Defects and Properties of Cast Metals: Continuous and DC Casting
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Mark Jolly, Cranfield University; Charles Monroe, University of Alabama; Brian Thomas, Colorado School of Mines; Peter Lee, University of Manchester
Wednesday 2:00 PM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Brian Thomas, Colorado School of Mines; Laurens Katgerman, Delft University
2:00 PM Introductory Comments
2:05 PM Keynote
Progress and Developments in DC Casting of Aluminium Alloys: Laurens Katgerman1; 1Delft University
The direct chill (DC) semi-continuous casting process has been the backbone of the aluminium industry for the production of ingots. Though the basic engineering of DC casting is relatively simple, the interaction of process parameters with occurrence of defects and micro-structural evolution is quite complex.Through understanding of the physical phenomena involved during casting, computational models give the opportunity to establish quantitative relationships between materials, processes, and performance. However, when it comes to accurately predicting casting performance and in particular, the occurrence of defects like cracks, segregation and porosity, there is certainly some way to go. In this paper, the current developments in DC casting technology will be reviewed.
2:25 PM Invited
The Influence of Mould Lubrication Index on Defect Formation during Continuous Casting of Steel: Pavel Ramirez Lopez1; 1Swerea MEFOS AB
Surface defects are recurrent during Continuous Casting due to introduction of new grades which are difficult to cast. Modelling has become a ubiquitous tool to analyse the formation of such defects. However, simulations are hampered by omission of important process details such as transient variations in material properties and operator’s practices. The present manuscript seeks to create awareness on these issues by revisiting key concepts such as interfacial resistance and Lubrication Index. This is done from a conceptual point of view based on industrial observations and modelling experiences, which allow a reformulation of outdated concepts and misconceptions regarding the influence of flow, heat-transfer and solidification on defect formation. Additionally, the manuscript addresses common challenges during industrial implementation such as lack of high-temperature properties and variability on casting practices; but also provides examples of improvements on quality and process stability achievable through a holistic approach to modelling combined with plant measurements.
Thermal-Mechanical Model of Depression Formation in Steel Continuous Casting: Matthew Zappulla1; Brian Thomas1; 1University of Illinois at Urbana-Champaign
Many serious defects in continuous casting of steel, including surface cracks and depressions, are related to thermal-mechanical behavior during solidification in the mold. A finite-element model has been developed to simulate temperature, stress, and shape of the steel shell near the strand surface, as it moves down the mold at the casting speed in a state of generalized plane strain. The thermal model simulates transient heat transfer in the solidifying steel shell and across the interfacial gap between the shell and the mold wall. It is coupled with a stress model that features temperature-, composition-, and phase- dependent thermal-elastic-visco-plastic constitutive behavior of the steel. Depressions are predicted to form when the shell is subjected to either excessive compression or tension, but the shapes differ. Predicted depression shapes are compared with previous plant observations. The model reveals new insights into the mechanisms of surface depressions and longitudinal cracks in this process.
Effect of Continuous Casting Processing Parameters on the Hot Ductility of Micro-alloyed Steels: Hossam Ibrahim1; Mohamed Soliman1; Heinz Palkowski1; 1Clausthal University of Technology
Different grades of continuously cast steel slabs are prone to cracking, taking place in the casting shop or even on the route to hot rolling. Low ductility during straightening at a temperature range between 700 °C – 1100 °C is one of the reasons. This effect is believed to be due to the presence of titanium and niobium precipitates at higher temperature ranges and a low percentage of formed ferrite during unbending at lower temperatures. The hot ductility behaviour of steel with 0.08% C, 0.12% Ti and 0.045% Nb was investigated by hot tensile testing using a thermo-mechanical simulator to draw a ductility map for the selected alloy. Ferrite formation was studied to define the Ar3 temperature. The amounts and variation of carbides and nitrides were modelled by ThermoCalc software and investigated by microstructural analysis by SEM. It is shown that increasing the strain rates is beneficial to hot ductility.
3:25 PM Break
Evaluation of Hot Cracking Sensitivity Using Multiphase Field and FE Methods during Continuous Casting of Nb Microalloyed Gear Steels: Viktor Kripak1; Ulrich Prahl1; Wolfgang Bleck1; 1RWTH Aachen
Integrated Computational Materials Engineering (ICME) is a simulation platform, used for numerical optimization of materials and process chains. As a part of this platform, hot cracking sensitivity of Nb alloyed steels are analyzed as a function of its chemical composition at continuous casting conditions. The factors like grain nucleation. segregation, phase evolution and precipitation which during solidification are expected to effect the cracking sensitivity, are numerically simulated on microscale using multiphase field approach. From the simulation results, the significant difference in the steels with and without Nb are quantitatively evaluated and correlated with hot cracking behavior using Rappaz-Drezet-Gremaud (RDG) criterion. FE model with integrative flow curves represents the local stress distribution as a function of the time, temperature and deformation on the macroscopic scale. By combining the capabilities of microscale and macroscale simulation provides the information to optimize process parameters and eventually reduce hot cracking during solidification in casting process.
Study for the Initiation Locations of Longitudinal Surface Cracks on Beam Blank in the Mold of Continuous Casting: Wei Chen1; 1North China University of Science and Technology
During beam blank continuous casting production, lots of longitudinal cracks easily appear on the surface. In order to study the initiation locations of longitudinal surface cracks in the mold, a coupled thermo–elasto–plastic finite element model was established on the software ABAQUS. According to the results, it can be inferred that the forming locations of longitudinal surface cracks easily appear on the surface of the fillet, the web center, the flange tip and the flange center. Moreover, initiation locations forming longitudinal surface cracks should be: on fillet at a distance of 200mm to the meniscus, and the other three sections at a distance of 180mm to the meniscus. This study can not only provide stress boundary conditions for the research of longitudinal surface cracks’ initiation and growth, but also help the actual production to decrease longitudinal cracks on the beam blank.
The Influence of SEN and Upper Nozzle Design on the Flow Character for the Slab Quality: Yu Yanwen1; 1Baoshan Iron & Steel Co. Ltd.
The behavior of the liquid steel in the mold will decisively influence the slab quality of a Continuous Casting machine by giving casting conditions, like oscillation parameters and so on. Reasonable flow distribution out of SEN can reduce the impact on the shell formation and the mold level fluctuation and this ensure the proper casting powder melting and uniform heat transfer, promote steel inclusion floating and avoid the involvement of the casting powder into the steel, all this will contribute a better quality of casting slab. A great deal research works had been done on the improvement of nozzle’s structure, Improve the sealing at the joints to reduce re-oxidation; proper preheating and thermo insulation. measures mentioned above can contribute to reduce nozzle clogging, but, can not eliminate the SEN clogging completely. This paper introduces a new design of the submerged nozzle to effectively solve the nozzle blockage of heterogeneous adhesion.
4:45 PM Concluding Comments