Simulation of solidification microstructure of Fe-6.5%Si alloy using cellular automaton-finite element method

3D microstructures of Fe–6.5%Si(mass fraction) alloys prepared under different cooling conditions were simulated via finite element-cellular automaton(CAFE) method. The simulated results were compared to experimental results and found to be in accordance. Variations in the temperature field and solid-liquid region, which plays important roles in determining solidification structures, were also examined under various cooling conditions. The proposed model was utilized to determine the effects of Gaussian distribution parameters to find that the lower the mean undercooling, the higher the equiaxed crystal zone ratio; also, the larger the maximum nucleation density, the smaller the grain size. The influence of superheat on solidification structure and columnar to equiaxed transition(CET) in the cast ingot was also investigated to find that decrease in superheat from 52 K to 20 K causes the equiaxed crystal zone ratio to increase from 58.13% to 65.6%, the mean gain radius to decrease from 2.102 mm to 1.871 mm, and the CET to occur ahead of schedule. To this effect, low superheat casting is beneficial to obtain finer equiaxed gains and higher equiaxed dendrite zone ratio in Fe–6.5%Si alloy cast ingots.

Numerical modeling for electron-beam evaporated process of magnetic alloy Fe-6.5%Si

Based on Langmuir equation and thermodynamic properties of iron-silicon binary alloy, a mathematical model about the process of electron-beam evaporated binary alloy Fe-6.5%Si was established. Variation of the composition of molten pool, vapor and deposit with time, length of transient time and the composition of molten pool, deposit under the steady condition were presented according to the numerical model. The experimental results on the composition of deposit were compared to the data calculated through the model. The results show that the model is applicable, after evaporating for about 50min, the compositions of the deposit are equal to those of the ingot.

Texture Evolutions in Fe-6.5%Si Produced by Rapid Solidification and Chemical Vapor Deposition

Fe-Si ribbons and thin sheets with 6.5%Si content were prepared by means of the single roller rapid solidification and chemical vapor deposition (CVD), respectively. The initial textures of rapidly solidified Fe-6.5%Si ribbons were characteristic of the {100} fiber-type, which became weakened during primary recrystallization in various atmospheres. At the stage of secondary recrystallization, the {100} texture formed in Ar and the {110} texture in hydrogen, while there occurred a texture transformation from the {100} type to the {110} type in vacuum with the increase of annealing temperature. For Fe-6.5%Si sheets prepared by Si deposition in cold-rolled Fe-3%Si matrix sheets, their textures were dominated by the η-fiber (<001>//RD) with the maximum density at the {120}<001> orientations. After homogenization annealing, the η-fiber could evolve into the {130}<001> type or become more concentrated on the {120}<001> orientations, depending on the cold rolling modes of Fe-3%Si matrix sheets.

Warm deformation behavior and work-softening mechanism of Fe- 6.5wt.%Si alloy

Warm deformation behavior of the Fe-6.5wt.%Si alloy was studied by isothermal compression in the temperature range of 300-700℃.The results show that the influence of the ordered phases on the flow stress gradually weakens with increasing deformation temperature.The flow stress of the furnace-cooled sample with the high degree of order at 300℃is higher than that of the quenched sample with the low degree of order,and the flow stresses of both samples are nearly the same at 500-700℃.The hardness difference between two samples deformed at 500℃gradually decreases with increasing strain,accompanying with a reduction in hardness of the furnace-cooled sample,which indicates a work-softening behavior.The analyses of dislocation configurations and ordered structure suggest that the dynamic recovery and deformation-induced disorder result in the work-softening behavior.An appropriate deformation temperature window for improving the formability of the Fe-6.5wt.%Si alloy is about 500-600℃.

Comprehensive impact of as-cast microstructure and ordered structures on formability of large-scale Fe-6.5 wt.%Si alloy ingots

Large-scale Fe-6.5 wt.%Si ingot with excellent formability is required for a pilot line producing sheets through hot/cold rolling.The variation of the as-cast microstructure,ordered structures and the formability of the Fe-6.5 wt.%Si alloy ingots with the cooling rate during casting was investigated.Under air-cooling condition,inhomogeneous microstructures with a low proportion of equiaxed grains were formed,but the formation of ordered structures was partially inhibited,especially DO3.Homogeneous microstructures with a high proportion of equiaxed grains were observed under the condition of furnace cooling,but the ordered structures were fully generated,and the degree of order is high.It is generally believed that high degree of order is the main factor of brittleness,but the homogeneous microstructure(including grain morphology and size)of the furnace-cooled sample helps to improve the formability.The influence of these two aspects on formability is contradictory.Therefore,the formability is tested through the flow stress during the compression and the microstructure after the compression.The results show that the furnace-cooled sample has better formability.For large-scale ingots,the control of as-cast microstructure becomes more significant than the control of degree of order.Slow cooling during casting is important for the large-scale ingots to have good formability meeting the requirements of direct hot rolling.

Deformation twinning in equiaxed-grained Fe-6.5 wt.%Si alloy after rotary swaging

Tensile behavior of an equiaxed-grained Fe-6.5 wt.%Si alloy,which was deformed intoφ6 mm bar by hot rotary swaging,was investigated at various temperatures(300–400℃)and stretching rates(0.42–1 mm/min).The results revealed an enhancement in the intermediate-temperature tensile ductility after heat treatments.Deformation twinning was found in the equiaxed-grained Fe-6.5 wt.%Si bars during the tensile test,and heat treatments can enhance the deformation twinning.More twins can be observed in the necking areas than other regions.The high Schmid factor values above 0.4 after heat treatments demonstrated that deformation twinning can easily occur in the equiaxed-grained Fe-6.5 wt.%Si alloy.Higher deformation temperatures,higher strain rates,and larger degree of order suppressed the formation of deformation twinning,while the grain sizes had little effect on the deformation twinning.The twinning stress of the Fe-6.5 wt.%Si alloy increased with the increasing grain size,which did not agree with the Hall–Petch type relationship.The deformation twinning resulted in the improved ductility of the Fe-6.5 wt.%Si alloy.

铁硅合金初次再结晶对立方织构形成的影响

Fe-3.2%Si合金通过真空退火发生二次再结晶,最终可形成立方织构电工钢。其中初次再结晶后的晶粒是发生二次再结晶的晶核。通过电子背散射衍射(EBSD)技术和取向成像显微(OIM)技术研究了硅钢初次再结晶对最终立方织构形成的影响。通过冷轧压下量70%和不同退火温度的工艺处理,研究了退火温度对初次再结晶的影响;发现在低温650℃下初次再结晶,形成的初次再结晶晶核有利于最终形成立方织构。

Effect of Ce on solute redistribution in liquid ahead of solid–liquid interface during solidification of Fe–4 wt.%Si alloy

The high efficiency of Ce addition in grain refinement ofδ-ferrite in a cast Fe–4 wt.%Si alloy was verified.In order to further understand the solute effect of Ce on the grain refinement of δ-ferrite,the conventional directional solidification technique,which enabled to freeze the solid–liquid interface to room temperature,was used to investigate the interfacial morphology and solute redistribution in the liquid at the front of the interface,together with thermodynamic calculation of the equilibrium partition coefficients of Ce and Si in Fe–4 wt.%Si–Ce system using the Equilib module and the FsStel database in FactSage software system.Metallographic examination using a laser scanning confocal microscope showed a transition of the solid–liquid interface from planar to cellular in the Fe–4 wt.%Si alloy after adding 0.0260 wt.%Ce during the directional solidification experiment.Further,electron probe microanalysis revealed an enhanced segregation of Si solute in the liquid at the front of the solid–liquid interface due to the Ce addition.This solute segregation is considered as the cause of planar to cellular interface transition,which resulted from the creation of constitutional supercooling zone.Thermodynamic calculation indicated that Ce also segregated at the solid–liquid interface and the Ce addition had negligible effect on the equilibrium partition coefficient of Si.It is reasonable to consider that the contribution of Ce to the grain refinement ofδ-ferrite in the cast Fe–4 wt.%Si alloy as a solute was marginal.

Numerical study of heat transfer of gas-atomized Fe-6.5 %Si （mass and solidification behavior fraction） droplets

During spray atomization process, the heat transfer and solidification of droplets play very important roles for the deposition quality. Due to the difficulties of experimental approach, a numerical model is developed, which integrates liquid undercooling, nucleation recalescence and post-re- calescence growth to present the full solidification process of Fe-6.5%Si （mass fraction） droplet. The droplet velocity, temperature, cooling rate as well as solid fraction profiles are simulated for droplets with different sizes to demonstrate the critical role of the size effect during the solidification process of droplets. The relationship between the simulated cooling rate and the experimentally obtained secondary dendrite arm spacing is in excellent agreement with the well-established formula. The pre-constant and exponent values lie in the range of various rapid solidified Fe-based alloys reported, which indicates the validity of the numerical model.