Convenience rice has become widely popular due to its easy availability for cooking. This study investigated the starch structure and composition of leachate and the microstructure of reheated convenience rice using n...Convenience rice has become widely popular due to its easy availability for cooking. This study investigated the starch structure and composition of leachate and the microstructure of reheated convenience rice using novel processing technologies: super-heated steaming(SHS), auto-electric cooking(AEC), and pressurized-steam cooking(PSC). Additionally, the effect of two different target water contents(58% and 63%) was also evaluated. The PSC_63% sample had the highest total solids and amylopectin amount in the leachate. The amylopectin amount in the leachate differed significantly based on the targeted water content. Morphological characterization revealed that the swelling of starch and the coated layer on the surface of rice grains were most pronounced in the PSC_63% sample due to the pressure processing. The textural hardness of the AEC_58% sample was much higher than that of the other samples. The PSC_63% sample had the highest textural adhesiveness value, which can be attributed to the highest amylopectin amount in the leachate. Sensory characterization showed that the PSC_63% sample had the highest glossiness, whiteness, moistness, and overall acceptability. The principal component analysis score plots presented substantial differences in the leachate and textural and sensory characteristics of reheated convenience rice among the different processing technologies.展开更多
Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are di...Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are dissipated into the gas as heat energy,some of them can be recycled during the expansion process in subsequent stages by the reheat effect,which should be helpful to improve the detonationdriven turbine efficiency.Taking this into account,this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine,and a stoichiometric hydrogen-air mixture was used.The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine.The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation,which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled,so that the efficiency of the two-stage turbine was improved.At a 95%confidence level,the efficiency improvement was stable at 4.5%—5.3%,demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.展开更多
Based on the thermal simulation method,a systematical analysis was conducted on the effect of welding peak temperature and the cooling time that takes place from 800 to 500℃ on microstructure,precipitates,substructur...Based on the thermal simulation method,a systematical analysis was conducted on the effect of welding peak temperature and the cooling time that takes place from 800 to 500℃ on microstructure,precipitates,substructure and microhardness of the reheated coarse-grained heat-affected zone(CGHAZ)of G115 novel martensitic heat-resistant steel.As revealed from the results,the microstructure of un-altered CGHAZ(UACGHAZ)and supercritically CGHAZ(SCCGHAZ)was lath martensite,and structural heredity occurred.Intercritically reheated CGHAZ(IRCGHAZ)exhibited martensite and over-tempered martensite,and subcritical CGHAZ(SCGHAZ)displayed martensite and under-tempered martensite.The austenite in UACGHAZ and SCCGHAZ was transformed with the diffusion mechanism during the first thermal cycle,but with the non-diffusion mechanism during the second thermal cycle.For this reason,A_(c1) and A_(c3) during the second thermal cycle were significantly lower than those during the first thermal cycle,and A_(c1) and A_(c3) were reduced by nearly 14 and 44℃,respectively.Since the content and stability of the austenite alloy during the second thermal cycle of IRCGHAZ were lower than those during the first thermal cycle,M_(s) increased by nearly 30℃.There were considerable precipitates in the over-tempered region of IRCGHAZ,and the Laves phase was contained,which was not conducive to high-temperature creep property.Moreover,the dislocation density and the number of sub-grains in the region were lower,resulting in a sharp decrease in the microhardness,and it was the weak area in the reheated CGHAZ.展开更多
Low-temperature slab-reheated grain-oriented silicon steel is characterized by a sharp {411}〈148〉 primary recrystallization texture. To date, the influence of this texture on secondary recrystallization is not clear...Low-temperature slab-reheated grain-oriented silicon steel is characterized by a sharp {411}〈148〉 primary recrystallization texture. To date, the influence of this texture on secondary recrystallization is not clear. Microtextures in primary and secondary reerystallized sheets of low-temperature reheated grain-oriented silicon steel were examined using electron backscatter diffraction. By comparing the textures and microstructures of specific primary reerystallized grains neighboring secondary grains with those of other primary grains, the influences of primary re- crystallization textures and microstructures on the orientations of secondary grains were investigated. Results show that for low-temperature reheated graiworiented silicon steel, the primary recrystallization sheet comprises { 411 } 〈148〉, {111}〈112〉, and {001}〈120〉 texture componems. During secondary recrystallization, the {111}〈112〉 primary recrystallized grains were easily consumed by abnormally grown Goss, deviated Goss, Brass, or {210}〈001〉grains ;the { 411 }〈148〉 primary recrystallized grains were more resistant to being swallowed; and the {001} 〈120 grains were the most resistant to being consumed. For a particular primary grain, the distribution of its surrounding grain boundaries determined how easily it is consumed during secondary recrystallization. Primary grains surrounded by 20°- 45° grain boundaries were consumed much earlier than those having grain boundaries above 45°, which is in accordance with high-energy grain boundary theory. In addition, special ∑9 boundaries between {411}〈148〉 and Goss grains move more slowly than ∑9 boundaries between {111 }〈112〉 and Goss grains, which is attributed to the different positions of 〈110〉 rotation axis with respect to the normals of grain boundaries.展开更多
We extend the Standard Model with a scalar warm dark matter field S with an interaction with the Higgs boson ∅. This warm dark matter scenario is in agreement with cosmological observations if S and ∅ come into t...We extend the Standard Model with a scalar warm dark matter field S with an interaction with the Higgs boson ∅. This warm dark matter scenario is in agreement with cosmological observations if S and ∅ come into thermal and diffusive equilibrium before the temperature drops below the Higgs boson mass m<sub>H</sub>. We study inflation driven by the fields ∅ or S, and also study preheating and reheating, in order to constrain the parameters of this extension of the Standard Model. It is remarkable that, with the current data, these models pass a closure test with no free parameters.展开更多
The structural evolution of non dendritic AlSi7Mg alloy during reheating in resistance furnace was studied. The alloy ingots were produced by electromagnetic stirring during solidification. It was found that, the Si p...The structural evolution of non dendritic AlSi7Mg alloy during reheating in resistance furnace was studied. The alloy ingots were produced by electromagnetic stirring during solidification. It was found that, the Si phase in eutectic dissolves in a way of diffusion toward α phase, its appearance changes from flake to dot like, and tends to be fine and spheroidal with increasing reheating temperature. The thinner the flake, the lower the temperature for the occurrence of this process, and the higher the transforming speed. The eutectic melts partially when Si phase dissolves to some extent, and the morphology and size of primary α phase begin to change. The dendrite and rosette α phases tends to sphericize. The size of the former becomes larger, while the size of the latter reduces to be 1/2~1/4 of the original size. The spheroidal primary α phase has a tendency of grain growth.展开更多
In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investig...In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investigated, then the reheating microstructures were investigated. Results show that: the difference of temperature between the outer and center is small and the difference of their microstructures are also small. During reheating at 576℃ the spheroidization of grains is significant after 5min and no rosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596℃, but the ripening process is faster. The grains growup to 30-60μm, fine enough for thixoforming.展开更多
The corundum plates with a groove were used to freeze molten flux into solid slice to simulate the flux film formed in continuous casting mold, and thereby to study the formation mechanism of flux film with different ...The corundum plates with a groove were used to freeze molten flux into solid slice to simulate the flux film formed in continuous casting mold, and thereby to study the formation mechanism of flux film with different surface roughness. The effect of some factors on the surface roughness of flux film, such as reheating rate, cooling rate, flux film thickness and crystallization ratio, was discussed.展开更多
Pour point depressants (PPD) are used to improve the theology of waxy crude. The affect of various factors on the theological properties, and the thermal characteristics of waxy crude treated by PPD have been invest...Pour point depressants (PPD) are used to improve the theology of waxy crude. The affect of various factors on the theological properties, and the thermal characteristics of waxy crude treated by PPD have been investigated. The conclusions are as follows: PPD can reduce the pour point and abnormal point of waxy crude, broaden the temperature range of Newtonian fluid of waxy crude, and lower greatly the viscosity of non-Newtonian fluid of waxy crude. The influence of reheating and high-rate shear on the effect of PPD mainly depends on their temperature. When the reheating temperature is more than the abnormal point of crude by 10℃, the reheating process has little effect on the modification effect of PPD. However, when the reheating temperature is below the abnormal point of crude, the reheating process will reduce the modification effect of PPD. When temperature is above the abnormal point of crude, the high-rate shear has little effect on the modification effect of PPD. At a temperature range where a lot of wax is precipitating, high-rate shear will greatly reduce the modification effect of PPD.展开更多
A dilatometer was used to study the kinetics of bainite-to-austenite transformation in low carbon microalloyed steel with the initial microstructure of bainite during the continuous reheating process. The bainite-to-a...A dilatometer was used to study the kinetics of bainite-to-austenite transformation in low carbon microalloyed steel with the initial microstructure of bainite during the continuous reheating process. The bainite-to-austenite trans- formation was observed to take place in two steps at low heating rate. The first step is the dissolution of bainite, and the second one is the remaining bainite-to-austenite transformation controlled by a dissolution process. The calculation result of the kinetics of austenite formation shows that the two steps occur by diffusion at low heating rate. However, at high heating rate the bainite-to-austenite transformation occurs in a single step, and the process is mainly dominated by shear. The growth rate of austenite reaches the maximum at about 835℃ at different heating rates and the growth rate of austenite as a function of temperature increases with the increase in heating rate.展开更多
Rehearing furnace is an important device with complex dynamic characteristicsin steel plants. The temperature tracing control of reheating furnace has great importance both tothe quality of slabs and energy saving. A ...Rehearing furnace is an important device with complex dynamic characteristicsin steel plants. The temperature tracing control of reheating furnace has great importance both tothe quality of slabs and energy saving. A model-based control strategy, multivariable constrainedcontrol (MCC) for the reheating furnace control is used. With this control method, the furnace istreated as a six-input-six-output general model with loops coupled in nature. Compared with thetraditional control, the proposed control strategy gets better temperature tracing accuracy andexhibits some energy saving feature. The simulation results show that the performance of the furnaceis greatly improved.展开更多
For the complex batch process with characteristics of unequal batch data length,a novel data-driven batch process monitoring method is proposed based on mixed data features analysis and multi-way kernel entropy compon...For the complex batch process with characteristics of unequal batch data length,a novel data-driven batch process monitoring method is proposed based on mixed data features analysis and multi-way kernel entropy component analysis(MDFA-MKECA)in this paper.Combining the mechanistic knowledge,different mixed data features of each batch including statistical and thermodynamics entropy features,are extracted to finish data pre-processing.After that,MKECA is applied to reduce data dimensionality and finally establish a monitoring model.The proposed method is applied to a reheating furnace industry process,and the experimental results demonstrate that the MDFA-MKECA method can reduce the calculated amount and effectively provide on-line monitoring of the batch process.展开更多
A two-dimensional cellular automaton (CA) model has been developed for thedescription of the normal grain coarsening process. The probabilistic CA method incorporatingMoore's definition of the neighbourhood is use...A two-dimensional cellular automaton (CA) model has been developed for thedescription of the normal grain coarsening process. The probabilistic CA method incorporatingMoore's definition of the neighbourhood is used to simulate the normal grain coarsening process witha new transition rule. The model simulates the grain coarsening process in as much detail that ispossible, from the point of initial nucleation to subsequent coarsening with computational times.The unique result is that the grain coarsening speed can be controlled by the specific method, thisresult is vital to model the grain coarsening quantitatively. In order to make this model valid,experimental work has been done to provide solid evidence for this model. Comparison of themodelling result and the experimental result has been carried out.展开更多
Cooled in water after isothermal relaxation of deformed austenite for different times, an Nb-bearing microalloyed steel always exhibits synthetic microstructures, in which bainitic ferrite ,dominates. Dislocation conf...Cooled in water after isothermal relaxation of deformed austenite for different times, an Nb-bearing microalloyed steel always exhibits synthetic microstructures, in which bainitic ferrite ,dominates. Dislocation configurations and distributions of strain induced precipitates inside bainitic ferrite of samples relaxed for different times were distinct. When compared with the austenite model steel, which maintained fcc structure even at room temperature, the strain induced precipitates were not found in the sample without relaxation whereas these were distributed outside dislocations in sample relaxed for 1000s. Most of the strain induced precipitates distribute along dislocations and pin dislocations in sample relaxed for appropriate time. After bainitic transformation, the dislocations formed in deformed austenite remain to be pinned by the precipitates. When these samples were reheated to and held at 650 or 700℃, the non-equilibrloas microstructures tended to evolve into equilibrioas ones. The sample relaxed for 60s displayed the highest thermo-stability, whereas microstructure evolution was the quickest in the sample relaxed for 1000s even though it was the softest prior to reheating. Dislocations inside laths got rid of pinning of precipitates, and their polygonization became the precursor to the evolution of microstructures during reheated and held, followed by gradual disappearance of lath boundaries caused by dislocation climbing. Finally, recrystallization occurred and polygonal ferrite appeared. By hardness measurement, it was found that softening is not a single process occurring during reheated, in which hardness fluctuates with time. There were two peaks in the hardness-time curve of each sample having undergone relaxation, while single peak occured in the curve of the sample not being relaxed. These results indicated that the thermo-stability of microstructures was determined by their history of formation to a considerable degree.展开更多
Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the rec...Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.展开更多
It has long been thought that a reheating furnace, with its inherent measurement difficulties and complex dynamics, posed almost insurmountable problems to engineers in steel plants. A novel software sensor is propos...It has long been thought that a reheating furnace, with its inherent measurement difficulties and complex dynamics, posed almost insurmountable problems to engineers in steel plants. A novel software sensor is proposed to make more effective use of those measurements that are already available, which has great importance both to slab quality and energy saving. The proposed method is based on the mixtures of Gaussian processes (GP) with the expectation maximization (EM) algorithm employed for parameter esti- mation of the mixture of models. The mixture model can alleviate the computational complexity of GP and also accords with the changes of operating condition in practical processes. It is demonstrated by on-line estimation of the furnace gas temperature in 1580 reheating furnace in Baosteel Corporation (Group).展开更多
A general numerical simulating program for three-dimensional (3-D) andtime-dependent fluid flow for a reheating furnace with multi-swirling-burners has been developedbased upon an arbitrary Lagrangian-Eulerian scheme ...A general numerical simulating program for three-dimensional (3-D) andtime-dependent fluid flow for a reheating furnace with multi-swirling-burners has been developedbased upon an arbitrary Lagrangian-Eulerian scheme (ALE) with the finite volume method. Theparameters of fluid flow in a reheating furnace with multi-swirling-burners was calculated and the3-D velocity distributions were obtained. The design of the burners was optimized for forming betterswirling flow. The simulation shows that the fluid flow in the reheating furnace with the optimizedburners is reasonable.展开更多
A novel 2D cellular automata (CA) model has been developed for description of normal grain coarsening and abnormal grain coarsening process. The program reflects the grain coarsening quite well even through the averag...A novel 2D cellular automata (CA) model has been developed for description of normal grain coarsening and abnormal grain coarsening process. The program reflects the grain coarsening quite well even through the average grain size becomes very large. Follow results have been obtained: (a) The model reflect the normal grain growth kinetics gradually increase with probability and grain growth speed can be controlled. Based on this result, temperature can be coupled in the model. (b) Abnormal grain growth is modelled successfully. (c) Methodology has been put forward to find the relationship between the experiment results and modelling results. The experimental work on the grain coarsening has been carried out. Graphical output matched the realistic microstructure in every detail. Because many physical parameters can be taken into account in the CA programme, this CA model could not only qualitatively demonstrate the grain growth process, but also quantitatively predict and analyse the grain coarsening process.展开更多
The corundum plates with a groove were used to freeze molten flux into solid slice to simulate the flux film formed in continuous casting mold,and thereby to study the formation mechanism of flux film with different s...The corundum plates with a groove were used to freeze molten flux into solid slice to simulate the flux film formed in continuous casting mold,and thereby to study the formation mechanism of flux film with different surface roughness.The effect of some factors on the surface roughness of flux film,such as reheating rate,cooling rate,flux film thickness and crystallization ratio,was discussed.展开更多
基金supported by the High Value-added Food Technology Development Program in Korea (Grant No. 323002-4)the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry, Republic of Korea。
文摘Convenience rice has become widely popular due to its easy availability for cooking. This study investigated the starch structure and composition of leachate and the microstructure of reheated convenience rice using novel processing technologies: super-heated steaming(SHS), auto-electric cooking(AEC), and pressurized-steam cooking(PSC). Additionally, the effect of two different target water contents(58% and 63%) was also evaluated. The PSC_63% sample had the highest total solids and amylopectin amount in the leachate. The amylopectin amount in the leachate differed significantly based on the targeted water content. Morphological characterization revealed that the swelling of starch and the coated layer on the surface of rice grains were most pronounced in the PSC_63% sample due to the pressure processing. The textural hardness of the AEC_58% sample was much higher than that of the other samples. The PSC_63% sample had the highest textural adhesiveness value, which can be attributed to the highest amylopectin amount in the leachate. Sensory characterization showed that the PSC_63% sample had the highest glossiness, whiteness, moistness, and overall acceptability. The principal component analysis score plots presented substantial differences in the leachate and textural and sensory characteristics of reheated convenience rice among the different processing technologies.
基金financially supported by the National Natural Science Foundation of China through Grant Nos.12372338 and U2241272the Natural Science Foundation of Shaanxi Province of China through Grant Nos.2023-JC-YB-352 and 2022JZ-20+1 种基金the Guangdong Basic and Applied Basic Research Foundation through Grant No.2023A1515011663the Practice and Innovation Funds for Graduate Students of Northwestern Polytechnical University through Grant No.PF2023010。
文摘Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are dissipated into the gas as heat energy,some of them can be recycled during the expansion process in subsequent stages by the reheat effect,which should be helpful to improve the detonationdriven turbine efficiency.Taking this into account,this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine,and a stoichiometric hydrogen-air mixture was used.The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine.The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation,which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled,so that the efficiency of the two-stage turbine was improved.At a 95%confidence level,the efficiency improvement was stable at 4.5%—5.3%,demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.
基金We would like to acknowledge the support of National Key R&D Program of China(No.2017YFB0305202)Inner Mongolia Natural Science Foundation(No.2016MS0510)Inner Mongolia Natural Science Foundation(No.2020MS05046).
文摘Based on the thermal simulation method,a systematical analysis was conducted on the effect of welding peak temperature and the cooling time that takes place from 800 to 500℃ on microstructure,precipitates,substructure and microhardness of the reheated coarse-grained heat-affected zone(CGHAZ)of G115 novel martensitic heat-resistant steel.As revealed from the results,the microstructure of un-altered CGHAZ(UACGHAZ)and supercritically CGHAZ(SCCGHAZ)was lath martensite,and structural heredity occurred.Intercritically reheated CGHAZ(IRCGHAZ)exhibited martensite and over-tempered martensite,and subcritical CGHAZ(SCGHAZ)displayed martensite and under-tempered martensite.The austenite in UACGHAZ and SCCGHAZ was transformed with the diffusion mechanism during the first thermal cycle,but with the non-diffusion mechanism during the second thermal cycle.For this reason,A_(c1) and A_(c3) during the second thermal cycle were significantly lower than those during the first thermal cycle,and A_(c1) and A_(c3) were reduced by nearly 14 and 44℃,respectively.Since the content and stability of the austenite alloy during the second thermal cycle of IRCGHAZ were lower than those during the first thermal cycle,M_(s) increased by nearly 30℃.There were considerable precipitates in the over-tempered region of IRCGHAZ,and the Laves phase was contained,which was not conducive to high-temperature creep property.Moreover,the dislocation density and the number of sub-grains in the region were lower,resulting in a sharp decrease in the microhardness,and it was the weak area in the reheated CGHAZ.
基金Item Sponsored by National High Technology Research and Development Program of China(2012AA03A505)
文摘Low-temperature slab-reheated grain-oriented silicon steel is characterized by a sharp {411}〈148〉 primary recrystallization texture. To date, the influence of this texture on secondary recrystallization is not clear. Microtextures in primary and secondary reerystallized sheets of low-temperature reheated grain-oriented silicon steel were examined using electron backscatter diffraction. By comparing the textures and microstructures of specific primary reerystallized grains neighboring secondary grains with those of other primary grains, the influences of primary re- crystallization textures and microstructures on the orientations of secondary grains were investigated. Results show that for low-temperature reheated graiworiented silicon steel, the primary recrystallization sheet comprises { 411 } 〈148〉, {111}〈112〉, and {001}〈120〉 texture componems. During secondary recrystallization, the {111}〈112〉 primary recrystallized grains were easily consumed by abnormally grown Goss, deviated Goss, Brass, or {210}〈001〉grains ;the { 411 }〈148〉 primary recrystallized grains were more resistant to being swallowed; and the {001} 〈120 grains were the most resistant to being consumed. For a particular primary grain, the distribution of its surrounding grain boundaries determined how easily it is consumed during secondary recrystallization. Primary grains surrounded by 20°- 45° grain boundaries were consumed much earlier than those having grain boundaries above 45°, which is in accordance with high-energy grain boundary theory. In addition, special ∑9 boundaries between {411}〈148〉 and Goss grains move more slowly than ∑9 boundaries between {111 }〈112〉 and Goss grains, which is attributed to the different positions of 〈110〉 rotation axis with respect to the normals of grain boundaries.
文摘We extend the Standard Model with a scalar warm dark matter field S with an interaction with the Higgs boson ∅. This warm dark matter scenario is in agreement with cosmological observations if S and ∅ come into thermal and diffusive equilibrium before the temperature drops below the Higgs boson mass m<sub>H</sub>. We study inflation driven by the fields ∅ or S, and also study preheating and reheating, in order to constrain the parameters of this extension of the Standard Model. It is remarkable that, with the current data, these models pass a closure test with no free parameters.
文摘The structural evolution of non dendritic AlSi7Mg alloy during reheating in resistance furnace was studied. The alloy ingots were produced by electromagnetic stirring during solidification. It was found that, the Si phase in eutectic dissolves in a way of diffusion toward α phase, its appearance changes from flake to dot like, and tends to be fine and spheroidal with increasing reheating temperature. The thinner the flake, the lower the temperature for the occurrence of this process, and the higher the transforming speed. The eutectic melts partially when Si phase dissolves to some extent, and the morphology and size of primary α phase begin to change. The dendrite and rosette α phases tends to sphericize. The size of the former becomes larger, while the size of the latter reduces to be 1/2~1/4 of the original size. The spheroidal primary α phase has a tendency of grain growth.
基金The National Natural Science Foundation of China (Grants No. 59974009) is greatly acknowledged for their financial support.
文摘In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investigated, then the reheating microstructures were investigated. Results show that: the difference of temperature between the outer and center is small and the difference of their microstructures are also small. During reheating at 576℃ the spheroidization of grains is significant after 5min and no rosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596℃, but the ripening process is faster. The grains growup to 30-60μm, fine enough for thixoforming.
文摘The corundum plates with a groove were used to freeze molten flux into solid slice to simulate the flux film formed in continuous casting mold, and thereby to study the formation mechanism of flux film with different surface roughness. The effect of some factors on the surface roughness of flux film, such as reheating rate, cooling rate, flux film thickness and crystallization ratio, was discussed.
文摘Pour point depressants (PPD) are used to improve the theology of waxy crude. The affect of various factors on the theological properties, and the thermal characteristics of waxy crude treated by PPD have been investigated. The conclusions are as follows: PPD can reduce the pour point and abnormal point of waxy crude, broaden the temperature range of Newtonian fluid of waxy crude, and lower greatly the viscosity of non-Newtonian fluid of waxy crude. The influence of reheating and high-rate shear on the effect of PPD mainly depends on their temperature. When the reheating temperature is more than the abnormal point of crude by 10℃, the reheating process has little effect on the modification effect of PPD. However, when the reheating temperature is below the abnormal point of crude, the reheating process will reduce the modification effect of PPD. When temperature is above the abnormal point of crude, the high-rate shear has little effect on the modification effect of PPD. At a temperature range where a lot of wax is precipitating, high-rate shear will greatly reduce the modification effect of PPD.
文摘A dilatometer was used to study the kinetics of bainite-to-austenite transformation in low carbon microalloyed steel with the initial microstructure of bainite during the continuous reheating process. The bainite-to-austenite trans- formation was observed to take place in two steps at low heating rate. The first step is the dissolution of bainite, and the second one is the remaining bainite-to-austenite transformation controlled by a dissolution process. The calculation result of the kinetics of austenite formation shows that the two steps occur by diffusion at low heating rate. However, at high heating rate the bainite-to-austenite transformation occurs in a single step, and the process is mainly dominated by shear. The growth rate of austenite reaches the maximum at about 835℃ at different heating rates and the growth rate of austenite as a function of temperature increases with the increase in heating rate.
基金This work was supported by a grant from State 863 High Technology R&D Project of China (No. 2001 AA413130) National Natural Science Foundation of China (No.60004001).]
文摘Rehearing furnace is an important device with complex dynamic characteristicsin steel plants. The temperature tracing control of reheating furnace has great importance both tothe quality of slabs and energy saving. A model-based control strategy, multivariable constrainedcontrol (MCC) for the reheating furnace control is used. With this control method, the furnace istreated as a six-input-six-output general model with loops coupled in nature. Compared with thetraditional control, the proposed control strategy gets better temperature tracing accuracy andexhibits some energy saving feature. The simulation results show that the performance of the furnaceis greatly improved.
基金supported by National Key R&D Program of China(Smart process control technology for aluminum&copper strip based on industrial big data)(2017YFB0306405)。
文摘For the complex batch process with characteristics of unequal batch data length,a novel data-driven batch process monitoring method is proposed based on mixed data features analysis and multi-way kernel entropy component analysis(MDFA-MKECA)in this paper.Combining the mechanistic knowledge,different mixed data features of each batch including statistical and thermodynamics entropy features,are extracted to finish data pre-processing.After that,MKECA is applied to reduce data dimensionality and finally establish a monitoring model.The proposed method is applied to a reheating furnace industry process,and the experimental results demonstrate that the MDFA-MKECA method can reduce the calculated amount and effectively provide on-line monitoring of the batch process.
文摘A two-dimensional cellular automaton (CA) model has been developed for thedescription of the normal grain coarsening process. The probabilistic CA method incorporatingMoore's definition of the neighbourhood is used to simulate the normal grain coarsening process witha new transition rule. The model simulates the grain coarsening process in as much detail that ispossible, from the point of initial nucleation to subsequent coarsening with computational times.The unique result is that the grain coarsening speed can be controlled by the specific method, thisresult is vital to model the grain coarsening quantitatively. In order to make this model valid,experimental work has been done to provide solid evidence for this model. Comparison of themodelling result and the experimental result has been carried out.
文摘Cooled in water after isothermal relaxation of deformed austenite for different times, an Nb-bearing microalloyed steel always exhibits synthetic microstructures, in which bainitic ferrite ,dominates. Dislocation configurations and distributions of strain induced precipitates inside bainitic ferrite of samples relaxed for different times were distinct. When compared with the austenite model steel, which maintained fcc structure even at room temperature, the strain induced precipitates were not found in the sample without relaxation whereas these were distributed outside dislocations in sample relaxed for 1000s. Most of the strain induced precipitates distribute along dislocations and pin dislocations in sample relaxed for appropriate time. After bainitic transformation, the dislocations formed in deformed austenite remain to be pinned by the precipitates. When these samples were reheated to and held at 650 or 700℃, the non-equilibrloas microstructures tended to evolve into equilibrioas ones. The sample relaxed for 60s displayed the highest thermo-stability, whereas microstructure evolution was the quickest in the sample relaxed for 1000s even though it was the softest prior to reheating. Dislocations inside laths got rid of pinning of precipitates, and their polygonization became the precursor to the evolution of microstructures during reheated and held, followed by gradual disappearance of lath boundaries caused by dislocation climbing. Finally, recrystallization occurred and polygonal ferrite appeared. By hardness measurement, it was found that softening is not a single process occurring during reheated, in which hardness fluctuates with time. There were two peaks in the hardness-time curve of each sample having undergone relaxation, while single peak occured in the curve of the sample not being relaxed. These results indicated that the thermo-stability of microstructures was determined by their history of formation to a considerable degree.
文摘Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.
基金This work was financially supported by the National High-Tech Research and Development Program of China(No.2002AA4120I0).
文摘It has long been thought that a reheating furnace, with its inherent measurement difficulties and complex dynamics, posed almost insurmountable problems to engineers in steel plants. A novel software sensor is proposed to make more effective use of those measurements that are already available, which has great importance both to slab quality and energy saving. The proposed method is based on the mixtures of Gaussian processes (GP) with the expectation maximization (EM) algorithm employed for parameter esti- mation of the mixture of models. The mixture model can alleviate the computational complexity of GP and also accords with the changes of operating condition in practical processes. It is demonstrated by on-line estimation of the furnace gas temperature in 1580 reheating furnace in Baosteel Corporation (Group).
基金This research was financially supported by the Inner Mongolia Key Research Project (No. 2002061003)
文摘A general numerical simulating program for three-dimensional (3-D) andtime-dependent fluid flow for a reheating furnace with multi-swirling-burners has been developedbased upon an arbitrary Lagrangian-Eulerian scheme (ALE) with the finite volume method. Theparameters of fluid flow in a reheating furnace with multi-swirling-burners was calculated and the3-D velocity distributions were obtained. The design of the burners was optimized for forming betterswirling flow. The simulation shows that the fluid flow in the reheating furnace with the optimizedburners is reasonable.
文摘A novel 2D cellular automata (CA) model has been developed for description of normal grain coarsening and abnormal grain coarsening process. The program reflects the grain coarsening quite well even through the average grain size becomes very large. Follow results have been obtained: (a) The model reflect the normal grain growth kinetics gradually increase with probability and grain growth speed can be controlled. Based on this result, temperature can be coupled in the model. (b) Abnormal grain growth is modelled successfully. (c) Methodology has been put forward to find the relationship between the experiment results and modelling results. The experimental work on the grain coarsening has been carried out. Graphical output matched the realistic microstructure in every detail. Because many physical parameters can be taken into account in the CA programme, this CA model could not only qualitatively demonstrate the grain growth process, but also quantitatively predict and analyse the grain coarsening process.
文摘The corundum plates with a groove were used to freeze molten flux into solid slice to simulate the flux film formed in continuous casting mold,and thereby to study the formation mechanism of flux film with different surface roughness.The effect of some factors on the surface roughness of flux film,such as reheating rate,cooling rate,flux film thickness and crystallization ratio,was discussed.