Papers by Keyword: Macrosegregation

Abstract: In this study, 3D numerical simulations were performed to study the effect of Mn on the macrosegregation behaviors of carbon and chromium in a 40 MT steel ingot using Finite Element Modeling (FEM). Two Mn contents of 0 and 5 wt.% were investigated. Thermophysical properties such as specific heat, density and phase fractions were determined using thermodynamic software Thermo-Calc^®. Simulation results indicated that higher Mn content increases the carbon macrosegregation while it tends to lower the one of chromium. Moreover, it changes the solute poor band into rich one in the case of chromium and no bands were obtained for carbon. These results are analyzed in terms of the changes of thermophysical properties, interactions between alloying elements and the change in the primary solidification mode from δ-ferrite to austenite resulting from the increase of Mn concentration.

Abstract: The impact of initial mold temperatures on the formation of macrosegregated zone during the solidification process of large size steel ingots was numerically investigated. Three initial mold temperatures, representing the most commonly encountered industrial conditions, were examined. The flows induced by pouring jet, the thermo-solutal convection, and the thermomechanical deformation of the phases were all taken into consideration. The results indicated that a higher mold temperature increased the macrosegregation intensity in the upper section of the casting, along the centerline and in the mid-radius solute-enriched bands. The increase was associated with the increased temperature gradient in the casting, the advance predominance of thermal convection, and the delayed solidification process.

Abstract: An advanced method called internal electromagnetic stirring (I-EMS) was investigated to resolve the engineering problems like coarse-grain, inhomogeneous structure and macrosegregation. The electromagnetic stirrer functioned with internal-cooling was inserted in the melt during DC casting. In this study, a round billet of 2219 alloy DC cast with a diameter of 880mm under I-EMS process condition was produced, and its structure and composition distribution were comparatively characterized. The results show that the mean grain size decreased from the range of 872, 1023, 332 μm to the range of 317, 438, 271 μm at different billet positions with I-EMS. I-EMS consequently produce superior grain refinement and homogeneity. The effect of I-EMS on the grain-refinement and macrosegregation was also discussed.

Abstract: In the present work, the segregation degrees of ferrite and austenite stabilizer alloying elements were analyzed for a high strength steel. For this, samples were taken from the surface and center of the hot-top and the upper section of a 40 MT ingot. The results showed that the positive segregation ratios for all the investigated elements were higher in the ingot center than in the surface with higher values for austenite stabilizer elements. The increase of austenite alloying element stabilizers was accompanied by the change in the primary solidification mode of the austenite phase. The obtained results are in good agreement with the observed presence of austenite, revealed by X-ray diffraction analysis, stabilized by the austenite alloying elements.

Abstract: To obtain fine microstructure and homogeneous distribution of alloying elements in the large-sized billet, the internal electromagnetic stirring as a new electromagnetic stirring method was proposed and utilized for the preparation of Ф508 mm 7050 aluminum alloy billet. The results demonstrate that the internal electromagnetic stirring could refine the microstructure and second phase, and alleviated the macrosegregation significantly. The grain size at the edge, 1/2 radius, and center of the billet decreased to 180 μm, 175 μm, and 185 μm, respectively. Moreover, the relative macrosegregation of Zn, Mg, and Cu at the edge and center decreased to 3.9% and 2.8%, 2.3% and 1.6%, 4.1% and 2.5%, respectively.

Abstract: Secondary dendrite arm spacing (SDAS) is a macrosegregation parameter directly linked to content of macrosegregation through cooling rates. The aim of this paper is to highlight the effect of cooling rate on the SDAS and macrosegregation patterns in a high strength steel. For this purpose, directionnal solidification in a cylinder was modeled with a plane-front solidification. Two cylinders were modeled with different boundary conditions (T_surface = 1000°C and 1200°C). Using the FEM software Thercast, 3D macrosegregation maps were generated with thermomechanic algorithm taking into account metal shrinkage. Using Won’s equation, the influence of cooling rates in the mushy zone on SDAS was determined. The results indicated that a 72% lower difference in the area of negative macrosegregation zone (macrosegregation ratio (r_seg) < -0.016%) for lower cooling rate (T_s = 1200°C). The difference of the area for positive segregation was 85% lower for higher cooling rates.

Abstract: A low frequency electromagnetic field was introduced into the direct chill (DC) casting process and the ingots of Al-Cu alloy were prepared to study the macrosegregation behaviour of the ingots under the influence of the electromagnetic field. The experimental results showed that there is an obvious positive segregation near to the surface and a negative segregation in the centre area of the ingot. Cu shows the highest segregation tendency among the main elements of Cu, Mg and Mn. Grain refiner element Ti shows a segregation trend opposite to that of Cu. With the application of electromagnetic field, the negative centreline segregation in the centre area of the ingot was evidently reduced although it didn’t show significant effect on the segregation near to the ingot surface. A significant grain refinement was also achieved with the application of electromagnetic field. The mechanism of the reduction of macrosegregation with electromagnetic field was also analyzed in the present work.

Abstract: Large steel ingots are the important material for the equipment manufacturing industry. It is still difficult to predict and control the macrosegregation in ingot. In this paper, the cooling curves at the surface of ingot and temperature variation of the mold were measured. The carbon distribution was measured through the local region dissection of ingot. Then, based on the definite the heat transfer coefficient at the interface of mold/ingot, a two-phase model with consideration of the motion of equiaxed grains is applied for the prediction of macrosegregation in 160-t steel ingot formed during the solidification. The results indicate that the heat transfer coefficient at the interface of mold/ingot decreases sharply after starting solidification and then varies slowly. Negative segregation at the bottom of ingot forms due to the interaction of solidification interface and equiaxed grains deposition during solidification. The positive segregation appears in the riser with thanks to the solidification shrinkage and the floating enriched solute. Finally, the results of the predicted and the measured are in good agreement.

Abstract: Macrosegregation occurs in casting the most case is as a result of slow interdendritic flow due to shrinkage geometry, solid deformation or gravity. In some cases could be the result of solid movement in the early stages of solidification[1]. The problem is that the observation of macrosegregation in steel material is not easy because of high temperature condition. This recent work uses low melting temperature material alloy to simulate the actual condition as a model material. Various efforts to prevent macrosegregation are aimed to control liquid flow and movement of solid, one of them is by cooling rate controling. In this experiment the mold is cooled in three types of cooling medias to represent three different cooling conditions in order to observe the influence of cooling rate on macrosegregation during solidification of the alloy. The outer part close to the mold wall and the bottom of casting contains less solute than inner location. This occurs in all cooling conditions but cooling rate can cause the solute in casting distributed differently. At high cooling rate condition, distribution of Bi rich grain is more uniform. It is mean that macrosegregation is reduced. Bi-richer grains accumulate at the bottom of the ingot. It could be caused by those grains settle due to their relative density to surrounding liquid during solidification.

Abstract: In the present work, the solidification behaviour of a metal analogues transparent binary solution (8 wt% of NH₄Cl in H₂O) under shear flow is investigated numerically. The shear flow in the mush is developed due to flow over an inclined cooling plate. The dendrites formed during solidification are fragmented under the shear flow and transported into the bulk solution. The suspended dendrites form a slurry layer in the domain. Consequently, a suitable mathematical model is considered to study the transport phenomena. In the mathematical model, the free surface of the solution is represented by the volume-of-fluid (VOF) method. The solidification process is modelled by a set of volume-averaged-single-phase mass, momentum, energy and species conservation equations. A separate equation is considered for the solid velocity based on Stokes model. The governing equations are solved based on the pressure-based semi-implicit finite volume method according to the SIMPLER algorithm using TDMA solver along with the enthalpy update scheme. Finally, the simulation predicts temperature, velocity, solid fraction and the species distributions in the computational domain. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}