| Because of its good corrosion resistance,TA10 titanium alloy is often used in the manufacture of chemical evaporators,wastewater treatment reactors,high corrosion resistance heat exchangers,etc.However,the unstable ingot quality and high production cost greatly limit its application and development prospect.Therefore,it is an important research direction of TA10 titanium alloy to optimize the production process of electron beam cold hearth melting by numerical simulation,improve product quality and reduce production cost.In this paper,a numerical model of large-scale TA10 titanium alloy slab ingot is established,and semi-continuous casting process is studied extensively.Based on ANSYS and ProCAST software,the inclusion migration,stress field,flow field and concentration field in the process of melting and casting of TA10 titanium alloy were studied,and the experiment of trial-producing TA10 large-scale slab ingot was carried out,and results were as follows:The simulation of water-cooled copper hearth shows that the solid-liquid interface of the cold hearth is W-shaped.With the increase of casting temperature and speed,the depth of molten pool increases,the solidification skull becomes thinner and the solid-liquid interface moves down.As the casting speed increases,the melt flow velocity in cold hearth and on the surface of the cold hearth increases continuously;with increases of melting temperature,the melt flow velocity in the cold hearth and on the surface of the cold hearth decreases continuously;However,in these two casting conditions,the speed decreases rapidly from the outlet to about 60 mm away from the outlet,and decreases relatively slowly when the distance is greater than 60 mm,and it is verified that the solidified shell can collect highdensity inclusions precipitated in the melt.At the same time,it is found that the solidified shell moving speed is very small,but not zero.Based on this,this paper puts forward some suggestions for industrial production of titanium alloy.In order to prevent inclusions from entering the crystallizer,the solidified shell should not be reused.Calculation based on DPM model,the trajectory of inclusions with various specifications in the cold hearth is obtained,and removal effects were tested.It was found that inclusions with a density of 4.5 g/cm3 is extremely difficult to remove at all diameters,casting speed and melting temperature.When the inclusion density of 3.5 g/cm3,the inclusions with a diameter of 10μm are not affected by casting speed and temperature,and all escape.However,with the increase of melting temperature,the number of inclusions with diameters of 40μm and 70μm increased a little.In two casting conditions,the inclusions with a density of 5.5 g/cm3 have a similar escape trend to those with a density of 3.5 g/cm3,that is,as increases of the diameter,the gravity of the inclusions continuously increases,making them easier to sink and be captured by the crust.For inclusions with a diameter of 10μm,removal effects were average.However,under different melting conditions,the diameters are 40μm,70μm and 100 μm.The escapable inclusions with a density of 5.5g/cm3 are basically those released from the semi-gate near the outlet,mainly because the melt velocity near the outlet is higher and the speed of inclusions is higher,so it is easier to flow out of the cold hearth and enter the crystallizer.Generally speaking,high-density and low-density inclusions with large diameter are easier to remove.This paper suggests that appropriate measures should be taken to promote the growth and polymerization of inclusions in metallurgical production,and the length of the cold hearth should be appropriately extended,and the gate of the cold hearth should be moved back away from the outlet.The calculation of stress field shows that the surface effective stress of TA10 alloy slab is obviously greater than the internal effective stress,and the effective stress greater than 900MPa mainly appears in the narrow face,corner and wide face of the mold,and the casting cracks are more likely to appear in these positions,and the cracks are more likely to appear on the surface.With the increase of pulling speed,the internal and external effective stress of TA10 alloy slab ingot has a decreasing trend,and its superelevation effect force greater than 900MPa is also significantly reduced.As increases of pouring temperature,the internal and external effective stress of TA10 alloy slab ingot will increase slowly,which will promote the appearance of local superelevation effect force.Due to the synergistic cooling effect of ingot pulling mechanism and crystallizer,the bottom of slab ingot produces great effective stress,which is also the fundamental reason for the cracking of the bottom of common ingot in semi-continuous casting process.By simulating the concentration field of TA10 titanium alloy slab ingot,it is revealed that the concentration gradient of Mo in the molten pool area becomes steep along the flow direction and gradually decreases along the flow direction,but the segregation of Mo in solidified ingot has little change.In addition,the content of Mo in liquid phase is generally lower than that in solidified ingot,and its concentration in solid phase is basically between 0.28%and 0.32%,and the segregation degree in solidified zone is low.The results show that the influence of pulling speed and pouring temperature on Mo segregation in the solidification region of TA10 alloy slab is limited,while Ni is mainly distributed between 0.73%and 1.53%.In the liquid phase,the Ni concentration in molten pool increases constantly along the flow direction,and the liquid phase concentration is usually higher than the ingot concentration in the solidification part.With increases of ingot pulling speed,molten pool becomes deeper,and two larger vortices are formed in the molten pool.As the vortices gradually grow larger,the two vortices produce two large flow regions in the molten pool,resulting in mixing effect.The increase in pulling speed makes the forming speed of slab ingot is accelerated and the diffusion time of solute is shortened.In addition,at higher pouring temperature,the molten pool becomes deeper and the eddy current effect becomes significant.As the pouring temperature increases significantly,the solute diffusion resistance decreases,and the mixing degree of the molten pool at the far end increases,resulting in the Ni segregation at the far end decreases.In addition,the fluid flow velocity in the molten pool drops sharply along the flow direction,and the velocity gradient in the middle and edge of the molten pool is steep within the research scope.The calculation shows that the segregation degree of Ni can be greatly improved by reducing the ingot drawing speed and increasing the pouring temperature within the data range studied in this paper.By comparing the measured data of experimental slab ingot with the simulated values,it was found that numerical calculation results of Mo and Ni segregation in conformity with the concentration change trend of test results,so it can be inferred that the numerical calculation has certain accuracy in predicting element segregation in EBCHM process.Moreover,the experimental value of the experimental ingot shows that the deviation of Mo content on each end face is almost within 0.05%,and the deviation of Ni content is almost within 0.1%.By analyzing as-cast structures,it is found that the grain size is decreasing from the symmetrical plane to the edge of the slab ingot,and through the analysis of XRD diffraction pattern,it was found that as-cast structures were main components ofα-Ti and β-Ti phases.Through researching of microstructures,it is found that ascast TA10 is mainly composed of lamellar widmanstatten structure.Using EPMA scanning,it is found that the micro-segregation of Mo element is very small and evenly distributed,but the segregation of Ni element is very obvious and enriched in β phase. |
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