Study On The Solidification Process Control Of Ultra-long And Ultra-thin TA1 And TC4 Slabs In An Electron Beam Cooling Bed Furnace

Titanium and titanium alloys are the key support materials in engineering technology and high-tech fields and important national defense strategic metal materials.Especially the high quality,heavy coil and wide titanium alloy strips,which have the more wider applications in oceaneering,aerospace,medical,chemical and so on,are produced as the extremely important foundational material of the many productions such as coiling welded titanium pipe,plate heat exchanger,condenser and composite plate,etc.The traditional production process of titanium alloy strip coil consists of the following stages:vacuum arc remelting?VAR?titanium alloy ingot,crossing forged and stamped into rectangular slabs,and finally rolling to titanium alloy strip coil.Previous observations have indicated that the ability of removing the low-density and high-density inclusions based on the EBCHM method is higher than the vacuum arc remelting?VAR?method.Moreover,the EBCHM for ultra-long and ultra-thin rectangular titanium ingot,applying the existing equipment of rolling steel,can be directly rolled to strip coil.However,there are some surface quality problems such as cold ahut and blemish during the EBCHM for ultra-long and ultra-thin?8000 mm×210mm?rectangular titanium slab ingot because of no relevant experience for reference.To achieve the high-quality production of titanium strip coil,the quality of the ultra-long and ultra-thin titanium slab ingot should be optimized during EBCHM.In this work,using the electron beam cold hearth equipment with international advanced level,the control mechanism of the solidification process of titanium slab ingot was studied to realize the effective control of titanium ingot metallurgy defect and solve the surface quality problem of the ultra-long and ultra-thin titanium slab ingot.To provide theoretical basis for optimizing process parameters,the temperature distribution based on the mix Lagrangian and Eulerian non-steady algorithm?MiLE?and grians structure of large-scale TA1 and TC4 slab ingot were investigated adopted the cellular automaton?CA?models coupled with finite element?FE?heat flux calculations?CAFE?.From the calculated results of temperature distribution during EBCHM for the ultra-long and ultra-thin TA1 slab ingot,with the pouring temperature and pulling speed improving,the depth of molten increase,and the length of the transition region shows a liner increase.Whereas the influence of pulling speed more sensitive on the depth of molten from the quantitative relationship.What's more,the grain structure of large-scale TA1 ingot was modelled based on the CAFE method.By the comparison of the predicted with experimental microstructure at the different cross-sections,the bulk nucleation parameters is?T_v,max?28?10 K,?_vT,_s?28?1 K,_vn,_max?28?2?10⁸m^-3,which was adopted in this CAFE mold using for predicted the microstructure at the different cross-sections,and the predicted microstructures at the different cross-sections are very close to the experimental micrographs.Therefore,the grain structure evolution under different process parameters were simulated based on the determined parameters.The quantitative analyses of the simulation results show that with the pulling speed increasing,the number of grains decreases,whereas the mean grain radius increases under identical thermal condition.When the pulling speed increases from 1×10^-4m/s to3×10^-4 m/s,the mean radius of grains increases from 1.97 cm to 2.55 cm.With the pouring temperature increasing from 2023 K to 2173 K,the mean grain radius linearly increases from 2.15 mm to 2.58 mm.Therefore,the decreasing of pulling speed and pouring temperature can reduce the average grain size on the cross-section,and the growth direction of columnar grain is parallel to the axial direction,which is beneficial to subsequent pressure processing.In addition,the formation mechanism of the surface defects of TA1 slab ingot was obtained based on the simulated analysis.Acrroding to the actual casting results,it incates that the high quality ultra-long and ultra-thin TA1slab ingot can be stably produced during EBCHM while using the 2123 K pouring temperature,attaching appropriate input energy near the crystallizer,and 2.35×10^-4 m/s pulling speed as the optimum matching process parameters.From the calculated results of temperature distribution during EBCHM for the large-scale TC4 slab ingot,with the pulling speed increasing,the mushy zone widens,as well as the length of the transition region shows a liner increase.While the same pulling speed,the positions of solidus move down and the depth of mushy zone decreases with the pouring temperature increasing.Reducing the pouring temperature can reduce the curvature of the solid-liquid interface so that the defects such as macrosegregation of titanium alloy ingots can be eliminated or reduced.Taken together,1973K was defined as the optimum pouring temperature in this simulation results.Under the productivity improvement.Besides,the effect of three-dimensional size of crystallizer on the solid-liquid interface morphology of TC4 slab ingot was studied quantitatively and a range of three-dimensional size was gained for designing crystallizer.To sum up,the quantitative relationships of the main process parameters with the depth of molten pool and grains structure were studied by mathematical calculation of ultra-long and ultra-thin TA1 and TC4 ingot during the solidification in EBCHM,which are very important to obtain the optimal structure of the ingots.Moreover,the study can provide theoretical basis for good quality large-scale TC4 slab ingot during the EB furnace melting.Thereby,the innovation ability and the processing level of Chinese titanium industry technology may be improved so as to promote the scientific and technological progress of titanium industry.