HSLA grades. However, producers of thin gage products face another challenge, which is the necessity of finish rolling in c + a region. In this case, the texture development may cause a problem for the mechanical properties of products, e.g., impact toughness. The concept of AHSS steels was built on another approach in which the amount of ferrite, bainite, martensite, and eventually retained austenite plays a crucial role in achieving a proper balance between strength and ductility.[1,2] In addition, the morphology and mechanical stability of these constituents are very important for properties and crash worthiness. SpecifMACIEJ PIETRZYK, JAN KUSIAK, and ŁUKASZ MADEJ, Professors, DANUTA SZELIGA, Assistant Professor, and RAFAŁ GOŁA ˛ B, Ph.D. Student, are with the AGH University of Science and Technology, Mickiewicza 30, 30-059 Krako´w, Poland. Contact e-mail: [email protected] ROMAN KUZIAK, Professor, is with the Institute for Ferrous Metallurgy, Karola Miarki 12, 44-100 Gliwice, Poland. Manuscript submitted February 22, 2014. Article published online June 25, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
ically, this refers to retained austenite whose stability is affected by the carbon segregation. Required relation between volume fractions of ferrite and martensite, which is crucial for the quality of steel,[1–3] is obtained through applying special cooling paths during laminar cooling after hot rolling or continuous annealing after cold rolling. The latter process was investigated in the earlier work.[4] The laminar cooling was considered in this paper. This is a complex process, therefore, physical and numerical simulations are particularly needed in design of manufacturing of DP steel products. Efficiency of numerical simulations in a support for technology design depends on the accuracy of models and their capability to reproduce properly physical phenomena occurring in the industrial process. Problem of a selection of an adequate model for a particular application, as well as problem of identification of model parameters, are crucial for the efficiency and effectiveness of simulations. Therefore, the objectives of the paper were twofold. Physical simulations of hot plastic deformation and heat treatment were performed and used to identify and validate models. Validated models were applied to simulate the manufacturing of DP steel strips by hot rolling and laminar cooling.
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NUMERICAL MODELS
Two numerical models of various complexities and various predictive capabilities are proposed in the paper. VOLUME 45A, DECEMBER 2014—5835
The first one is based on t
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