Mathematical Model for Electroslag Remelting Process

A mathematical model, including electromagnetic field equation, fluid flow equation, and temperature field equation, was established for the simulation of the electroslag remelting process. The distribution of temperature field was obtained by solving this model. The relationship between the local solidification time and the interdendritic spacing during the ingot solidification process was established, which has been regarded as a criterion for the evaluation of the quality of crystallization. For a crucible of 950 mm in diameter, the local solidification time is more than 1 h at the center of the ingot with the longest interdendritic spacing, whereas it is the shortest at the edge of the ingot according to the calculated results. The model can be used to understand the ESR process and to predict the ingot quality.

Role of fragmentation in as-cast structure:numerical study and experimental validation

A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.

INFLUENCE OF MOULD ROTATION ON MACROSEGREGATION IN INGOT

The macrosegregation formation in an ingot and the influence of rotating mould upon it were analysed on the basis of interdendritic flow.When the ingot mould rotates unidirectionally,the centrifugal volume force acts on all inner parts,and when the ingot mould rotates alternately, the tangential alternate force is also formed,and both have various influences on the different modes of interdendritic flow.It is shown that as the ingot mould rotates unidirectionally or alternately with a moderate angular speed,the interdendritic unstable flow may be controlled effectively and the formation of segregation may be restrained.Thus,it seems to be significant for reducing the segregation such as A-type etc.,in the steel ingot.

Segregation of Niobium During Electroslag Remelting Process

Experiment was carried out after the process parameters were calculated by the model previously established. The relationship between interdendritic spacing and local solidification time （LST） mainly determined by process parameters was exposed. Furthermore, the extent of segregation was studied. The results indicate that LST and interdendritic spacing are the largest and the amount of Laves phase as a result of the niobium segregation is the highest in the center of the ingot, whereas the opposite results are obtained at the edge of ingot. The extent of element segregation and the amount of Laves phase can be reduced when appropriate parameters are used. Therefore, the duration of subsequent homogenization treatments for 718 is shortened and the alloy quality is improved.

Influences of the Texture Characteristic and Interdendritic LPSO Phase Distribution on the Tensile Properties of Mg–Gd–Y–Zn–Zr Sheets Through Hot Rolling

The Mg–Gd–Y–Zn–Zr alloy sheets with different texture characteristics and distribution of the interdendritic long periodstacking ordered(LPSO) phases were fabricated through altering the final rolling reduction(FRR). The results showed that the texture characteristic was closely related to FRR and affected the tensile properties of the resulted sheets to some extent. The Schmid factor(SF) of the basal 〈a〉 slip improved with further FRR, which was ascribed to that the dynamic recrystallization(DRX) grains expand into the deformed grains with basal texture. However, the improvement of the tensile yield strength(TYS) with further FRR indicates that the strengthening effect from DRX grains surpasses the weakening effect from the elevated SF. The formation of the line-distributed interdendritic 14 H-LPSO phases can also affect the tensile properties of the resulted sheets. The line-distributed interdendritic 14 H-LPSO phases along rolling direction(RD) can act as reinforcing fiber and contribute to the higher TYS along RD and 45° to some extent, which resulted in the higher TYS along 45° compared with that along transverse direction(TD) for each resulted sheet under the circumstance of approximate basal 〈a〉 and pyramid 〈c + a〉 friction stress. Thus, the tensile yield strength is not only related to the texture, but also depends on the grain size and line-distributed interdendritic LPSO phases. The micro-cracks spread perpendicular to the tension direction, and thus, the larger cracks form within the line-distributed 14 H-LPSO phases during tension along TD, which accounts for the lower fracture elongation along TD.

Simulation of Secondary Dendritic Arm Spacing of Free Cutting Steel 38MnVS

The secondary dendritic arm spacing （SDAS） of free cutting steel 38MnVS during continuous casting process was simulated based on a Mixed Lagrangian and Eulerian Method （MILE Method） and SDAS model. The simulation results are basically in agreement with measured ones. The effect of composition, superheat and casting speed on SDAS are studied, and the relationship between SDAS and interdendritic segregation is discussed. The results show that SDAS increases with increasing carbon and silicon content, and decreases with increasing manganese and sulfur content. The increase of superheat and casting speed also makes SDAS increase. The permeability of co lumnar mushy zone which is parallel to the primary dendritic arms is calculated based on Carman-Kozeny relationship, and the increase of SDAS makes the permeability increase, which exacerbates interdendritic segregation of columnar crystal zone.