The distributions of heat flux along the height and the circumferential direction of round billet mould were measured continuously.The influence of casting speed,carbon content,powder,and pouring temperature on the av...The distributions of heat flux along the height and the circumferential direction of round billet mould were measured continuously.The influence of casting speed,carbon content,powder,and pouring temperature on the average longitudinal and circumferential heat flux in the ＂high heat flux region＂ was discussed.The experimental and analytical results provide a basis for an intelligent mould with online detection of defects,adjustment of operational parameters,optimization of the monitoring system,and even prediction of abnormal heat transfer.展开更多
The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbul...The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbulence model,coupling velocity,temperature,and phase field was established to study the effect of the ladle shroud immersion depth on the slag eye formation,slag entrainment,slag dragging,air dragging,and flow characteristics during the ladle change-over process of a two-strand tundish.The results showed that reducing the immersion depth decreases the high-velocity region area under the slag layer in the quasi-steady process.During the emptying stage,as the molten bath level gradually decreases,the outlet temperature exhibits a trend of initially decreasing and subsequently increasing across all three shroud immersion depths.However,under a 210 mm shroud immersion depth,molten slag and air are dragged into the shroud,forming slag droplets and causing significant fluctuations,with a maximum scalar velocity of 0.0764 m/s at the monitoring point.In the filling stage,air and molten slag are dragged into the molten bath,forming bubbles and slag droplets at an immersion depth of 210 mm.Bubbles are observed within the molten slag layer,which can readily cause an emulsification phenomenon,making it easier to be dragged as slag droplets.Additionally,the slag eye area measured under 210 mm immersion depth at 45 s is 0.303 m^(2),while the maximum scalar velocity of 2.4259 m/s is detected at 12 s.At an immersion depth of 360 mm,the average area of the slag eye is minimized to 0.06268 m2,with corresponding variances of 0.006753,representing the optimal immersion depth.展开更多
A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysi...A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.展开更多
The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was est...The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.展开更多
Directional solidification continuous casting (DSCC) process is a new manufacturing technology for metallic materials which combines advantages of both directional solidification technology and continuous casting tech...Directional solidification continuous casting (DSCC) process is a new manufacturing technology for metallic materials which combines advantages of both directional solidification technology and continuous casting technology. Unlimited long shaped metal with directionally solidifying microstructure can be produced by this process. It is experimentally shown that controlling condition of stable and continuous growth of single crystal structure means the precise control of the location of the S/L interface, which is affected and determined by seven process parameters. Moreover, these parameters are also interacted each other, so the disturbance of any parameters may cause the failure of controlling of S/L interface. In this paper, on the basis of analyzing the forming conditions of continuously directional microstructures in DSCC process, the control model of DSCC procedure by neural network control (NNC) method was proposed and discussed. Combining with the experiments, we first used the computer to simulate the effects of the solidification parameters on destination control variable (S/L interface) and the interactions among these parameters during DSCC procedure. Secondly many training samples necessary for neural network calculation can be obtained through the simulation. Moreover, these samples are inputted into neural network software (NNs) and trained, then the control model can be built up.展开更多
The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large de...The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments,the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined.With SPA-H weathering steel as a specific research steel grade,the distributions of tem-perature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite ele-ment model.High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures,and a prediction model of the critical strain for two typical cracks,combining the effects of strain rate and temperature,was proposed by incorporating the Zener-Hollomon parameter.The crack risks with different LCR schemes were calculated using the crack risk prediction model,and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm×1600 mm was 41.8 mm,with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8,7.3,6.5,6.4,and 5.8 mm,respectively.展开更多
The microstructure and properties of a 1030B Al strip were improved by applying ultrasonic melt treatment(UMT)in a Hazelett continuous casting direct rolling production line.The microstructure and properties of the 10...The microstructure and properties of a 1030B Al strip were improved by applying ultrasonic melt treatment(UMT)in a Hazelett continuous casting direct rolling production line.The microstructure and properties of the 1030B Al strip were investigated by scanning electron microscopy,electron backscatter diffraction,and tensile testing.Applying UMT reduced the average grain size of the as-cast sheet by more than 28.0%with respect to that of the normal samples without UMT.When UMT was applied,the rolled strip inherited the refined grains from the as-cast sheet with an average grain size smaller than 63.0μm.Meanwhile,the dislocation density was increased by the grain refinement,dynamic recovery,and recrystallization during rolling.Accordingly,the strain-hardening rates of the rolled samples after UMT were generally higher than those of the normal samples,and the strength of the rolled strip was also improved.Furthermore,the rolled strip exhibited better formability with higher strain-hardening exponents and Erichsen index values.展开更多
The electromagnetic swirling flow in nozzle(EMSFN)technique is designed to mitigate the adverse effects of unstable and uneven flow within the submerged entry nozzle in continuous casting.Utilizing electromagnetic for...The electromagnetic swirling flow in nozzle(EMSFN)technique is designed to mitigate the adverse effects of unstable and uneven flow within the submerged entry nozzle in continuous casting.Utilizing electromagnetic forces,EMSFN stabilizes the flow within the nozzle,leading to a more controlled flow in the mold.Numerical simulations were used to quantitatively analyze the magnetic and flow fields in a slab continuous casting system under EMSFN.Results indicate that EMSFN significantly stabilizes the outflow from the nozzle,with stability increasing with higher current intensity.At 10,000 Ampere-turns(At)of the coil,meniscus fluctuations were unstable.They stabilized at 13,000 At,with minimal changes observed beyond this point.The optimal current intensity for stable mold flow,at a casting speed of 1.56 m/min,is 13,000 At.These findings confirm the effectiveness of EMSFN in stabilizing the internal flow field of the slab mold and determining optimal operational current intensity.展开更多
Precipitation of carbides, nitrides, and carbonitrides is an important factor influencing the formation of surface transverse cracks in the continuous casting of microalloyed steel, affecting the quality and yield of ...Precipitation of carbides, nitrides, and carbonitrides is an important factor influencing the formation of surface transverse cracks in the continuous casting of microalloyed steel, affecting the quality and yield of the final product. Based on previous investigation, the precipitation sequence and temperature, position and mode, as well as the size, morphology, and number of different types of precipitates were reviewed. The effects of C, N, Nb, Ti, and V on the precipitation behavior and surface transverse cracks in continuous casting slabs were summarized, with a particular emphasis on the new achievements concerning Ti addition. The critical amounts of different elements to avoid serious surface cracks during continuous casting were proposed. The control mechanisms and industrial effects of composition optimization, cooling design, and chamfered mold configuration to improve surface transverse cracks in continuous casting slabs were also illustrated, and the recent application of surface microstructure control technology was emphasized. The characteristics, advantages, and shortcomings of existing theoretical and experimental methods in investigating continuous casting surface cracks regarding precipitation are finally discussed, and a new setup with advanced functions is introduced.展开更多
A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comp...A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comparison,the model was used to investigate slab cracking tendency near precipitated phases,considering various locations,sizes and shapes of them.The results show that the jet from submerged entry nozzle creates a“double roll”flow pattern during continuous casting,resulting in more uniform temperature distributions at slab corner and wide surface center compared with narrow surface center.Consequently,precipitated phases,particularly those located on the narrow surface,readily induce stress concentration and thus increase cracking tendency.A smaller precipitated phase size can reduce the stress concentration zone,while a more spherical shape can distribute surrounding stress along its surface and lower the internal stress within it,thereby decreasing the risk of slab cracking during continuous casting.The optimal precipitated phase exhibits a spherical or ellipsoidal shape with a major axis of less than 5µm,minimizing its potential to initiate cracks.展开更多
The crankshaft is subjected to complex rotational centrifugal force,periodic gas inertia force,and reciprocating inertia force during its working process.Consequently,the homogeneity requirement for crankshaft steel i...The crankshaft is subjected to complex rotational centrifugal force,periodic gas inertia force,and reciprocating inertia force during its working process.Consequently,the homogeneity requirement for crankshaft steel is exceptionally high.The distribution characteristics of center segregation and spot segregation of continuous casting bloom 42CrMoA crankshaft steel were analyzed by experiments,and the control mechanism of spot segregation by soft reduction zone and reduction amount was discussed.When the center solid fraction is between 0.61 and 1.00,an 8-mm soft reduction has a negligible impact on the flow of liquid steel at the end of solidification.Although it effectively improves center segregation,the improvement of spot segregation is limited.On the other hand,when the center solid fraction is between 0.31 and 1.00,a reduction of 10–12 mm,along with an expanded reduction zone and increased reduction amount,significantly promotes the flow of liquid steel at the end of solidification,reduces the size of equiaxed grains,mitigates the center negative segregation,and decreases the maximum size of spot segregation from 2954.29 to 1354.07μm.The number of spot segregations and the solutes enrichment degree of C,Cr,and Mn have also been significantly improved.An appropriate soft reduction zone and reduction amount can markedly ameliorate the semi-macro spot segregation of crankshaft steel blooms,thereby providing high-quality raw materials for subsequent products and enhancing the competitiveness of crankshaft products.展开更多
The continuous growth behavior of austenite grain in 20Cr peritectic steel was analyzed by experiment and theoretical modeling.The peculiar casting experiment with different cooling rates was achieved by multigradient...The continuous growth behavior of austenite grain in 20Cr peritectic steel was analyzed by experiment and theoretical modeling.The peculiar casting experiment with different cooling rates was achieved by multigradient operation scheme,and different morphologies in austenite grain were observed at the target location.The increase in austenite grain size with increasing cooling rate was firstly revealed in steels.The anomalous grain growth theoretically results from the mechanism of peritectic transformation transiting from the diffusional to massive type,and the additional energy storage stimulates the grain boundary migration.A new kinetic model to predict the growth behavior of austenite grain during continuous cooling process was developed,and the energy storage induced by massive type peritectic transformation was novelly taken into account.The parameters in the model were fitted by multiphase field modeling and experimental results.The kinetic model was finally verified by austenite grain size in laboratory test as well as the trial data at different locations in continuously cast bloom.The coarsening behavior of austenite grain during continuous casting was predicted based on the simulated temperature history.It is found that the grain coarsening occurs generally in the mold zone at high temperature for 20Cr steel and then almost levels off in the following process.The austenite finish transformation temperature Tγand primary cooling intensity show great influence on the grain coarsening.As Tγdecreases by 1℃,the austenite grain size decreases by 4μm linearly.However,the variation of Tγagainst heat flux is in a nonlinear relationship,suggesting that low cooling rate is much more harmful for austenite grain coarsening in continuous casting.展开更多
High temperature tensile were performed by using a thermo-mechanical GW1600 to simulate the deformation of Ti microalloy steels at high temperatures and low deformation rates similar to those during continuous casting...High temperature tensile were performed by using a thermo-mechanical GW1600 to simulate the deformation of Ti microalloy steels at high temperatures and low deformation rates similar to those during continuous casting.An equivalent austenite diameter was proposed,taking into account the weakening effects of proeutectoid ferrite films and Ti carbonitride precipitation.Based on this,a hot ductility prediction model for the slab was established to investigated hot ductility.The results show that as Ti content increases,the hot ductility of Ti microalloy steel initially increases and then decreases.At low Ti content,the pinning effect of Ti carbonitrides increases with the increase in Ti content,which inhibits grain coarsening for improving hot ductility.As Ti content increases,the size of carbonitrides grows,weakening the pinning effect and leading to austenite grain coarsening.Simultaneously,the formation of Ti carbonitrides inhibits proeutectoid ferrite film formation,leading to a reduction in its thickness.These combined factors reduce the hot ductility of the continuous casting steel.According to the hot ductility prediction model,in order of severity,the factors affecting hot ductility are:proeutectoid ferrite film,chain-like nanoscale Ti carbonitrides,austenite grain size,and dispersed nanoscale Ti carbonitrides.An accuracy error of less than 10%is shown by the model.展开更多
The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence thethermoplasticity,thereby affecting the quality of the slab.In this work,a prediction model...The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence thethermoplasticity,thereby affecting the quality of the slab.In this work,a prediction model for two-stage austenite growth under varyingcooling rates was established by incorporating the effect of second-phase pinning and high-temperature ferrite-austenite phase transform-ation and growth theory.The results indicate that with 0.02wt%Ti,the high-temperature ferrite growth exhibits typical parabolic growthcharacteristics.When the Ti content increases to 0.04wt%,the high-temperature ferrite grain boundary migration rate significantly slowsduring the initial solidification stage.The predicted austenite grain sizes for 0.02wt%Ti microalloyed steel at the center,quarter,and sur-face of the slab are 5592,3529,and 1524μm,respectively.For 0.04wt%Ti microalloyed steel,the austenite grain sizes are 4074,2942,and 1179μm at the same positions.The average error is within 5%.As the Ti content increases from 0.02wt% to 0.04wt%,the austenitegrain refinement at the center is most significant,with an average grain size reduction of 27.14%.展开更多
Controlling molten steel flow in the mold and stabilizing the meniscus are critical challenges during the continuous casting,directly impacting the surface quality and internal quality of the final steel slab product....Controlling molten steel flow in the mold and stabilizing the meniscus are critical challenges during the continuous casting,directly impacting the surface quality and internal quality of the final steel slab product.The effects of electromagnetic swirling flow in nozzle(EMSFN)technology on molten steel flow in the mold during slab continuous casting under various casting speeds were investigated.A real-time adjustable EMSFN was developed,and a three-dimensional unsteady Reynolds-averaged Navier–Stokes turbulence mathematical model was established to simulate the flow field within the mold.The results demonstrate that the EMSFN effectively stabilizes the outflow from nozzle,reduces the impact depth and surface velocity of the molten steel,mitigates meniscus fluctuations,and promotes stable flow within the mold.However,a certain matching relationship exists between the casting speed and the current intensity.For the experimental medium-thick slab specifications,the optimal current intensities were found to be 100,130,and 200 A at casting speeds of 1.0,1.5,and 2.0 m/min,respectively.EMSFN can optimize the mold flow field under different casting speeds,providing theoretical support for improving the quality of continuously cast slab products.展开更多
To address the current issues with the conventional slide gate system utilized in the steel teeming process,a unique electromagnetic induction controlled automated steel teeming(EICAST)technology has been developed.Co...To address the current issues with the conventional slide gate system utilized in the steel teeming process,a unique electromagnetic induction controlled automated steel teeming(EICAST)technology has been developed.Cooling means of spiral coil in this technology is directly related to its service life.Firstly,heat transfer processes of air cooling and spray cooling were compared and analyzed.Secondly,the impacts of water temperature,water flow rate and air flow rate were examined in order to maximize the spray cooling effect.To maintain coil temperature at a low value consistently throughout the entire thermal cycle process of the ladle,a combined cooling mode was finally employed.Numerical simulation was applied to examine the coil temperature variation with different cooling systems and characteristics.Before coil operation,spray cooling is said to be more effective.By controlling the water flow rate and air flow rate,the spray cooling effect is enhanced.However,water temperature has little or no impact when using spray cooling.Air cooling during the secondary refining process and spray cooling prior to coil operation are combined to further lower coil temperature.When the direction of the spray cooling is from bottom to top,the coil temperature is lowered below 165℃.A practical induction coil cooling plan was provided for the EICAST technology’s production process.展开更多
An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-...An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring(REMS).The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS,which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom.The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m,which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone.CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core,improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front,and the width of the liquid core increases by 4.2 mm at maximum.This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity,shrinkage cavity and crack defects in the center of the bloom.展开更多
During the continuous casting process of low carbon steel,the solidified hook formed in the mold has great effects on the surface quality of the cast slab.Some factory experiments have been conducted to investigate th...During the continuous casting process of low carbon steel,the solidified hook formed in the mold has great effects on the surface quality of the cast slab.Some factory experiments have been conducted to investigate the microscopic characteristics and reveal the influence of process parameters on solidified hooks.The depth of the hooks showed a positive correlation with the deflection angle,length,and oscillation mark(OM)depth,which indicates that the OM depth can serve as an approximate indicator for evaluating the depth of the solidified hooks.On the wide and narrow faces of the cast slab,the depth of the solidified hooks and the temperature distribution in the mold show opposite trends,with lower depths of solidified hooks at positions with higher temperatures.In addition,the influence of process parameters on solidified hooks was analyzed.With the increase in superheat,not only the depth of solidified hooks gradually decreases,but also the ratio of depression-typed marks increases.Increasing casting speed and decreasing immersion depth of the submerged entry nozzle will both lead to a decrease in the depth of the solidified hook.展开更多
A comprehensive mathematical model of annulus-electromagnetic direct chill （A-EMDC） casting of A357 aluminum alloy was established with corresponding experimental verification. The model was based on a combination o...A comprehensive mathematical model of annulus-electromagnetic direct chill （A-EMDC） casting of A357 aluminum alloy was established with corresponding experimental verification. The model was based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT. The effects of structural parameters on fluid flow, temperature field and solidification during A-EMDC process were investigated numerically. The results show that structural parameters such as annulus gap width, annulus gap position, and centre pipe length influence the flow and temperature fields. The smaller the annulus gap width is, the more uniform the temperature is, and the smaller the temperature gradient is. With increasing the centre pipe length, the circular flow would decrease due to the dislocation of centre pipe. Specially, when the annulus gap is located at periphery of the billet, the temperature gradient of the longitudinal direction in the solidification region falls evidently.展开更多
基金Item Sponsored by Science and Technology Research Project of Ministry of Education of China(03051)
文摘The distributions of heat flux along the height and the circumferential direction of round billet mould were measured continuously.The influence of casting speed,carbon content,powder,and pouring temperature on the average longitudinal and circumferential heat flux in the ＂high heat flux region＂ was discussed.The experimental and analytical results provide a basis for an intelligent mould with online detection of defects,adjustment of operational parameters,optimization of the monitoring system,and even prediction of abnormal heat transfer.
基金supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)the Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064)+1 种基金the Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)the Fundamental Research Funds for the Central Universities(No.N2425004).
文摘The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbulence model,coupling velocity,temperature,and phase field was established to study the effect of the ladle shroud immersion depth on the slag eye formation,slag entrainment,slag dragging,air dragging,and flow characteristics during the ladle change-over process of a two-strand tundish.The results showed that reducing the immersion depth decreases the high-velocity region area under the slag layer in the quasi-steady process.During the emptying stage,as the molten bath level gradually decreases,the outlet temperature exhibits a trend of initially decreasing and subsequently increasing across all three shroud immersion depths.However,under a 210 mm shroud immersion depth,molten slag and air are dragged into the shroud,forming slag droplets and causing significant fluctuations,with a maximum scalar velocity of 0.0764 m/s at the monitoring point.In the filling stage,air and molten slag are dragged into the molten bath,forming bubbles and slag droplets at an immersion depth of 210 mm.Bubbles are observed within the molten slag layer,which can readily cause an emulsification phenomenon,making it easier to be dragged as slag droplets.Additionally,the slag eye area measured under 210 mm immersion depth at 45 s is 0.303 m^(2),while the maximum scalar velocity of 2.4259 m/s is detected at 12 s.At an immersion depth of 360 mm,the average area of the slag eye is minimized to 0.06268 m2,with corresponding variances of 0.006753,representing the optimal immersion depth.
基金supported by the National Natural Science Foundation of China(No.52274318).
文摘A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.
基金support from the National Natural Science Foundation of China(Grant Nos.52174313 and 52304350)thank all members of the Hebei High Quality Steel Continuous Casting Engineering Technology Research Center at North China University of Science and Technology,Tangshan,China.
文摘The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.
文摘Directional solidification continuous casting (DSCC) process is a new manufacturing technology for metallic materials which combines advantages of both directional solidification technology and continuous casting technology. Unlimited long shaped metal with directionally solidifying microstructure can be produced by this process. It is experimentally shown that controlling condition of stable and continuous growth of single crystal structure means the precise control of the location of the S/L interface, which is affected and determined by seven process parameters. Moreover, these parameters are also interacted each other, so the disturbance of any parameters may cause the failure of controlling of S/L interface. In this paper, on the basis of analyzing the forming conditions of continuously directional microstructures in DSCC process, the control model of DSCC procedure by neural network control (NNC) method was proposed and discussed. Combining with the experiments, we first used the computer to simulate the effects of the solidification parameters on destination control variable (S/L interface) and the interactions among these parameters during DSCC procedure. Secondly many training samples necessary for neural network calculation can be obtained through the simulation. Moreover, these samples are inputted into neural network software (NNs) and trained, then the control model can be built up.
基金supported by the National Natural Science Foundation of China(No.52474355)the Liaoning Province Science and Technology Plan Joint Program(Key Research and Development Program Project),China(Nos.2022JH25/10200003 and 2023JH2/101800058).
文摘The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments,the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined.With SPA-H weathering steel as a specific research steel grade,the distributions of tem-perature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite ele-ment model.High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures,and a prediction model of the critical strain for two typical cracks,combining the effects of strain rate and temperature,was proposed by incorporating the Zener-Hollomon parameter.The crack risks with different LCR schemes were calculated using the crack risk prediction model,and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm×1600 mm was 41.8 mm,with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8,7.3,6.5,6.4,and 5.8 mm,respectively.
基金the National Natural Science Foundation of China(No.52004254)the Major Science and Technology Project of Henan Province,China(No.221100240300).
文摘The microstructure and properties of a 1030B Al strip were improved by applying ultrasonic melt treatment(UMT)in a Hazelett continuous casting direct rolling production line.The microstructure and properties of the 1030B Al strip were investigated by scanning electron microscopy,electron backscatter diffraction,and tensile testing.Applying UMT reduced the average grain size of the as-cast sheet by more than 28.0%with respect to that of the normal samples without UMT.When UMT was applied,the rolled strip inherited the refined grains from the as-cast sheet with an average grain size smaller than 63.0μm.Meanwhile,the dislocation density was increased by the grain refinement,dynamic recovery,and recrystallization during rolling.Accordingly,the strain-hardening rates of the rolled samples after UMT were generally higher than those of the normal samples,and the strength of the rolled strip was also improved.Furthermore,the rolled strip exhibited better formability with higher strain-hardening exponents and Erichsen index values.
基金supported by the Application Technology of Automotive Steels(No.2021040300048)the National Natural Science Foundation of China(No.52304347)+2 种基金Hebei Provincial Natural Science Foundation(No.E2019501008),China Baowu Low Carbon Metallurgy Innovation Foundation(BWLCF202320)Natural Science Foundation of Liaoning Province(Nos.2023-MSBA-135 and 2023-BSBA-107)Fundamental Research Funds for the Central Universities(Nos.N2409008 and N2409006).
文摘The electromagnetic swirling flow in nozzle(EMSFN)technique is designed to mitigate the adverse effects of unstable and uneven flow within the submerged entry nozzle in continuous casting.Utilizing electromagnetic forces,EMSFN stabilizes the flow within the nozzle,leading to a more controlled flow in the mold.Numerical simulations were used to quantitatively analyze the magnetic and flow fields in a slab continuous casting system under EMSFN.Results indicate that EMSFN significantly stabilizes the outflow from the nozzle,with stability increasing with higher current intensity.At 10,000 Ampere-turns(At)of the coil,meniscus fluctuations were unstable.They stabilized at 13,000 At,with minimal changes observed beyond this point.The optimal current intensity for stable mold flow,at a casting speed of 1.56 m/min,is 13,000 At.These findings confirm the effectiveness of EMSFN in stabilizing the internal flow field of the slab mold and determining optimal operational current intensity.
基金supported by the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-017A3)National Natural Science Foundation of China(No.51874026).
文摘Precipitation of carbides, nitrides, and carbonitrides is an important factor influencing the formation of surface transverse cracks in the continuous casting of microalloyed steel, affecting the quality and yield of the final product. Based on previous investigation, the precipitation sequence and temperature, position and mode, as well as the size, morphology, and number of different types of precipitates were reviewed. The effects of C, N, Nb, Ti, and V on the precipitation behavior and surface transverse cracks in continuous casting slabs were summarized, with a particular emphasis on the new achievements concerning Ti addition. The critical amounts of different elements to avoid serious surface cracks during continuous casting were proposed. The control mechanisms and industrial effects of composition optimization, cooling design, and chamfered mold configuration to improve surface transverse cracks in continuous casting slabs were also illustrated, and the recent application of surface microstructure control technology was emphasized. The characteristics, advantages, and shortcomings of existing theoretical and experimental methods in investigating continuous casting surface cracks regarding precipitation are finally discussed, and a new setup with advanced functions is introduced.
基金supported by National Natural Science Foundation of China(Nos.52325406 and 52374330)Fundamental Research Funds for the Central Universities(No.N2225046).
文摘A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comparison,the model was used to investigate slab cracking tendency near precipitated phases,considering various locations,sizes and shapes of them.The results show that the jet from submerged entry nozzle creates a“double roll”flow pattern during continuous casting,resulting in more uniform temperature distributions at slab corner and wide surface center compared with narrow surface center.Consequently,precipitated phases,particularly those located on the narrow surface,readily induce stress concentration and thus increase cracking tendency.A smaller precipitated phase size can reduce the stress concentration zone,while a more spherical shape can distribute surrounding stress along its surface and lower the internal stress within it,thereby decreasing the risk of slab cracking during continuous casting.The optimal precipitated phase exhibits a spherical or ellipsoidal shape with a major axis of less than 5µm,minimizing its potential to initiate cracks.
基金funded by the National Natural Science Foundation of China(NSFC)(Grant No.U1860111)Weifang Science and Technology Development Plan Project(Project No.2023ZJ1166).
文摘The crankshaft is subjected to complex rotational centrifugal force,periodic gas inertia force,and reciprocating inertia force during its working process.Consequently,the homogeneity requirement for crankshaft steel is exceptionally high.The distribution characteristics of center segregation and spot segregation of continuous casting bloom 42CrMoA crankshaft steel were analyzed by experiments,and the control mechanism of spot segregation by soft reduction zone and reduction amount was discussed.When the center solid fraction is between 0.61 and 1.00,an 8-mm soft reduction has a negligible impact on the flow of liquid steel at the end of solidification.Although it effectively improves center segregation,the improvement of spot segregation is limited.On the other hand,when the center solid fraction is between 0.31 and 1.00,a reduction of 10–12 mm,along with an expanded reduction zone and increased reduction amount,significantly promotes the flow of liquid steel at the end of solidification,reduces the size of equiaxed grains,mitigates the center negative segregation,and decreases the maximum size of spot segregation from 2954.29 to 1354.07μm.The number of spot segregations and the solutes enrichment degree of C,Cr,and Mn have also been significantly improved.An appropriate soft reduction zone and reduction amount can markedly ameliorate the semi-macro spot segregation of crankshaft steel blooms,thereby providing high-quality raw materials for subsequent products and enhancing the competitiveness of crankshaft products.
基金supported by the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-017A3)National Natural Science Foundation of China(No.51874026).
文摘The continuous growth behavior of austenite grain in 20Cr peritectic steel was analyzed by experiment and theoretical modeling.The peculiar casting experiment with different cooling rates was achieved by multigradient operation scheme,and different morphologies in austenite grain were observed at the target location.The increase in austenite grain size with increasing cooling rate was firstly revealed in steels.The anomalous grain growth theoretically results from the mechanism of peritectic transformation transiting from the diffusional to massive type,and the additional energy storage stimulates the grain boundary migration.A new kinetic model to predict the growth behavior of austenite grain during continuous cooling process was developed,and the energy storage induced by massive type peritectic transformation was novelly taken into account.The parameters in the model were fitted by multiphase field modeling and experimental results.The kinetic model was finally verified by austenite grain size in laboratory test as well as the trial data at different locations in continuously cast bloom.The coarsening behavior of austenite grain during continuous casting was predicted based on the simulated temperature history.It is found that the grain coarsening occurs generally in the mold zone at high temperature for 20Cr steel and then almost levels off in the following process.The austenite finish transformation temperature Tγand primary cooling intensity show great influence on the grain coarsening.As Tγdecreases by 1℃,the austenite grain size decreases by 4μm linearly.However,the variation of Tγagainst heat flux is in a nonlinear relationship,suggesting that low cooling rate is much more harmful for austenite grain coarsening in continuous casting.
基金financially supported by the Central Government Guiding Local Science and Technology Development Fund of Henan Province(Z20241471091)the Independent R&D Funds of State Key Laboratory of Advanced Metallurgy(41624025).
基金financially supported by the National Natural Science Foundation of China(No.51974078)the Liaoning Province Science and Technology Plan Joint Program(Key Research and Development Program Project,Nos.2022 JH25/10200003 and 2023 JH2/101800058)the Fundamental Research Funds for the Central Universities(No.N25YJS003).
文摘High temperature tensile were performed by using a thermo-mechanical GW1600 to simulate the deformation of Ti microalloy steels at high temperatures and low deformation rates similar to those during continuous casting.An equivalent austenite diameter was proposed,taking into account the weakening effects of proeutectoid ferrite films and Ti carbonitride precipitation.Based on this,a hot ductility prediction model for the slab was established to investigated hot ductility.The results show that as Ti content increases,the hot ductility of Ti microalloy steel initially increases and then decreases.At low Ti content,the pinning effect of Ti carbonitrides increases with the increase in Ti content,which inhibits grain coarsening for improving hot ductility.As Ti content increases,the size of carbonitrides grows,weakening the pinning effect and leading to austenite grain coarsening.Simultaneously,the formation of Ti carbonitrides inhibits proeutectoid ferrite film formation,leading to a reduction in its thickness.These combined factors reduce the hot ductility of the continuous casting steel.According to the hot ductility prediction model,in order of severity,the factors affecting hot ductility are:proeutectoid ferrite film,chain-like nanoscale Ti carbonitrides,austenite grain size,and dispersed nanoscale Ti carbonitrides.An accuracy error of less than 10%is shown by the model.
基金financially supported by the National Natural Science Foundation of China(No.52474355)the Liaoning Province Science and Technology Plan Joint Program(Key Research and Development Program Project,Nos.2022JH25/10200003 and 2023JH2/101800058)the Fundamental Research Funds for the Central Universities(Nos.N25YJS003 and N25DCG006)。
文摘The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence thethermoplasticity,thereby affecting the quality of the slab.In this work,a prediction model for two-stage austenite growth under varyingcooling rates was established by incorporating the effect of second-phase pinning and high-temperature ferrite-austenite phase transform-ation and growth theory.The results indicate that with 0.02wt%Ti,the high-temperature ferrite growth exhibits typical parabolic growthcharacteristics.When the Ti content increases to 0.04wt%,the high-temperature ferrite grain boundary migration rate significantly slowsduring the initial solidification stage.The predicted austenite grain sizes for 0.02wt%Ti microalloyed steel at the center,quarter,and sur-face of the slab are 5592,3529,and 1524μm,respectively.For 0.04wt%Ti microalloyed steel,the austenite grain sizes are 4074,2942,and 1179μm at the same positions.The average error is within 5%.As the Ti content increases from 0.02wt% to 0.04wt%,the austenitegrain refinement at the center is most significant,with an average grain size reduction of 27.14%.
基金National Natural Science Foundation of China(Nos.U21A20117,52104347 and 52272078)the Fundamental Research Funds for the Central Universities(No.N2409006)Natural Science Foundation of Liaoning Province(2023-MSBA-135)for the financial support.
文摘Controlling molten steel flow in the mold and stabilizing the meniscus are critical challenges during the continuous casting,directly impacting the surface quality and internal quality of the final steel slab product.The effects of electromagnetic swirling flow in nozzle(EMSFN)technology on molten steel flow in the mold during slab continuous casting under various casting speeds were investigated.A real-time adjustable EMSFN was developed,and a three-dimensional unsteady Reynolds-averaged Navier–Stokes turbulence mathematical model was established to simulate the flow field within the mold.The results demonstrate that the EMSFN effectively stabilizes the outflow from nozzle,reduces the impact depth and surface velocity of the molten steel,mitigates meniscus fluctuations,and promotes stable flow within the mold.However,a certain matching relationship exists between the casting speed and the current intensity.For the experimental medium-thick slab specifications,the optimal current intensities were found to be 100,130,and 200 A at casting speeds of 1.0,1.5,and 2.0 m/min,respectively.EMSFN can optimize the mold flow field under different casting speeds,providing theoretical support for improving the quality of continuously cast slab products.
基金supported by the Startup Foundation of Shenyang Agriculture University(No.X2023050)the Fundamental Research Funds for the Central Universities(No.N2209006)the National Natural Science Foundation of China(No.U22A20173).
文摘To address the current issues with the conventional slide gate system utilized in the steel teeming process,a unique electromagnetic induction controlled automated steel teeming(EICAST)technology has been developed.Cooling means of spiral coil in this technology is directly related to its service life.Firstly,heat transfer processes of air cooling and spray cooling were compared and analyzed.Secondly,the impacts of water temperature,water flow rate and air flow rate were examined in order to maximize the spray cooling effect.To maintain coil temperature at a low value consistently throughout the entire thermal cycle process of the ladle,a combined cooling mode was finally employed.Numerical simulation was applied to examine the coil temperature variation with different cooling systems and characteristics.Before coil operation,spray cooling is said to be more effective.By controlling the water flow rate and air flow rate,the spray cooling effect is enhanced.However,water temperature has little or no impact when using spray cooling.Air cooling during the secondary refining process and spray cooling prior to coil operation are combined to further lower coil temperature.When the direction of the spray cooling is from bottom to top,the coil temperature is lowered below 165℃.A practical induction coil cooling plan was provided for the EICAST technology’s production process.
基金the National Natural Science Foundation of China(Grant No.U1760206 and Grant No.51574083)the 111 Project(2.0)of China(No.BP0719037)for the financial support。
文摘An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring(REMS).The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS,which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom.The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m,which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone.CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core,improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front,and the width of the liquid core increases by 4.2 mm at maximum.This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity,shrinkage cavity and crack defects in the center of the bloom.
基金the financial support of National Key Research and Development Plan(No.2021YFB3702000)National Natural Science of China(Nos.52074076,52174306 and U20A20272)Fundamental Research Funds for the Central Universities(Nos.N2225023 and N2425006).Author information。
文摘During the continuous casting process of low carbon steel,the solidified hook formed in the mold has great effects on the surface quality of the cast slab.Some factory experiments have been conducted to investigate the microscopic characteristics and reveal the influence of process parameters on solidified hooks.The depth of the hooks showed a positive correlation with the deflection angle,length,and oscillation mark(OM)depth,which indicates that the OM depth can serve as an approximate indicator for evaluating the depth of the solidified hooks.On the wide and narrow faces of the cast slab,the depth of the solidified hooks and the temperature distribution in the mold show opposite trends,with lower depths of solidified hooks at positions with higher temperatures.In addition,the influence of process parameters on solidified hooks was analyzed.With the increase in superheat,not only the depth of solidified hooks gradually decreases,but also the ratio of depression-typed marks increases.Increasing casting speed and decreasing immersion depth of the submerged entry nozzle will both lead to a decrease in the depth of the solidified hook.
基金Project (2009AA03Z534) supported by the Hi-tech Research and Development Program of China Project (2006CB605203) supported by National Basic Research Program of China
文摘A comprehensive mathematical model of annulus-electromagnetic direct chill （A-EMDC） casting of A357 aluminum alloy was established with corresponding experimental verification. The model was based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT. The effects of structural parameters on fluid flow, temperature field and solidification during A-EMDC process were investigated numerically. The results show that structural parameters such as annulus gap width, annulus gap position, and centre pipe length influence the flow and temperature fields. The smaller the annulus gap width is, the more uniform the temperature is, and the smaller the temperature gradient is. With increasing the centre pipe length, the circular flow would decrease due to the dislocation of centre pipe. Specially, when the annulus gap is located at periphery of the billet, the temperature gradient of the longitudinal direction in the solidification region falls evidently.
