Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of prec...Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of precast concrete slab(PCS)is vital for keeping the initial track regularity.However,the cast-in-place process of the self-compacting concrete(SCC)filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC,even cracking of PCS.Currently,the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.Design/methodology/approach–In this work,a Computational Fluid Dynamics(CFD)model is established to calculate the buoyancy of PCS caused by the flowing SCC.The main influencing factors,including the inlet speed and flowability of SCC,have been analyzed and discussed.A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.Findings–The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.Originality/value–The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.展开更多
This study investigates the formation feasibility of the integrated bottom car body components with dual die casting injection molding technology.During the production of a die-cast super-large one-piece body part wei...This study investigates the formation feasibility of the integrated bottom car body components with dual die casting injection molding technology.During the production of a die-cast super-large one-piece body part weighing over 10,000 t,a thorough comparison and investigation were conducted on the arising issues,using both single and double injection systems.Particular attention was given to meticulously discussing the die casting filling problems and microstructural defects that originated from the filling process.The research findings indicate that the implementation of a double injection system can significantly minimize cold shuts and reduce the solidification time.The effectiveness of this die casting technique was further confirmed by the production of high-quality castings using a scaled model that replicated real casting conditions at a 1:3 ratio,thereby maintaining a one-to-one correspondence in essential aspects.This successful study offers both theoretical insights and practical applications for the production of integrated bottom car bodies utilizing die casting in conjunction with a dual injection system.展开更多
In this work,the influences of surface layer slurry at different temperatures(10℃,14℃,18℃,22℃)on wax patterns deformation,shrinkage,slurry coating characteristics,and the surface quality of the casting were invest...In this work,the influences of surface layer slurry at different temperatures(10℃,14℃,18℃,22℃)on wax patterns deformation,shrinkage,slurry coating characteristics,and the surface quality of the casting were investigated by using a single factor variable method.The surface morphologies of the shell molds produced by different temperatures of the surface(first)layer slurries were observed via electron microscopy.Furthermore,the microscopic composition of these shell molds was obtained by EDS,and the osmotic effect of the slurry on the wax patterns at different temperatures was also assessed by the PZ-200 Contact Angle detector.The forming reasons for the surface cracks and holes of thick and large ZTC4 titanium alloy by investment casting were analyzed.The experimental results show that the surface of the shell molds prepared by the surface layer slurry with a low temperature exhibits noticeable damage,which is mainly due to the poor coating performance and the serious expansion and contraction of wax pattern at low temperatures.The second layer shell material(SiO_(2),Al_(2)O_(3))immerses into the crack area of the surface layer,contacts and reacts with the molten titanium to form surface cracks and holes in the castings.With the increase of the temperature of surface layer slurry,the damage to the shell surface tends to weaken,and the composition of the shell molds'surface becomes more uniform with less impurities.The results show that the surface layer slurry at 22℃is evenly coated on the surface of the wax patterns with appropriate thickness,and there is no surface shell mold rupture caused by sliding slurry after sand leaching.The surface layer slurry temperature is consistent with the wax pattern temperature and the workshop temperature,so there is no damage of the surface layer shell caused by expansion and contraction.Therefore,the shell mold prepared by the surface layer slurry at this temperature has good integrity,isolating the contact between the low inert shell material and the titanium liquid effectively,and the ZTC4 titanium alloy cylinder casting prepared by this shell mold is smooth,without cracks and holes.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 impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and...The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded,and the microstructures,cracks morphology,and precipitated phases were analyzed using optical microscope,scanning electron microscope,transmission electron microscope,and energy dispersive X-ray spectrometer.The results reveal that the dimensions of casting defects significantly affect the weldability of K4951.Deep defects(greater than 2 mm)lead to rapid crack propagation,while wider defects can moderate the propagation process of cracks.Elemental segregation and the formation of precipitated phases,such as MC carbides,are observed in the fusion zone,contributing to welding cracks.An optimal groove aspect ratio(depth-to-width)between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength,resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.展开更多
A suction casting experiment was conducted on Zr_(55)Cu_(30)Al_(10)Ni_(5)(at%)amorphous alloy.Using ProCAST software,numerical simulations were performed to analyze the filling and solidification processes.The velocit...A suction casting experiment was conducted on Zr_(55)Cu_(30)Al_(10)Ni_(5)(at%)amorphous alloy.Using ProCAST software,numerical simulations were performed to analyze the filling and solidification processes.The velocity field during the filling process and the temperature field during the solidification process of the alloy melt under different process parameters were obtained.Based on the simulation results,a Zr-based amorphous alloy micro-gear was prepared via casting.The results indicate that increasing the suction casting temperature enhances the fluidity of alloy melt but induces unstable flow rate during filling,which is detrimental to complete filling.Zr-based amorphous micro-gears with a module of 0.6 mm,a tooth top diameter of 8 mm,and 10 teeth were prepared through the suction casting.X-ray diffraction and differential scanning calorimetry analyses confirm that the fabricated micro-gear exhibits characteristic amorphous structural features,demonstrating well-defined geometrical contours and satisfactory forming completeness.展开更多
A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact e...A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact energy.The experimental results demonstrate that the addition of elements such as Nb,V and Ce can markedly improve the strength of the low-alloy cast steel.Maintaining a constant level of elements such as Nb,V and Ce,while reducing the content of Si to 0.28 wt.%,leads to substantial enhancements in impact energy at−40℃,meeting the mechanical properties criteria of X80 pipeline steel.The excellent mechanical properties of the multi-microalloyed low-alloy cast steel result from the reason that the multi-addition of microalloying elements refines the grains and facilitates the formation of nanoprecipitates like NbC.Moreover,decreasing Si content can enhance the recovery of martensitic laths in cast steel during the tempering process,reducing stress from dislocation movement and improving plasticity.展开更多
Deep learning has achieved great progress in image recognition,segmentation,semantic recognition and game theory.In this study,a latest deep learning model,a conditional diffusion model was adopted as a surrogate mode...Deep learning has achieved great progress in image recognition,segmentation,semantic recognition and game theory.In this study,a latest deep learning model,a conditional diffusion model was adopted as a surrogate model to predict the heat transfer during the casting process instead of numerical simulation.The conditional diffusion model was established and trained with the geometry shapes,initial temperature fields and temperature fields at t_(i) as the condition and random noise sampled from standard normal distribution as the input.The output was the temperature field at t_(i+1).Therefore,the temperature field at t_(i+1)can be predicted as the temperature field at t_(i) is known,and the continuous temperature fields of all the time steps can be predicted based on the initial temperature field of an arbitrary 2D geometry.A training set with 3022D shapes and their simulated temperature fields at different time steps was established.The accuracy for the temperature field for a single time step reaches 97.7%,and that for continuous time steps reaches 69.1%with the main error actually existing in the sand mold.The effect of geometry shape and initial temperature field on the prediction accuracy was investigated,the former achieves better result than the latter because the former can identify casting,mold and chill by different colors in the input images.The diffusion model has proved the potential as a surrogate model for numerical simulation of the casting process.展开更多
Hardenability significantly impacts the distortion of gear during heat treatment,correlated to the uniformity of solute distribution in steel matrix.The experimental analysis was conducted on the macrostructure,solute...Hardenability significantly impacts the distortion of gear during heat treatment,correlated to the uniformity of solute distribution in steel matrix.The experimental analysis was conducted on the macrostructure,solute distribution,dendrite structure,and rod hardenability of 20CrMnTiH gear steel in continuously cast blooms and hot roller rods.The evaluation approach by the standards for the hardenability of gear steel rods and the corresponding blooms was analyzed,and the inheritance mechanism from solidification segregation to hardenability fluctuation of gear steel was revealed.The results indicate that semi-macroscopic spot segregation located in the equiaxed zone exhibits larger size,higher solute enrichment,and worse solute homogeneity,leading to significant solute fluctuations in the blooms and hardenability fluctuation in the rods.By increasing the liquid steel superheat from 35 to 40℃,reducing the mold electromagnetic stirring from 300 to 100 A,and implementing the soft reduction(SR)of 7 mm at the solidification end,the equiaxed ratio of the strand decreased from 26.42%to 6.69%.Consequently,the solute fluctuation range and standard deviation decrease significantly in the transverse section,while the maximum segregation ratio,average fluctuation range,and average standard deviation of solutes C,Cr,and Mn in the spot segregation decrease at the same time.At the meanwhile,the equiaxed ratio of the rod decreased from 24.89%to 4.09%,and the structure of the hardenability detection zone was transformed from equiaxed crystals to columnar crystals.Furthermore,the solute fluctuation range and standard deviation in the transverse section decreased,while the homogeneity in spot segregation was also improved.The hardness difference of A and B surfaces at J9 and J15 positions was smaller than 2 HRC,meeting the qualification standard for hardenability.展开更多
In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occur...In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occurs due to the intrusion of gases generated during the resin burning of the sand core into castings during the casting process.Therefore,a gas generation and flow constitution model was established,in which the gas generation rate is a function of temperature and time,and the flow of gas is controlled by the gas release,conservation,and Darcy's law.The heat transfer and gas flow during casting process was numerically simulated.The dangerous point of cores is firstly identified by a virtual heat transfer method based on the similarity between heat transfer and gas flow in the sand core.The gas pores in castings are predicted by the gas pressure,the viscosity and state of the melt for these dangerous points.Three distinct sand core structures were designed and used for the production of iron castings,and the simulated gas pore results were validated by the obtained castings.展开更多
Achieving high thermal stability in the 6xxx series alloys remains a challenging task,which limits their engineering application.Herein,Al-Mg-Si-Cu alloys with various Mg/Si ratios(0.5,1,2,and 4)were fab-ricated by tw...Achieving high thermal stability in the 6xxx series alloys remains a challenging task,which limits their engineering application.Herein,Al-Mg-Si-Cu alloys with various Mg/Si ratios(0.5,1,2,and 4)were fab-ricated by twin-roll casting(TRC),and the microstructure evolution and mechanical properties during long-term thermal exposure of 150℃/1000 h were studied.The results disclosed that alloys with a high Mg/Si ratio exhibited better thermal stability.The alloys with the Mg/Si ratio of 2(Mg/Si∼2)achieved a stable high yield strength of∼330 MPa and meanwhile maintained a satisfactory fracture elongation(>10%)throughout the thermal exposure process.This excellent thermal stability can be attributed to the microstructure consisting of high-density L phases and fineα-AlFeSi phases,which was related to the optimized Mg/Si ratio.Specifically,L phases were dominated in peak-aged Mg/Si∼2 alloys,while the counterparts in alloys with the Mg/Si ratio of 1(Mg/Si∼1)wereβ’’and Q’phases.During the thermal exposure process,the L phases remained stable without coarsening,which was mainly due to the high coherence and low interfacial energy of the L-matrix interface.Meanwhile,the main Fe-containing phases in Mg/Si∼2 and Mg/Si∼1 alloys were fine near-spheroidalα-AlFeSi and large-size needle-likeβ-AlFeSi,re-spectively,which lead to a better ductility of Mg/Si∼2 alloys.This work may provide a strategy for the preparation of 6xxx series alloys with high thermal stability.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
In the foundry industries,process design has traditionally relied on manuals and complex theoretical calculations.With the advent of 3D design in casting,computer-aided design(CAD)has been applied to integrate the fea...In the foundry industries,process design has traditionally relied on manuals and complex theoretical calculations.With the advent of 3D design in casting,computer-aided design(CAD)has been applied to integrate the features of casting process,thereby expanding the scope of design options.These technologies use parametric model design techniques for rapid component creation and use databases to access standard process parameters and design specifications.However,3D models are currently still created through inputting or calling parameters,which requires numerous verifications through calculations to ensure the design rationality.This process may be significantly slowed down due to repetitive modifications and extended design time.As a result,there are increasingly urgent demands for a real-time verification mechanism to address this issue.Therefore,this study proposed a novel closed-loop model and software development method that integrated contextual design with real-time verification,dynamically verifying relevant rules for designing 3D casting components.Additionally,the study analyzed three typical closed-loop scenarios of agile design in an independent developed intelligent casting process system.It is believed that foundry industries can potentially benefit from favorably reduced design cycles to yield an enhanced competitive product market.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 microstructural evolution and mechanical properties of Mg-8.0Al-xYb-0.5Zn(wt%,x=0,1,2)cast alloys were investigated.With increasing Yb content,a significant grain refinement was observed,accompanied by the continu...The microstructural evolution and mechanical properties of Mg-8.0Al-xYb-0.5Zn(wt%,x=0,1,2)cast alloys were investigated.With increasing Yb content,a significant grain refinement was observed,accompanied by the continuous refinement and fragmentation of the initial β-Mg_(17)Al_(12) phase network.Concurrently,the Al_(3)Yb phase formed and coarsened.Calculations including formation enthalpy and lattice misfit,confirm that the Al_(3)Yb phase,which nucleates prior to theα-Mg and β-Mg_(17)Al_(12) phases and exhibits a low lattice misfit with their low-index planes,serves as an effective heterogeneous nucleation site,significantly contributing to the observed microstructural refinement.Furthermore,Yb addition fundamentally suppresses constitutional supercooling by consuming Al atoms,which possess a high growth restriction factor,for the formation of Al-Yb phases.Subsequent tensile testing reveals that Yb solute promotes the generation of extension twins and the accumulation of dislocations during deformation,leading to a marked enhancement in the work-hardening capacity of the Yb-containing alloys.Benefiting from the refined microstructure and enhanced work hardening,the Mg-8.0Al-1.0Yb-0.5Zn alloy exhibits a favorable balance between mechanical strength and ductility,achieving an ultimate tensile strength of~249.8 MPa and an elongation of~11.70%,respectively.展开更多
Achieving optimal mechanical performance in high-pressure die-cast(HPDC)Mg-based alloys through experimental methods is both costly and time-intensive due to significant variations in composition.This study leverages ...Achieving optimal mechanical performance in high-pressure die-cast(HPDC)Mg-based alloys through experimental methods is both costly and time-intensive due to significant variations in composition.This study leverages machine learning(ML)techniques to accelerate the development of high-performance Mg-based alloys.Data on alloy composition and mechanical properties were collected from literature sources,focusing on HPDC Mg-based alloys.Six ML models—extra trees,CatBoost,k-nearest neighbors,random forest,gradient boosting,and decision tree—were trained to predict mechanical behavior.Cat Boost yielded the highest prediction accuracy with R^(2) scores of 0.95 for ultimate tensile strength(UTS)and 0.92 for yield strength(YS).Further validation using published datasets reaffirmed its reliability,demonstrating R^(2) values of 0.956(UTS)and 0.936(YS),MAE of 1%and 2.8%,and RMSE of 1%and 3.5%,respectively.Among these,the CatBoost model demonstrated the highest predictive accuracy,outperforming other ML techniques across multiple optimization metrics.展开更多
文摘Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of precast concrete slab(PCS)is vital for keeping the initial track regularity.However,the cast-in-place process of the self-compacting concrete(SCC)filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC,even cracking of PCS.Currently,the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.Design/methodology/approach–In this work,a Computational Fluid Dynamics(CFD)model is established to calculate the buoyancy of PCS caused by the flowing SCC.The main influencing factors,including the inlet speed and flowability of SCC,have been analyzed and discussed.A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.Findings–The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.Originality/value–The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.
基金supported by the National Natural Science Foundation of China(No.52175284)the National Key Research and Development Program of China(Grant No.2022YFB3404201).
文摘This study investigates the formation feasibility of the integrated bottom car body components with dual die casting injection molding technology.During the production of a die-cast super-large one-piece body part weighing over 10,000 t,a thorough comparison and investigation were conducted on the arising issues,using both single and double injection systems.Particular attention was given to meticulously discussing the die casting filling problems and microstructural defects that originated from the filling process.The research findings indicate that the implementation of a double injection system can significantly minimize cold shuts and reduce the solidification time.The effectiveness of this die casting technique was further confirmed by the production of high-quality castings using a scaled model that replicated real casting conditions at a 1:3 ratio,thereby maintaining a one-to-one correspondence in essential aspects.This successful study offers both theoretical insights and practical applications for the production of integrated bottom car bodies utilizing die casting in conjunction with a dual injection system.
文摘In this work,the influences of surface layer slurry at different temperatures(10℃,14℃,18℃,22℃)on wax patterns deformation,shrinkage,slurry coating characteristics,and the surface quality of the casting were investigated by using a single factor variable method.The surface morphologies of the shell molds produced by different temperatures of the surface(first)layer slurries were observed via electron microscopy.Furthermore,the microscopic composition of these shell molds was obtained by EDS,and the osmotic effect of the slurry on the wax patterns at different temperatures was also assessed by the PZ-200 Contact Angle detector.The forming reasons for the surface cracks and holes of thick and large ZTC4 titanium alloy by investment casting were analyzed.The experimental results show that the surface of the shell molds prepared by the surface layer slurry with a low temperature exhibits noticeable damage,which is mainly due to the poor coating performance and the serious expansion and contraction of wax pattern at low temperatures.The second layer shell material(SiO_(2),Al_(2)O_(3))immerses into the crack area of the surface layer,contacts and reacts with the molten titanium to form surface cracks and holes in the castings.With the increase of the temperature of surface layer slurry,the damage to the shell surface tends to weaken,and the composition of the shell molds'surface becomes more uniform with less impurities.The results show that the surface layer slurry at 22℃is evenly coated on the surface of the wax patterns with appropriate thickness,and there is no surface shell mold rupture caused by sliding slurry after sand leaching.The surface layer slurry temperature is consistent with the wax pattern temperature and the workshop temperature,so there is no damage of the surface layer shell caused by expansion and contraction.Therefore,the shell mold prepared by the surface layer slurry at this temperature has good integrity,isolating the contact between the low inert shell material and the titanium liquid effectively,and the ZTC4 titanium alloy cylinder casting prepared by this shell mold is smooth,without cracks and holes.
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National Natural Science Foundation of China(52201054,52175368)National Science and Technology Major Projects(J2019-VI-0018-0133)+2 种基金Liaoning Provincial Science and Technology Program(2023-BS-019,2023-MS-020)National Key R&D Program of China(2021YFB3700401)Key Specialized Research and Development Break-Through-Unveiling and Commanding the Special Project Program in Liaoning Province(2021JH15)。
文摘The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded,and the microstructures,cracks morphology,and precipitated phases were analyzed using optical microscope,scanning electron microscope,transmission electron microscope,and energy dispersive X-ray spectrometer.The results reveal that the dimensions of casting defects significantly affect the weldability of K4951.Deep defects(greater than 2 mm)lead to rapid crack propagation,while wider defects can moderate the propagation process of cracks.Elemental segregation and the formation of precipitated phases,such as MC carbides,are observed in the fusion zone,contributing to welding cracks.An optimal groove aspect ratio(depth-to-width)between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength,resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.
基金National Natural Science Foundation of China(51971103)Key Research and Development Program in Gansu Province(20YF8GA052)。
文摘A suction casting experiment was conducted on Zr_(55)Cu_(30)Al_(10)Ni_(5)(at%)amorphous alloy.Using ProCAST software,numerical simulations were performed to analyze the filling and solidification processes.The velocity field during the filling process and the temperature field during the solidification process of the alloy melt under different process parameters were obtained.Based on the simulation results,a Zr-based amorphous alloy micro-gear was prepared via casting.The results indicate that increasing the suction casting temperature enhances the fluidity of alloy melt but induces unstable flow rate during filling,which is detrimental to complete filling.Zr-based amorphous micro-gears with a module of 0.6 mm,a tooth top diameter of 8 mm,and 10 teeth were prepared through the suction casting.X-ray diffraction and differential scanning calorimetry analyses confirm that the fabricated micro-gear exhibits characteristic amorphous structural features,demonstrating well-defined geometrical contours and satisfactory forming completeness.
基金supported by the National Natural Science Foundation of China(No.52071195)Key Project of the National Natural Science Foundation of China(No.52130109).
文摘A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact energy.The experimental results demonstrate that the addition of elements such as Nb,V and Ce can markedly improve the strength of the low-alloy cast steel.Maintaining a constant level of elements such as Nb,V and Ce,while reducing the content of Si to 0.28 wt.%,leads to substantial enhancements in impact energy at−40℃,meeting the mechanical properties criteria of X80 pipeline steel.The excellent mechanical properties of the multi-microalloyed low-alloy cast steel result from the reason that the multi-addition of microalloying elements refines the grains and facilitates the formation of nanoprecipitates like NbC.Moreover,decreasing Si content can enhance the recovery of martensitic laths in cast steel during the tempering process,reducing stress from dislocation movement and improving plasticity.
基金sponsored by Tsinghua-Toyota Joint Research Fund
文摘Deep learning has achieved great progress in image recognition,segmentation,semantic recognition and game theory.In this study,a latest deep learning model,a conditional diffusion model was adopted as a surrogate model to predict the heat transfer during the casting process instead of numerical simulation.The conditional diffusion model was established and trained with the geometry shapes,initial temperature fields and temperature fields at t_(i) as the condition and random noise sampled from standard normal distribution as the input.The output was the temperature field at t_(i+1).Therefore,the temperature field at t_(i+1)can be predicted as the temperature field at t_(i) is known,and the continuous temperature fields of all the time steps can be predicted based on the initial temperature field of an arbitrary 2D geometry.A training set with 3022D shapes and their simulated temperature fields at different time steps was established.The accuracy for the temperature field for a single time step reaches 97.7%,and that for continuous time steps reaches 69.1%with the main error actually existing in the sand mold.The effect of geometry shape and initial temperature field on the prediction accuracy was investigated,the former achieves better result than the latter because the former can identify casting,mold and chill by different colors in the input images.The diffusion model has proved the potential as a surrogate model for numerical simulation of the casting process.
基金supported by the Weifang Science and Technology Development Plan Project in China(No.2023ZJ1166).
文摘Hardenability significantly impacts the distortion of gear during heat treatment,correlated to the uniformity of solute distribution in steel matrix.The experimental analysis was conducted on the macrostructure,solute distribution,dendrite structure,and rod hardenability of 20CrMnTiH gear steel in continuously cast blooms and hot roller rods.The evaluation approach by the standards for the hardenability of gear steel rods and the corresponding blooms was analyzed,and the inheritance mechanism from solidification segregation to hardenability fluctuation of gear steel was revealed.The results indicate that semi-macroscopic spot segregation located in the equiaxed zone exhibits larger size,higher solute enrichment,and worse solute homogeneity,leading to significant solute fluctuations in the blooms and hardenability fluctuation in the rods.By increasing the liquid steel superheat from 35 to 40℃,reducing the mold electromagnetic stirring from 300 to 100 A,and implementing the soft reduction(SR)of 7 mm at the solidification end,the equiaxed ratio of the strand decreased from 26.42%to 6.69%.Consequently,the solute fluctuation range and standard deviation decrease significantly in the transverse section,while the maximum segregation ratio,average fluctuation range,and average standard deviation of solutes C,Cr,and Mn in the spot segregation decrease at the same time.At the meanwhile,the equiaxed ratio of the rod decreased from 24.89%to 4.09%,and the structure of the hardenability detection zone was transformed from equiaxed crystals to columnar crystals.Furthermore,the solute fluctuation range and standard deviation in the transverse section decreased,while the homogeneity in spot segregation was also improved.The hardness difference of A and B surfaces at J9 and J15 positions was smaller than 2 HRC,meeting the qualification standard for hardenability.
基金funded by the Beijing Nature Sciences Fund Haidian Originality Cooperation Project (Grant No. L212002)。
文摘In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occurs due to the intrusion of gases generated during the resin burning of the sand core into castings during the casting process.Therefore,a gas generation and flow constitution model was established,in which the gas generation rate is a function of temperature and time,and the flow of gas is controlled by the gas release,conservation,and Darcy's law.The heat transfer and gas flow during casting process was numerically simulated.The dangerous point of cores is firstly identified by a virtual heat transfer method based on the similarity between heat transfer and gas flow in the sand core.The gas pores in castings are predicted by the gas pressure,the viscosity and state of the melt for these dangerous points.Three distinct sand core structures were designed and used for the production of iron castings,and the simulated gas pore results were validated by the obtained castings.
基金Financial supports are from the National Natural Science Foun-dation of China(Nos.52261015 and U22A20109)the Inner Mongolia Natural Science Foundation(No.2022QN05005)+2 种基金the Basic Scientific Research Expenses Program of Universities directly under Inner Mongolia Autonomous Region(No.JY20220109)the Scientific Research Project of Inner Mongolia University of Technology(No.ZZ202104)the Science Research Project of Hebei Education Department(No.BJK2024023 and BJK2024061).
文摘Achieving high thermal stability in the 6xxx series alloys remains a challenging task,which limits their engineering application.Herein,Al-Mg-Si-Cu alloys with various Mg/Si ratios(0.5,1,2,and 4)were fab-ricated by twin-roll casting(TRC),and the microstructure evolution and mechanical properties during long-term thermal exposure of 150℃/1000 h were studied.The results disclosed that alloys with a high Mg/Si ratio exhibited better thermal stability.The alloys with the Mg/Si ratio of 2(Mg/Si∼2)achieved a stable high yield strength of∼330 MPa and meanwhile maintained a satisfactory fracture elongation(>10%)throughout the thermal exposure process.This excellent thermal stability can be attributed to the microstructure consisting of high-density L phases and fineα-AlFeSi phases,which was related to the optimized Mg/Si ratio.Specifically,L phases were dominated in peak-aged Mg/Si∼2 alloys,while the counterparts in alloys with the Mg/Si ratio of 1(Mg/Si∼1)wereβ’’and Q’phases.During the thermal exposure process,the L phases remained stable without coarsening,which was mainly due to the high coherence and low interfacial energy of the L-matrix interface.Meanwhile,the main Fe-containing phases in Mg/Si∼2 and Mg/Si∼1 alloys were fine near-spheroidalα-AlFeSi and large-size needle-likeβ-AlFeSi,re-spectively,which lead to a better ductility of Mg/Si∼2 alloys.This work may provide a strategy for the preparation of 6xxx series alloys with high thermal stability.
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the financial support of the Natural Science Foundation of Hubei Province,China (Grant No.2022CFB770)。
文摘In the foundry industries,process design has traditionally relied on manuals and complex theoretical calculations.With the advent of 3D design in casting,computer-aided design(CAD)has been applied to integrate the features of casting process,thereby expanding the scope of design options.These technologies use parametric model design techniques for rapid component creation and use databases to access standard process parameters and design specifications.However,3D models are currently still created through inputting or calling parameters,which requires numerous verifications through calculations to ensure the design rationality.This process may be significantly slowed down due to repetitive modifications and extended design time.As a result,there are increasingly urgent demands for a real-time verification mechanism to address this issue.Therefore,this study proposed a novel closed-loop model and software development method that integrated contextual design with real-time verification,dynamically verifying relevant rules for designing 3D casting components.Additionally,the study analyzed three typical closed-loop scenarios of agile design in an independent developed intelligent casting process system.It is believed that foundry industries can potentially benefit from favorably reduced design cycles to yield an enhanced competitive product market.
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 Natural Science Foundation Project of CQ CSTC(Grant Nos.CSTB2024NSCQ-MSX0473 and CSTC2020JCYJ-MSXMX0170)the National Natural Science Foundation of China(Grant No.51975484)+1 种基金the Research Initiation Project under the Talent Introduction Program at Southwest University(Grant No.SWU-KR24001)the Postgraduate Research and Innovation Program at Southwest University(Grant No.SWUS24106).
文摘The microstructural evolution and mechanical properties of Mg-8.0Al-xYb-0.5Zn(wt%,x=0,1,2)cast alloys were investigated.With increasing Yb content,a significant grain refinement was observed,accompanied by the continuous refinement and fragmentation of the initial β-Mg_(17)Al_(12) phase network.Concurrently,the Al_(3)Yb phase formed and coarsened.Calculations including formation enthalpy and lattice misfit,confirm that the Al_(3)Yb phase,which nucleates prior to theα-Mg and β-Mg_(17)Al_(12) phases and exhibits a low lattice misfit with their low-index planes,serves as an effective heterogeneous nucleation site,significantly contributing to the observed microstructural refinement.Furthermore,Yb addition fundamentally suppresses constitutional supercooling by consuming Al atoms,which possess a high growth restriction factor,for the formation of Al-Yb phases.Subsequent tensile testing reveals that Yb solute promotes the generation of extension twins and the accumulation of dislocations during deformation,leading to a marked enhancement in the work-hardening capacity of the Yb-containing alloys.Benefiting from the refined microstructure and enhanced work hardening,the Mg-8.0Al-1.0Yb-0.5Zn alloy exhibits a favorable balance between mechanical strength and ductility,achieving an ultimate tensile strength of~249.8 MPa and an elongation of~11.70%,respectively.
基金supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(2021R1A6A1A10044950)。
文摘Achieving optimal mechanical performance in high-pressure die-cast(HPDC)Mg-based alloys through experimental methods is both costly and time-intensive due to significant variations in composition.This study leverages machine learning(ML)techniques to accelerate the development of high-performance Mg-based alloys.Data on alloy composition and mechanical properties were collected from literature sources,focusing on HPDC Mg-based alloys.Six ML models—extra trees,CatBoost,k-nearest neighbors,random forest,gradient boosting,and decision tree—were trained to predict mechanical behavior.Cat Boost yielded the highest prediction accuracy with R^(2) scores of 0.95 for ultimate tensile strength(UTS)and 0.92 for yield strength(YS).Further validation using published datasets reaffirmed its reliability,demonstrating R^(2) values of 0.956(UTS)and 0.936(YS),MAE of 1%and 2.8%,and RMSE of 1%and 3.5%,respectively.Among these,the CatBoost model demonstrated the highest predictive accuracy,outperforming other ML techniques across multiple optimization metrics.
