Research Area:
Dr. Sengupta joined Prof. Thomas’ research group as a Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellow in August 2003. He came to UIUC from the University of British Columbia (UBC), where he received his doctoral degree in Metals and Materials Engineering. Prior to this, he spent four years in Tata Engineering & Locomotive Company, India as a quality assurance professional in the automotive engines division. Dr. Sengupta earned his master’s degree in Metallurgical Engineering from the Indian Institute of Technology (IIT) at Kharagpur, India.
Dr. Sengupta was selected as one of the two Young Leaders for the year 2005 by the Light Metals Division of the Minerals, Metals & Materials Society (TMS). His Ph.D. thesis won the first prize (2002) in the graduate thesis competition organized every year by the Canadian Institute of Mining, Metallurgy and Petroleum (CIM). He also received the prestigious Margaret Fulton Award for the year 2002, which is awarded to an individual on campus who has made a significant contribution to student welfare by the UBC Campus Advisory Board on Student Development. He also received the University Graduate Fellowship, the J. Keith Brimacombe Award and the John S. Nadeau Prize while pursuing his graduate studies at UBC. He was awarded the Institute Silver Medal in Metallurgical Engineering by IIT Kharagpur.
Dr. Sengupta’s paper on the use of water cooling during continuous casting of steel and aluminum alloys (coauthors: Prof. B. G. Thomas and Prof. Mary Wells, UBC) published in Metallurgical and Materials Transactions A was chosen by the Editors of TMS as a “must read” in January 2005. He has co-authored 19 papers in international journals and conference proceedings, and numerous industrial reports. He has collaborated with Alcan International Limited, Canada and POSCO Steel, South Korea during his doctoral and post-doctoral research work, respectively. In addition to his research, he has lectured and ran tutorials in second-year materials engineering for a number of years and was involved in student and academic governance at several levels at UBC.
However, he still continues to struggle with his “zee” instead of “zed” during his presentations.
Education:
N/A
Projects:
Characterization of hooks & oscillation Marks using optical & scanning electron microscopy (UIUC):
Hooks and other sub-surface features in continuous-cast ultra-low carbon steel samples have been examined by optical microscopy, EDXS, and EPMA techniques. Special etching reagents revealed the dendrites growing from both sides of the line of hook origin (refer to figure). Results provided evidence of both solidification and subsequent overflow of the liquid steel meniscus. The instantaneous meniscus shape governs the shape and microstructure of the final hook, and the extent of the liquid steel overflow determines the shape of the oscillation mark.
Collaboration:
Pohang University of Science & Technology, South Korea
POSCO Gwangyang Works, South Korea
Acknowledgements:
H. J. Shin, G. G. Lee, B. G. Thomas, S. H. Kim
)Effect of a sudden level fluctuation on hook formation during continuous casting of ultra-low carbon steel slabs (UIUC)
A transient finite-element model, CON2D has been used to compute temperature, stress development, and distortion of a steel shell during the initial stages of solidification. Temperature-dependent properties, phase transformations and thermal shrinkage effects have been included. The model uses a creep-type elastic-viscoplastic constitutive equation for steel and has been applied to study the effect of a sudden metal level fluctuation for different steel grades. The results (refer to figure) show that thermal stress can indeed cause the exposed portion of the thin shell to bend away from the mold as the liquid level suddenly drops, which may ultimately initiate hook formation.
Collaboration:
Continuous Casting Consortium Members
Acknowledgements:
Y. Meng, C. Ojeda, C. Li, B. G. Thomas & NSERC
Electron Backscattered Diffraction (EBSD) analysis of hook marks in ultra-low carbon steel (UIUC):
The distribution of crystallographic orientation (refer to figure) in the microstructure near the hook region was analyzed by EBSD method using a JEOL JSM-7000F field emission analytical scanning electron microscope. The microscope was equipped with a HKL Technology EBSD system with a high resolution (up to 1.2 nm for a 30 kV accelerating voltage) detector that allowed accurate analysis of Kikuchy patterns over an area of 300 m x 400 m in steps of 2 m. The data obtained from EBSD was analyzed using HKL Technology Channel 5 suite of programs, which can display subtle changes in orientation along a line running across grains or sub-grains.
Collaboration:
Continuous Casting Consortium Members
Acknowledgements:
B. G. Thomas, M. A. Wells, C. W. Sinclair, H. Ahmed, G. G. Lee & J. Mabon
A new mechanism for hook formation in ultra-low carbon steel slabs during continuous casting (UIUC):
The initial stages of solidification near the meniscus (refer to figure) during continuous casting of steel slabs involve many complex inter-related transient phenomena, which cause periodic oscillation marks, sub-surface hooks, and related defects. A detailed mechanism for the formation of curved hooks and their associated oscillation marks has been developed based on a careful analysis of numerous specially-etched samples from ultra-low carbon steel slabs combined with previous measurements, observations, and theoretical modeling results. It has been demonstrated that hooks form by solidification and dendritic growth at the liquid meniscus during the negative strip period. Oscillation marks are generated when molten steel overflows over the curved hook and solidifies by nucleation of undercooled liquid. The validity of this mechanism has been justified by its explanation of several plant observations.
Collaboration & Acknowledgement:
B. G. Thomas & UIUC Continuous Casting Consortium Industrial Members
A 3-D transient thermal model to predict cooling behaviour of DC cast AA5182 aluminum alloy ingots (UBC):
This comprehensive mathematical model has been developed to describe heat transfer during the start-up phase of the direct chill (DC) casting process. The model, based on the commercial finite element package ABAQUS, includes primary cooling via the mould, secondary cooling via the chill water, and ingot base cooling. Specialty boundary conditions, such as water ejection (refer to figure) and water incursion were incorporated. The model has been validated against temperature measurements obtained from industry. Comparison of the model predictions with the data collected from the cast/embedded thermocouples indicates that the model is capable of describing the flow of heat in the early stages of the casting process satisfactorily.
Collaboration:
Arvida Research & Development Centre, Alcan Int. Ltd.
Acknowledgements:
S. L. Cockcroft, M. A. Wells, D. M. Maijer & NSERC
Effect of constitutive laws on strain and butt curl predicted by thermomechanical models for DC casting (UBC):
A critical aspect of these process models is the way the constitutive behaviour of the material is modeled in the solid state, as this can influence the stress, strain, and butt curl predictions during the casting process. This work compares four different methods of modeling constitutive behaviour (refer to figure), in the solid state, available in the commercial FE package ABAQUS, namely: elastic-plastic, elastic-rate dependent plastic, elastic-creep, and combined elastic-creep-plastic using data measured on as-cast AA5182 at strain rates and temperatures consistent with those typically seen during direct chill (DC) casting. The comparison of the different methods was done using a 2-D uncoupled axisymmetric thermal and stress model of an aluminum billet during the start-up phase of the DC casting process.
Acknowledgements:
N. J. McDonald, M. A. Wells, D. M. Maijer, S. L. Cockcroft & NSERC
Residual stress measurement on DC cast ingots based on core-hole drilling method (UBC):
The ring-hole method was used to measure the near-surface residual stress at several locations on the rolling face of a direct chill cast aluminum ingot. The strain measurements were made using Micro-Measurements 125 mW strip gages, which were glued inside a 7.92 mm deep central hole. Epoxy glue was used to attach the strain gages and was cured by resistively heating each strain gage. A high-speed air turbine and jig (shown in the figure) were used to machine the initial hole and surrounding ring. A sequence of strain measurements was taken at each measurement location as the depth of the ring was increased in 0.13 mm increments until full strain relief was achieved at ~11.43 mm depth.
Acknowledgements:
G. Schajer, S. Marte, R. Stapleton, S. L. Cockcroft
Quantification of thermal and stress evolution in DC cast ingots during start-up phase (UBC):
A coupled thermal-stress FE model, based on ABAQUS, has been formulated to describe thermal and stress/strain fields during the start-up phase of the direct chill casting process for AA5182 aluminum ingots. The stress analysis employs a temperature dependent elastic rate-dependent plastic material constitutive behavior. The model has been validated against temperature and displacement measurements obtained from two ingots, cast under different start-up conditions. The stress analysis was further validated by residual stress data obtained from the cold cast ingot. Comparison of the model predictions with the industrial and laboratory data indicates that the model is capable of satisfactorily simulating the thermomechanical behavior of the ingot during the start-up phase (refer to figure).
Collaboration:
Arvida Research & Development Centre, Alcan Int. Ltd.
Acknowledgements:
S. L. Cockcroft, M. A. Wells, D. M. Maijer & NSERC
Implementation of a strain-based hot tearing criterion in DC cast aluminum ingots (UBC):
Hot tearing in DC cast AA5182 alloy ingots (refer to figure) has been investigated using a total strain-based hot tearing criterion, which has been implemented into a 3-D fully coupled thermal-stress finite element (FE) process model. In a critical region just above the ingot lip, the plastic strain accumulated during solidification may exceed the ductility limit at a temperature of about 575 oC, depending on the cooling conditions, and can become susceptible to hot tearing. In contrast, both further up the ingot, and out towards the edge of the rolling face, the accumulated strain has been found to be within the ductility limit of the cast material.
Collaboration:
Arvida Research & Development Centre, Alcan Int. Ltd.
Acknowledgements:
A. Phillion, S. L. Cockcroft & NSERC
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