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
The characteristics and sensitivity of solidification cracks in peritectic steels were investigated using directional solidifi-cation technology.Interdendritic cracks were observed in both hypoperitectic steels(12CrlM...The characteristics and sensitivity of solidification cracks in peritectic steels were investigated using directional solidifi-cation technology.Interdendritic cracks were observed in both hypoperitectic steels(12CrlMoV,15CrMo)and hyper-peritectic steel(20CrMo)during solidification at growth velocities of 15,50,and 80 pm/s.At the dendritic boundaries,sulphide precipitates were found,promoting crack formation.Based on the statistical analysis of interdendritic cracks in peritectic steels,the area ratio(RA)of interdendritic cracks in a directional solidification structure was proposed to evaluate the crack sensitivity of peritectic steels.Furthermore,the crack sensitivities of peritectic steels(12CrlMoV,15CrMo,and 20CrMo)were tested,evaluated,and compared with the surface crack rates of three types of steels produced from a steel plant.The results demonstrated that RA was in good agreement with that of the steel plant,and the crack sensitivity of 12CrlMoV steel was the strongest,followed by that of 15CrMo and 20CrMo steels.Thus,RA can be used to evaluate the crack sensitivity of peritectic steel.展开更多
Peritectic reaction was studied by directional solidification of Cu-Ge alloys.A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during per...Peritectic reaction was studied by directional solidification of Cu-Ge alloys.A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during peritectic reaction.Under different growth conditions and compositions,different growth morphologies of triple junction region are presented.For the hypoperitectic Cu-13.5%Ge alloy,as the pulling velocity（v） increases from 2 to 5 μm/s,the morphological instability of the peritectic phase occurs during the peritectic reaction and the remelting interface of the primary phase is relatively stable.However,for the hyperperitectic Cu-15.6%Ge alloy wim v=5 μm/s,the nonplanar remelting interface near the trijunction is presented.The morphological stabilities of the solidifying peritectic phase and the remelting primary phase are analyzed in terms of the constitutional undercooling criterion.展开更多
Abnormal mold level fluctuation is frequently observed in high-speed casting,especially for peritectic steels,which has been shown to severely deteriorate product quality.Both an online electromagnetic sensor and an i...Abnormal mold level fluctuation is frequently observed in high-speed casting,especially for peritectic steels,which has been shown to severely deteriorate product quality.Both an online electromagnetic sensor and an ibaAnalyzer are used to analyze the frequency and amplitude of massive mold level fluctuation data from the slab casting process of different steel grades using different casting speeds,slab widths and physical parameters of mold flux.The results show that in the slab continuous casting process of peritectic steels,the main frequency and equivalent amplitude of abnormal mold level fluctuations first increase and then decrease with increasing the carbon content.In the production of various grades of steel,the main frequency of abnormal mold level fluctuation and the equivalent amplitude increase with increasing the casting speed,while the main frequency of abnormal mold level fluctuation changes little with increasing the casting width.The main frequency of abnormal mold level fluctuation is positively related to the surface tension of the mold flux.Based on these results,a new mechanism has been presented.It is shown that the abnormal mold level fluctuation is mainly induced by shell bulging while moving through the rollers,and resonance occurs when the frequency approaches the natural frequency of the molten steel in mold,which results in a large amplitude of the abnormal mold level fluctuation.Based on this mechanism,a new equation for the resonance frequency of molten steel is proposed.The improved method based on this mechanism has proved to be effective in controlling abnormal mold fluctuations.展开更多
In this paper the solidification behavior of Sn-Sb peritectic alloy and the mechanism of grain refinement in solidification process under high-intensity ultrasonic field are investigated. Three different powers of hig...In this paper the solidification behavior of Sn-Sb peritectic alloy and the mechanism of grain refinement in solidification process under high-intensity ultrasonic field are investigated. Three different powers of high-intensity ultrasound are introduced into molten Sn-Sb peritectic alloy to study the refining effectiveness. The results show that the application of high-intensity ultrasound during solidification process of Sn-Sb peritectic alloy can refine α phase and β phase and eliminate gravity segregation of the alloy. As acoustic intensity is increased from 400 W to 800 W, not only the homogenous fine structure can be obtained, but also the cubic β phase crystals tend to be spherical. Microstructure of the sample treated by 600 W high-intensity ultrasound demonstrates the best refining effect.展开更多
In high speed continuous casting of peritectic steel slabs, mold fluxes with high basicity are required for less surface defect product. However, the basicity of remaining liquid slag film tends to decrease in casting...In high speed continuous casting of peritectic steel slabs, mold fluxes with high basicity are required for less surface defect product. However, the basicity of remaining liquid slag film tends to decrease in casting process because of the crystallization of 3CaO ·2SiO2 · CaF2. Thus, a way is put forward to improve mold fluxesr properties by raising the original basicity. In order to confirm the possibility of this method, the effect of rising original basicity on the properties of mold fluxes is discussed. Properties of high fluorine based mold fluxes with different basicities and contents of CaF2 , Na2 O, and MgO were measured, respectively. Then, properties of higher basicity mold fluxes were discussed and compared with traditional ones. The results show that increasing the basicity index can improve the melting and flow property of mold fluxes. With the increasing basicity, crystallization rate of mold fluxes increases obviously and crystallization temperature tends to decrease when the basicity exceeds 1.35. The method presen- ted before is proved as a potential way to resolve the contradiction between horizontal heat transfer controlling and solidified shell lubricating for peritectic steel slab casting. But further study on improving the flow property of liquid slag is needed. This work can be used to guide mold fluxes design for high speed continuous casting of peritectic steel slabs.展开更多
A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was...A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was found that the phase separation occurred if the Fe-Cu liquid was undercooled to a certain extent before solidification.In the big particles macroscopic separation of Fe-rich phase always appeared in the cented of the particles, and in the small ones the Fe-rich phase usually solidified as little spheres. In the flakes the Fe-rich and Cu-rich layers alternatively displayed from top to bottom.展开更多
TiN,which is ubiquitous in Ti-bearing steel,has a critical influence on both the mechanical properties and the welding process of steel,and therefore researche on the precipitation behavior of TiN in molten steel bath...TiN,which is ubiquitous in Ti-bearing steel,has a critical influence on both the mechanical properties and the welding process of steel,and therefore researche on the precipitation behavior of TiN in molten steel bath is of great significance.In this paper,Ti-bearing peritectic steel was taken as the study object and FactSage was adopted to explore how the precipitation behavior of typical inclusions in steel was affected by the steel composition.Furthermore,microsegregation models were used to analyze the precipitation process of TiN at solidification front,and the calculation results were finally verified by scanning electron microscope(SEM).Research showed that a multitude of dispersed particles of high melting oxide MgAl2O4 or MgO always existed in molten steel after magnesium treatment.In consideration of the segregation and enrichment of solute elements at the solidification front,the Ohnaka microsegregation model was employed to compute the precipitation during solidification.In the event of the solid fraction reaching 0.95 or more,the concentration product of[Ti][N]at the solidification front exceeded the equilibrium concentration product,then TiN began to precipitate.MgO or MgAl2O4 cores were generally found in TiN particles of peritectic steel after the magnesium treatment,which was consistent with the thermodynamic calculation results.Moreover,the average size of TiN particles was reduced by approximately 49%.This demonstrated that Mg-rich high melting inclusions were formed after the magnesium treatment,by which the heterogeneous nucleation of TiN was promoted it;therefore,favorable nucleation sites were provided for further refining the high-temperature ferrite phase.展开更多
Compared with the growing applications of peritectic alloy,none research on the freckle formation during peritectic solidification has been reported before.Observation on the dendritic mushy zone of Sn-36 at.%Ni perit...Compared with the growing applications of peritectic alloy,none research on the freckle formation during peritectic solidification has been reported before.Observation on the dendritic mushy zone of Sn-36 at.%Ni peritectic alloy during directional solidification at different growth velocities shows that the freckles are formed in two different regions:region I before peritectic reaction and region II after peritectic reaction.In addition,more freckles can be observed at lower growth velocities.Examination on the experimental results demonstrates that both the temperature gradient zone melting(TGZM)and Gibbs-Thomson(G–T)effects have obvious influences on the morphology of dendritic network during directional solidification.The current theories onKI Rayleigh number Racharacterizing the thermosolutal convection of dendritic mushy zone to predict freckle formation through the maximum of Ra can only explain the existence of region I while the appearance of region II after peritectic reaction cannot be predicted.Thus,a new Rayleigh number RaP is proposed in consideration of evolution of dendritic mushy zone by both effects and peritectic reaction.Theoretical prediction of RaPalso shows a maximum after peritectic reaction in addition to that before peritectic reaction,thus,agreeing well with the freckle formation in region II.In addition,more severe thermosolutal convection can be predicted by the new Rayleigh number RaP at lower growth velocities,which further demonstrates the reliability of RaP in describing the dependence of freckle formation on growth velocity.展开更多
The effect of a high magnetic field on the microstructural evolution of a peritectic Al—18 at.%Ni alloy during directional solidification and its dependence on pulling speed were investigated.At a low pulling speed,t...The effect of a high magnetic field on the microstructural evolution of a peritectic Al—18 at.%Ni alloy during directional solidification and its dependence on pulling speed were investigated.At a low pulling speed,the application of a 2 T magnetic field triggered the appearance of a primary Al_(3)Ni_(2)phase.At higher pulling speeds,a high magnetic field application induced primary Al_(3)Ni_(2)phase segregation that formed close to the central alloy regions.For all pulling speeds,the application of a high magnetic field induced bulk Al_(3)Ni/Al eutectic formation on the upper and lower parts of the alloys,and promoted elongated growth of the peritectic Al_3Ni phase along the magnetic field direction.Microstructural analysis indicated that microstructural evolution that was induced by high magnetic fields can be attributed to solute migration and melt flow that is regulated by magnetic,Lorentz,and thermoelectric magnetic forces and their coupling effects during peritectic solidification.展开更多
The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth...The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.展开更多
Different from other alloys,the observation in this work on the dendritic mushy zone shows that the freckles are formed in two different regions before and after peritectic reaction in directional solidification of Sn...Different from other alloys,the observation in this work on the dendritic mushy zone shows that the freckles are formed in two different regions before and after peritectic reaction in directional solidification of Sn−Ni peritectic alloys.In addition,the experimental results demonstrate that the dendritic morphology is influenced by the temperature gradient zone melting and Gibbs−Thomson effects.A new Rayleigh number(Ra_(P))is proposed in consideration of both effects and peritectic reaction.The prediction of Ra_(P) confirms the freckle formation in two regions during peritectic solidification.Besides,heavier thermosolutal convection in samples with larger diameter is also demonstrated.展开更多
The solidification of Sn-Ni peritectic alloys in which both the primary Ni_(3)Sn_(2)and peritectic Ni_(3)Sn_(4)phases were intermetallic compound phases(IMCs)with narrow solubility ranges was investigated through conf...The solidification of Sn-Ni peritectic alloys in which both the primary Ni_(3)Sn_(2)and peritectic Ni_(3)Sn_(4)phases were intermetallic compound phases(IMCs)with narrow solubility ranges was investigated through confocal laser scanning microscope.Analysis on the interface migration at different cooling rates shows that the rate of peritectic reaction is much smaller than previous reports,and the growth of peritectic phase is mainly attributed to direct precipitation from the melt in Sn-Ni alloy after peritectic reaction.In addition,different from other peritectic alloys where the solidified phases are solid solution phases,the"step"growth of both Ni_(3)Sn_(2)and Ni_(3)Sn_(4)phases was observed.The dependences of the step thickness on both the cooling rate and solidification time were measured,which shows that the step thicknesses of both phases gradually decrease as solidification proceeds.This was confirmed to be attributed to the difference between the actual and equilibrium melt concentrations during solidification.In addition,the increase of the normal growth velocity of Ni_(3)Sn_(4)phase with increasing cooling rate was also proved through both the experimental observation and quantitative prediction.展开更多
For the first time, the undercooling of a magnetostrictive material a near peritectic Tb 0.27 Dy 0.73 Fe 1.90 alloy was realized by vacuum electromagnetic levitation melting and 60 K undercooling was obt...For the first time, the undercooling of a magnetostrictive material a near peritectic Tb 0.27 Dy 0.73 Fe 1.90 alloy was realized by vacuum electromagnetic levitation melting and 60 K undercooling was obtained. There is one recalescence behavior during solidification of the undercooled melt,which can attribute to the priority precipitation of REFe 2 phase instead of REFe 3 phase, due to preferential nucleation and higher crystal growth rate of REFe 2 phase and the suppression of peritectic reaction. According to the crystal structural characteristics of REFe 2 and REFe 3, REFe 2 is a Laves phase intermetallics with MgCu 2 type structure, which has similar polytetrahedral structure with short range ordered structure in undercooled melt and has lower potential barrier for nucleation than that of REFe 3,which lead to the preferential nucleation of REFe 2 phase directly from the undercooled melt. Also, the similarity of structures between REFe 2 phase and undercooled melt leads to higher crystal growth rate of REFe 2 phase than that of REFe 3.展开更多
This paper reports on laser surface remelting experiments performed on a Zn-2wt.%Cu hypoperitectic alloy by employing a 5kW CW CO2 laser at scanning velocities between 6 and 1207mm/s. The growth velocities of the mi- ...This paper reports on laser surface remelting experiments performed on a Zn-2wt.%Cu hypoperitectic alloy by employing a 5kW CW CO2 laser at scanning velocities between 6 and 1207mm/s. The growth velocities of the mi- crostructures in the laser molten pool were accurately measured. The planar interface structure caused by the high velocity absolute stability was achieved at a growth velocity of 210 mm/s. An implicit expression of the critical solidification velocity for the cellular-planar transition was carried out by nonlinear stability analyses of the planar interface. The results showed a better agreement with the measured critical velocity than that predicted by M-S theory. Cell-free structures were observed throughout the whole molten pool at a scanning velocity of 652 mm/s and the calculated minimum temperature gradient in this molten pool was very close to the critical temperature gradient for high gradient absolute stability （HGAS） of the η phase. This indicates that HGAS was successfully achieved in the present experiments.展开更多
The morphologies of intermetallic phases(IMCs)during directional solidification of the Sn-Cu(L+Cu_(3)Sn→Cu_(6)Sn_(5))and Sn-Co(L+CoSn→CoSn_(2))peritectic systems were analyzed.The primary Cu_(3)Sn and peritectic Cu_...The morphologies of intermetallic phases(IMCs)during directional solidification of the Sn-Cu(L+Cu_(3)Sn→Cu_(6)Sn_(5))and Sn-Co(L+CoSn→CoSn_(2))peritectic systems were analyzed.The primary Cu_(3)Sn and peritectic Cu_(6)Sn_(5)phases in Sn-Cu alloy are IMCs whose solubility ranges are narrow,while both the primary CoSn and peritectic CoSn_(2)phases in Sn-Co alloy are IMCs whose solubility ranges are nil in equilibrium condition.The experimental results before acid corrosion shows that the dendritic morphology of both the Cu_(6)Sn_(5)and CoSn_(2)phases can be observed.The investigation on the local dendritic morphology after deep acid corrosion shows that these dendrites are composed of small sub-structures with faceted feature.Faceted growth of the primary Cu_(3)Sn and CoSn phases is also confirmed,and a faceted to non-faceted transition in their morphologies is observed with increasing growth velocities.Further analysis shows that the dendritic morphology is formed in the solidified phases whose solubility range is larger during peritectic solidification.展开更多
A cellular automaton model has been developed to simulate the microstructure evolution of a C-Mn steel during the peritectic solidification. In the model, the thermodynamics and solute diffusion of multi-component sys...A cellular automaton model has been developed to simulate the microstructure evolution of a C-Mn steel during the peritectic solidification. In the model, the thermodynamics and solute diffusion of multi-component systems were taken into account by using Thermo-Calc and Dictra software package. Scheil model was used to predict the relationship between the solid fraction and the temperature, which was used to calculate the movement velocity of the L/δ and the L/y interfaces. A mixed-mode model in multi-component systems was adopted to calculate the movement velocity of the 6/7 interface. To validate the cellular automaton model, the variation of manganese distribution was studied. The simulated results showed a good agreement with experimental results reported in literatures. Meanwhile, the simulated growth kinetics of peritectic solidification agreed well with the experimental results obtained using confocal scanning laser microscopy （CSLM）. The model can simulate the growth kinetics of the peritectic solidification and the distribution of concentrations of all components in grains.展开更多
Taking Fe-C binary alloy as an example,based on the multi-phase field model,the nucleation and growth ofδphase,peritectic reaction,peritectic transformation,and the growth of subsequent austenite are simulated.Effect...Taking Fe-C binary alloy as an example,based on the multi-phase field model,the nucleation and growth ofδphase,peritectic reaction,peritectic transformation,and the growth of subsequent austenite are simulated.Effects of the nucleation site of austenite on the peritectic reaction rate and the starting time of the peritectic transformation were studied.The simulation results show that theγphase,as a shell,surrounds theδphase and grows rapidly when the peritectic reaction occurs between the dendriticδgrains,and a layer ofγphase shell is formed aroundδphase after the peritectic reaction.After theδphase is surrounded byγphase completely,the membrane shell separates the L phase from theδphase,so that the phase transfers from peritectic reaction to peritectic transformation.During the peritectic transformation,since the solute diffusion coefficient of the liquid phase is much greater than that of the solid phase,the average growth rate of austenite in the liquid phase is visibly higher than that of theδphase.The peritectic reaction rate is related to the curvature of the nucleation site of theγphase on theδphase grains.The peritectic reaction rate at the large curvatures is faster than that at small curvatures.展开更多
This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, wh...This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of δ-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe-7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.展开更多
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 Science and Technology Plan Foundation of Xingtai,China (Grant No.2022zz099)the Jiangsu Key Laboratory of Oil-Gas Storage and Transportation Technology (Grant No.CDYQCY202204)Science and Technology Project of Hebei Education Department (Grant No.ZD2021338).
文摘The characteristics and sensitivity of solidification cracks in peritectic steels were investigated using directional solidifi-cation technology.Interdendritic cracks were observed in both hypoperitectic steels(12CrlMoV,15CrMo)and hyper-peritectic steel(20CrMo)during solidification at growth velocities of 15,50,and 80 pm/s.At the dendritic boundaries,sulphide precipitates were found,promoting crack formation.Based on the statistical analysis of interdendritic cracks in peritectic steels,the area ratio(RA)of interdendritic cracks in a directional solidification structure was proposed to evaluate the crack sensitivity of peritectic steels.Furthermore,the crack sensitivities of peritectic steels(12CrlMoV,15CrMo,and 20CrMo)were tested,evaluated,and compared with the surface crack rates of three types of steels produced from a steel plant.The results demonstrated that RA was in good agreement with that of the steel plant,and the crack sensitivity of 12CrlMoV steel was the strongest,followed by that of 15CrMo and 20CrMo steels.Thus,RA can be used to evaluate the crack sensitivity of peritectic steel.
基金Projects (50901025,50975060,51331005) supported by the National Natural Science Foundation of ChinaProject (2011CB610406) supported by the National Basic Research Program of China+2 种基金Projects (201104420,20090450840) supported by China Postdoctoral Science FoundationProject (JC201209) supported by Outstanding Young Scientist Foundation of Heilongjiang Province,ChinaProject (HIT.BRET1.20100008) supported by the Fundamental Research Funds for Central Universities,China
文摘Peritectic reaction was studied by directional solidification of Cu-Ge alloys.A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during peritectic reaction.Under different growth conditions and compositions,different growth morphologies of triple junction region are presented.For the hypoperitectic Cu-13.5%Ge alloy,as the pulling velocity（v） increases from 2 to 5 μm/s,the morphological instability of the peritectic phase occurs during the peritectic reaction and the remelting interface of the primary phase is relatively stable.However,for the hyperperitectic Cu-15.6%Ge alloy wim v=5 μm/s,the nonplanar remelting interface near the trijunction is presented.The morphological stabilities of the solidifying peritectic phase and the remelting primary phase are analyzed in terms of the constitutional undercooling criterion.
基金National Natural Science Foundation of China(No.U1560207)Special thanks are given to Shanghai Meishan Iron and Steel Co.,Ltd.for industrial trials and application.
文摘Abnormal mold level fluctuation is frequently observed in high-speed casting,especially for peritectic steels,which has been shown to severely deteriorate product quality.Both an online electromagnetic sensor and an ibaAnalyzer are used to analyze the frequency and amplitude of massive mold level fluctuation data from the slab casting process of different steel grades using different casting speeds,slab widths and physical parameters of mold flux.The results show that in the slab continuous casting process of peritectic steels,the main frequency and equivalent amplitude of abnormal mold level fluctuations first increase and then decrease with increasing the carbon content.In the production of various grades of steel,the main frequency of abnormal mold level fluctuation and the equivalent amplitude increase with increasing the casting speed,while the main frequency of abnormal mold level fluctuation changes little with increasing the casting width.The main frequency of abnormal mold level fluctuation is positively related to the surface tension of the mold flux.Based on these results,a new mechanism has been presented.It is shown that the abnormal mold level fluctuation is mainly induced by shell bulging while moving through the rollers,and resonance occurs when the frequency approaches the natural frequency of the molten steel in mold,which results in a large amplitude of the abnormal mold level fluctuation.Based on this mechanism,a new equation for the resonance frequency of molten steel is proposed.The improved method based on this mechanism has proved to be effective in controlling abnormal mold fluctuations.
文摘In this paper the solidification behavior of Sn-Sb peritectic alloy and the mechanism of grain refinement in solidification process under high-intensity ultrasonic field are investigated. Three different powers of high-intensity ultrasound are introduced into molten Sn-Sb peritectic alloy to study the refining effectiveness. The results show that the application of high-intensity ultrasound during solidification process of Sn-Sb peritectic alloy can refine α phase and β phase and eliminate gravity segregation of the alloy. As acoustic intensity is increased from 400 W to 800 W, not only the homogenous fine structure can be obtained, but also the cubic β phase crystals tend to be spherical. Microstructure of the sample treated by 600 W high-intensity ultrasound demonstrates the best refining effect.
基金Item Sponsored by National Natural Science Foundation of China(50904083)
文摘In high speed continuous casting of peritectic steel slabs, mold fluxes with high basicity are required for less surface defect product. However, the basicity of remaining liquid slag film tends to decrease in casting process because of the crystallization of 3CaO ·2SiO2 · CaF2. Thus, a way is put forward to improve mold fluxesr properties by raising the original basicity. In order to confirm the possibility of this method, the effect of rising original basicity on the properties of mold fluxes is discussed. Properties of high fluorine based mold fluxes with different basicities and contents of CaF2 , Na2 O, and MgO were measured, respectively. Then, properties of higher basicity mold fluxes were discussed and compared with traditional ones. The results show that increasing the basicity index can improve the melting and flow property of mold fluxes. With the increasing basicity, crystallization rate of mold fluxes increases obviously and crystallization temperature tends to decrease when the basicity exceeds 1.35. The method presen- ted before is proved as a potential way to resolve the contradiction between horizontal heat transfer controlling and solidified shell lubricating for peritectic steel slab casting. But further study on improving the flow property of liquid slag is needed. This work can be used to guide mold fluxes design for high speed continuous casting of peritectic steel slabs.
文摘A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was found that the phase separation occurred if the Fe-Cu liquid was undercooled to a certain extent before solidification.In the big particles macroscopic separation of Fe-rich phase always appeared in the cented of the particles, and in the small ones the Fe-rich phase usually solidified as little spheres. In the flakes the Fe-rich and Cu-rich layers alternatively displayed from top to bottom.
基金Projects(51774208,52074186,U1860205)supported by the National Natural Science Foundation of China。
文摘TiN,which is ubiquitous in Ti-bearing steel,has a critical influence on both the mechanical properties and the welding process of steel,and therefore researche on the precipitation behavior of TiN in molten steel bath is of great significance.In this paper,Ti-bearing peritectic steel was taken as the study object and FactSage was adopted to explore how the precipitation behavior of typical inclusions in steel was affected by the steel composition.Furthermore,microsegregation models were used to analyze the precipitation process of TiN at solidification front,and the calculation results were finally verified by scanning electron microscope(SEM).Research showed that a multitude of dispersed particles of high melting oxide MgAl2O4 or MgO always existed in molten steel after magnesium treatment.In consideration of the segregation and enrichment of solute elements at the solidification front,the Ohnaka microsegregation model was employed to compute the precipitation during solidification.In the event of the solid fraction reaching 0.95 or more,the concentration product of[Ti][N]at the solidification front exceeded the equilibrium concentration product,then TiN began to precipitate.MgO or MgAl2O4 cores were generally found in TiN particles of peritectic steel after the magnesium treatment,which was consistent with the thermodynamic calculation results.Moreover,the average size of TiN particles was reduced by approximately 49%.This demonstrated that Mg-rich high melting inclusions were formed after the magnesium treatment,by which the heterogeneous nucleation of TiN was promoted it;therefore,favorable nucleation sites were provided for further refining the high-temperature ferrite phase.
基金financially supported by the National Natural Science Foundation of China(No.51871118)the 2018 joint Foundation of Ministry of Education for Equipment Pre-research(No.6141A020332)+3 种基金the Key Research and Development Plan of Gansu Province(No.18YF1GA102)the Fundamentalx Research Funds for the Central Universities(No.lzujbky-2019-sp03)the Fund of Science and Technology Project of Lanzhou City(No.2019-1-30)the Fund of State Key Laboratory of Special Rare Metal Materials(No.SKL2020K003)。
文摘Compared with the growing applications of peritectic alloy,none research on the freckle formation during peritectic solidification has been reported before.Observation on the dendritic mushy zone of Sn-36 at.%Ni peritectic alloy during directional solidification at different growth velocities shows that the freckles are formed in two different regions:region I before peritectic reaction and region II after peritectic reaction.In addition,more freckles can be observed at lower growth velocities.Examination on the experimental results demonstrates that both the temperature gradient zone melting(TGZM)and Gibbs-Thomson(G–T)effects have obvious influences on the morphology of dendritic network during directional solidification.The current theories onKI Rayleigh number Racharacterizing the thermosolutal convection of dendritic mushy zone to predict freckle formation through the maximum of Ra can only explain the existence of region I while the appearance of region II after peritectic reaction cannot be predicted.Thus,a new Rayleigh number RaP is proposed in consideration of evolution of dendritic mushy zone by both effects and peritectic reaction.Theoretical prediction of RaPalso shows a maximum after peritectic reaction in addition to that before peritectic reaction,thus,agreeing well with the freckle formation in region II.In addition,more severe thermosolutal convection can be predicted by the new Rayleigh number RaP at lower growth velocities,which further demonstrates the reliability of RaP in describing the dependence of freckle formation on growth velocity.
基金the National Natural Science Foundation of China(Nos.51690161,51774086,and 21701022)the Fundamental Research Funds for the Central Universities(Nos.N180915002,N170902002 and N170908001)Liaoning Innovative Research Team in University,China(No.LT2017011)。
文摘The effect of a high magnetic field on the microstructural evolution of a peritectic Al—18 at.%Ni alloy during directional solidification and its dependence on pulling speed were investigated.At a low pulling speed,the application of a 2 T magnetic field triggered the appearance of a primary Al_(3)Ni_(2)phase.At higher pulling speeds,a high magnetic field application induced primary Al_(3)Ni_(2)phase segregation that formed close to the central alloy regions.For all pulling speeds,the application of a high magnetic field induced bulk Al_(3)Ni/Al eutectic formation on the upper and lower parts of the alloys,and promoted elongated growth of the peritectic Al_3Ni phase along the magnetic field direction.Microstructural analysis indicated that microstructural evolution that was induced by high magnetic fields can be attributed to solute migration and melt flow that is regulated by magnetic,Lorentz,and thermoelectric magnetic forces and their coupling effects during peritectic solidification.
基金financially supported by the National Natural Science Foundation of China (Nos.51774075 and52174307)Liao Ning Revitalization Talents Program,China(No.XLYC1802032)
文摘The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.
基金the National Natural Science Foundation of China(No.51871118)the Basic Scientific Research Business Expenses of the Central University and Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education,Lanzhou University,China(No.LZUMMM2021005)+1 种基金the Science and Technology Project of Lanzhou City,China(No.2019-1-30)the State Key Laboratory of Special Rare Metal Materials,China(No.SKL2020K003).
文摘Different from other alloys,the observation in this work on the dendritic mushy zone shows that the freckles are formed in two different regions before and after peritectic reaction in directional solidification of Sn−Ni peritectic alloys.In addition,the experimental results demonstrate that the dendritic morphology is influenced by the temperature gradient zone melting and Gibbs−Thomson effects.A new Rayleigh number(Ra_(P))is proposed in consideration of both effects and peritectic reaction.The prediction of Ra_(P) confirms the freckle formation in two regions during peritectic solidification.Besides,heavier thermosolutal convection in samples with larger diameter is also demonstrated.
基金financially supported by the National Natural Science Foundation of China(No.51871118)the Fundamental Research Funds for the Central Universities(No.lzujbky-2019-sp03)the fund of Science and Technology Project of Lanzhou(No.2019-1-30)。
文摘The solidification of Sn-Ni peritectic alloys in which both the primary Ni_(3)Sn_(2)and peritectic Ni_(3)Sn_(4)phases were intermetallic compound phases(IMCs)with narrow solubility ranges was investigated through confocal laser scanning microscope.Analysis on the interface migration at different cooling rates shows that the rate of peritectic reaction is much smaller than previous reports,and the growth of peritectic phase is mainly attributed to direct precipitation from the melt in Sn-Ni alloy after peritectic reaction.In addition,different from other peritectic alloys where the solidified phases are solid solution phases,the"step"growth of both Ni_(3)Sn_(2)and Ni_(3)Sn_(4)phases was observed.The dependences of the step thickness on both the cooling rate and solidification time were measured,which shows that the step thicknesses of both phases gradually decrease as solidification proceeds.This was confirmed to be attributed to the difference between the actual and equilibrium melt concentrations during solidification.In addition,the increase of the normal growth velocity of Ni_(3)Sn_(4)phase with increasing cooling rate was also proved through both the experimental observation and quantitative prediction.
文摘For the first time, the undercooling of a magnetostrictive material a near peritectic Tb 0.27 Dy 0.73 Fe 1.90 alloy was realized by vacuum electromagnetic levitation melting and 60 K undercooling was obtained. There is one recalescence behavior during solidification of the undercooled melt,which can attribute to the priority precipitation of REFe 2 phase instead of REFe 3 phase, due to preferential nucleation and higher crystal growth rate of REFe 2 phase and the suppression of peritectic reaction. According to the crystal structural characteristics of REFe 2 and REFe 3, REFe 2 is a Laves phase intermetallics with MgCu 2 type structure, which has similar polytetrahedral structure with short range ordered structure in undercooled melt and has lower potential barrier for nucleation than that of REFe 3,which lead to the preferential nucleation of REFe 2 phase directly from the undercooled melt. Also, the similarity of structures between REFe 2 phase and undercooled melt leads to higher crystal growth rate of REFe 2 phase than that of REFe 3.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 50201012 and 50471065）.
文摘This paper reports on laser surface remelting experiments performed on a Zn-2wt.%Cu hypoperitectic alloy by employing a 5kW CW CO2 laser at scanning velocities between 6 and 1207mm/s. The growth velocities of the mi- crostructures in the laser molten pool were accurately measured. The planar interface structure caused by the high velocity absolute stability was achieved at a growth velocity of 210 mm/s. An implicit expression of the critical solidification velocity for the cellular-planar transition was carried out by nonlinear stability analyses of the planar interface. The results showed a better agreement with the measured critical velocity than that predicted by M-S theory. Cell-free structures were observed throughout the whole molten pool at a scanning velocity of 652 mm/s and the calculated minimum temperature gradient in this molten pool was very close to the critical temperature gradient for high gradient absolute stability （HGAS） of the η phase. This indicates that HGAS was successfully achieved in the present experiments.
基金the support of the National Natural Science Foundation of China (Grant No. 51871118)the Fast Support Project (Grant No. JZX7Y20210162400301)the fund of State Key Laboratory of Special Rare Metal Materials (Grant No. SKL2020K003)
文摘The morphologies of intermetallic phases(IMCs)during directional solidification of the Sn-Cu(L+Cu_(3)Sn→Cu_(6)Sn_(5))and Sn-Co(L+CoSn→CoSn_(2))peritectic systems were analyzed.The primary Cu_(3)Sn and peritectic Cu_(6)Sn_(5)phases in Sn-Cu alloy are IMCs whose solubility ranges are narrow,while both the primary CoSn and peritectic CoSn_(2)phases in Sn-Co alloy are IMCs whose solubility ranges are nil in equilibrium condition.The experimental results before acid corrosion shows that the dendritic morphology of both the Cu_(6)Sn_(5)and CoSn_(2)phases can be observed.The investigation on the local dendritic morphology after deep acid corrosion shows that these dendrites are composed of small sub-structures with faceted feature.Faceted growth of the primary Cu_(3)Sn and CoSn phases is also confirmed,and a faceted to non-faceted transition in their morphologies is observed with increasing growth velocities.Further analysis shows that the dendritic morphology is formed in the solidified phases whose solubility range is larger during peritectic solidification.
基金funded by the National Science and Technology Major Project of China (No.2011ZX04014-052)
文摘A cellular automaton model has been developed to simulate the microstructure evolution of a C-Mn steel during the peritectic solidification. In the model, the thermodynamics and solute diffusion of multi-component systems were taken into account by using Thermo-Calc and Dictra software package. Scheil model was used to predict the relationship between the solid fraction and the temperature, which was used to calculate the movement velocity of the L/δ and the L/y interfaces. A mixed-mode model in multi-component systems was adopted to calculate the movement velocity of the 6/7 interface. To validate the cellular automaton model, the variation of manganese distribution was studied. The simulated results showed a good agreement with experimental results reported in literatures. Meanwhile, the simulated growth kinetics of peritectic solidification agreed well with the experimental results obtained using confocal scanning laser microscopy （CSLM）. The model can simulate the growth kinetics of the peritectic solidification and the distribution of concentrations of all components in grains.
基金the National Natural Science Foundation of China(Grant Nos.:11504149,51661020)Natural Science Foundation of Gansu Province of China(Grant No.:18JR3RA147).
文摘Taking Fe-C binary alloy as an example,based on the multi-phase field model,the nucleation and growth ofδphase,peritectic reaction,peritectic transformation,and the growth of subsequent austenite are simulated.Effects of the nucleation site of austenite on the peritectic reaction rate and the starting time of the peritectic transformation were studied.The simulation results show that theγphase,as a shell,surrounds theδphase and grows rapidly when the peritectic reaction occurs between the dendriticδgrains,and a layer ofγphase shell is formed aroundδphase after the peritectic reaction.After theδphase is surrounded byγphase completely,the membrane shell separates the L phase from theδphase,so that the phase transfers from peritectic reaction to peritectic transformation.During the peritectic transformation,since the solute diffusion coefficient of the liquid phase is much greater than that of the solid phase,the average growth rate of austenite in the liquid phase is visibly higher than that of theδphase.The peritectic reaction rate is related to the curvature of the nucleation site of theγphase on theδphase grains.The peritectic reaction rate at the large curvatures is faster than that at small curvatures.
基金financially supported by China National Basic Research Development Project(973 Program:No.2010CB630802)China National Natural Science Foundation(No.51074104)+1 种基金Shanghai Science and Technology Development Funds(No.12QA1401200)the Fund of the State Key Laboratory of Solidification Processing at NWPU(No.SKLSP201222)
文摘This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of δ-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe-7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.
