In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium a...In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.展开更多
A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulat...A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.展开更多
The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting(VAR)process have important effect on the subsequent mechanical p...The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting(VAR)process have important effect on the subsequent mechanical processes like forging,rolling and welding.In order to determine the fluid motion of molten pool,a 2D finite element model is established using ANSYS10.0 software,combined with the turbulent fluid flow and heat transfer.The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study.The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile.It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.展开更多
The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understan...The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process,a 3D finite element model is developed by the ANSYS software.The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA.The molten pool depth increases gradually from 30 to 320 s,then the change of molten pool depth is very small during the steady state stage from 320 to 386 s,and lastly the molten pool depth becomes shallow after 386 s.The melting rate and temperature of superheat increase with the remelting current increasing,which leads to the augment of molten pool volume.In the end,the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.展开更多
采用Gleeble热压缩试验建立了真空自耗法制备φ220 mm TiAl合金铸锭的高温变形本构方程,将该本构方程嵌入Deform-3D软件后对不同工艺条件下TiAl合金铸锭的热挤压过程进行了数值模拟,获得了在不同模具锥角及不同挤压速度下棒材内的等效...采用Gleeble热压缩试验建立了真空自耗法制备φ220 mm TiAl合金铸锭的高温变形本构方程,将该本构方程嵌入Deform-3D软件后对不同工艺条件下TiAl合金铸锭的热挤压过程进行了数值模拟,获得了在不同模具锥角及不同挤压速度下棒材内的等效应变场、温度场,得出70%变形量下TiAl合金最佳的挤压工艺。研究发现,模具锥角对棒材等效应变场、温度场和均匀变形区尺寸均有较大影响;而挤压速度对棒材等效应变场影响不大,但对棒材的温度场有显著影响。展开更多
The effects of vacuum induction melting(VIM) and vacuum arc remelting(VAR) processes on the microstructure and stress rupture properties of Ni-based GTD-111 superalloy were investigated. Samples of GTD-111 master allo...The effects of vacuum induction melting(VIM) and vacuum arc remelting(VAR) processes on the microstructure and stress rupture properties of Ni-based GTD-111 superalloy were investigated. Samples of GTD-111 master alloy were melted in VIM and VAR furnaces and then poured into a preheated ceramic mold for VIM melt or into a water-cooled copper mold for VAR melt. The as-cast samples were examined radiographically to ensure that no casting defects were present in the final castings; the samples were then heat-treated using a standard heat-treatment cycle. The microstructure of the samples was investigated using optical microscopy and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy for microanalysis. On the basis of standard ASTM-E139, stress rupture tests were carried out at 1000°C under a stress of 300 MPa. The results showed that a γ matrix, fine γ′ precipitates, a γ–γ′ eutectic structure, carbide particles, and some harmful phases such as σ and η phases were present in the as-cast samples. The γ′ precipitates with cubic morphology appeared in the matrix after the standard heat-treatment process. The extent of segregation and the amount of γ–γ′ eutectic structure formed in the VAR-prepared sample were less than in the VIM-prepared sample. The results of stress rupture tests showed that the rupture time for the VAR sample was 43% longer than that for the VIM sample.展开更多
基金Project(2007CB613802) supported by the National Basic Research Program of China
文摘In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.
基金financially supported by National Natural Science Foundation of China(Nos.U1908223 and U1960203)Fundamental Research Funds for the Central Universities(Grant No.N2125017)Talent Project of Revitalizing Liaoning(Grant No.XLYC1902046).
文摘A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.
基金the National Basic Research Program (973) of China(No.2007CB613802)
文摘The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting(VAR)process have important effect on the subsequent mechanical processes like forging,rolling and welding.In order to determine the fluid motion of molten pool,a 2D finite element model is established using ANSYS10.0 software,combined with the turbulent fluid flow and heat transfer.The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study.The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile.It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.
基金the National Basic Research Program(973) of China (No.2007CB613802)
文摘The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process,a 3D finite element model is developed by the ANSYS software.The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA.The molten pool depth increases gradually from 30 to 320 s,then the change of molten pool depth is very small during the steady state stage from 320 to 386 s,and lastly the molten pool depth becomes shallow after 386 s.The melting rate and temperature of superheat increase with the remelting current increasing,which leads to the augment of molten pool volume.In the end,the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.
文摘采用Gleeble热压缩试验建立了真空自耗法制备φ220 mm TiAl合金铸锭的高温变形本构方程,将该本构方程嵌入Deform-3D软件后对不同工艺条件下TiAl合金铸锭的热挤压过程进行了数值模拟,获得了在不同模具锥角及不同挤压速度下棒材内的等效应变场、温度场,得出70%变形量下TiAl合金最佳的挤压工艺。研究发现,模具锥角对棒材等效应变场、温度场和均匀变形区尺寸均有较大影响;而挤压速度对棒材等效应变场影响不大,但对棒材的温度场有显著影响。
文摘The effects of vacuum induction melting(VIM) and vacuum arc remelting(VAR) processes on the microstructure and stress rupture properties of Ni-based GTD-111 superalloy were investigated. Samples of GTD-111 master alloy were melted in VIM and VAR furnaces and then poured into a preheated ceramic mold for VIM melt or into a water-cooled copper mold for VAR melt. The as-cast samples were examined radiographically to ensure that no casting defects were present in the final castings; the samples were then heat-treated using a standard heat-treatment cycle. The microstructure of the samples was investigated using optical microscopy and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy for microanalysis. On the basis of standard ASTM-E139, stress rupture tests were carried out at 1000°C under a stress of 300 MPa. The results showed that a γ matrix, fine γ′ precipitates, a γ–γ′ eutectic structure, carbide particles, and some harmful phases such as σ and η phases were present in the as-cast samples. The γ′ precipitates with cubic morphology appeared in the matrix after the standard heat-treatment process. The extent of segregation and the amount of γ–γ′ eutectic structure formed in the VAR-prepared sample were less than in the VIM-prepared sample. The results of stress rupture tests showed that the rupture time for the VAR sample was 43% longer than that for the VIM sample.
