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A review on prediction of casting defects in steel ingots:from Macrosegregation to multi-defect model

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Journal of Iron and Steel Research(International) 2022年第12期29卷 1901-1914页

作者： Jun Li Xiao-wei Xu Neng Ren Ming-xu Xia Jian-guo Li School of Materials Science and Engineering Shanghai Jiao Tong UniversityShanghai 200240China Shanghai Key Laboratory of Advanced High-Temperature Materials and Precision Forming Shanghai 200240China

Due to the nature of the solute redistribution,the reduction in the solidification rate with time in a square root relationship,and the multiphase melt flow during the solidification,casting defects such as Macrosegregation,shrinkage cavity,and porosity will inevitably occur in the steel ingot and intensify with the increase in ingot size.These defects directly affect the performance of the final product and severely restrict the choice of subsequent thermal processing methods and process windows.Therefore,the solidification defects including Macrosegregation,shrinkage/porosity,and inclusions encountered in the preparation of large steel ingots and their formation mechanisms were reviewed.The development progress and the latest development of the Macrosegregation model for steel ingots were introduced in detail,especially the latest progress in the coupling prediction of Macrosegregation and shrinkage as well as Macrosegregation and inclusions.Some methods to reduce Macrosegregation of ingots were discussed as well.Finally,a new casting method called layered casting was introduced in detail.This method can effectively improve the uniformity of the macrostructure and reduce the Macrosegregation of the large ingots and therefore is a promising method for preparing large ingots with high homogeneity.

关键词： Steel ingot Macrosegregation Numerical modeling Multiphase model Solidification defect

Application of heat absorption method to reduce Macrosegregation during solidification of bearing steel ingot

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Journal of Iron and Steel Research(International) 2022年第12期29卷 1915-1926页

作者： Sheng Yu Long-qiang Zhu Jin-hu Lai Ming-xu Pan Yue-yun Liu Wei-dong Xuan Jiang Wang Chuan-jun Li Zhong-ming Ren State Key Laboratory of Advanced Special Steel and Shanghai Key Laboratory of Advanced Ferrometallurgy and School of Materials Science and Engineering Shanghai UniversityShanghai 200444China Daye Special Steel Co. Ltd.Huangshi 435001HubeiChina

The control of Macrosegregation is still a difficult problem for the production of large steel ingots.In order to develop new techniques for producing low-Macrosegregation and high-quality steel ingots,the effect of the heat absorption method(HAM)used by the inorganic material rods to cool the liquid steel on the formation of Macrosegregation during solidification of a 5-t GCr15SiMn bearing steel ingot was studied using experiment and mathematical simulation.The inorganic material was a mixture of CaF2 and CaO.The levels of Macrosegregation in the longitudinal sections of two ingots with and without HAM were compared.Experimental results showed that the application of HAM reduced the positive segregation in the upper part of the ingot and the negative segregation in the lower part.The levels of carbon segregation along the longitudinal centerline and horizontal direction at different heights were all alleviated and the fluctuation of carbon segregation was significantly reduced.The simulation results confirmed that the melting and floating of the inorganic material could carry the sensible heat to the top of the liquid steel quickly.This leads to the acceleration of the cooling rate of the liquid steel,thereby alleviating the level of Macrosegregation.

关键词： Large steel ingot Macrosegregation Inorganic material Heat absorption method Mathematical simulation

A comparative study on Sn Macrosegregation behavior of ternary Al-Sn-Cu alloys prepared by gravity casting and squeeze casting

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China Foundry 2023年第1期20卷 63-70页

作者： Ming Xu Yan-guo Yin Cong-min Li Cong-chong Duan College of Mechanical Engineering Hefei University of TechnologyHefei 230002China Anhui Yihui New Materials Co. Ltd.Hefei 230000China

A comprehensive study on Sn Macrosegregation behavior in ternary Al-Sn-Cu alloys was carried out by comparative analysis between gravity casting and squeeze casting samples.The microstructure and Sn distribution of the castings were characterized by metallography,scanning electron microscopy(SEM),energy-dispersive X-ray(EDX)spectroscopy,and a direct reading spectrometer.Results show that there are obvious differences in Sn morphology between gravity casting and squeeze casting alloys.Under squeeze casting condition,the grain size of the casting is smaller and the distribution ofβ(Sn)is uniform.This effectively reduces the segregation of triangular grain boundary as well as the segregation of Sn.The segregation types of Sn in gravity casting and squeeze casting samples are obviously different.The upper surfaces of gravity casting samples show severe negative segregation,while all the lower surfaces have positive segregation.Compared with gravity casting,squeeze casting solidifies under isostatic pressure.Due to the direct contact between the upper surface of the casting and the mold,the casting solidifies faster under higher undercooling degree and pressure.Consequently,the uniform distribution of Sn reduces the segregation phenomenon on the surface of the casting.

关键词： ternary Al-Sn-Cu alloy squeeze casting Macrosegregation mechanism

Numerical simulation of Macrosegregation in billet continuous casting influenced by electromagnetic stirring

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Journal of Iron and Steel Research(International) 2022年第4期29卷 612-627页

作者： Qi-peng Dong Jiong-ming Zhang Yan-bin Yin Hiromi Nagaumi School of Iron and Steel High-Performance Metal Structural Materials Research InstituteSoochow UniversitySuzhou 215021JiangsuChina State Key Laboratory of Advanced Metallurgy University of Science and Technology BeijingBeijing 100083China

A three-dimensional numerical model coupling the Macrosegregation and magnetohydrodynamic simulations was developed to investigate the effects of electromagnetic stirring(EMS)on the Macrosegregation.The results show that a significant swirling flow was induced by the in-mold EMS,which further changed the shape of the solidification shell and homogenized the solute elements in mold.However,the effects were only confined to the initial billet shell.The improvement in centerline segregation was observed with the usage of the final EMS(F-EMS),which led to the forced convection at the final solidification stage.The solute elements in the mushy zone were significantly even,with the maximum segregation degree of solute C reducing from 1.311 to 1.237.In addition,the effects of the stirrer positions and currents of F-EMS on the Macrosegregation alleviation were numerically studied.Different values of centerline segregation were predicted with various stirrer positions and currents,and there is an optimum stirrer parameter to obtain the best Macrosegregation alleviation.In the experimental conditions,the optimum position was about 7 m away from meniscus,and the optimum current was 300 A.

关键词： Numerical simulation Macrosegregation Electromagnetic stirring Continuous casting

Structures and Macrosegregation of a 2024 aluminum alloy fabricated by direct chill casting with double cooling field

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China Foundry 2022年第1期19卷 1-8页

作者： Cheng Zhu Zhi-hao Zhao Qing-feng Zhu Gao-song Wang Yu-bo Zuo Gao-wu Qin Research Center for Metallic Wires School of Materials Science and EngineeringNortheastern UniversityShenyang 110819China Key Laboratory of Electromagnetic Processing of Materials Ministry of EducationNortheastern UniversityShenyang 110819China Key Laboratory of Anisotropy and Texture of Materials Ministry of EducationNortheastern UniversityShenyang 110819China

Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the Macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.

关键词： aluminum alloy direct chill casting double cooling field grain refinement Macrosegregation

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

Finite element modeling of Macrosegregation coupled with shrinkage cavity in steel ingots using arbitrary Lagrangian-Eulerian model

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China Foundry 2019年第5期16卷 291-299页

作者： Kang-xin Chen Hao Shi Hou-fa Shen Key Laboratory for Advanced Materials Processing Technology Ministry of EducationSchool of Materials Science and Engineering Tsinghua University

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.

关键词： steel ingot Macrosegregation shrinkage cavity ALE model finite element modeling

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 study of Macrosegregation formation of ingot cast in normal sand mold and water-cooled sand mold

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Acta Metallurgica Sinica(English Letters) 2011年第1期24卷 54-64页

作者： Dongrong LIU Xiuhong KANG Baoguanq SANG Dianzhong LI Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China School of Materials Science and Engineering Harbin University of Science and TechnologyHarbin 150040 China

Formation of Macrosegregation of 5 t steel ingots cast in sand molds with and without water-cooled copper tube is simulated by solving macroscopic mass, momentum, species and energy conservation equations with the consideration of shrinkage formation. Predicted Macrosegregation pattern of the ingots shows a fair agreement with the experimental data. Both calculations and experiments reveal that some positive segregation patches are formed at the bottom of ingot. With the water-cooled copper tube inserted in the sand mold, the ingot cast has a less intensive Macrosegregation. Mechanisms of Macrosegregation formation are numerically analyzed. Explanations regarding the influences of fluid flow and temperature change upon the segregation formation are provided.

关键词： Macrosegregation Water-cooled mold Fe-C alloy Numericalsimulation