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Hervé Combeau - One of the best experts on this subject based on the ideXlab platform.

  • Three Dimensional Methodology to Characterize Large Dendritic Equiaxed Grains in Industrial Steel Ingots
    Materials, 2018
    Co-Authors: Marvin Gennesson, Julien Zollinger, Dominique Daloz, Bernard Rouat, Joëlle Demurger, Hervé Combeau
    Abstract:

    The primary phase grain size is a key parameter to understand the formation of the macrosegregation pattern in large Steel Ingots. Most of the characterization techniques use two-dimensional measurements. In this paper, a characterization method has been developed for equiaxed dendritic grains in industrial Steel castings. A total of 383 contours were drawn two-dimensionally on twelve 6.6 cm 2 slices. A three-dimensional reconstruction method is performed to obtain 171 three-dimensional grains. Data regarding the size, shape and orientation of equiaxed grains is presented and thereby shows that equiaxed grains are centimeter-scale complex objects. They appear to be a poly-dispersed collection of non-isotropic objects possessing preferential orientations. In addition, the volumetric grain number density is 2.2 × 10 7 grains/m 3 , which compares to the 0.5 × 10 7 grains/m 3 that can be obtained with estimation from 2D measurements. The 2.2 × 10 7 grains/m 3 value is ten-times smaller than that previously used in the literature to simulate the macrosegregation profile in the same 6.2 ton ingot.

  • Multiphysics and multiscale modeling and simulation of solidification processes
    2016
    Co-Authors: Hervé Combeau, Miha Založnik
    Abstract:

    Prediction of solidification structures and defects such as grain microstructures, macrosegregations and microporosities is a key issue for industry. Models that predict these structures at the process scale need to account for couplings between various physical phenomena across several imbricated length scales. The goal of this presentation is to provide an overview of existing multiscale models and their principles, as well as of the specific algorithms needed to solve the large number of strongly coupled partial differential equations. Recent applications of these models to industrial solidification processes (casting of Steel Ingots, DC casting of aluminum alloys) are presented. Their ability to help in the understanding of complex phenomena, such as the competition between nucleation and growth of grains in the presence of convection of the liquid and of grain motion, is demonstrated and their predictive capabilities are discussed. Finally, the key remaining questions for future research are addressed.

  • Experimental and Numerical Studies on the Influence of Hot Top Conditions on the Macrosegregation in an Industrial Steel Ingot
    2012
    Co-Authors: Arvind Kumar, Hervé Combeau, Joëlle Demurger, Miha Založnik, Jean Wendenbaum
    Abstract:

    Although a significant amount of work has been already devoted to the prediction of the macrosegration in Steel Ingots, the majority of studies considered the solid phase as fixed. It has been shown that with such an assumption it is not possible to predict the macrosegregation in the centre of heavy Steel Ingots. The motion of the equiaxed grains is generally suspected to be the cause of this macrosegregation. We developed a multiphase and multi-scale model, which is able to describe the evolution of the equiaxed crystals and to take into account their motion. Fragments of dendrites are assumed to be at the origin of the equiaxed grains. The flow of the interdendritic liquid when the grains pile up and are packed is also described. The model was numerically implemented using a 2D finite-volume formulation. We applied the model to study the development of the macrosegregation and the macrostructure in a 65 ton Steel ingot that was experimentally analyzed. The ingot was cast with particular conditions. A metallographic study was performed and the macrosegregation pattern was characterized. The macrosegregation pattern predicted by the model is presented and compared to experimental results. It is shown that in the case of such a heavy ingot, the motion of the equiaxed grains is indeed the main cause of the negative macrosegregation in the centre of the product

  • thermosolutal flow in Steel Ingots and the formation of mesosegregates
    International Journal of Thermal Sciences, 2010
    Co-Authors: Miha Založnik, Hervé Combeau
    Abstract:

    Abstract The influence of the thermosolutal convection of the liquid Steel in the solidifying core of a 3.3-ton ingot on the formation of banded mesosegregates is investigated by a multiscale solidification model. We first show how the thermosolutal flow structure in the solidifying core depends on the relation between the interacting thermal and solutal buoyancy forces and the coupling by the phase-change kinetics. We further show that banded mesosegregates are triggered by instabilities of the solidification front, that their location is determined by flow instabilities, and that their “A” or “V” orientation depends on the global direction of the flow circulation. Moreover, the results show that local remelting is not necessary to develop a channel mesosegregate. Destabilization of the mushy zone with local variations of the solidification velocity is sufficient.

  • Modeling of equiaxed grain evolution and macrosegregations development in Steel Ingots
    Transactions of The Indian Institute of Metals, 2009
    Co-Authors: Hervé Combeau, Arvind Kumar, Miha Zalo·nik
    Abstract:

    The phenomena responsible for the formation of macrosegregations, and grain structures during solidification are closely related. The development of models combining these two aspects is still at its beginning. The application of these models to processes like Steel ingot production is a challenging problem mainly due to the size of the products and the variety of the phenomena to be accounted for. In this article we present simulation results using a multiphase and multiscale model in terms of prediction of grain structures, and macrosegregations during solidification. It is shown for the case of 3.3-ton Steel ingot that when the grains are globular, grain settling is the predominant mechanism of macrosegregation formation. However, when the morphology is dendritic, the direct contribution of grain settling on the segregation formation is negligible; the interdendritic flow in the more permeable sedimentation layer controls the macrosegregation. The globular-dendritic morphology evolution and dendritic-to-globular morphological transition with increases in local grain density, and its impact on the macrosegregation are discussed.

Xiu Hong Kang - One of the best experts on this subject based on the ideXlab platform.

  • hot top design and its influence on feeder channel segregates in 100 ton Steel Ingots
    Materials & Design, 2015
    Co-Authors: Shengwen Qian, Yanfei Cao, Xiu Hong Kang
    Abstract:

    Abstract The influence of hot top design on feeder channel segregates (F-CS) and centerline shrinkage porosities (C-SP) were investigated both experimentally and numerically. Two 100-ton 30Cr2Ni4MoV Steel Ingots with different insulating hot tops were longitudinally sectioned. The experimental results showed few channel segregates but severe shrinkage porosities appeared in the ingot with poorly insulated hot top, while it was the opposite case after the improved hot topping practice. By employing the finite element numerical simulation, the critical condition for the formation of F-CS in 30Cr2Ni4MoV Steel was verified to be R2.1G ≤ 1.0 × 10− 5 °C mm1.1 s− 2.1. Through coupling with the published C-SP criterion (GR− 0.5 ≤ 2.5 °C mm− 1.5 s0.5), it was found out that the increase of hot-top height and preheating temperature would aggravate F-CS while alleviate C-SP contrarily. Hence, to comprehensively control those two defects, the optimum hot-top height and preheating temperature for 100-ton ingot were suggested to be 700 mm and 600 °C, respectively. Ultimately, the ratio of the solidification time for the whole ingot to the ingot body (tf/tb) was proposed as a novel criterion for hot top design. This practical criterion has been successfully utilized to optimize the hot top of a 5-ton Steel ingot.

  • Study on macrosegregation in heavy Steel Ingots
    International Journal of Cast Metals Research, 2010
    Co-Authors: Baoguang Sang, Xiu Hong Kang, Dongrong Liu
    Abstract:

    Macrosegregation in heavy Steel Ingots was studied through numerical and experimental studies of a 500 kg ingot. The numerical model used heat conduction coupled with thermal convection. Simulation results confirm that a small 500 kg ingot poured in a sand mould has a solidification time that is equal to that of a 10 000 kg industrial ingot cast in an iron mould. Accordingly, the sand moulded ingot exhibits more severe macrosegregation compared to the iron moulded ingot, indicating the possibility that a relatively small ingot in sand can simulate conditions in a much heavier Steel ingot in a conventional iron mould. Experiment demonstrated that a 500 kg ingot exhibited all the types of macrosegregation, including A- and V-segregates and negative and positive segregation commonly found in a 65 000 kg Steel ingot.

  • A novel technique for reducing macrosegregation in heavy Steel Ingots
    Journal of Materials Processing Technology, 2010
    Co-Authors: Baoguang Sang, Xiu Hong Kang
    Abstract:

    Abstract Solid Steel balls were added to the melt during the pouring process. A reference 500 kg Steel ingot with no addition of solid balls was poured to provide a realistic comparison with the typical macrosegregation found in conventional industry heavy Ingots. The experiments show that by adding solid balls the degree of macrosegregation is reduced, the formation of A-type segregation is prevented, a generally refined microstructure is obtained and the mechanical properties are improved. Numerical simulation of the solidification process confirms that the addition of solid balls increases the cooling rate, imposing large temperature gradient which refine the microstructure and alleviate the extent of macrosegregation.

Houfa Shen - One of the best experts on this subject based on the ideXlab platform.

  • Finite element modeling of macrosegregation coupled with shrinkage cavity in Steel Ingots using arbitrary Lagrangian-Eulerian model
    China Foundry, 2019
    Co-Authors: Kang-xin Chen, Hao Shi, Houfa Shen
    Abstract:

    Shrinkage cavity has significant influence on macrosegregation in Steel Ingots. An arbitrary Lagrangian-Eulerian (ALE) model based on volume averaging method is developed to predict the coupled formation progress of macrosegregation and shrinkage cavity during solidification of Steel Ingots. The combined effect of thermal-solutal convection and solidification shrinkage on macrosegregation is considered in the model. A specially designed mesh update algorithm is proposed to consider the formation of shrinkage cavity. The streamline-upwind/Petrov-Galerkin (SUPG) stabilized finite element algorithm is adopted to solve the conservation equations. Two solution methods for the energy conservation equation are proposed, i.e. the temperature-based solver and enthalpy-based solver. A Pb-48wt.%Sn solidification benchmark is used for validation. Then, the ALE model is applied to a Fe-3.6wt.%C industrial Steel ingot. The formation progress of macrosegregation coupled with shrinkage cavity is predicted. By comparison with the predictions of the finite element model and finite volume model, the effect of shrinkage cavity formation on macrosegregation is investigated. Results show that the formation of shrinkage cavity can significantly change the segregation region and segregation degree at the hot top. It is demonstrated that the ALE model can predict the coupled formation of macrosegregation and shrinkage cavity in Steel Ingots.

  • Numerical Simulation of Macrosegregation with Solid Deformation During the Solidification of Steel Ingots Using a Single-Phase/Two-Phase Integrated Model
    Metals, 2019
    Co-Authors: Kang-xin Chen, Houfa Shen
    Abstract:

    Macrosegregation, a serious defect formed during the solidification of Steel Ingots, impairs the performance of the final components. To predict macrosegregation caused by thermal-solutal convection and solid deformation, a volume-averaged single-phase/two-phase integrated model is developed. During the deformation stage, the two-phase model coupling the solid deformation and liquid flow in the mushy zone is utilized. Before or after the deformation stage, the motion of the solid phase is neglected, and the single-phase model is solved. A 450 kg Steel ingot punching test is considered for application. The results show that when the solid shell of the ingot is being punched, the solid phase in the mushy core at punching height is compressed, and a relative liquid flow is induced. This in turn causes a transition of positive segregation to negative segregation in the compressed mushy core of the ingot. According to numerical sensitivity tests of different punching parameters, as the punching start time and punching velocity increase, the effect of punching on macrosegregation will be smaller. It is demonstrated that the single-phase/two-phase integrated model can predict macrosegregation in the Steel Ingots which are deformed during solidification.

  • Numerical Simulation of Macrosegregation in a 535 Tons Steel Ingot with a Multicomponent-Multiphase Model
    The Minerals Metals & Materials Series, 2017
    Co-Authors: Kang-xin Chen, Houfa Shen
    Abstract:

    To accurately simulate the formation of macrosegregation, a major defect commonly encountered in large Ingots, solidification researchers have developed various mathematical models and conducted corresponding Steel ingot dissection experiments for validation. A multicomponent and multiphase solidification model was utilized to predict macrosegregation of Steel Ingots in this research. The model described the multi-phase flow phenomenon during solidification, with the feature of strong coupling among mass, momentum, energy, and species conservation equations. Impact factors as thermo-solutal buoyancy flow, grains sedimentation, and shrinkage-induced flow on the macroscopic scale were taken into consideration. Additionally, the interfacial concentration constraint relations were derived to close the model by solving the solidification paths in the multicomponent alloy system. A finite-volume method was employed to solve the governing equations of the model. In particular, a multi-phase SIMPLEC (semi-implicit method for pressure-linked equations-consistent) algorithm was utilized to solve the velocity-pressure coupling for the specific multiphase flow system. Finally, the model was applied to simulate the macrosegregation in a 535 tons Steel ingot. The simulated results were compared with the experimental results and the predictions reproduced the classical macrosegregation patterns. Good agreement is shown generally in quantitative comparisons between experimental results and numerical predictions of carbon, chromium and molybdenum concentration. It is demonstrated that the multicomponent-multiphase solidification model can well predict macrosegregation in Steel Ingots and help optimize the ingot production process.

  • Numerical simulation of convection and inclusion distribution during solidification in a heavy Steel ingot
    IOP Conference Series: Materials Science and Engineering, 2015
    Co-Authors: Rui Lin, Houfa Shen
    Abstract:

    Inclusions content in the Steel ingot is an important index for homogeneity, and it becomes more serious for heavy Steel Ingots which are used for major equipment. However, knowledge about the formation of inclusion in Steel ingot is limited, and modeling of inclusion distribution is still challenging, so it is of great significance to research the behavior of inclusion. In this paper, fluid flow during solidification is numerically simulated based on the equilibrium equations of mass, momentum and energy, and then inclusion distribution is modeled according to the Lagrangian Stokes trajectory method. The Results show that the inclusion distribution in the Steel ingot is influenced by the flow pattern which is affected by the solidification pattern. Therefore, inclusion distribution could be controlled by the solidification front with the optimization of heat transfer condition such as the hot top design of Steel ingot for the high quality Steel production.

  • Modelling of macrosegregation in a 231-ton Steel ingot with multi-pouring process
    Materials Research Innovations, 2015
    Co-Authors: Houfa Shen, Baicheng Liu
    Abstract:

    AbstractLarge Steel Ingots with homogeneous internal quality are critical to the key components of the heavy equipments. Multi-pouring (MP) process, i.e. the sequential pouring with different carbon concentration, is widely applied for the production of Steel Ingots. Multi-pouring process aims to build an initial delaminated carbon concentration distribution for the solidification of Steel Ingots. However, it still remains unclear on the effect of initial concentration distribution on the macrosegregation. The purpose of current study is to assess this effect by a two phase solidification model. Non-orthgonal grids have been adopted for the geometry boundary fitness. Both teeming and subsequent solidification are included in current simulations for a 231-ton Steel with two ladles poured. Besides, a prediction with homogeneous initial concentration distribution is adopted as the reference case. Predictions are compared with measurements along different transverse sections of ingot. It is demonstrated that ...

Baicheng Liu - One of the best experts on this subject based on the ideXlab platform.

  • Modelling of macrosegregation in a 231-ton Steel ingot with multi-pouring process
    Materials Research Innovations, 2015
    Co-Authors: Houfa Shen, Baicheng Liu
    Abstract:

    AbstractLarge Steel Ingots with homogeneous internal quality are critical to the key components of the heavy equipments. Multi-pouring (MP) process, i.e. the sequential pouring with different carbon concentration, is widely applied for the production of Steel Ingots. Multi-pouring process aims to build an initial delaminated carbon concentration distribution for the solidification of Steel Ingots. However, it still remains unclear on the effect of initial concentration distribution on the macrosegregation. The purpose of current study is to assess this effect by a two phase solidification model. Non-orthgonal grids have been adopted for the geometry boundary fitness. Both teeming and subsequent solidification are included in current simulations for a 231-ton Steel with two ladles poured. Besides, a prediction with homogeneous initial concentration distribution is adopted as the reference case. Predictions are compared with measurements along different transverse sections of ingot. It is demonstrated that ...

  • modeling of species transport and macrosegregation in heavy Steel Ingots
    Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2014
    Co-Authors: Wensheng Li, Houfa Shen, Xiong Zhang, Baicheng Liu
    Abstract:

    In the current study, two significant phenomena involved in heavy Steel ingot casting, i.e., species transport and macrosegregation, were numerically simulated. First, a ladle–tundish–mold species transport model describing the entire multiple pouring process of heavy Steel Ingots was proposed. Carbon distribution and variation in both the tundish and the mold of a 292-ton Steel ingot were predicted. Results indicate high carbon concentration in the bottom of the mold while low concentration carbon at the top of mold after the pouring process. Such concentration distribution helps in reducing both negative segregation in the bottom of the solidified ingot and positive segregation at the top. Second, a two-phase multiscale macrosegregation model was used to simulate the solidification process of industrial Steel Ingots. This model takes into account heat transfer, fluid flow, solute transport, and equiaxed grain motion on a system scale, as well as grain nucleation and growth on a microscopic scale. The model was first used to analyze a three-dimensional industry-scale Steel ingot as a benchmark. Then, it was applied to study macrosegregation formation in a 53-ton Steel ingot. Macrosegregation predicted by the numerical model was presented and compared with experimental measurements. Typical macrosegregation patterns in heavy Steel Ingots are found to be well reproduced with the two-phase model.

  • numerical simulation of macrosegregation in Steel Ingots using a two phase model
    International Journal of Minerals Metallurgy and Materials, 2012
    Co-Authors: Houfa Shen, Baicheng Liu
    Abstract:

    A two-phase model for the prediction of macrosegregation formed during solidification is presented. This model incorporates the descriptions of heat transfer, melt convection, solute transport, and solid movement on the system scale with microscopic relations for grain nucleation and growth. Then the model is used to simulate the solidification of a benchmark industrial 3.3-t Steel ingot. Simulations are performed to investigate the effects of grain motion and pipe shrinkage formation on the final macrosegregation pattern. The model predictions are compared with experimental data and numerical results from literatures. It is demonstrated that the model is able to express the overall macrosegregation patterns in the ingot. Furthermore, the results show that it is essential to consider the motion of equiaxed grains and the formation of pipe shrinkage in modelling. Several issues for future model improvements are identified.

  • Modelling of macrosegregation in Steel Ingots: benchmark validation and industrial application
    IOP Conference Series: Materials Science and Engineering, 2012
    Co-Authors: Bingzhen Shen, Houfa Shen, Baicheng Liu
    Abstract:

    The paper presents the recent progress made by the authors on modelling of macrosegregation in Steel Ingots. A two-phase macrosegregation model was developed that incorporates descriptions of heat transfer, melt convection, solute transport, and solid movement on the process scale with microscopic relations for grain nucleation and growth. The formation of pipe shrinkage at the ingot top is also taken into account in the model. Firstly, a recently proposed numerical benchmark test of macrosegregation was used to verify the model. Then, the model was applied to predict the macrosegregation in a benchmark industrial-scale Steel ingot. The predictions were validated against experimental data from the literature. Furthermore, macrosegregation experiment of an industrial 53-t Steel ingot was performed. The simulation results were compared with the measurements. It is indicated that the typical macrosegregation patterns encountered in Steel Ingots, including a positively segregated zone in the hot top and a negative segregation in the bottom part of the ingot, are well reproduced with the model.

  • Three‐dimensional Simulation of Thermosolutal Convection and Macrosegregation in Steel Ingots
    steel research international, 2010
    Co-Authors: Houfa Shen, Baicheng Liu
    Abstract:

    Thermosolutal convection and macrosegregation formation during the solidification of Steel Ingots are numerically simulated in three dimensions. The simulation is based on a fully coupled model for mass, momentum, energy, and species conservation equations. The interdendritic flow in the mushy zone is governed by Darcy's law, and the permeability term is discretized using an interpolated liquid fraction method. The numerical results for a benchmark test of macrosegregation in a Pb-Sn alloy are compared with experimental data taken from the literature. The present model is applied to simulate the solidification of industrial Steel Ingots. Preliminary predictions are obtained, including the positive segregation in the hot top, and the conically shaped negative segregation zone at the bottom of the ingot. The predicted variation of the segregation ratio in carbon along the vertical centreline of an ingot is compared with measurements, and generally good agreement is observed. Future attention should be paid to the precision of prediction by considering complex solidification issues, such as the sedimentation of free equiaxed grains and the formation of shrinkage cavity.

F. P. A. Robinson - One of the best experts on this subject based on the ideXlab platform.

  • A study of high temperature cracking in ferritic stainless Steels
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1992
    Co-Authors: Siu Wah Wai, Michael B. Cortie, F. P. A. Robinson
    Abstract:

    Abstract The cracking that can occur in cast ferritic stainless Steel Ingots or slabs during cooling to room temperature is considered. The present work is focused particularly on the solid state cracking phenomenon sometimes called “clinking”. Examination of samples of industrial and laboratory-produced material indicated that the mechanism of cracking was transgranular cleavage. Experimental results for the toughness of 17 wt.% Cr ferritic stainless Steel castings and slabs are given and these indicate that the ductile-to-brittle transition temperature under plane strain conditions is high and that the cast material is quite brittle at temperatures below about 300 °C. An interrupted tensile test was performed to identify preferential crack initiation sites. A computer model has been used to simulate the morphology of the cracking, and to examine its interaction with the microstructure.