The nozzle clogging behavior of Ti-bearing IF steel was studied by metallographic analysis,scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）,and X-ray diffraction（XRD）.According to the exper...The nozzle clogging behavior of Ti-bearing IF steel was studied by metallographic analysis,scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）,and X-ray diffraction（XRD）.According to the experimental results,nozzle clogging primarily appears three layers.There are a lot of large-sized iron particles in the inner layer and mainly slag phase in the middle and outer layers.The principal clog constituents of the inner layer are loose alumina cluster inclusions and granular shaped alumina inclusions,containing iron particles. The clog constituents of the middle layer are mainly dendrite alumina inclusions.The primary phases existing in nozzle clogging are FeO·TiO2 and FeO·Al2O3 besidesα-Al2O3 and a-Fe.The FeO·TiO2 phases among the deposits adhere the deposits together firmly enough to lead to the inferior castability of Ti-bearing ultra low carbon steel compared with that of Ti-free low carbon Al-killed steel.展开更多
Non-metallic inclusion distribution in the surface layer of IF steel slabs during unsteady casting was investigated using the original position statistic distribution analysis（OPA）method.It was found that most non-m...Non-metallic inclusion distribution in the surface layer of IF steel slabs during unsteady casting was investigated using the original position statistic distribution analysis（OPA）method.It was found that most non-metallic inclusions larger than 10 μm existed in the subsurface layers of 0.5-3.5 mm from the slab surfaces and very few large non-metallic inclusions were found in the inner regions（≥4.5 mm from slab surfaces）.In addition,it was found that at high casting speed level（1.4 m/min）,even a slight change of casting speed could result in a remarkable increase of the non-metallic inclusions.Thus,at high casting speed,changing the casting speed should be avoided or considerably lower speed changing rate must be used.展开更多
FeO-containing slag originated from the basic oxygen furnace to the ladle is a major reoxidation source during the following secondary refining.Ladle slag reduction treatment(slag treatment)is one of the common counte...FeO-containing slag originated from the basic oxygen furnace to the ladle is a major reoxidation source during the following secondary refining.Ladle slag reduction treatment(slag treatment)is one of the common countermeasures adopted to eliminate the steel contamination by FeO reoxidation.The oxygen transfer phenomenon between molten steel and slag was studied during the industrial production of interstitial-free(IF)steel,the measured and calculated oxygen activities in steel were compared,and the Fe–O equilibrium at the slag–molten steel interface was investigated by thermodynamic analysis.With slag treatment,the oxygen potential is higher in the molten steel than in the pre-deoxidation slag;this causes oxygen transfer from the molten steel to the slag,decreasing the efficiency of slag treatment.Based on this,a two-step slag deoxidation process was optimized.The second step further reduced the FeO content.On the other hand,the CaO/Al2O3(C/A)ratio in the refining slag must be controlled,because it affects the FeO activity and inclusion absorption capacity of the slag.The results suggest that the C/A ratio of 1.2–1.5 and the FeO content of\6%are beneficial to refine IF steel.展开更多
The excellent deep drawability of interstitial free steel （IF steel） is closely related to its texture formed during recrystallization. The nucleation process of cold rolled IF steel at the early stage of recrystall...The excellent deep drawability of interstitial free steel （IF steel） is closely related to its texture formed during recrystallization. The nucleation process of cold rolled IF steel at the early stage of recrystallization was inves-tigated by electron back scattered diffraction （EBSD）. The characteristics of the microstructure after deformation and the orientation of nucleation were observed. The results show that the deformed microstructure with 80% reduction could be subdivided into two groups. These two types of microstructure were characterized by their orientation and internal local misorientations. The nuclei with γ-orientation preferred to form in deformed bands with γ-orientation and at the boundaries between deformed grains with different orientations. The recrystallized grains with { 111 } 〈 110〉 orientation appeared firstly in deformed matrix with {111} 〈112〉 orientation and consumed the matrix with {111 } 〈112〉 to grow up, while the recrystallized grains with {111} 〈112〉 orientation were observed secondly in de-formed matrix with { 111 }〈110〉 orientation and consumed matrix with { 111} 〈110〉 to grow up.展开更多
Single cold rolling and double cold rolling were applied to hot rolled strips with different reduction ratios. The evolutions of { 100}, { 111} and Goss face texture during double rolling were investigated by comparin...Single cold rolling and double cold rolling were applied to hot rolled strips with different reduction ratios. The evolutions of { 100}, { 111} and Goss face texture during double rolling were investigated by comparing the orientation distribution function （ODF） of the double rolled sample with that of the single rolled one. The double cold rolling texture is characterized by a higher γ-texture and a lower α-texture, and the { 111}〈112〉 component is improved remarkably. Based on the TEM observation and mechanical properties test, it is found that the reduction ratio assignment significantly affects the texture variation, as-annealing microstructures, and properties of the double cold rolled samples. These results may provide a theoretical guide for the industrial production of double cold rolled IF steel.展开更多
The recrystallization and oxidation of a Mn-containing interstitial free(IF)steel were investigated simultaneously using confocal scanning laser microscope(CSLM)under controlled atmosphere of Ar 95%and H25%(in volume ...The recrystallization and oxidation of a Mn-containing interstitial free(IF)steel were investigated simultaneously using confocal scanning laser microscope(CSLM)under controlled atmosphere of Ar 95%and H25%(in volume percent)at different temperatures.It was found that the grain boundary played a significant role in controlling recrystallization and oxidation in overall oxidation kinetics of the steel.The surface morphology was composed of two networks along the original and new grain boundaries respectively,which did not coexist.The grain boundary moved in different directions with different velocities during annealing process.The recrystallization processes were studied by CSLM motion video through observing the moving grain boundary to estimate the time for 50%recrystallization,and the activation energy for recrystallization was therefore calculated.The oxidation mechanism was discussed through comparison of the fluxes among mass transfer of water vapor,dissociation of water vapor and outward diffusion alloying elements.The results indicated that the oxidation was controlled by the mass transfer from the bulk gas to the surface,or dissociation rate,or outward diffusion of manganese,which depended on the temperature to form a grain boundary ridge or groove.展开更多
The effects of oxidizing slag on oxygen mass transfer and inclusions in different stages of IF(interstitial-free)steel refining were investigated by several heat simulation experiments.The results of the experiments s...The effects of oxidizing slag on oxygen mass transfer and inclusions in different stages of IF(interstitial-free)steel refining were investigated by several heat simulation experiments.The results of the experiments showed that the oxidizability of slag changed considerably during different refining stages.Keeping the content of FeO in the slag within 1 wt.%would narrow the difference of slag oxidizability,stabilize the content of[Al]s in the steel,avoid secondary oxidation of molten steel by the slag,and reduce the inclusions.When the mass transfer of FeO in the slag phase was a limiting step,the secondary oxidation reaction occurred at the steel–slag interface;when the diffusion of oxygen in the molten steel was a limiting step,the secondary oxidation reaction took place inside the molten steel.The oxygen transfer rate was affected by the mass transfer coefficient of oxygen.For every 0.0001m/s increase in mass transfer coefficient,the oxygen transfer rate increased by about 2.2×10^-6 min^-1.By changing the mass transfer coefficient,the oxygen transfer rate of the slag to the molten steel can be controlled.展开更多
Surface tension of molten IF steel containing Ti and contact angle between the liquid steel and solid alumina were measured with sessile droplet method under Ar gas atmosphere at 1500, 1575 and 1600°C. The result...Surface tension of molten IF steel containing Ti and contact angle between the liquid steel and solid alumina were measured with sessile droplet method under Ar gas atmosphere at 1500, 1575 and 1600°C. The results show that titanium decreases the surface tension of the molten IF steel and the contact angle. The interfacial tension between the molten IF steel containing Ti and solid alumina decreases with increase in titanium content. The work of adhesion between molten IF steel containing Ti and solid alumina decreases slightly at 1550°C, but increases at 1600°C with increasing titanium content. It can be deduced that fine bubbles and fine alumina inclusions are easily entrapped in solidifying interface for IF steel containing Ti.展开更多
High strength IF steel sheets with sufficient formability had been extensively used in automotive industry.In this paper,a new type of high strength cold-rolled IF steel with higher carbon and niobium contents was stu...High strength IF steel sheets with sufficient formability had been extensively used in automotive industry.In this paper,a new type of high strength cold-rolled IF steel with higher carbon and niobium contents was studied.Thermal plastic and continuous annealing were performed on thermo-mechanical simulator.The transformation points were tested by thermal expansion apparatus.Optical microscopy and transmission election microscope(TEM)were used to analyze the microstructure and the secondary precipitates of the steel.The results showed,the ductibility temperature range was from 950℃to 1250℃and the transformation points were 887℃and 913℃respectively.The grain size of this steel was smaller than that of conventional high strength IF steel.At the mean time,there were many fine Nb(C,N)precipitates distributed in the intra-granular regions and the PFZ(precipitate free zone)were formed in the neighborhood of grain boundaries.Due to the unique micro-structural feature,the yield strength and the yield ratio of the steel were decreased while the tensile strength was increased.With the increasing of the annealing temperature,the strength decreased,the total elongation A50,r-value at 15%strain and n-value were all increased.In order to obtain the favorable mechanical properties,the skin-pass rolling rate should be chosen at 0.6-0.8%.展开更多
The influence of chemical composition and annealing parameters on the behavior of FeTiP precipitation has been investigated. With increasing Ti content the yield strength and tensile strength were reduced, and the ten...The influence of chemical composition and annealing parameters on the behavior of FeTiP precipitation has been investigated. With increasing Ti content the yield strength and tensile strength were reduced, and the tendency of FeTiP precipitation became more remarkable. No FeTiP precipitate was observed and the best mechanical properties have been obtained in the steel sheet, of which the atom ratio of Ti to N is approximately equal to 1. In the temperature range of 700 to 800℃ the FeTiP precipitation could appear easily. The precipitation process was suppressed when the annealing temperature was below 600℃, and the FeTiP phase was dissolved above 900℃. The FeTiP precipitates would inhibit the migration of grain boundaries during the recrystallization in certain extent, and weaken the density of {111} fiber texture, which resulted in the reduction of r value. The relationship between composition and processing parameters, as well as their influence on the mechanical properties is discussed.展开更多
The effects of minor alloying elements（antimony,boron） on the recrystallization and oxidation of Mn-containing interstitial free（IF） steels were investigated using confocal scanning laser microscope（CSLM） under ...The effects of minor alloying elements（antimony,boron） on the recrystallization and oxidation of Mn-containing interstitial free（IF） steels were investigated using confocal scanning laser microscope（CSLM） under controlled atmosphere of 95% Ar and 5% H2（volume percent） at different temperatures.The results indicated that oxidation and recrystallization were primarily controlled by the grain boundaries,which moved due to release of the stored energy or acted as the fast path diffusion of alloying elements.It was found that the addition of antimony suppressed both surface oxidation and internal oxidation,whereas boron addition accelerated surface oxidation but decreased internal oxidation.The reasons caused were that the alloying elements of antimony or boron were known to segregate on the surfaces or grain boundaries to occupy the surface adsorption sites,which were expected to be less catalytic than bare iron on the transportation of alloying elements.The recrystallization was also retarded through adding minor antimony and boron elements.The oxidation kinetics of formation of grain boundary oxides were studied through calculating the areas along grain boundaries,and it was found that the areas parabolically increased with increasing time.展开更多
In this paper,low-and high-strength lath martensite(350 and 640 HV)was fabricated in an IF steel via high pressure martensitic transformation.The microstructure and the softening during their tempering from 200°C...In this paper,low-and high-strength lath martensite(350 and 640 HV)was fabricated in an IF steel via high pressure martensitic transformation.The microstructure and the softening during their tempering from 200°C to 800°C for 1 h were systematically investigated.A carbon-irrelevant tempering process was proposed,exhibiting a three-stage structural evolution pattern depending upon the tempering de-gree(1-(HV-HV FP)/(HV NP-HV FP),where the HV is the instant hardness,HV NP is the non-tempered hard-ness and HV FP is the fully tempered hardness):(1)low tempered(<10%),removing the loose dislocations and dislocation boundaries within martensitic variants;(2)medium tempered(10%-50%),eliminating the martensitic variant laths via the migration of their terminal tips;(3)highly tempered(>50%),clearing up the remained variant laths via the migration of the triple junctions.Martensite-type microstructure is tailored by low-index lamellar variant boundaries and is thus intrinsically thermally stable,whereas the mobile terminal tips decrease the tempering resistance.The underlying mechanism for such carbon-irrelevant process was discussed and the potential effect on the tempering behavior of carbon-contained martensite was highlighted.展开更多
The mechanism responsible for the formation of recrystallization texture in cold-rolled Ti bearing interstitial free （IF） steel sheets was investigated using electron back-scatter diffraction （EBSD）. In addition, ...The mechanism responsible for the formation of recrystallization texture in cold-rolled Ti bearing interstitial free （IF） steel sheets was investigated using electron back-scatter diffraction （EBSD）. In addition, the origin of nuclei with specific orientations was studied. The formation of recrystallization texture was explained by oriented nucleation. Most nuclei have a high misorientation angle of 25-55° with the surrounding deformed matrices, but no specific orientation of misorientation axis between the nucleus and the surrounding deformed matrix is observed. The stored energy of deformed grains is in the decreasing order of the {111}〈112〉,{111}〈110〉, {112}〈110〉 and {001}〈110〉 orientations. New {111}〈110〉 grains are nucleated within deformed {111}〈112〉 grains and new {111}〈112〉 grains originate in the deformed {111}〈110〉 grains.展开更多
The Nb-Ti microalloyed high strength IF steel sheet was used to study the effect of annealing temperature on the microstructures,mechanical properties and textures.The experimental results show that experimental steel...The Nb-Ti microalloyed high strength IF steel sheet was used to study the effect of annealing temperature on the microstructures,mechanical properties and textures.The experimental results show that experimental steel is incomplete recrystallization at 750℃annealing,but complete recrystallization from 780℃to 870℃under experimental conditions.When the annealing temperature was increased,the yield strength and tensile strength would gradually reduce,the plastic strain ratio and yield point elongation would gradually increase.The yield strength,tensile strength,elongation,the plastic strain ratio and the strain hardening exponent were approximate 300MPa,410MPa,36.5%,1.7 and 0.22 respectively under annealing temperature 810℃to 840℃.When the annealing temperature was increased,theα-textures andγ-textures were gradually weakened,and theα-textures have a trend to{111}texture.Therefore,the suggestion of the optimal recrystallization annealing temperature is about 810℃to 840℃in industrial production.展开更多
The variational regulation of inclusions and total oxygen in the IF Molten Steel during the RH refining process after deoxidization was studied.The results show that the relationship between total oxygen content and t...The variational regulation of inclusions and total oxygen in the IF Molten Steel during the RH refining process after deoxidization was studied.The results show that the relationship between total oxygen content and time is in accord with the following equation,T.O=271.25e-1.53t+23.49,R2=0.9966.The inclusion analysis investigation during RH pure circulation process indicates that the main inclusion of the IF molten steel after 2 minutes from the beginning of deoxidization is cluster inclusions of pure Al2O3 system.After 6 minutes from the aluminum deoxidization,the quantity of inclusion decreases and the inclusion style changes into block inclusions of Al2O3 system with the size of 5μm.In the other hand,some inclusions are of Al2O3-MgO.Complex inclusions of Al2O3-TiOx with the size of below 5μm,and the single particle or cluster complex inclusions with the typical square shape of Al2O3-TiN system are found after 3 minutes from titanium-ferrous alloy added.Then,the content of titanium of complex inclusions of Al2O3-TiOx decreases and the aluminum content rises along with the RH pure circulation time process.That means the inclusions of Al2O3-TiOx is not steady,and it trends to transfer into Al2O3.展开更多
This paper presents a review on roles of refractories playing in IF steel technology, problems and countermeasures in refractory applications and developments of refractories in ladle lining, concasting, tundish and m...This paper presents a review on roles of refractories playing in IF steel technology, problems and countermeasures in refractory applications and developments of refractories in ladle lining, concasting, tundish and mold metallurgy. Greater attention has been paid to the carbon and oxygen pick up and inclusion defects caused by re- fractories that are concerned most in IF steel technology.展开更多
The effect of revolution on inhomogeneous plastic deformation of HPT processed IF steel was investigated using experimental and simulation approaches. The results indicate that the degree of inhomogeneous plastic defo...The effect of revolution on inhomogeneous plastic deformation of HPT processed IF steel was investigated using experimental and simulation approaches. The results indicate that the degree of inhomogeneous plastic deformation increases as the revolutions increase along the radial direction on the transversal plane of disks. In addition, the hardness and the microstructure distributions verify the trend that the effective strain of the HPT processed disks at the early torsion stage is gradually deformed from the edge to the center with the revolutions increases.展开更多
Based on the current process and equipment conditions of No.3 steelmaking and continuous rolling plant,which consists of desulphurization and slag skimming of hot metal,260t combined blown BOF,rimmed steel tapping wit...Based on the current process and equipment conditions of No.3 steelmaking and continuous rolling plant,which consists of desulphurization and slag skimming of hot metal,260t combined blown BOF,rimmed steel tapping with slag stopping process,RH-TB vacuum treatment process and medium thin slab continuous casting,the methods for improving cleanliness of IF steel in BOF smelting,RH vacuum treatment and continuous casting were investigated.According to results of theoretical analysis and experiments,a series of quality controlling schemes were proposed for improving cleanliness of IF steel via controlling chemical composition,T[O]content,tapping temperature,shrouded casting and controlling stability of continuous casting.展开更多
The texture evolution from rolling process to annealing process of 440 MPa grade Nb-bearing high strength IF steel （IF-HSS） was studied. Moreover, the texture of different section in thickness direction of steel she...The texture evolution from rolling process to annealing process of 440 MPa grade Nb-bearing high strength IF steel （IF-HSS） was studied. Moreover, the texture of different section in thickness direction of steel sheet after annealing was investigated. Macro-texture measurements using XRD shows that hot rolling texture in Nb-bearing IF-HSS includes a weak γ-fiber and α-fiber, of which main texture components are {001}〈110〉,{111}〈110〉 and {111}〈112〉. It is worthy of note that the γ-fiber skeleton line formed after hot rolling. During cold rolling, the absolute maximum shifts to {111}〈112〉 along the γ-fiber and the maximum along the α-fiber shifts to {112} 〈110〉. During recrystallization annealing process, the weaker α-fiber and stronger γ-fiber cold rolling texture transformed to a very strong γ-fiber annealing texture. After annealing the main components from surface to mid-section along thickness display the same character for both α-fiber and γ-fiber, while textures intensity at 1/4 section is higher than that of surface and mid-section.展开更多
In order to analyze the effect of electromagnetic stirring on the slab＇ s surface purity, the continuously cast slab surface inclusions and subsurface blisters have been investigated. The results indicate that the mo...In order to analyze the effect of electromagnetic stirring on the slab＇ s surface purity, the continuously cast slab surface inclusions and subsurface blisters have been investigated. The results indicate that the mold electromagnetic stirrer （M -EMS） is useful for the improvement of IF steel slabs＇ surface quality. The continuously cast slab surface inclusions and subsurface blisters have been significantly reduced. The distribution of bubbles in the slab is non-homogeneous in terms of both width and depth. The continuously cast slab surface inclusions tend to miniaturization through M-EMS and most of the inclusions are less than 10 μm in size.展开更多
基金supported by the National Key Technologies R&D Program of China(No.2006BAE03A06)
文摘The nozzle clogging behavior of Ti-bearing IF steel was studied by metallographic analysis,scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）,and X-ray diffraction（XRD）.According to the experimental results,nozzle clogging primarily appears three layers.There are a lot of large-sized iron particles in the inner layer and mainly slag phase in the middle and outer layers.The principal clog constituents of the inner layer are loose alumina cluster inclusions and granular shaped alumina inclusions,containing iron particles. The clog constituents of the middle layer are mainly dendrite alumina inclusions.The primary phases existing in nozzle clogging are FeO·TiO2 and FeO·Al2O3 besidesα-Al2O3 and a-Fe.The FeO·TiO2 phases among the deposits adhere the deposits together firmly enough to lead to the inferior castability of Ti-bearing ultra low carbon steel compared with that of Ti-free low carbon Al-killed steel.
文摘Non-metallic inclusion distribution in the surface layer of IF steel slabs during unsteady casting was investigated using the original position statistic distribution analysis（OPA）method.It was found that most non-metallic inclusions larger than 10 μm existed in the subsurface layers of 0.5-3.5 mm from the slab surfaces and very few large non-metallic inclusions were found in the inner regions（≥4.5 mm from slab surfaces）.In addition,it was found that at high casting speed level（1.4 m/min）,even a slight change of casting speed could result in a remarkable increase of the non-metallic inclusions.Thus,at high casting speed,changing the casting speed should be avoided or considerably lower speed changing rate must be used.
基金The authors are grateful for financial support from the National Natural Science Foundation of China under Grant No.51404020the National Key R&D Program of China under Grant Nos.2017YFB0304000 and 2017YFB0304001.
文摘FeO-containing slag originated from the basic oxygen furnace to the ladle is a major reoxidation source during the following secondary refining.Ladle slag reduction treatment(slag treatment)is one of the common countermeasures adopted to eliminate the steel contamination by FeO reoxidation.The oxygen transfer phenomenon between molten steel and slag was studied during the industrial production of interstitial-free(IF)steel,the measured and calculated oxygen activities in steel were compared,and the Fe–O equilibrium at the slag–molten steel interface was investigated by thermodynamic analysis.With slag treatment,the oxygen potential is higher in the molten steel than in the pre-deoxidation slag;this causes oxygen transfer from the molten steel to the slag,decreasing the efficiency of slag treatment.Based on this,a two-step slag deoxidation process was optimized.The second step further reduced the FeO content.On the other hand,the CaO/Al2O3(C/A)ratio in the refining slag must be controlled,because it affects the FeO activity and inclusion absorption capacity of the slag.The results suggest that the C/A ratio of 1.2–1.5 and the FeO content of\6%are beneficial to refine IF steel.
基金Sponsored by National Key Technology Research and Development Program of China(2011BAE13B03)National Natural Science Foundation of China(50231030)Scientific and Technological Project in Liaoning Province of China(2011220020)
文摘The excellent deep drawability of interstitial free steel （IF steel） is closely related to its texture formed during recrystallization. The nucleation process of cold rolled IF steel at the early stage of recrystallization was inves-tigated by electron back scattered diffraction （EBSD）. The characteristics of the microstructure after deformation and the orientation of nucleation were observed. The results show that the deformed microstructure with 80% reduction could be subdivided into two groups. These two types of microstructure were characterized by their orientation and internal local misorientations. The nuclei with γ-orientation preferred to form in deformed bands with γ-orientation and at the boundaries between deformed grains with different orientations. The recrystallized grains with { 111 } 〈 110〉 orientation appeared firstly in deformed matrix with {111} 〈112〉 orientation and consumed the matrix with {111 } 〈112〉 to grow up, while the recrystallized grains with {111} 〈112〉 orientation were observed secondly in de-formed matrix with { 111 }〈110〉 orientation and consumed matrix with { 111} 〈110〉 to grow up.
文摘Single cold rolling and double cold rolling were applied to hot rolled strips with different reduction ratios. The evolutions of { 100}, { 111} and Goss face texture during double rolling were investigated by comparing the orientation distribution function （ODF） of the double rolled sample with that of the single rolled one. The double cold rolling texture is characterized by a higher γ-texture and a lower α-texture, and the { 111}〈112〉 component is improved remarkably. Based on the TEM observation and mechanical properties test, it is found that the reduction ratio assignment significantly affects the texture variation, as-annealing microstructures, and properties of the double cold rolled samples. These results may provide a theoretical guide for the industrial production of double cold rolled IF steel.
基金Item Sponsored by National Natural Science Foundation of China(50902003)National Key Technology Research and Development Program in 11th Five-Year Plan of China(2009BAC64B05)
文摘The recrystallization and oxidation of a Mn-containing interstitial free(IF)steel were investigated simultaneously using confocal scanning laser microscope(CSLM)under controlled atmosphere of Ar 95%and H25%(in volume percent)at different temperatures.It was found that the grain boundary played a significant role in controlling recrystallization and oxidation in overall oxidation kinetics of the steel.The surface morphology was composed of two networks along the original and new grain boundaries respectively,which did not coexist.The grain boundary moved in different directions with different velocities during annealing process.The recrystallization processes were studied by CSLM motion video through observing the moving grain boundary to estimate the time for 50%recrystallization,and the activation energy for recrystallization was therefore calculated.The oxidation mechanism was discussed through comparison of the fluxes among mass transfer of water vapor,dissociation of water vapor and outward diffusion alloying elements.The results indicated that the oxidation was controlled by the mass transfer from the bulk gas to the surface,or dissociation rate,or outward diffusion of manganese,which depended on the temperature to form a grain boundary ridge or groove.
基金The authors would like to express their appreciation to the National Natural Science Foundation of China(No.51471002).
文摘The effects of oxidizing slag on oxygen mass transfer and inclusions in different stages of IF(interstitial-free)steel refining were investigated by several heat simulation experiments.The results of the experiments showed that the oxidizability of slag changed considerably during different refining stages.Keeping the content of FeO in the slag within 1 wt.%would narrow the difference of slag oxidizability,stabilize the content of[Al]s in the steel,avoid secondary oxidation of molten steel by the slag,and reduce the inclusions.When the mass transfer of FeO in the slag phase was a limiting step,the secondary oxidation reaction occurred at the steel–slag interface;when the diffusion of oxygen in the molten steel was a limiting step,the secondary oxidation reaction took place inside the molten steel.The oxygen transfer rate was affected by the mass transfer coefficient of oxygen.For every 0.0001m/s increase in mass transfer coefficient,the oxygen transfer rate increased by about 2.2×10^-6 min^-1.By changing the mass transfer coefficient,the oxygen transfer rate of the slag to the molten steel can be controlled.
文摘Surface tension of molten IF steel containing Ti and contact angle between the liquid steel and solid alumina were measured with sessile droplet method under Ar gas atmosphere at 1500, 1575 and 1600°C. The results show that titanium decreases the surface tension of the molten IF steel and the contact angle. The interfacial tension between the molten IF steel containing Ti and solid alumina decreases with increase in titanium content. The work of adhesion between molten IF steel containing Ti and solid alumina decreases slightly at 1550°C, but increases at 1600°C with increasing titanium content. It can be deduced that fine bubbles and fine alumina inclusions are easily entrapped in solidifying interface for IF steel containing Ti.
文摘High strength IF steel sheets with sufficient formability had been extensively used in automotive industry.In this paper,a new type of high strength cold-rolled IF steel with higher carbon and niobium contents was studied.Thermal plastic and continuous annealing were performed on thermo-mechanical simulator.The transformation points were tested by thermal expansion apparatus.Optical microscopy and transmission election microscope(TEM)were used to analyze the microstructure and the secondary precipitates of the steel.The results showed,the ductibility temperature range was from 950℃to 1250℃and the transformation points were 887℃and 913℃respectively.The grain size of this steel was smaller than that of conventional high strength IF steel.At the mean time,there were many fine Nb(C,N)precipitates distributed in the intra-granular regions and the PFZ(precipitate free zone)were formed in the neighborhood of grain boundaries.Due to the unique micro-structural feature,the yield strength and the yield ratio of the steel were decreased while the tensile strength was increased.With the increasing of the annealing temperature,the strength decreased,the total elongation A50,r-value at 15%strain and n-value were all increased.In order to obtain the favorable mechanical properties,the skin-pass rolling rate should be chosen at 0.6-0.8%.
文摘The influence of chemical composition and annealing parameters on the behavior of FeTiP precipitation has been investigated. With increasing Ti content the yield strength and tensile strength were reduced, and the tendency of FeTiP precipitation became more remarkable. No FeTiP precipitate was observed and the best mechanical properties have been obtained in the steel sheet, of which the atom ratio of Ti to N is approximately equal to 1. In the temperature range of 700 to 800℃ the FeTiP precipitation could appear easily. The precipitation process was suppressed when the annealing temperature was below 600℃, and the FeTiP phase was dissolved above 900℃. The FeTiP precipitates would inhibit the migration of grain boundaries during the recrystallization in certain extent, and weaken the density of {111} fiber texture, which resulted in the reduction of r value. The relationship between composition and processing parameters, as well as their influence on the mechanical properties is discussed.
基金Item Sponsored by National Natural Science Foundation of China(50902003,51172003)National Key Technology Research and Development Program in 12th Five-Year Plan of China(2010BAE00316,2011BAB02B05)
文摘The effects of minor alloying elements（antimony,boron） on the recrystallization and oxidation of Mn-containing interstitial free（IF） steels were investigated using confocal scanning laser microscope（CSLM） under controlled atmosphere of 95% Ar and 5% H2（volume percent） at different temperatures.The results indicated that oxidation and recrystallization were primarily controlled by the grain boundaries,which moved due to release of the stored energy or acted as the fast path diffusion of alloying elements.It was found that the addition of antimony suppressed both surface oxidation and internal oxidation,whereas boron addition accelerated surface oxidation but decreased internal oxidation.The reasons caused were that the alloying elements of antimony or boron were known to segregate on the surfaces or grain boundaries to occupy the surface adsorption sites,which were expected to be less catalytic than bare iron on the transportation of alloying elements.The recrystallization was also retarded through adding minor antimony and boron elements.The oxidation kinetics of formation of grain boundary oxides were studied through calculating the areas along grain boundaries,and it was found that the areas parabolically increased with increasing time.
基金the Natural Science Foundation-Steel and Iron Foundation of Hebei Province(No.E2021203051)the Hundred Outstanding Creative Talents Projects in Universities of Hebei Province,China,and the Project Program of Heavy Machinery Collaborative Innovation Center,China.
文摘In this paper,low-and high-strength lath martensite(350 and 640 HV)was fabricated in an IF steel via high pressure martensitic transformation.The microstructure and the softening during their tempering from 200°C to 800°C for 1 h were systematically investigated.A carbon-irrelevant tempering process was proposed,exhibiting a three-stage structural evolution pattern depending upon the tempering de-gree(1-(HV-HV FP)/(HV NP-HV FP),where the HV is the instant hardness,HV NP is the non-tempered hard-ness and HV FP is the fully tempered hardness):(1)low tempered(<10%),removing the loose dislocations and dislocation boundaries within martensitic variants;(2)medium tempered(10%-50%),eliminating the martensitic variant laths via the migration of their terminal tips;(3)highly tempered(>50%),clearing up the remained variant laths via the migration of the triple junctions.Martensite-type microstructure is tailored by low-index lamellar variant boundaries and is thus intrinsically thermally stable,whereas the mobile terminal tips decrease the tempering resistance.The underlying mechanism for such carbon-irrelevant process was discussed and the potential effect on the tempering behavior of carbon-contained martensite was highlighted.
基金This work was supported by the National Natural Science Foundation of China under grant No. 50171040.
文摘The mechanism responsible for the formation of recrystallization texture in cold-rolled Ti bearing interstitial free （IF） steel sheets was investigated using electron back-scatter diffraction （EBSD）. In addition, the origin of nuclei with specific orientations was studied. The formation of recrystallization texture was explained by oriented nucleation. Most nuclei have a high misorientation angle of 25-55° with the surrounding deformed matrices, but no specific orientation of misorientation axis between the nucleus and the surrounding deformed matrix is observed. The stored energy of deformed grains is in the decreasing order of the {111}〈112〉,{111}〈110〉, {112}〈110〉 and {001}〈110〉 orientations. New {111}〈110〉 grains are nucleated within deformed {111}〈112〉 grains and new {111}〈112〉 grains originate in the deformed {111}〈110〉 grains.
文摘The Nb-Ti microalloyed high strength IF steel sheet was used to study the effect of annealing temperature on the microstructures,mechanical properties and textures.The experimental results show that experimental steel is incomplete recrystallization at 750℃annealing,but complete recrystallization from 780℃to 870℃under experimental conditions.When the annealing temperature was increased,the yield strength and tensile strength would gradually reduce,the plastic strain ratio and yield point elongation would gradually increase.The yield strength,tensile strength,elongation,the plastic strain ratio and the strain hardening exponent were approximate 300MPa,410MPa,36.5%,1.7 and 0.22 respectively under annealing temperature 810℃to 840℃.When the annealing temperature was increased,theα-textures andγ-textures were gradually weakened,and theα-textures have a trend to{111}texture.Therefore,the suggestion of the optimal recrystallization annealing temperature is about 810℃to 840℃in industrial production.
文摘The variational regulation of inclusions and total oxygen in the IF Molten Steel during the RH refining process after deoxidization was studied.The results show that the relationship between total oxygen content and time is in accord with the following equation,T.O=271.25e-1.53t+23.49,R2=0.9966.The inclusion analysis investigation during RH pure circulation process indicates that the main inclusion of the IF molten steel after 2 minutes from the beginning of deoxidization is cluster inclusions of pure Al2O3 system.After 6 minutes from the aluminum deoxidization,the quantity of inclusion decreases and the inclusion style changes into block inclusions of Al2O3 system with the size of 5μm.In the other hand,some inclusions are of Al2O3-MgO.Complex inclusions of Al2O3-TiOx with the size of below 5μm,and the single particle or cluster complex inclusions with the typical square shape of Al2O3-TiN system are found after 3 minutes from titanium-ferrous alloy added.Then,the content of titanium of complex inclusions of Al2O3-TiOx decreases and the aluminum content rises along with the RH pure circulation time process.That means the inclusions of Al2O3-TiOx is not steady,and it trends to transfer into Al2O3.
文摘This paper presents a review on roles of refractories playing in IF steel technology, problems and countermeasures in refractory applications and developments of refractories in ladle lining, concasting, tundish and mold metallurgy. Greater attention has been paid to the carbon and oxygen pick up and inclusion defects caused by re- fractories that are concerned most in IF steel technology.
文摘The effect of revolution on inhomogeneous plastic deformation of HPT processed IF steel was investigated using experimental and simulation approaches. The results indicate that the degree of inhomogeneous plastic deformation increases as the revolutions increase along the radial direction on the transversal plane of disks. In addition, the hardness and the microstructure distributions verify the trend that the effective strain of the HPT processed disks at the early torsion stage is gradually deformed from the edge to the center with the revolutions increases.
文摘Based on the current process and equipment conditions of No.3 steelmaking and continuous rolling plant,which consists of desulphurization and slag skimming of hot metal,260t combined blown BOF,rimmed steel tapping with slag stopping process,RH-TB vacuum treatment process and medium thin slab continuous casting,the methods for improving cleanliness of IF steel in BOF smelting,RH vacuum treatment and continuous casting were investigated.According to results of theoretical analysis and experiments,a series of quality controlling schemes were proposed for improving cleanliness of IF steel via controlling chemical composition,T[O]content,tapping temperature,shrouded casting and controlling stability of continuous casting.
基金Funded by the Major Project of Science and Technology,Beijing Municipal Commission of Science and Technology (Nos. D07010300700000 and D07010300700701)
文摘The texture evolution from rolling process to annealing process of 440 MPa grade Nb-bearing high strength IF steel （IF-HSS） was studied. Moreover, the texture of different section in thickness direction of steel sheet after annealing was investigated. Macro-texture measurements using XRD shows that hot rolling texture in Nb-bearing IF-HSS includes a weak γ-fiber and α-fiber, of which main texture components are {001}〈110〉,{111}〈110〉 and {111}〈112〉. It is worthy of note that the γ-fiber skeleton line formed after hot rolling. During cold rolling, the absolute maximum shifts to {111}〈112〉 along the γ-fiber and the maximum along the α-fiber shifts to {112} 〈110〉. During recrystallization annealing process, the weaker α-fiber and stronger γ-fiber cold rolling texture transformed to a very strong γ-fiber annealing texture. After annealing the main components from surface to mid-section along thickness display the same character for both α-fiber and γ-fiber, while textures intensity at 1/4 section is higher than that of surface and mid-section.
文摘In order to analyze the effect of electromagnetic stirring on the slab＇ s surface purity, the continuously cast slab surface inclusions and subsurface blisters have been investigated. The results indicate that the mold electromagnetic stirrer （M -EMS） is useful for the improvement of IF steel slabs＇ surface quality. The continuously cast slab surface inclusions and subsurface blisters have been significantly reduced. The distribution of bubbles in the slab is non-homogeneous in terms of both width and depth. The continuously cast slab surface inclusions tend to miniaturization through M-EMS and most of the inclusions are less than 10 μm in size.
