The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozz...The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozzle port not only increases the velocity of molten steel, but also enhances the wall shear stress, F number and heat flux. This clogging has the greatest effect on the behavior of molten steel. However, clogging at the top 1/3 of the nozzle only increases the velocity of molten steel and has little influence. Clogging at the bottom of the nozzle almost has no influence.展开更多
In order to make clear the formation mechanism of centerline cracks incontinuously cast slabs, the form, distribution and other characteristics of the cracks wereanalyzed. The final solidification point, surface tempe...In order to make clear the formation mechanism of centerline cracks incontinuously cast slabs, the form, distribution and other characteristics of the cracks wereanalyzed. The final solidification point, surface temperature of the slabs and strain in solidifyingshell were investigated. The results were that: (1) Five relatively low temperature zones exist onslab surface below the three water spraying nozzles and near the two edges, respectively, whichcorresponds to the places of centerline cracks and triangle-zone cracks. (2) Centerline cracks andtriangle-zone cracks occur because of weak secondary cooling, uneven cooling along slab width, andlarge variation of roll gap. (3) After minimizing the variation of roll gap and applying the newsecondary cooling pattern, the occurring frequency of centerline and triangle-zone cracks minimizesto zero.展开更多
In order to reduce the transverse corner cracks of high strength weathering steel Q450NQR1,the factors influencing transverse corner cracks on continuously cast slab,such as level fluctuation of molten steel in mold,m...In order to reduce the transverse corner cracks of high strength weathering steel Q450NQR1,the factors influencing transverse corner cracks on continuously cast slab,such as level fluctuation of molten steel in mold,mold taper,primary cooling,mold powder,secondary cooling,nitrogen content in steel,spray nozzle structure,processing parameters and equipment of CC,etc.,were analyzed.Based on this,a series of comprehensive countermeasures have been proposed.The operation shows by the use of key technologies,including stabilizing steel level,optimizing the mold taper,weakening the primary cooling and the secondary cooling,reforming the mold powder,and adjusting spray nozzle structure,the transverse corner cracks on continuously cast slab have been significantly reduced,and the edge cracks on hot rolled sheet have been eliminated due to the transverse corner cracks.The qualified slabs are delivered to produce weathering cold forming sectional steel,whose yield strength is greater than 450MPa.展开更多
The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large de...The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments,the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined.With SPA-H weathering steel as a specific research steel grade,the distributions of tem-perature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite ele-ment model.High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures,and a prediction model of the critical strain for two typical cracks,combining the effects of strain rate and temperature,was proposed by incorporating the Zener-Hollomon parameter.The crack risks with different LCR schemes were calculated using the crack risk prediction model,and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm×1600 mm was 41.8 mm,with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8,7.3,6.5,6.4,and 5.8 mm,respectively.展开更多
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
Controlling molten steel flow in the mold and stabilizing the meniscus are critical challenges during the continuous casting,directly impacting the surface quality and internal quality of the final steel slab product....Controlling molten steel flow in the mold and stabilizing the meniscus are critical challenges during the continuous casting,directly impacting the surface quality and internal quality of the final steel slab product.The effects of electromagnetic swirling flow in nozzle(EMSFN)technology on molten steel flow in the mold during slab continuous casting under various casting speeds were investigated.A real-time adjustable EMSFN was developed,and a three-dimensional unsteady Reynolds-averaged Navier–Stokes turbulence mathematical model was established to simulate the flow field within the mold.The results demonstrate that the EMSFN effectively stabilizes the outflow from nozzle,reduces the impact depth and surface velocity of the molten steel,mitigates meniscus fluctuations,and promotes stable flow within the mold.However,a certain matching relationship exists between the casting speed and the current intensity.For the experimental medium-thick slab specifications,the optimal current intensities were found to be 100,130,and 200 A at casting speeds of 1.0,1.5,and 2.0 m/min,respectively.EMSFN can optimize the mold flow field under different casting speeds,providing theoretical support for improving the quality of continuously cast slab products.展开更多
Longitudinal cracks are common defects of continuous casting slabs and may lead to serious quality accidents. Image capturing and recognition of hot slabs is an effective way for on-line detection of cracks, and recog...Longitudinal cracks are common defects of continuous casting slabs and may lead to serious quality accidents. Image capturing and recognition of hot slabs is an effective way for on-line detection of cracks, and recognition of cracks is essential because the surface of hot slabs is very complicated. In order to detect the surface longitudinal cracks of the slabs, a new feature extraction method based on Curvelet transform and kernel locality preserving projections （KLPP） is proposed. First, sample images are decomposed into three levels by Curvelet transform. Second, Fourier transform is applied to all sub-band images and the Fourier amplitude spectrum of each sub-band is computed to get features with translational invariance. Third, five kinds of statistical features of the Fourier amplitude spectrum are computed and combined in different forms. Then, KLPP is employed for dimensionality reduction of the obtained 62 types of high-dimensional combined features. Finally, a support vector machine （SVM） is used for sample set classification. Experiments with samples from a real production line of continuous casting slabs show that the algorithm is effective to detect longitudinal cracks, and the classification rate is 91.89%.展开更多
The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production （CSP） technique was investigated. Using transmission electron microscop...The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production （CSP） technique was investigated. Using transmission electron microscopy analysis, it was seen that a majority of manganese sulfides precipitated at austenite grain boundaries, the morphologies of which were spherical or close to the spherical shape and the size of MnS precipitates ranged from 30 nm to 100 nm. A mathematical model of the manganese sulfide precipitation in this process was developed based on classical nucleation theory. Under the given conditions, the starting and finishing precipitation temperatures of MnS in the continuous casting thin slab of the studied low-carbon steel are 1 189 ℃ and 1 171 ℃, respectively, and the average diameter of MnS precipitates is about 48 nm within this precipitation temperature range. The influences of chemical components and thermo-mechanical processing conditions on the precipitation behavior of MnS in the same process were also discussed.展开更多
According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The ma...According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The magnetic fields and flow fields of melt were simulated with SEMS. It's shown that the electromagnetic forces with inward and sidelong components produced by travel magnetic field at the wide faces of slab make the melt whirling in horizontal section,and the convection of the melt is strengthened obviously there. In addition,magnetic flux density attenuates from the edge to the center of slab,and the profile of the melt velocity along slab thickness in the center of the horizontal section takes a two-opposite-peak configuration. Ultimately,the stirring intensity and features are determined by the electromagnetic parameters,coil arrangement and stirring types.展开更多
Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its c...Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its change regularity at slab center during continuous casting were obtained.The influence of distribution and change of stress on the propagation of longitudinal cracks on slab surface was discussed.The results show that the tensional stress appears on slab surface at the inner arc side and the compressive stress appears on slab surface at the outer arc side at stages 6-8 in straightening zone during continuous casting.Longitudinal cracks generally appear on slab top surface and do not appear on slab bottom surface,which are also observed in industry.展开更多
In the current study, the transformation in the composition of non-metallic inclusions from the molten steel to the solidified steel was studied and the composition distribution of inclusions on the cross section of a...In the current study, the transformation in the composition of non-metallic inclusions from the molten steel to the solidified steel was studied and the composition distribution of inclusions on the cross section of a linepine continuous casting slab was predicted. During cooling and solidification of the continuous casting strand, Al_(2)O_(3)-CaO inclusions reacted with the bulk steel and transformed to CaS-Al_(2)O_(3)-MgO-(CaO) ones in the continuous casting slab. The composition of inclusions on the cross section of the slab varied with locations due to the varied cooling rate. A model was established to predict the distribution of the composition of inclusions on the cross section of the continuous casting slab, coupling solidification and heat transfer of the continuous casting slab, the kinetic mass transfer of the dissolved elements in the solid steel, and thermodynamic calculation of inclusion transformation at different temperatures. The composition transformation of inclusions mainly occurred at the temperature between the liquidus and solidus of the linepipe steel. Inclusions were mainly CaS-Al_(2)O_(3)-MgO-(CaO) in slab center and were MgO-Al_(2)O_(3)-CaO-CaS within the subsurface of the slab. In the slab, the transformation fraction of inclusions was less than 10 % at corners while it reached 70 % at 50 mm below the surface of the slab.展开更多
A grain-oriented silicon steel strip with AlN as main inhibitor was produced by thin slab casting and rolling（TSCR）process.The microstructure,texture and precipitates of the hot-rolled strip were investigated by use...A grain-oriented silicon steel strip with AlN as main inhibitor was produced by thin slab casting and rolling（TSCR）process.The microstructure,texture and precipitates of the hot-rolled strip were investigated by use of optical microscope（OM）,X-ray diffractometer,transmission electron microscope（TEM）and energy dispersive spectroscope（EDS）.The result shows that the microstructure and texture exhibit a through-thickness gradient similar to that of the hot-rolled strip produced by conventional high-temperature slab-reheating process;the preferred orientation varies from {110}〈001〉in the surface layer to{001}〈110〉in the center layer,and the Goss texture with a maximum intensity mainly concentrates on the surface layer.In addition,some other texture components,for example rotated Goss texture,form in the 1/4thickness layer,which are not observed in the hotrolled strip produced by conventional high-temperature slab-reheating process.The precipitates in the hot-rolled strip are mainly（Mn,Cu）S and AlN compound particles with dimension of 100-200 nm,and the fine precipitates are significantly less than that in the hot-rolled strip produced by conventional high-temperature slab-reheating process.Moreover,the areal density of the fine precipitates in the center layer is more than that in the surface layer.展开更多
Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoptio...Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoption of the amount of reduction upon the given final solidification zone through roll gap adjustments. The synchronization of the clamping cylinders for roll gap adjustments should be very important to the application of soft reduction, including the synchronization of the clamping cylinders adjustments in the same and different segments. The synchronization of clamping cylinders adjustments is mainly affected by the adjustable accuracy of the four position-controlled clamping cylinders mounted in the upper frames of the segments according to a predetermined transformation relationship between the signals of displacement sensors and aimed roll gap, which, however, is also influenced by the installation accuracy, the precision of displacement sensors, the deformation of the segment frames and/or its bearing pedestals. Due to the actual asynchronous adjustments of the four clamping cylinders, the dynamic soft reduction operation is normally applied at non-ideal mechanical conditions. Here 7 possible situations of asynchronous adjustments of the local segments which may induce gap deviation have been presented. The roll gap deviation in the soft reduction region of a slab casting has been studied by a 3-D visco-elastic plastic FEM model, through which the additional inter-roll bulging, the related triangular cracks induced by one kind of the possible asynchronous adjustment situation and the effectiveness of soft reduction have been analyzed. A critical tolerance for the gap adjustments has been proposed for better contribution of soft reduction to the internal quality of slabs.展开更多
By means of Gleeble-1500 testing machine, the simulation of continuous casting process forAH32 steel was carried out and hot ductility and strength were determined. The cracking sensitivity was studied under the diffe...By means of Gleeble-1500 testing machine, the simulation of continuous casting process forAH32 steel was carried out and hot ductility and strength were determined. The cracking sensitivity was studied under the different temperatures and strain rates. The Precipitations of AIN at different temperatures and the fractures of high-temperature tensile samples were observed by using TEM （transmission electron microscope） and SEM （scanning electron microscope）. The factors affecting the brittle temperature zone were discussed.展开更多
Two-dimension unsteady heat transfer model was applied to obtain the surfacetemperature and the shell thickness of continuous casting slabs during the process ofsolidification. On the basis of which, the mathematical ...Two-dimension unsteady heat transfer model was applied to obtain the surfacetemperature and the shell thickness of continuous casting slabs during the process ofsolidification. On the basis of which, the mathematical model of strain at the interface of solidand liquid steel was set up. Through which, the strain in the solidifying shell under normal andabnormal operation conditions was gained. The results indicate that the strain is small under thenormal operation conditions and the internal crack never happens. However, when the variation of theroll gap is above 2 mm, the strain caused by which is greater than that caused by bulging.Furthermore, the total strain exceeds the critical one and the internal crack is the result. So itis of great importance to maintain the fine state of continuous casting machine to avoid theappearance of internal crack.展开更多
The surface temperature of casting slab is an important parameter in the metallurgy field.Because the surface emissivity is uncertain and also unknown,it is difficult to measure the slab surface temperature accurately...The surface temperature of casting slab is an important parameter in the metallurgy field.Because the surface emissivity is uncertain and also unknown,it is difficult to measure the slab surface temperature accurately.A method based on preceded reflector and multi-wavelength was put forward to deal with the difficulty in surface temperature measurement of casting slab.On the premise of preceded reflector and non-preceded reflector,the method establishes the radiation energy equations and works out the emissivity and temperature in the equations.Also,the multilayer modeling of casting slab surface and multiple reflection-absorption process modeling were built by Monte Carlo method.The temperature measuring method had been applied in the continuous casting field.In order to verify the measured result,the thermal imaging method was adopted when the slab surface emissivity was set by repeated tests.Finally,the measured and verified temperature curves keep a same tendency and the error of the values is lower than 5℃.The comparison result shows that the method can measure temperature accurately.展开更多
The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the she...The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the shearing flow near the narrow face of mold, the entrapment caused by vortexes around the submerged entry nozzle （SEN）, and the entrapment caused by the Ar bubbling. Both the velocity of the surface flow and the level fluctuation of the liquids are enlarged with increasing the casting speed, reducing the submersion depth of SEN, decreasing the downward angles of the nozzle outlets, and increasing the Ar flowrate, all of which increase the tendency of mold powder entrapment. Among the four above-mentioned factors, casting speed has the largest effect.展开更多
A mercury model has been developed to investigate the influences of Electromagnetic Mold Brake Ruler(EMBr-Ruler) and Flow Control Mold(FC Mold) on metal flow in slab continuous casting mold with the practical casting ...A mercury model has been developed to investigate the influences of Electromagnetic Mold Brake Ruler(EMBr-Ruler) and Flow Control Mold(FC Mold) on metal flow in slab continuous casting mold with the practical casting speed 1.0,1.3 and 2.0 m/min respectively.FC-Mold can efficiently repress the surface flow and its fluctuation.The expanding space of the jets is compressed by EMBr-Ruler and FC-Mold respectively,then the 'flow passage' where the vertical velocity of flow increases sharply is developed near the narrow wall with EMBr-Ruler and FC-Mold.It is bad for the development of the plug like flow.Only the nozzle ports are placed in the braking magnetic field region and the casting speed is suitable,EMBr can be beneficial to the formation of the plug like flow.The flow regime is improved with FC Mold when the casting speed is high(2.0 m/min),but EMBr can improve the flow field with medium casting speed(1.3 m/min),but when the casting speed is low(1.0 m/min),the effects of two types of EMBr are both unsatisfactory.展开更多
In the thin slab continuous casting （TSCC） of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of f...In the thin slab continuous casting （TSCC） of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of final products. In the current work, a full-scale physical mod- eling of a thin slab easter on the basis of dimensionless Reynolds and Froude similarity criteria was constructed. The flow pattern in the funnel shaped mold with a new tetra-furcated submerged entry nozzle （SEN） was investigated. To determinate optimum operational parameters, some experiments were carried out under various casting conditions. The results show that the tetra-furcated design of the nozzle leads to a special flow pattern in the mold cavity with three-dimensional recirculating flow. It is also shown that the increase of casting speed and gas injection results in surface turbulence. On the other hand, using a higher depth of SEN decreases the vortex in the free surface of the caster. To avoid surface turbulent and related casting problems, it is recommended to use 30-cm and 40-cm SEN depth at the casting speeds of 3.5 and 4.5 m/min, respectively.展开更多
The operating conditions during the continuous casting process have a great effect on the microstructure of slab solidification, including primary and secondary dendritic arm spacing. On the basis of the analysis of a...The operating conditions during the continuous casting process have a great effect on the microstructure of slab solidification, including primary and secondary dendritic arm spacing. On the basis of the analysis of available work, a revised expression for describing secondary dendritic arm spacing during solidification of slab continuous casting was presented, and the relation between the ratio of primary dendritic arm spacing to secondary dendritic arm spacing and the cooling rate was obtained.展开更多
文摘The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozzle port not only increases the velocity of molten steel, but also enhances the wall shear stress, F number and heat flux. This clogging has the greatest effect on the behavior of molten steel. However, clogging at the top 1/3 of the nozzle only increases the velocity of molten steel and has little influence. Clogging at the bottom of the nozzle almost has no influence.
文摘In order to make clear the formation mechanism of centerline cracks incontinuously cast slabs, the form, distribution and other characteristics of the cracks wereanalyzed. The final solidification point, surface temperature of the slabs and strain in solidifyingshell were investigated. The results were that: (1) Five relatively low temperature zones exist onslab surface below the three water spraying nozzles and near the two edges, respectively, whichcorresponds to the places of centerline cracks and triangle-zone cracks. (2) Centerline cracks andtriangle-zone cracks occur because of weak secondary cooling, uneven cooling along slab width, andlarge variation of roll gap. (3) After minimizing the variation of roll gap and applying the newsecondary cooling pattern, the occurring frequency of centerline and triangle-zone cracks minimizesto zero.
文摘In order to reduce the transverse corner cracks of high strength weathering steel Q450NQR1,the factors influencing transverse corner cracks on continuously cast slab,such as level fluctuation of molten steel in mold,mold taper,primary cooling,mold powder,secondary cooling,nitrogen content in steel,spray nozzle structure,processing parameters and equipment of CC,etc.,were analyzed.Based on this,a series of comprehensive countermeasures have been proposed.The operation shows by the use of key technologies,including stabilizing steel level,optimizing the mold taper,weakening the primary cooling and the secondary cooling,reforming the mold powder,and adjusting spray nozzle structure,the transverse corner cracks on continuously cast slab have been significantly reduced,and the edge cracks on hot rolled sheet have been eliminated due to the transverse corner cracks.The qualified slabs are delivered to produce weathering cold forming sectional steel,whose yield strength is greater than 450MPa.
基金supported by the National Natural Science Foundation of China(No.52474355)the Liaoning Province Science and Technology Plan Joint Program(Key Research and Development Program Project),China(Nos.2022JH25/10200003 and 2023JH2/101800058).
文摘The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments,the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined.With SPA-H weathering steel as a specific research steel grade,the distributions of tem-perature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite ele-ment model.High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures,and a prediction model of the critical strain for two typical cracks,combining the effects of strain rate and temperature,was proposed by incorporating the Zener-Hollomon parameter.The crack risks with different LCR schemes were calculated using the crack risk prediction model,and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm×1600 mm was 41.8 mm,with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8,7.3,6.5,6.4,and 5.8 mm,respectively.
基金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National Natural Science Foundation of China(Nos.U21A20117,52104347 and 52272078)the Fundamental Research Funds for the Central Universities(No.N2409006)Natural Science Foundation of Liaoning Province(2023-MSBA-135)for the financial support.
文摘Controlling molten steel flow in the mold and stabilizing the meniscus are critical challenges during the continuous casting,directly impacting the surface quality and internal quality of the final steel slab product.The effects of electromagnetic swirling flow in nozzle(EMSFN)technology on molten steel flow in the mold during slab continuous casting under various casting speeds were investigated.A real-time adjustable EMSFN was developed,and a three-dimensional unsteady Reynolds-averaged Navier–Stokes turbulence mathematical model was established to simulate the flow field within the mold.The results demonstrate that the EMSFN effectively stabilizes the outflow from nozzle,reduces the impact depth and surface velocity of the molten steel,mitigates meniscus fluctuations,and promotes stable flow within the mold.However,a certain matching relationship exists between the casting speed and the current intensity.For the experimental medium-thick slab specifications,the optimal current intensities were found to be 100,130,and 200 A at casting speeds of 1.0,1.5,and 2.0 m/min,respectively.EMSFN can optimize the mold flow field under different casting speeds,providing theoretical support for improving the quality of continuously cast slab products.
基金Sponsored by Program for New Century Excellent Talents in University of China(NCET-08-0726)Beijing Nova Program of China(2007B027)
文摘Longitudinal cracks are common defects of continuous casting slabs and may lead to serious quality accidents. Image capturing and recognition of hot slabs is an effective way for on-line detection of cracks, and recognition of cracks is essential because the surface of hot slabs is very complicated. In order to detect the surface longitudinal cracks of the slabs, a new feature extraction method based on Curvelet transform and kernel locality preserving projections （KLPP） is proposed. First, sample images are decomposed into three levels by Curvelet transform. Second, Fourier transform is applied to all sub-band images and the Fourier amplitude spectrum of each sub-band is computed to get features with translational invariance. Third, five kinds of statistical features of the Fourier amplitude spectrum are computed and combined in different forms. Then, KLPP is employed for dimensionality reduction of the obtained 62 types of high-dimensional combined features. Finally, a support vector machine （SVM） is used for sample set classification. Experiments with samples from a real production line of continuous casting slabs show that the algorithm is effective to detect longitudinal cracks, and the classification rate is 91.89%.
基金Item Sponsored by National Natural Science Foundation of China (50334010) and Fokying Tung Education Foundation (104017)
文摘The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production （CSP） technique was investigated. Using transmission electron microscopy analysis, it was seen that a majority of manganese sulfides precipitated at austenite grain boundaries, the morphologies of which were spherical or close to the spherical shape and the size of MnS precipitates ranged from 30 nm to 100 nm. A mathematical model of the manganese sulfide precipitation in this process was developed based on classical nucleation theory. Under the given conditions, the starting and finishing precipitation temperatures of MnS in the continuous casting thin slab of the studied low-carbon steel are 1 189 ℃ and 1 171 ℃, respectively, and the average diameter of MnS precipitates is about 48 nm within this precipitation temperature range. The influences of chemical components and thermo-mechanical processing conditions on the precipitation behavior of MnS in the same process were also discussed.
基金Item Sponsored by National Key Fundamental Research Development Project of China(G1998061510)National High Technology Research and Development Project of China(2001AA337040)
文摘According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The magnetic fields and flow fields of melt were simulated with SEMS. It's shown that the electromagnetic forces with inward and sidelong components produced by travel magnetic field at the wide faces of slab make the melt whirling in horizontal section,and the convection of the melt is strengthened obviously there. In addition,magnetic flux density attenuates from the edge to the center of slab,and the profile of the melt velocity along slab thickness in the center of the horizontal section takes a two-opposite-peak configuration. Ultimately,the stirring intensity and features are determined by the electromagnetic parameters,coil arrangement and stirring types.
基金Project(50634030) supported by the National Natural Science Foundation of ChinaProject(20090042120005) supported by the Doctorate Foundation of the Ministry of Education of ChinaProject(2006CB605208-1) supported by the State Basic Research Program of China
文摘Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its change regularity at slab center during continuous casting were obtained.The influence of distribution and change of stress on the propagation of longitudinal cracks on slab surface was discussed.The results show that the tensional stress appears on slab surface at the inner arc side and the compressive stress appears on slab surface at the outer arc side at stages 6-8 in straightening zone during continuous casting.Longitudinal cracks generally appear on slab top surface and do not appear on slab bottom surface,which are also observed in industry.
基金supported financially by the National Science Foundation China(Nos.U1860206 and 51725402)the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-17-001C2 and FRF-TP-19-037A2Z)+1 种基金the High Steel Center(HSC)at Yanshan UniversityBeijing International Center of Advanced and Intelligent Manufacturing of High Quality Steel Materials(ICSM)and the High Quality Steel Consortium(HQSC)at University of Science and Technology Beijing(USTB),China。
文摘In the current study, the transformation in the composition of non-metallic inclusions from the molten steel to the solidified steel was studied and the composition distribution of inclusions on the cross section of a linepine continuous casting slab was predicted. During cooling and solidification of the continuous casting strand, Al_(2)O_(3)-CaO inclusions reacted with the bulk steel and transformed to CaS-Al_(2)O_(3)-MgO-(CaO) ones in the continuous casting slab. The composition of inclusions on the cross section of the slab varied with locations due to the varied cooling rate. A model was established to predict the distribution of the composition of inclusions on the cross section of the continuous casting slab, coupling solidification and heat transfer of the continuous casting slab, the kinetic mass transfer of the dissolved elements in the solid steel, and thermodynamic calculation of inclusion transformation at different temperatures. The composition transformation of inclusions mainly occurred at the temperature between the liquidus and solidus of the linepipe steel. Inclusions were mainly CaS-Al_(2)O_(3)-MgO-(CaO) in slab center and were MgO-Al_(2)O_(3)-CaO-CaS within the subsurface of the slab. In the slab, the transformation fraction of inclusions was less than 10 % at corners while it reached 70 % at 50 mm below the surface of the slab.
基金funded by National Natural Science Foundation of China(51274155)Provincial Natural Science Foundation of Hubei Province of China(2014CFB819)
文摘A grain-oriented silicon steel strip with AlN as main inhibitor was produced by thin slab casting and rolling（TSCR）process.The microstructure,texture and precipitates of the hot-rolled strip were investigated by use of optical microscope（OM）,X-ray diffractometer,transmission electron microscope（TEM）and energy dispersive spectroscope（EDS）.The result shows that the microstructure and texture exhibit a through-thickness gradient similar to that of the hot-rolled strip produced by conventional high-temperature slab-reheating process;the preferred orientation varies from {110}〈001〉in the surface layer to{001}〈110〉in the center layer,and the Goss texture with a maximum intensity mainly concentrates on the surface layer.In addition,some other texture components,for example rotated Goss texture,form in the 1/4thickness layer,which are not observed in the hotrolled strip produced by conventional high-temperature slab-reheating process.The precipitates in the hot-rolled strip are mainly（Mn,Cu）S and AlN compound particles with dimension of 100-200 nm,and the fine precipitates are significantly less than that in the hot-rolled strip produced by conventional high-temperature slab-reheating process.Moreover,the areal density of the fine precipitates in the center layer is more than that in the surface layer.
文摘Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoption of the amount of reduction upon the given final solidification zone through roll gap adjustments. The synchronization of the clamping cylinders for roll gap adjustments should be very important to the application of soft reduction, including the synchronization of the clamping cylinders adjustments in the same and different segments. The synchronization of clamping cylinders adjustments is mainly affected by the adjustable accuracy of the four position-controlled clamping cylinders mounted in the upper frames of the segments according to a predetermined transformation relationship between the signals of displacement sensors and aimed roll gap, which, however, is also influenced by the installation accuracy, the precision of displacement sensors, the deformation of the segment frames and/or its bearing pedestals. Due to the actual asynchronous adjustments of the four clamping cylinders, the dynamic soft reduction operation is normally applied at non-ideal mechanical conditions. Here 7 possible situations of asynchronous adjustments of the local segments which may induce gap deviation have been presented. The roll gap deviation in the soft reduction region of a slab casting has been studied by a 3-D visco-elastic plastic FEM model, through which the additional inter-roll bulging, the related triangular cracks induced by one kind of the possible asynchronous adjustment situation and the effectiveness of soft reduction have been analyzed. A critical tolerance for the gap adjustments has been proposed for better contribution of soft reduction to the internal quality of slabs.
文摘By means of Gleeble-1500 testing machine, the simulation of continuous casting process forAH32 steel was carried out and hot ductility and strength were determined. The cracking sensitivity was studied under the different temperatures and strain rates. The Precipitations of AIN at different temperatures and the fractures of high-temperature tensile samples were observed by using TEM （transmission electron microscope） and SEM （scanning electron microscope）. The factors affecting the brittle temperature zone were discussed.
文摘Two-dimension unsteady heat transfer model was applied to obtain the surfacetemperature and the shell thickness of continuous casting slabs during the process ofsolidification. On the basis of which, the mathematical model of strain at the interface of solidand liquid steel was set up. Through which, the strain in the solidifying shell under normal andabnormal operation conditions was gained. The results indicate that the strain is small under thenormal operation conditions and the internal crack never happens. However, when the variation of theroll gap is above 2 mm, the strain caused by which is greater than that caused by bulging.Furthermore, the total strain exceeds the critical one and the internal crack is the result. So itis of great importance to maintain the fine state of continuous casting machine to avoid theappearance of internal crack.
基金Item Sponsored by National Natural Science Foundation of China(61004135)
文摘The surface temperature of casting slab is an important parameter in the metallurgy field.Because the surface emissivity is uncertain and also unknown,it is difficult to measure the slab surface temperature accurately.A method based on preceded reflector and multi-wavelength was put forward to deal with the difficulty in surface temperature measurement of casting slab.On the premise of preceded reflector and non-preceded reflector,the method establishes the radiation energy equations and works out the emissivity and temperature in the equations.Also,the multilayer modeling of casting slab surface and multiple reflection-absorption process modeling were built by Monte Carlo method.The temperature measuring method had been applied in the continuous casting field.In order to verify the measured result,the thermal imaging method was adopted when the slab surface emissivity was set by repeated tests.Finally,the measured and verified temperature curves keep a same tendency and the error of the values is lower than 5℃.The comparison result shows that the method can measure temperature accurately.
文摘The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the shearing flow near the narrow face of mold, the entrapment caused by vortexes around the submerged entry nozzle （SEN）, and the entrapment caused by the Ar bubbling. Both the velocity of the surface flow and the level fluctuation of the liquids are enlarged with increasing the casting speed, reducing the submersion depth of SEN, decreasing the downward angles of the nozzle outlets, and increasing the Ar flowrate, all of which increase the tendency of mold powder entrapment. Among the four above-mentioned factors, casting speed has the largest effect.
基金Item Sponsored by National Natural Science Foundation of China[No.50674066]
文摘A mercury model has been developed to investigate the influences of Electromagnetic Mold Brake Ruler(EMBr-Ruler) and Flow Control Mold(FC Mold) on metal flow in slab continuous casting mold with the practical casting speed 1.0,1.3 and 2.0 m/min respectively.FC-Mold can efficiently repress the surface flow and its fluctuation.The expanding space of the jets is compressed by EMBr-Ruler and FC-Mold respectively,then the 'flow passage' where the vertical velocity of flow increases sharply is developed near the narrow wall with EMBr-Ruler and FC-Mold.It is bad for the development of the plug like flow.Only the nozzle ports are placed in the braking magnetic field region and the casting speed is suitable,EMBr can be beneficial to the formation of the plug like flow.The flow regime is improved with FC Mold when the casting speed is high(2.0 m/min),but EMBr can improve the flow field with medium casting speed(1.3 m/min),but when the casting speed is low(1.0 m/min),the effects of two types of EMBr are both unsatisfactory.
文摘In the thin slab continuous casting （TSCC） of steel, the issue of optimum fluid flow is very important due to higher casting speeds and has direct influence on the formation of solidified shells and the quality of final products. In the current work, a full-scale physical mod- eling of a thin slab easter on the basis of dimensionless Reynolds and Froude similarity criteria was constructed. The flow pattern in the funnel shaped mold with a new tetra-furcated submerged entry nozzle （SEN） was investigated. To determinate optimum operational parameters, some experiments were carried out under various casting conditions. The results show that the tetra-furcated design of the nozzle leads to a special flow pattern in the mold cavity with three-dimensional recirculating flow. It is also shown that the increase of casting speed and gas injection results in surface turbulence. On the other hand, using a higher depth of SEN decreases the vortex in the free surface of the caster. To avoid surface turbulent and related casting problems, it is recommended to use 30-cm and 40-cm SEN depth at the casting speeds of 3.5 and 4.5 m/min, respectively.
基金Item Sponsored by Program for New Century Excellent Talents in University of Ministry of Education (NCET-04-0285)
文摘The operating conditions during the continuous casting process have a great effect on the microstructure of slab solidification, including primary and secondary dendritic arm spacing. On the basis of the analysis of available work, a revised expression for describing secondary dendritic arm spacing during solidification of slab continuous casting was presented, and the relation between the ratio of primary dendritic arm spacing to secondary dendritic arm spacing and the cooling rate was obtained.
