Programm- und Modellentwicklung zur Simulation von Makroseigerungsentstehungsphänomenen beim Brammenstranggießen von Stahl mit besonderem Augenmerk auf die Phänomene ″Feeding″ und ″Bulging″.

Translated title of the contribution: Program and model development for simulation of phenomena which lead to macrosegregation in slab continuous casting of steel with particular attention to the phenomena "feeding" and "bulging".

Florian Mayer

Research output: ThesisDoctoral Thesis

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Abstract

In continuous casting of steel concentration inhomogeneities of alloying elements, the so-called macrosegregation, are formed. In further production, these inhomogeneities can cause lower product quality and are therefore undesirable. At the chair of Simulation and Modelling of Metallurgical Processes (SMMP), Department Metallurgy at the University of Leoben, a module that is addressing the topic of "modeling of deformation induced reduction of macrosegragation and shrinkage porosities during softreduction of steel" was implemented as part of a Christian Doppler Laboratory (CDL) for multiphase simulation of metallurgical processes in cooperation with the companies SIEMENS VAI (voest-alpine Industrieanlagenabau - since 2015: Primetals Technologies)and voestalpine Stahl Linz (VASL) as well as voestalpine Stahl Donawitz (VASD). The presented work deals with simulation of a continuous casting process for a binary carbon steel St52 (0,18wt.%C). For this purpose, the theoretic principles of macrosegregation formation, which is often accompanied by shrinkage porosity, are given and currently used processes to avoid these material inhomogeneities are discussed. By using numerical simulation the formation of macrosegregation is investigated by an Euler Euler CFD multiphase approach (Volume Averaging model). Here, the multi-phase model of ANSYS/FLUENT, involving User Defined Functions (UDFs), is developed for simulation of continuous casting of steel. In specific, the mass transfer rate calculation is extended and a solidification- and pore-model, as well as a model for considering the strand bulge between the guide rollers ("Bulging") are implemented and applied to 101 pairs of guide rollers. In order to compare and validate the simulation results with actual segregation profiles, a way of calculating concentration profiles based on microprobe values (concentration mapping) using a MATLAB code is developed. The two main phenomena responsible for forming macrosegregation during slab continous casting of steel are solidification induced shrinkage flow ("Feeding") and "Bulging" induced flow. The effect of these two phenomena on macrosegregation in the solidified strand is investigated individually, as well as coupled and the obtained results are analyzed, compared, interpreted and discussed. The velocity fields and their effect on the macrosegregation are investigated in detail. The analysis of the results show that there is a negative centerline segregation due to shrinkage induced flow and a positive one due to "Bulging". For the given parameters, the coupling of the two phenomena results in a positive centerline segreggation by "Bulging", which is minimized by "Feeding". This positive macrosegregation in the center coincides with measurement results and confirms the results encountered in literature for the calculation with two or six pairs of rollers. Based on the results of this work, it is possible (i) to determine the relative speed of the melt by simulation, (ii) to explain the main causes for macrosegregation, (iii) to validate centerline segregation and thus to (iv) provide important insights into solidification during continuous casting of steel.
Translated title of the contributionProgram and model development for simulation of phenomena which lead to macrosegregation in slab continuous casting of steel with particular attention to the phenomena "feeding" and "bulging".
Original languageGerman
QualificationDr.mont.
Supervisors/Advisors
  • Bernhard, Christian, Assessor B (internal)
  • Ludwig, Andreas, Assessor A (internal)
Publication statusPublished - 2015

Bibliographical note

embargoed until null

Keywords

  • continuous casting
  • simulation
  • program- and model development
  • macrosegregation
  • phenomena of formation
  • feeding
  • bulging
  • concentration mapping
  • validation

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