Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

Solidification Simulation of Investment Castings of Single Crystal Hollow Turbine Blade

The three-dimensional solidification simulation of the investment castings of single crystal hollow turbine blade at the withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min has been performed with the finite element thermal analysis. The calculated results are in accordance with the experimental ones. The results show that with the increase of withdrawal rate the concave curvature of the liquidus isotherm is larger and larger, and the temperature gradients of the blades increase. No effects of withdrawal rate on the distribution of the temperature gradients of the starter and helical grain selector of the blades are observed at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min. The relatively high temperature gradient between 500℃/cm and 1000℃/cm in the starter and helical grain selector is obtained at three withdrawal rates.

Electro-Pulse on Improving Steel Ingot Solidification Structure

Pulse Electric Discharging (PED) is a novel technique that can modify solidifying structure and reduce grain size. ItS effectsapplied to the high carbon liquid steel were presented here. The macrostructure and microstructure of the high carbon alloy steel werealso observed. Results show that (1 ) the length of columnar crystal at the edge of ingot without PED treatment is much longer than thatwith PED, and (2) the perlite lamellae of steel billets after deposed by PED are twisted and shortened. An explanation of those experimental results is given.

Continuous melting and directional solidification of silicon ingot with an electromagnetic cold crucible

In order to avoid contamination from the crucible and to modify the structures,a new solidification method based on cold crucible technology was used to prepare silicon ingots.A silicon ingot with square cross section was directionally solidified with a cold crucible.The mechanism of the cold crucible directional solidification of silicon ingot was revealed.Due to the induction heat that was released in the surface layer and the incomplete contact between the crucible and the melt,the lateral heat loss was reduced and the silicon ingot was directionally solidified.The structures,dislocation defects and the grain growth orientation of the ingot were determined.The results show that neither intergranular nor intragranular precipitates are found in the ingot,except for the top part that was the last to solidify.The average dislocation density is about 1 to 2×106 cm-2.The grains are preferentially <220> orientated.

Numerical Simulation of Transport Phenomena in Solidification of Multicomponent Ingot Using a Continuum Model

A continuum model proposed for dendrite solidification of multicomponent alloys, with any partial solid back diffusion, was used to numerically simulate the macroscopic solidification transport phenomena and macrosegregations in an upwards directionally solidified plain carbon steel ingot. The computational results of each macroscopic field of the physical variables involved in the solidification process at a middle solidification stage were presented.

Effect of hollow insulation riser on shrinkage porosity and solidification structure of ingot

The thermal insulation performance of riser is very important to the shrinkage porosity and solidification structure of ingot,but it is difficult to significantly improve due to the limit of thermal conductivity of riser material.A new type of hollow insulation riser was proposed based on the low thermal conductivity of air,which aims to improve the thermal insulation performance of riser.A 14.5-t steel ingot was prepared using the hollow insulation riser,and the casting temperature was 1500°C.The temperature evolution of the external surface of mold during solidification was measured using an infrared temperature instrument.A numerical model was established to simulate the porosity and solidification structure of ingot.The reliability of numerical simulation was verified by comparing simulation and experimental results.Results show that the insulation performance of the riser can be significantly improved through application of the hollow insulation sleeve.Compared with solid insulation sleeve,the shrinkage cavity depth was decreased and the position of porosity was raised when hollow insulation riser was applied.

Mathematical Modeling of ESR Process for Hollow Ingot with Current Supplying Mould

With ificreasing demand for large cylindrical forgings, a new technology--electroslag remelting （ESR） for direct manufacture of hollow ingots rather than solid ingots has been developed. The main features of the process include a T-shaped current supplying mould （CSM）, double power supply, an ingot withdrawing system, a metal level automatic control system based on a level sensor using the electromagnetic eddy current method, and the exchange of a consumable multi-electrode. ANSYS software was used to calculate the fluid flow and heat transfer in the slag bath 1 and metal pool of this ESR hollow ingot process with its T-shaped CSM. The mathematmal model was Verified by measuring the geometry of the liquid metal pool as observed in the macrostructure of 4650 mm （external diameter）/ 4450 mm （internal diameter） hollow ingots by sulphur print method： the. observed shape and depth of the s!ag bath were consistent with the simulated results. Simulation of the ESR process can improve understanding of the process and allow better operating parameters to be selected.

Numerical Modeling of Magnetohydrodynamics and Solidification Phenomena in PAM Processed Ti-6Al-4V Ingots

This paper presents a methodology for modeling and analysis of the interaction between two electromagnetic(EM)fields in a solidifying Ti-6A1-4V(Ti-6-4)ingot processed by the plasma arc cold hearth melting(PAM)process. The two EM fields are generated by the induction coils(stirrer)around the ingot mold and by the plasma torch.This methodology is based on the numerical solution of Maxwell's equations,fluid flow,and heat transfer equations,and modeling of the grain structure.Numerical simulations at the macro-level were conducted using a CFD software.A stochastic model was developed and applied to simulate the grain structure at the mesoscopic level.Simulation results for 5-in and 8-in diameter Ti-6-4 ingots show that the plasma torch and the EM stirrer can have strong effects on both the fluid flow and the solidification structure.A comparison with an experimental grain structure of a 5-in diameter Ti-6-4 ingot is also provided.

Modeling on Directional Solidification of Solar Cell Grade Multicrystalline Silicon Ingot Casting

Solar energy is considered as one of the best alternative energy in the future.Multicrystalline silicon ingot casting is the main production process for major supply of solar cell.However,the casting process cannot be understood clearly because of some difficulties,such as enclosed furnace,long cycle time of production and so on.In this paper,an integrated model,including casting process analysis,quality prediction and production parameters optimization,is proposed and the preliminary results are acquired.The framework of the proposed model is introduced and the numerical simulation results on the temperature field and grain growth process are also given out and discussed.

C70600白铜空心锭立式连铸工艺参数对凝固过程的影响

为了获得Ф260×Ф80 C70600白铜空心锭立式连铸合理的工艺参数,通过数值模拟定量分析了各种工艺参数对温度场和应力场的影响。结果表明:浇铸温度每提高20℃,液穴深度增加10 mm;拉坯速度每提高10 mm/min,液穴深度增加20 mm;液穴深度随着石墨芯管冷却强度的增大而减小。基于正交试验和方差分析发现,F_(A)>F_(0.01)(3,3),F_(B)>F_(D)>F_(0.1)(3,3),F_(C)<F_(0.1)(3,3),因此,拉坯速度对液穴深度的影响最显著,一冷强度对其影响不显著。根据模拟结果提出了合理工艺参数为:一冷强度24 m^(3)/h、拉坯速度80 mm/min、浇铸温度1280℃、芯管采用空冷。在此基础上成功试制出了合格的C70600白铜空心锭成品。

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

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.

Simulation of macrosegregation in a 36-t steel ingot using a multiphase model

Macrosegregation is the major defect in large steel ingots caused by solute partitioning and melt convection during casting.In this study,a three-phase(liquid,columnar dendrites,and equiaxed grains)model is proposed to simulate macrosegregation in a 36-t steel ingot.A supplementary set of conservation equations are employed in the model such that two types of equiaxed grains,either settling or adhering to the solid shell,are well simulated.The predicted concentration agrees quantitatively with the experimental value.A negative segregation cone was located at the bottom owing to the grain settlement and solute-enriched melt leaving from the mushy zone.The interdendritic liquid flow was carefully analyzed,and the formation of A-type segregations in the mid-height of the ingot is discussed.Negative segregation was observed near the riser neck due to the specific relationship between flow direction and temperature gradient.Additionally,the as-cast macrostructure of the ingot is presented,including the grain size distribution and columnar–equiaxed transition.

Industrial test of a 6-m long bearing steel ingot by electroslag remelting withdrawing process

In this study, the key technologies of a 6-m long bearing steel ingot produced by electroslag remelting withdrawing(ESRW) process, including bifilar mode supply, slag system development, and design of mold, were studied based on the laboratory research achievements. The 6-m long ingot of bearing steel GGr15 with a cross-section of 300 mm × 340 mm was produced using the ESRW process with a bifilar mode and a multi-taper T-mold in a plant. The testing results show that the melting rate using the ESRW bifilar mode technology is three times faster than traditional electroslag remelting(ESR), and the power consumption is only 1,320 k Wh per ton steel. Through testing for the chemical composition, macrostructure and inclusions of remelted ingot, it can be concluded that the ESRW bifilar mode technology not only retains the characteristics of traditional ESR, but also improves the production efficiency and reduces the cost compared to traditional ESR.

超大宽厚比钢锭多水口浇铸的模拟研究

在超大宽厚比钢锭铸造过程中,水口的数量和位置会影响钢液的流动轨迹和温度分布,水口设计不合理会导致钢液卷渣、钢锭内部缺陷增多等问题。本文基于ProCAST软件对超大宽厚比钢锭模铸过程进行模拟,研究单、双和三水口对超大宽厚比钢锭充型和凝固过程的影响。结果表明,多水口浇铸时钢液循环范围扩大,上升流股冲力小;三水口铸锭的疏松缩孔体积比单水口铸锭减少14.2%,比双水口铸锭减少36.9%,三水口浇铸工艺利于减少疏松缩孔缺陷。

32t钢锭凝固组织模拟研究

以32 t钢锭及辅具为对象,建立凝固过程传质、传热和凝固组织的数学模型。模拟特定冷却条件下,整个过程中的温度分布和凝固组织的形成,对比不同初始温度对凝固组织的影响,计算结果与实验结果相符,为实际生产和工艺优化提供理论依据与指导。

退火过程对硅锭热应力与位错影响的数值分析

利用CGSim软件对定向凝固多晶硅从长晶过程开始到退火过程结束进行瞬态数值模拟,研究不同退火温度和退火时间对多晶硅锭内热应力及位错密度的影响。通过软件中热弹性应力非稳态模型(Haasen-Alexander-Sumino模型)计算出位错和Von-Mises应力。结果表明:随着退火温度的升高和退火时间的增加,热应力及位错增殖速率的逐渐减小,在退火1 h后热应力和位错增殖速率大幅减小,退火3 h后减小效果减弱。高温退火时热应力和位错密度低于低温退火,在1250℃下退火3 h是比较合适的方案。

空心钢锭凝固过程温度场模拟与缩孔、疏松预测

对空心钢锭凝固过程的温度场进行了有限元分析 ,讨论了芯部传热系数、耐火材料厚度对最终凝固位置、内筒壁最高温度及缩孔疏松的影响 ,并研究了耐火材料典型部位的温度随凝固时间的变化。通过凝固过程的温度场的模拟分析 ,对空心钢锭缩孔、缩松进行了预测 。

T型导电结晶器电渣重熔空心钢锭过程的数值模拟

基于新开发的电渣重熔空心钢锭技术,建立了渣池和空心钢锭的三维准稳态数学模型.利用商业软件ANSYS模拟并得到了非导电和导电结晶器工况下,电渣重熔空心钢锭过程的电磁场、流场与温度场.计算结果表明:导电结晶器工况下,渣池的电流密度和焦耳热最大值均出现在T型结晶器的导电段部分,导电结晶器附近的熔池流动速度较快,渣池的温度场更为均匀,金属熔池形状更为浅平.导电结晶器在交换电极时持续保持渣池和金属熔池温度,能够避免渣池温度迅速下降而导致靠近结晶器壁的钢水迅速凝固而出现渣沟,可大大提高钢锭的凝固质量和表面质量.

等轴晶移动对宏观偏析影响的数值模拟

建立了自由等轴晶移动对宏观偏析影响的数学模型,对铸锭凝固过程中的对流和溶质分布进行了数值模拟.在模型中按照临界固相分数将糊状区分为紧密树枝晶和自由等轴晶两个不同的区域.对带冒口铸钢锭的宏观偏析进行了数值模拟,并同实验结果进行了比较.与假设糊状区内固相静止的模型相比,考虑等轴晶移动的模型得到的溶质分布结果与实验结果更接近.在凝固过程中,等轴晶随液体流动并在铸锭的底部中心聚集,在凝固后的铸锭中形成锥形的负偏析.还发现,在铸锭的中心靠上的区域形成正偏析,在铸锭的外部区域形成负偏析.

工艺参数对电渣重熔空心钢锭凝固过程影响的数值模拟

凝固过程的控制对于保证和提高钢锭的质量十分重要,电渣重熔空心钢锭过程的凝固控制主要是对电渣重熔过程中金属熔池形状和深度进行控制,尤其以熔池深度作为凝固控制的主要参数.本文基于ANSYS和CFX软件对电渣重熔空心钢锭的凝固过程进行数值模拟研究,通过改变渣池深度、电极插入深度、电极布置方式来比较不同工艺参数对电渣重熔空心钢锭金属熔池形状的影响.模拟结果表明,在相同输入功率下,随着渣池深度的增加,金属熔池逐渐变浅;随电极插入深度的加深,金属熔池逐渐变深;十电极布置方式比八电极布置的金属熔池深,但渣/金界面的温度变化相对较小.