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Numerical Simulation of Macrosegregation Caused by Thermal–Solutal Convection and Solidification Shrinkage Using ALE Model

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Acta Metallurgica Sinica(English Letters) 2019年第11期32卷 1396-1406页

作者： Kang-Xin Chen hou-fa shen Key Laboratory for Advanced Materials Processing Technology Ministry of Education School of Materials Science and Engineering Tsinghua University

Solidifi cation shrinkage has been recognized as an important factor for macrosegregation formation. An arbitrary Lagrangian–Eulerian(ALE) model is constructed to predict the macrosegregation caused by thermal–solutal convection and solidi-fi cation shrinkage. A novel mesh update algorithm is developed to account for the domain change induced by solidifi cation shrinkage. The velocity–pressure coupling between the non-homogenous mass conservation equation and momentum equation is addressed by a modifi ed pressure correction method. The governing equations are solved by the streamline-upwind/Petrov–Galerkin-stabilized fi nite element algorithm. The application of the model to the Pb-19.2 wt%Sn alloy solidifi cation problem is considered. The inverse segregation is successfully predicted, and reasonable agreement with the literature results is obtained. Thus, the ALE model is established to be a highly effective tool for predicting the macrosegregation caused by solidifi cation shrinkage and thermal–solutal convection. Finally, the effect of solidifi cation shrinkage is analyzed. The results demonstrate that solidifi cation shrinkage delays the advance of the solidifi cation front and intensifi es the segregation.

关键词： Macrosegregation Solidification shrinkage Finite element method Arbitrary Lagrangian–Eulerian(ALE)

Internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio

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China Foundry 2021年第2期18卷 110-117页

作者： Jing-an Yang hou-fa shen School of Transportation Science and Engineering Beihang UniversityBeijing 100191China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China

Steel ingot with a large height-to-diameter ratio is utilized to produce multiple products by one stock in *** cooling is a usual way to enhance production ***,the combination of the two factors will generate internal defects,such as shrinkage porosity and hot *** characteristic of internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio was examined by an ultrasonic test.A slice was sectioned from the ingot middle part where billets containing star-like crack were further *** billets were examined by X-ray high energy industrial CT,and the compactness was reconstructed in three *** near the crack was observed using scanning electron microscopy,and the solidification process and grain size were studied by high temperature confocal ***,thermo-mechanical simulation and post-processing were carried out to analyze the formation of shrinkage porosity and hot crack.A new criterion considering mushy zone mechanical behavior in brittle temperature as well as grain size distribution was proposed to evaluate hot cracking potential in the *** results show that a deep shrinkage porosity band easily forms in the center line of such an ingot with a large height-to-diameter ratio,and water-cooling further generates excessive tensile stress tearing the liquid films around the ***,hot cracks begin to propagate along grain *** grain size in the upper and center of the ingot is large,which leads to an inverted cone shape defects zone in the ingot center.

关键词： steel ingot porosity hot crack industrial CT thermo-mechanical simulation

Influence of N/C ratio on microstructure and properties of new highstrength weathering steels

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Journal of Iron and Steel Research International 2019年第1期26卷 84-90页

作者： Jian Cheng Yue-hua Guo hou-fa shen The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and TechnologyWuhan 430081HubeiChina Key Laboratory for Advanced Materials Processing Technology School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Pangang Group Research Institute Co. Ltd.State Key Laboratory of Vanadium and Titanium Comprehensive UtilizationPanzhihua 617000SichuanChina

Influence of the N/C ratio on the microstructure and properties of new-generation high-strength weathering steels was investigated using calculation of phase diagram(CALPHAD)and *** microstructures of weathering steels containing different N/C ratios were predicted by a CALPHAD approach,and only three phases were predicted in these steels within the rolling temperature range of 850-1050℃.The precipitation fraction of VN/V(C,N)in creases with increasing N/C *** of the four tested steels were all experimentally determined to contain bainite,ferrite,and VN precipitates after air cooling to room *** bainite fraction increases with in creasing N/C ratio,and it is 85%in the steel containing 0.038% N and 0.032% C,The results of the tensile tests and impact tests demonstrated that the yield strength and tensile strength of the steel containing 0.038%N and 0.032%C are greater than 550 and 650 MPa,respectively,and the elongation is greater than 24%,which satisfies the design objectives for mechanical *** impact toughness values of the four steels at 0,-20,and-40℃ are all greater than 24 *** increasing N/C ratio,the bainite fraction and the precipitation fraction of VN/V(C,N)increase,resulting in increasing yield strength and tensile strength.

关键词： CALPHAD Weathering steel Tensile test-Impact test Microstructure

Numerical simulation of macrosegregation during solidification of binary alloys

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Rare Metals 2016年第8期35卷 591-597页

作者： Wu-Tao Tu hou-fa shen Bai-Cheng Liu Key Laboratory for Advanced Materials Processing Technology Ministry of Education School of Materials Science and Engineering Tsinghua University

Macrosegregation as a consequence of solidifi- cation of a binary Pb-48 wt% Sn alloy in two-dimensional rectangle cavity was investigated by two-phase model instead of the common used continuum model. The macroscopic transport of mass, momentum, species and energy was cou- pled with the microscopic descriptions of grain nucleation and growth. The mathematic equations of the two-phase model were discretized on staggered grids and solved by the finite volume method. The final tin concentrations along different heights over the bottom face were compared with the ex- periment measurements. Simulations with different mi- crostructure parameters （second dendrite arm spacing （SDAS）） were conducted to ascertain the influence of microstructure on the final macrosegregation. The results show that with the decrease in SDAS value, the drag force as the resistance to relative motion between solid and liquid phase increases, and the macrosegregation during solidification is alleviated.

关键词： Macrosegregation Two-phase model Solidification Second dendrite arm spacing

A Numerical Study of the Effect of Multiple Pouring on Macrosegregation in a 438-Ton Steel Ingot

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Acta Metallurgica Sinica(English Letters) 2015年第9期28卷 1123-1133页

作者： Zhen-Hu Duan hou-fa shen Bai-Cheng Liu Key Laboratory for Advanced Materials Processing Technology Ministry of Education School of Materials Science and Engineering Tsinghua University

In present paper, a ladle-tundish-mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring （MP） process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring （SP） and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.

关键词： Multiple pouring process Macrosegregation Numerical simulation Large steel ingot

Numerical simulation of macrosegregation in steel ingots using a two-phase model

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International Journal of Minerals,Metallurgy and Materials 2012年第9期19卷 787-794页

作者： Wen-sheng Li hou-fa shen Bai-cheng Liu The Key Laboratory of the Ministry of Education of China for Advanced Materials Processing Technology Deparanent of Mechanical EngineeringTsinghna UniversityBeijing 100084China

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 per- formed 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.

关键词： steel ingots solidification segregation shrinkage modelling

Temperature distribution and dynamic control of secondary cooling in slab continuous casting

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International Journal of Minerals,Metallurgy and Materials 2009年第6期16卷 626-631页

作者： Liang-hang Guo Yong Tian Man Yao hou-fa shen School of Materials Science and Engineering Dalian University of Technology Dalian 116023 China Anshan Iron and Steel Group Anshan 114021 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

To predict and optimize the temperature distribution of slab continuous casting in steady operational state, a three-dimensional model （named ＂offline model＂） based on the heat transfer and solidification theories was developed. Both heat transfer and flux distribution characteristics of the nozzle sprays on the slab were considered, and the complicated boundary conditions, such as spray cooling, natural convection, thermal radiation as well as contact cooling of individual rolls were involved in the model. By using the calibrated caster dependent model factors, the calculated temperature and shell thickness accorded well with the measured. Furthermore, a dynamic secondary water cooling control system was also developed on the basis of a two-dimensional transient heat transfer model （named ＂online model＂） and incremental PID control algorithm to reduce slab surface temperature fluctuation in unsteady state. Compared with the traditional spray table control method, the present online model and dynamic PID control demonstrate a higher capability and flexibility to adjust cooling water flowrate and reduce slab surface temperature fluctuation when the casting speed is changed.

关键词： mathematical model slab temperature dynamic control continuous casting

Intelligent casting:Empowering the future foundry industry

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China Foundry 2024年第5期21卷 409-426页

作者： Jin-wu Kang Bao-lin Liu Tao Jing hou-fa shen School of Materials Science and Engineering Key Laboratory for Advanced Materials Processing TechnologyTsinghua UniversityBeijing 100084China

Emerging technological advances are reshaping the casting sector in latest *** technology is evolving towards intelligent casting paradigm that involves automation,greenization and intelligentization,which attracts more and more attention from the academic and industry *** this paper,the main features of casting technology were briefly summarized and forecasted,and the recent developments of key technologies and the innovative efforts made in promoting intelligent casting process were ***,the technical visions of intelligent casting process were also put *** key technologies for intelligent casting process comprise 3D printing technologies,intelligent mold technologies and intelligent process control *** future,the intelligent mold that derived from mold with sensors,control devices and actuators will probably incorporate the Internet of Things,online inspection,embedded simulation,decision-making and control system,and other technologies to form intelligent cyber-physical casting system,which may pave the way to realize intelligent *** is promising that the intelligent casting process will eventually achieve the goal of real-time process optimization and full-scale control,with the defects,microstructure,performance,and service life of the fabricated castings can be accurately predicted and tailored.

关键词： intelligent casting 3D printing intelligent mold process control cyber-physical casting system embedded simulation

Real-time observation of bainite formation at heterogeneous phases in a high-strength weathering steel

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Journal of Iron and Steel Research International 2019年第3期26卷 301-309页

作者： Jian Cheng Jia-sheng Qing Yue-hua Guo hou-fa shen Key Laboratory for Advanced Materials Processing Technology Ministry of EducationSchool of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Pangang Group Research Institute Co. Ltd.State Key Laboratory of Vanadium and Titanium Comprehensive UtilizationPanzhihua 617000SichuanChina

Due to the excellent comprehensive mechanical properties and toughness of bainite steels,bainite is regarded as a most desirable microstructure for the new generation of high-strength weathering *** formation of bainite was observed in real time in a high-strength weathering steel,and the results showed that bainite laths show impingement during phase *** preferred regions of nucleation sites were identified,and the growth rate of bainite was *** growth mechanism of bainite was demonstrated to exhibit growth rate contributions from both the diffusion mechanism and the shear ***,the heterogeneous phases that form preferred sites for bainite nucleation were quantitatively identified by scanning electron microscopy(SEM),energy-dispersive X-ray spectrometry(EDS),and calculation of phase diagram(CALPHAD).The austenite grain sizes in crease with increasing austenite temperature,which leads to longer bainite *** influence of a small lattice disregistry between the heterogeneous phases and bainite on the bainite nucleation was *** disregistries between the favorable heterogeneous phases of VN,VC,TiN,or TiC and the ot-Fe in bainite are 2.9,3.1,3.9,and 4.6%,***,VN,VC,TiN,and TiC can act as highly effective nuclei for bainite during the bainite transformation.

关键词： Bainite Real-time observation Plasticity Phase transformation Weathering steel