A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comp...A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comparison,the model was used to investigate slab cracking tendency near precipitated phases,considering various locations,sizes and shapes of them.The results show that the jet from submerged entry nozzle creates a“double roll”flow pattern during continuous casting,resulting in more uniform temperature distributions at slab corner and wide surface center compared with narrow surface center.Consequently,precipitated phases,particularly those located on the narrow surface,readily induce stress concentration and thus increase cracking tendency.A smaller precipitated phase size can reduce the stress concentration zone,while a more spherical shape can distribute surrounding stress along its surface and lower the internal stress within it,thereby decreasing the risk of slab cracking during continuous casting.The optimal precipitated phase exhibits a spherical or ellipsoidal shape with a major axis of less than 5µm,minimizing its potential to initiate cracks.展开更多
Several 35CrMo4 and 38MnV7 steels with different additions of Ti and V were manufactured by electroslag remelting. The influence of the alloying and microalloying elements on phase transformation at different cooling ...Several 35CrMo4 and 38MnV7 steels with different additions of Ti and V were manufactured by electroslag remelting. The influence of the alloying and microalloying elements on phase transformation at different cooling rates was studied and the continuous cooling transformation diagrams were plotted. In order to optimize the heat treatment and improve the mechanical properties, the range of cooling rates leading to a fully bainitic microstructure （without ferrite, pearlite and especially without martensite） was determined. Bainite and martensite transformation start temperatures （Bs, Ms） were also established and compared with the values predicted by empirical equations. The important role of precipitates （especially V carbonitride particles） on final microstructure and mechanical properties was assessed.展开更多
This paper presents an equalization algorithm for continuous phase modulation （CPM） over frequency-selective channels. A specific training sequence is first embedded in each data packet. By recursive least-squares ...This paper presents an equalization algorithm for continuous phase modulation （CPM） over frequency-selective channels. A specific training sequence is first embedded in each data packet. By recursive least-squares （RLS） estimation, the channel information parameters can be acquired, and a fractionally Simulation results show that the proposed algorithm can acquire the spaced equalizer performs joint decoding and equalization. channel information parameters rapidly and accurately, and that the fractionally spaced equalizer can eliminate the intersymbol interference （ISI） effectively, and is not sensitive to timing inaccuracy, so this algorithm can be exploited for demodulation system in burst mode.展开更多
A reduced state Soft Input Soft Output (SISO) a posteriori probability algorithm for Seri-ally Concatenated Continuous Phase Modulation (SCCPM) is proposed in this paper. Based on the Reduced State Sequence Detection ...A reduced state Soft Input Soft Output (SISO) a posteriori probability algorithm for Seri-ally Concatenated Continuous Phase Modulation (SCCPM) is proposed in this paper. Based on the Reduced State Sequence Detection (RSSD),it has more general form compared with other reduced state SISO algorithms. The proposed algorithm can greatly reduce the state number,thus leads to the computation complexity reduction. It also minimizes the degradation in Euclidean distance with decision feedback in the reduced state trellis. Analysis and simulation results show that the perform-ance degradation is little with proper reduction scheme.展开更多
In this study,a high-ductility AZ91 magnesium alloy was fabricated by the novel continuous rheo-squeeze casting-extrusion(CRSCE)process.The semi-solid slurry was prepared by ultrasonic vibration(UV)treatment,then soli...In this study,a high-ductility AZ91 magnesium alloy was fabricated by the novel continuous rheo-squeeze casting-extrusion(CRSCE)process.The semi-solid slurry was prepared by ultrasonic vibration(UV)treatment,then solidified under pressure,and finally hot extruded.UV treatment can reduce the Al element content in primary grains and increase it in secondary grains.The refined Mg_(17)Al_(12) phase was scattered along secondary grain boundaries and then stretched into narrow,fibrous bands during the hot extrusion.The fibrous bands with proper separation distances can accelerate the dynamic recrystallization(DRX)process and suppress the growth of DRXed grains.Microcracks were initiated inside the brittle Mg_(17)Al_(12) phase and tended to propagate along the continuously distributed Mg_(17)Al_(12) phase during the tensile test.Thus,the tiny Mg_(17)Al_(12) phase in the billet and narrow,fibrous bands in as-extruded rods can prevent cracks from spreading and enhance ductility.Therefore,excellent comprehensive mechanical properties were obtained,with an ultimate tensile strength of 326.3 MPa and an elongation of 16.46%.The CRSCE method offers a novel way to fabricate high-ductility and high-alloyed magnesium alloys without homogenization.Microstructure regulation mechanisms of CRSCE,microstructural hereditary laws,and the effect of the Mg_(17)Al_(12) phase on mechanical properties were further discussed.展开更多
The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence thethermoplasticity,thereby affecting the quality of the slab.In this work,a prediction model...The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence thethermoplasticity,thereby affecting the quality of the slab.In this work,a prediction model for two-stage austenite growth under varyingcooling rates was established by incorporating the effect of second-phase pinning and high-temperature ferrite-austenite phase transform-ation and growth theory.The results indicate that with 0.02wt%Ti,the high-temperature ferrite growth exhibits typical parabolic growthcharacteristics.When the Ti content increases to 0.04wt%,the high-temperature ferrite grain boundary migration rate significantly slowsduring the initial solidification stage.The predicted austenite grain sizes for 0.02wt%Ti microalloyed steel at the center,quarter,and sur-face of the slab are 5592,3529,and 1524μm,respectively.For 0.04wt%Ti microalloyed steel,the austenite grain sizes are 4074,2942,and 1179μm at the same positions.The average error is within 5%.As the Ti content increases from 0.02wt% to 0.04wt%,the austenitegrain refinement at the center is most significant,with an average grain size reduction of 27.14%.展开更多
C-rowth rate, microstructure and phase composition of scale layer formed during oxidation in 56 % H2O9%O2 N2 and following continuous cooling in ambient air were experimentally investigated by means of optical microsc...C-rowth rate, microstructure and phase composition of scale layer formed during oxidation in 56 % H2O9%O2 N2 and following continuous cooling in ambient air were experimentally investigated by means of optical microscopy, scanning electron microscopy （SEM）, energy-dispersive spectroscopy （EDS） and X-ray diffraction （XRD） for 45, 20CrMnTi and TTS443M steels respectively, to examine the effects of strand surface temperature and steel composition on the scale formation in simulated continudus casting process. The growth rates were found to be ap proximately parabolic and the calculated activation energy of TTS443M steel is much higher than those of the two other steels. For 45 and 20CrMnTi steels, the scale layers were looser and a distinct gap formed at the scale-sub strate interface at higher strand surface temperature. The dominant phases within the scale were iron oxides except for FeO · Cr2O3 phase simuhaneously existing in the oxide scale of 20CrMnTi steel. On the other hand, the scale layer formed on TTS443M steel was compact and tightly attached to the steel surface. At both lower and higher strand surface temperature, iron oxide was main phase in external layer of the scale, while chromia was dominant in inner layer with an appreciable Cr enrichment.展开更多
A model based on Avrami equation and Scheil's additivity rule was proposed to simulate the phase transformation in plain carbon steels during continuous cooling in hot strip mill. In this model, a wide range of co...A model based on Avrami equation and Scheil's additivity rule was proposed to simulate the phase transformation in plain carbon steels during continuous cooling in hot strip mill. In this model, a wide range of composition, cooling rate, primary austenite grain size and retained strain has been taken into account. It can be used to calculate the phase fraction transformed at different temperatures during continuous cooling. The phase equilibrium and transformation starting temperature can be determined by using Thermo-Calc and DICTRA. The simulated results containing the transformation at starting and finishing temperatures, Ae1, Ae3 and the maximum volume fraction for Q235B, were obtained. The calculated phase volume fractions are in good agreement with .the experimental results.展开更多
A data-aided technique for cartier frequency offset estimation with continuous phase modulation （CPM） in burst- mode transmission is presented. The proposed technique first exploits a special pilot sequence, or trai...A data-aided technique for cartier frequency offset estimation with continuous phase modulation （CPM） in burst- mode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio （SNR） required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods： it eliminates the need for fast Fourier transform （FFT） and modulation removal, and exhibits faster convergence rate without accuracy degradation.展开更多
Oil-in-water(o/w) emulsions were produced with a membrane emulsification system. The effect of the continuous phase viscosity on the emulsification was studied. The theoretical analyses show that the continuous phase ...Oil-in-water(o/w) emulsions were produced with a membrane emulsification system. The effect of the continuous phase viscosity on the emulsification was studied. The theoretical analyses show that the continuous phase viscosity influences not only the flow field of the continuous phase but also the interfacial tension. The droplet size distribution and disperse phase flux for different continuous phase viscosity were investigated experimentally at constant wall shear stress and constant volume flow rate of the continuous phase respectively.展开更多
Differential detection of continuous phase modulation suffers from significant intersymbol interference. To reduce bit error rate, multi-branch fractional multi-bit differential detection (MFMDD) with decision feed-ba...Differential detection of continuous phase modulation suffers from significant intersymbol interference. To reduce bit error rate, multi-branch fractional multi-bit differential detection (MFMDD) with decision feed-back is proposed. By introducing decision feedback in multi-bit differential detected signals, severe inter-symbol interference can be removed. Simulation results show that the proposed structure can greatly im-proves the performance compared with MFMDD without decision feedback, and the performance of 9 FMDD is very near to the performance of the coherent detection.展开更多
Effects of solute rare earth(RE)on continuous cooling transformation of a low-alloy Cr–Mo–V bainitic steel are investigated in detail by dilatometry,optical microscopy(OM),scanning electron microscopy(SEM)and transm...Effects of solute rare earth(RE)on continuous cooling transformation of a low-alloy Cr–Mo–V bainitic steel are investigated in detail by dilatometry,optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Microstructures appeared in thermal dilatometric samples of both low-alloy Cr–Mo–V(RE)steels are composed of quasi-polygonal ferrite(QPF),degenerate pearlite(DP),granular bainite(GB),lath bainite(LB),and martensite(M)depending on cooling rate.When cooling rate is lower than 2°C/s,the addition of RE suppresses QPF transformation,and thereby inducing a broader transformation region of GB.When cooling rate ranges from 2 to 100°C/s,the addition of RE decreases the start temperature of bainitic transformation distinctly,which results in finer bainitic ferrite grain size and higher dislocation density.The addition of RE can enhance the hardness of the low alloy Cr–Mo–V steel by affecting the aforementioned diffusional and/or partly displacive transformation.However,when cooling rate increases up to 150°C/s,two steels have the same hardness value of about 435 HV due to only martensite obtained by displacive transformation.展开更多
Microstructures of Cu-4.7Sn(%) alloys prepared by two-phase zone continuous casting(TZCC)technology contain large columnar grains and small grains.A compound grain structure,composed of a large columnar grain and at l...Microstructures of Cu-4.7Sn(%) alloys prepared by two-phase zone continuous casting(TZCC)technology contain large columnar grains and small grains.A compound grain structure,composed of a large columnar grain and at least one small grain within it,is observed and called as grain-covered grains(GCGs).Distribution of small grains,their numbers and sizes as well as numbers and sizes of columnar grains were characterized quantitatively by metallographic microscope.Back propagation(BP) artificial neural network was employed to build a model to predict microstructures produced by different processing parameters.Inputs of the model are five processing parameters,which are temperatures of melt,mold and cooling water,speed of TZCC,and cooling distance.Outputs of the model are nine microstructure quantities,which are numbers of small grains within columnar grains,at the boundaries of the columnar grains,or at the surface of the alloy,the maximum and the minimum numbers of small grains within a columnar grain,numbers of columnar grains with or without small grains,and sizes of small grains and columnar grains.The model yields precise prediction,which lays foundation for controlling microstructures of alloys prepared by TZCC.展开更多
In this paper,the problem of 3-D steady heat conduction including the influenceof phase change on billets is turned into the 2-D transient problem by a suitable transformation technique. The effective specific heat ha...In this paper,the problem of 3-D steady heat conduction including the influenceof phase change on billets is turned into the 2-D transient problem by a suitable transformation technique. The effective specific heat has been employed to substitutefor the effect of the phase ceange.The computational formulation of finite element has been presented. And the careful disposal of the phase change region has also beengiven.展开更多
Aim To develop a high speed and high resolution dynamic rangefinding device for the measurement of large distances.Methods The device was comprised of an ultrasonic transmitter and a receiver,and a receiver , and a co...Aim To develop a high speed and high resolution dynamic rangefinding device for the measurement of large distances.Methods The device was comprised of an ultrasonic transmitter and a receiver,and a receiver , and a continuous ultrasonic wave amplitude-modulated by a low- frequency acoustic signal was used. The rangefinding was achieved by detecting the phase difference between the transmitted and received ultrasonic signals. The design principle. hard- ware implementation , experimental results and performance analysis of the device are included. Results and Conclusion Experiments show that the accuracy of the device are included. within 1.5m while its dynamic data update rate can be up to 40kHz.展开更多
The 3D turbulence k-ε model flow of the steel melt （continuous phase） and the trajectories of individual gas bubbles （dispersed phase） in a continuous casting mold were simulated using an Eulerian-Lagrangian appr...The 3D turbulence k-ε model flow of the steel melt （continuous phase） and the trajectories of individual gas bubbles （dispersed phase） in a continuous casting mold were simulated using an Eulerian-Lagrangian approach. In order to investigate the effect of bubble size distribution, the radii of bubbles are set with an initial value of 0. 1- 2.5 mm which follows the normal distribution. The presented results indicate that, in the submerged entry nozzle （SEN）, the distribution of void fraction is only near the wall. Due to the fact that the bubbles motion is only limited to the wall, the deoxidization products have no access to contacting the wall, which prevents clogging. In the mold, the bubbles with a radius of 0. 25--2.5 mm will move to the top surface. Larger bubbles issuing out of the ports will attack the menis- cus and induce the fluid flows upwards in the top surface near the nozzle. It may induce mold powder entrapment into the mold. The bubbles with a radius of 0.1--0.25 mm will move to the zone near the narrow surface and the wide surface. These small bubbles will probably be trapped by the solidification front. Most of the bubbles moving to the narrow surface will flow with the ascending flow, while others will flow with the descending flow.展开更多
The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable ...The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase's time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_(0.1), tensile tests and scanning electronic microscopy(SEM).The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.展开更多
An Eulerian-Eulerian two-fluid model was developed to study the vortex flow inside a slab continuous casting mold with argon gas injection. Interracial momentum transfer that accommodated various interracial forces in...An Eulerian-Eulerian two-fluid model was developed to study the vortex flow inside a slab continuous casting mold with argon gas injection. Interracial momentum transfer that accommodated various interracial forces including drag force, lift force, virtual mass force, and turbulent dispersion force was considered. Predicted results agree well vaith experimental measurements of the water model in two-phase flow pattern and vortex flow structures. Three typical flow patterns with different argon steel ratios （ASRs） have been obtained： ＂double roll＂, ＂three roll＂, and ＂single roll＂. The flow pattern inside the mold alternates among the three types or it may attain some intermedi ate condition. With increasing ASR, the positions of vortices move from the submerged entry nozzle to the narrow face of the mold, and the sizes of vortices are reduced gradually. The rotating directions of vortices are all from high velocity area to low velocity area. Two mechanisms of vortex formation on the top surface have been suggested, i. e. , congruous shear flow and incongruous shear flow.展开更多
The effects of various factors on the flow speed of interdendritic melt were analyzed in detail in the process of continuous casting slabs. When the solid-liquid interface bends periodically, the expression of solute ...The effects of various factors on the flow speed of interdendritic melt were analyzed in detail in the process of continuous casting slabs. When the solid-liquid interface bends periodically, the expression of solute distribution in the columnar crystal zone was deduced, and the quantitative calculation was also made. The results show that the bulge and the interdendritic spacing are responsible for the flow speed of interdendritic melt. At the initial stage of solidification the bulge operates, and at the final stage the interdendritic spacing operates. The experimental results of macrosegregation in the slabs validated the calculated results of the flow speed of interdendritic melt, which shows that the calculated results are basically consistent with the experimental ones.展开更多
The direct hydroxylation of benzene to phenol catalyzed by activated carbon-supported Fe （Fe/AC） in acetonitrile using H2O2 as the oxidant was studied in a continuous flow reactor. Results showed that the continuous...The direct hydroxylation of benzene to phenol catalyzed by activated carbon-supported Fe （Fe/AC） in acetonitrile using H2O2 as the oxidant was studied in a continuous flow reactor. Results showed that the continuous operation could obtain high phenol yield of 28.1%, coupled with the turnover frequency of 3 h^-1, and high selectivity of 98% under mild condition. The catalyst was characterized by N2 adsorption/desorption, Boehm titration, X-ray photoelectron spectra, and Fourier transform infrared spectroscopy. It was observed that iron may interact with the carboxyl group forming iron-carboxylate like species, which act as the active phase. The apparent activation energy obtained by fitting an Arrhenius model to the experimental data was 13.4 kJ/mol. The reaction order was calculated to be about i, 0.2 for benzene and 0.7 for H202.展开更多
基金supported by National Natural Science Foundation of China(Nos.52325406 and 52374330)Fundamental Research Funds for the Central Universities(No.N2225046).
文摘A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comparison,the model was used to investigate slab cracking tendency near precipitated phases,considering various locations,sizes and shapes of them.The results show that the jet from submerged entry nozzle creates a“double roll”flow pattern during continuous casting,resulting in more uniform temperature distributions at slab corner and wide surface center compared with narrow surface center.Consequently,precipitated phases,particularly those located on the narrow surface,readily induce stress concentration and thus increase cracking tendency.A smaller precipitated phase size can reduce the stress concentration zone,while a more spherical shape can distribute surrounding stress along its surface and lower the internal stress within it,thereby decreasing the risk of slab cracking during continuous casting.The optimal precipitated phase exhibits a spherical or ellipsoidal shape with a major axis of less than 5µm,minimizing its potential to initiate cracks.
基金the financial support of Spanish Ministry of Economy and Competitiveness through the project ref.MAT2011-29039-C02-02
文摘Several 35CrMo4 and 38MnV7 steels with different additions of Ti and V were manufactured by electroslag remelting. The influence of the alloying and microalloying elements on phase transformation at different cooling rates was studied and the continuous cooling transformation diagrams were plotted. In order to optimize the heat treatment and improve the mechanical properties, the range of cooling rates leading to a fully bainitic microstructure （without ferrite, pearlite and especially without martensite） was determined. Bainite and martensite transformation start temperatures （Bs, Ms） were also established and compared with the values predicted by empirical equations. The important role of precipitates （especially V carbonitride particles） on final microstructure and mechanical properties was assessed.
文摘This paper presents an equalization algorithm for continuous phase modulation （CPM） over frequency-selective channels. A specific training sequence is first embedded in each data packet. By recursive least-squares （RLS） estimation, the channel information parameters can be acquired, and a fractionally Simulation results show that the proposed algorithm can acquire the spaced equalizer performs joint decoding and equalization. channel information parameters rapidly and accurately, and that the fractionally spaced equalizer can eliminate the intersymbol interference （ISI） effectively, and is not sensitive to timing inaccuracy, so this algorithm can be exploited for demodulation system in burst mode.
基金Supported by NSFC & Microsoft Asia (60372048)China TRAPOYT, NSFC key project (60496316)+2 种基金863 Project (2005AA123910)RFDP (20050701007)MOE Key Project (104171).
文摘A reduced state Soft Input Soft Output (SISO) a posteriori probability algorithm for Seri-ally Concatenated Continuous Phase Modulation (SCCPM) is proposed in this paper. Based on the Reduced State Sequence Detection (RSSD),it has more general form compared with other reduced state SISO algorithms. The proposed algorithm can greatly reduce the state number,thus leads to the computation complexity reduction. It also minimizes the degradation in Euclidean distance with decision feedback in the reduced state trellis. Analysis and simulation results show that the perform-ance degradation is little with proper reduction scheme.
基金funded by the National Natural Science Foundation of China(No.52175321).
文摘In this study,a high-ductility AZ91 magnesium alloy was fabricated by the novel continuous rheo-squeeze casting-extrusion(CRSCE)process.The semi-solid slurry was prepared by ultrasonic vibration(UV)treatment,then solidified under pressure,and finally hot extruded.UV treatment can reduce the Al element content in primary grains and increase it in secondary grains.The refined Mg_(17)Al_(12) phase was scattered along secondary grain boundaries and then stretched into narrow,fibrous bands during the hot extrusion.The fibrous bands with proper separation distances can accelerate the dynamic recrystallization(DRX)process and suppress the growth of DRXed grains.Microcracks were initiated inside the brittle Mg_(17)Al_(12) phase and tended to propagate along the continuously distributed Mg_(17)Al_(12) phase during the tensile test.Thus,the tiny Mg_(17)Al_(12) phase in the billet and narrow,fibrous bands in as-extruded rods can prevent cracks from spreading and enhance ductility.Therefore,excellent comprehensive mechanical properties were obtained,with an ultimate tensile strength of 326.3 MPa and an elongation of 16.46%.The CRSCE method offers a novel way to fabricate high-ductility and high-alloyed magnesium alloys without homogenization.Microstructure regulation mechanisms of CRSCE,microstructural hereditary laws,and the effect of the Mg_(17)Al_(12) phase on mechanical properties were further discussed.
基金financially supported by the National Natural Science Foundation of China(No.52474355)the Liaoning Province Science and Technology Plan Joint Program(Key Research and Development Program Project,Nos.2022JH25/10200003 and 2023JH2/101800058)the Fundamental Research Funds for the Central Universities(Nos.N25YJS003 and N25DCG006)。
文摘The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence thethermoplasticity,thereby affecting the quality of the slab.In this work,a prediction model for two-stage austenite growth under varyingcooling rates was established by incorporating the effect of second-phase pinning and high-temperature ferrite-austenite phase transform-ation and growth theory.The results indicate that with 0.02wt%Ti,the high-temperature ferrite growth exhibits typical parabolic growthcharacteristics.When the Ti content increases to 0.04wt%,the high-temperature ferrite grain boundary migration rate significantly slowsduring the initial solidification stage.The predicted austenite grain sizes for 0.02wt%Ti microalloyed steel at the center,quarter,and sur-face of the slab are 5592,3529,and 1524μm,respectively.For 0.04wt%Ti microalloyed steel,the austenite grain sizes are 4074,2942,and 1179μm at the same positions.The average error is within 5%.As the Ti content increases from 0.02wt% to 0.04wt%,the austenitegrain refinement at the center is most significant,with an average grain size reduction of 27.14%.
基金Sponsored by National Natural Science Foundation of China(51174052,51174049,51374062,51374057)Fundamental Research Funds for the Central Universities of China(110402009)
文摘C-rowth rate, microstructure and phase composition of scale layer formed during oxidation in 56 % H2O9%O2 N2 and following continuous cooling in ambient air were experimentally investigated by means of optical microscopy, scanning electron microscopy （SEM）, energy-dispersive spectroscopy （EDS） and X-ray diffraction （XRD） for 45, 20CrMnTi and TTS443M steels respectively, to examine the effects of strand surface temperature and steel composition on the scale formation in simulated continudus casting process. The growth rates were found to be ap proximately parabolic and the calculated activation energy of TTS443M steel is much higher than those of the two other steels. For 45 and 20CrMnTi steels, the scale layers were looser and a distinct gap formed at the scale-sub strate interface at higher strand surface temperature. The dominant phases within the scale were iron oxides except for FeO · Cr2O3 phase simuhaneously existing in the oxide scale of 20CrMnTi steel. On the other hand, the scale layer formed on TTS443M steel was compact and tightly attached to the steel surface. At both lower and higher strand surface temperature, iron oxide was main phase in external layer of the scale, while chromia was dominant in inner layer with an appreciable Cr enrichment.
基金This work was financially supported by the National Key Foundational Research Project(grant No.G1998061512).
文摘A model based on Avrami equation and Scheil's additivity rule was proposed to simulate the phase transformation in plain carbon steels during continuous cooling in hot strip mill. In this model, a wide range of composition, cooling rate, primary austenite grain size and retained strain has been taken into account. It can be used to calculate the phase fraction transformed at different temperatures during continuous cooling. The phase equilibrium and transformation starting temperature can be determined by using Thermo-Calc and DICTRA. The simulated results containing the transformation at starting and finishing temperatures, Ae1, Ae3 and the maximum volume fraction for Q235B, were obtained. The calculated phase volume fractions are in good agreement with .the experimental results.
基金supported by the National Natural Science Foundation of China(Grant No.61301179)the Doctorial Programs Foundation of the Ministry of Education,China(Grant No.20110203110011)the Programme of Introducing Talents of Discipline to Universities,China(Grant No.B08038)
文摘A data-aided technique for cartier frequency offset estimation with continuous phase modulation （CPM） in burst- mode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio （SNR） required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods： it eliminates the need for fast Fourier transform （FFT） and modulation removal, and exhibits faster convergence rate without accuracy degradation.
基金Supported by the National Natural Science Foundation of China(No.29506050)and DAAD scholarship
文摘Oil-in-water(o/w) emulsions were produced with a membrane emulsification system. The effect of the continuous phase viscosity on the emulsification was studied. The theoretical analyses show that the continuous phase viscosity influences not only the flow field of the continuous phase but also the interfacial tension. The droplet size distribution and disperse phase flux for different continuous phase viscosity were investigated experimentally at constant wall shear stress and constant volume flow rate of the continuous phase respectively.
文摘Differential detection of continuous phase modulation suffers from significant intersymbol interference. To reduce bit error rate, multi-branch fractional multi-bit differential detection (MFMDD) with decision feed-back is proposed. By introducing decision feedback in multi-bit differential detected signals, severe inter-symbol interference can be removed. Simulation results show that the proposed structure can greatly im-proves the performance compared with MFMDD without decision feedback, and the performance of 9 FMDD is very near to the performance of the coherent detection.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52101059)the Shenyang National Laboratory for Materials Science(Grant No.L2019F48).
文摘Effects of solute rare earth(RE)on continuous cooling transformation of a low-alloy Cr–Mo–V bainitic steel are investigated in detail by dilatometry,optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Microstructures appeared in thermal dilatometric samples of both low-alloy Cr–Mo–V(RE)steels are composed of quasi-polygonal ferrite(QPF),degenerate pearlite(DP),granular bainite(GB),lath bainite(LB),and martensite(M)depending on cooling rate.When cooling rate is lower than 2°C/s,the addition of RE suppresses QPF transformation,and thereby inducing a broader transformation region of GB.When cooling rate ranges from 2 to 100°C/s,the addition of RE decreases the start temperature of bainitic transformation distinctly,which results in finer bainitic ferrite grain size and higher dislocation density.The addition of RE can enhance the hardness of the low alloy Cr–Mo–V steel by affecting the aforementioned diffusional and/or partly displacive transformation.However,when cooling rate increases up to 150°C/s,two steels have the same hardness value of about 435 HV due to only martensite obtained by displacive transformation.
基金financially supported by the National Key Research and Development Plan of China (No.2016YFB0301300)the National Natural Science Foundation of China (Nos.51374025,51674027 and U1703131)the Beijing Municipal Natural Science Foundation (No.2152020)
文摘Microstructures of Cu-4.7Sn(%) alloys prepared by two-phase zone continuous casting(TZCC)technology contain large columnar grains and small grains.A compound grain structure,composed of a large columnar grain and at least one small grain within it,is observed and called as grain-covered grains(GCGs).Distribution of small grains,their numbers and sizes as well as numbers and sizes of columnar grains were characterized quantitatively by metallographic microscope.Back propagation(BP) artificial neural network was employed to build a model to predict microstructures produced by different processing parameters.Inputs of the model are five processing parameters,which are temperatures of melt,mold and cooling water,speed of TZCC,and cooling distance.Outputs of the model are nine microstructure quantities,which are numbers of small grains within columnar grains,at the boundaries of the columnar grains,or at the surface of the alloy,the maximum and the minimum numbers of small grains within a columnar grain,numbers of columnar grains with or without small grains,and sizes of small grains and columnar grains.The model yields precise prediction,which lays foundation for controlling microstructures of alloys prepared by TZCC.
文摘In this paper,the problem of 3-D steady heat conduction including the influenceof phase change on billets is turned into the 2-D transient problem by a suitable transformation technique. The effective specific heat has been employed to substitutefor the effect of the phase ceange.The computational formulation of finite element has been presented. And the careful disposal of the phase change region has also beengiven.
文摘Aim To develop a high speed and high resolution dynamic rangefinding device for the measurement of large distances.Methods The device was comprised of an ultrasonic transmitter and a receiver,and a receiver , and a continuous ultrasonic wave amplitude-modulated by a low- frequency acoustic signal was used. The rangefinding was achieved by detecting the phase difference between the transmitted and received ultrasonic signals. The design principle. hard- ware implementation , experimental results and performance analysis of the device are included. Results and Conclusion Experiments show that the accuracy of the device are included. within 1.5m while its dynamic data update rate can be up to 40kHz.
基金Item Sponsored by National Natural Science Foundation of China(50874130,50974034)
文摘The 3D turbulence k-ε model flow of the steel melt （continuous phase） and the trajectories of individual gas bubbles （dispersed phase） in a continuous casting mold were simulated using an Eulerian-Lagrangian approach. In order to investigate the effect of bubble size distribution, the radii of bubbles are set with an initial value of 0. 1- 2.5 mm which follows the normal distribution. The presented results indicate that, in the submerged entry nozzle （SEN）, the distribution of void fraction is only near the wall. Due to the fact that the bubbles motion is only limited to the wall, the deoxidization products have no access to contacting the wall, which prevents clogging. In the mold, the bubbles with a radius of 0. 25--2.5 mm will move to the top surface. Larger bubbles issuing out of the ports will attack the menis- cus and induce the fluid flows upwards in the top surface near the nozzle. It may induce mold powder entrapment into the mold. The bubbles with a radius of 0.1--0.25 mm will move to the zone near the narrow surface and the wide surface. These small bubbles will probably be trapped by the solidification front. Most of the bubbles moving to the narrow surface will flow with the ascending flow, while others will flow with the descending flow.
文摘The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase's time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_(0.1), tensile tests and scanning electronic microscopy(SEM).The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.
基金Sponsored by National Natural Science Foundation of China(51210007,51004029)
文摘An Eulerian-Eulerian two-fluid model was developed to study the vortex flow inside a slab continuous casting mold with argon gas injection. Interracial momentum transfer that accommodated various interracial forces including drag force, lift force, virtual mass force, and turbulent dispersion force was considered. Predicted results agree well vaith experimental measurements of the water model in two-phase flow pattern and vortex flow structures. Three typical flow patterns with different argon steel ratios （ASRs） have been obtained： ＂double roll＂, ＂three roll＂, and ＂single roll＂. The flow pattern inside the mold alternates among the three types or it may attain some intermedi ate condition. With increasing ASR, the positions of vortices move from the submerged entry nozzle to the narrow face of the mold, and the sizes of vortices are reduced gradually. The rotating directions of vortices are all from high velocity area to low velocity area. Two mechanisms of vortex formation on the top surface have been suggested, i. e. , congruous shear flow and incongruous shear flow.
基金This study was financially supported by the National Natural Science Foundation of China (No.50374043).
文摘The effects of various factors on the flow speed of interdendritic melt were analyzed in detail in the process of continuous casting slabs. When the solid-liquid interface bends periodically, the expression of solute distribution in the columnar crystal zone was deduced, and the quantitative calculation was also made. The results show that the bulge and the interdendritic spacing are responsible for the flow speed of interdendritic melt. At the initial stage of solidification the bulge operates, and at the final stage the interdendritic spacing operates. The experimental results of macrosegregation in the slabs validated the calculated results of the flow speed of interdendritic melt, which shows that the calculated results are basically consistent with the experimental ones.
文摘The direct hydroxylation of benzene to phenol catalyzed by activated carbon-supported Fe （Fe/AC） in acetonitrile using H2O2 as the oxidant was studied in a continuous flow reactor. Results showed that the continuous operation could obtain high phenol yield of 28.1%, coupled with the turnover frequency of 3 h^-1, and high selectivity of 98% under mild condition. The catalyst was characterized by N2 adsorption/desorption, Boehm titration, X-ray photoelectron spectra, and Fourier transform infrared spectroscopy. It was observed that iron may interact with the carboxyl group forming iron-carboxylate like species, which act as the active phase. The apparent activation energy obtained by fitting an Arrhenius model to the experimental data was 13.4 kJ/mol. The reaction order was calculated to be about i, 0.2 for benzene and 0.7 for H202.
