Abstract: The blowing hole location and the gas flow in a 150 t elliptic ladle were optimized by establishing a 1:4 water model.Based on the similarity criterion,high pressure nitrogen was used to simulate argon in the water modelling experiment. Experimental results show that the mixing of liquid steel is weak in the original ladle because the two blowing holes are close to each other. A critical gas flow exists at different locations. Beyond the critical value,the increase in kinetic energy mainly is used to stir liquid steel and blow the slag surface. After optimization,the two blowing holes distribute in 180° and are arranged at the 0.6 radius of the major axis respectively. The mixing time of liquid steel shortens and the exposed area of liquid steel reduces greatly compared with the original ladle with the same gas flow. Moreover,the total oxygen decreases to 47×10-6 from 58×10-6 during calcium treatment,and the average nitrogen pick-up amount is less than 3×10-6 during the soft stirring process.
Abstract: The solubility of nitrogen and the influence of the content of vanadium and niobium alloy on the solubility of nitrogen in HRB400 were studied by thermodynamic calculation. The results show that the addition of vanadium and niobium can increase the solubility of nitrogen without monotone relationship,and as the current content of alloy element in steel(V0.02%、Nb0.03%),niobium is more effective to improve the solubility of nitrogen.
Abstract: An industrial experiment was carried out to study the evolution of billet surface porosity in hot rolling of round steel.Holes were drilled at the head of a billet. Linear cracks were spot at the surface of rolled round steel in parallel. Slight decarburization appears around these cracks,which can be seen from the metallograph. Crack measurement results show that the crack depth is mainly influenced by the hole depth. When the hole depth exceeds 4 mm,serious cracks will be generated on the round steel. The crack length is mainly dependent on the hole diameter. When the hole diameter ranges from 1 to 2.5 mm,the crack length limits to 2 to 8 cm.
Abstract: In the converter steelmaking process,oxygen lance position is adjusted to realize slagging,decarburization,heating and stirring. The effect of oxygen lance position on molten pool flow was studied when blowing by a four-hole supersonic oxygen lance in a 100 t converter. It is found that low lance position has significant benefit to increase the impact depth and the flow velocity of molten steel at the surface,but high lance position is in favor of enlarging the jet flow impact area,improving the uniform velocity distribution of molten steel in the radial direction and increasing the flow velocity of molten steel at the furnace bottom. When the lance position increases from 1.2 m to 1.8 m,the impact cavity of the slag layer enlarges from 2.119 m to 2.645 m and the impact depth of jet flow decreases obviously.
Abstract: The heat-insulating properties of heat insulating coatings were studied by adding different coating binders and changing micro bead size,temperature and coating thickness. It is found that the optimal adiabatic effect is obtained when the thickness of E800 binder based coatings is 0.42 mm. PA80 high-temperature gel is not suitable to be used in heat insulation coatings for its strong corrosive effect. Experimental results show that the coatings in the best adiabatic effect are based on soluble glass dissolved with 0.5% carboxymethyl cellulose. The smaller the micro bead size is,the better the heat-insulating properties of the coatings with the same thickness and binder are. The coating with the components of 5000 mesh micro beads and soluble glass based 0.5% carboxymethyl cellulose was chosen to paint on the steel ladle in-wall. The temperature drop per minute of the steel ladle with a 0.8 mm coating is 0.41℃ less than that without the coating. It is indicated that this coating is suitable to be implemented.
Abstract: In order to improve the leaching and carbonation rates of calcium and magnesium ions in steelmaking slag,the chemical and phase compositions were analyzed by fluorescence spectrometry and X-ray diffraction(XRD). The leaching effect of different amounts of hydrochloric acid and acetic acid and the influence of temperature and stirring conditions on the leaching rate were investigated in detail. Hydrochloric acid as a leaching reagent can achieve a better leaching result and its leaching rate is up to 93.4%,higher than 85.8% for acetic acid; moreover,the purity of calcium carbonate is 91.02% and the conversion rate is 56.5%. The leaching rate with acetic acid is higher than that with hydrochloric acid at 80℃. Stirring is favorable for calcium and magnesium ion leaching.
Abstract: The influence of the holding time of molten steel in the ladle after RH vacuum process on the T[O] content and nonmetal inclusion content of interstitial-free(IF) steel in the tundish was studied to optimize the RH process parameters and improve the cleanliness of IF steel after RH treatment. Experimental results show that as the holding time increases,the T[O]and non-metal inclusion contents decrease at first and then increase. The T[O]content is basically steady below 30×10-4% in the holding time range of 30 min to 40 min except for 4.76% of heats. It is suggested that under current process conditions,the steel mill should control the holding time between 30 min and 40 min.
Abstract: Based on the developed model of decarburization and denitrogenation in VOD for ultra clean ferritic stainless steel,the oxygen utilization rate for decarburization and the denitrogenation ability at different initial carbon contents were studied in the oxygen-blowing decarburization stage. The decarburization and denitrogenation ability were analyzed during the VCD stage. The effects of carbon content at the oxygen blowing end on decarburization process and temperature control were discussed to provide technical supports for optimizing the VOD operation.
Abstract: In LF refining process of Al-killed steel,the accurate control of acid-dissolved aluminum content and oxygen content and the less consumption of aluminum wire provide substantial economic value to steel plants. A one-dimensional heat transfer mathematical model was proposed to describe the melting behavior of aluminum wire injected into molten steel during LF refining process.The model was validated by experimental results from previous literatures. The effects of wire speed,wire diameter and bath superheat on the melting of aluminum wire were investigated by using the model. It is found that wire speed and bath superheat seem to be the most important factors affecting the travelled distance of aluminum wire. In addition,large wire diameter and small wire speed are recommended under high bath superheat.
Abstract: Based on the mechanism that the oxidation rate of carbon is primarily related to oxygen supply in the earlier stage and mass transfer of carbon in molten steel in the later stage,a mathematical model was proposed to describe the argon oxygen decarburization(AOD) oxidation refining process of low carbon twinning induced plasticity(TWIP) steel. The variations of C,Si and Mn contents in molten steel in an 8 t AOD converter during the oxidation refining process were analyzed by this model. The result shows that the error of the calculated carbon content is less than 5% compared with the measured values. It is also found that the critical carbon content of decarburization of the TWIP steel in the 8 t AOD converter is between 0.33% and 0.38%.
Abstract: The influence of different permeable brick layout parameters,gas flowrate,feeding location and change in permeability of permeable bricks,on the refining effect was investigated by using water model experiment according to the prototype of a 250 t ladle with bottom argon blowing. It is shown that the mixing time of liquid steel with an arrangement of two permeable bricks at 0.75R(the position from the center of the ladle bottom to permeable bricks is 0.75 times the radius R of the ladle bottom) is shorter than that of permeable brick arrangements at 0.64 R and 0.5R,but this permeable brick arrangement results in a serious erosion of the ladle wall.Moreover,the mixing time of liquid steel with an arrangement of two permeable bricks at larger angles(135°,180°) is shorter than that at smaller angles(45°,90°). Thus the 0.64R-180° arrangement of two permeable bricks is the optimal solution. When material for liquid steel refining is added above permeable bricks or in the perpendicular bisector zone of the connection line of two permeable bricks,the mixing time of liquid steel is the shortest. The optimal bottom gas-blowing flowrate is 67 to 70 m3·h-1,which can meet the clean steel production requirement,i. e.,the mixing time of liquid steel is short,slag entrapment can be avoided,and the gas mixing energy can fully be used. The mixing time of liquid steel under the condition of permeable brick clogging prolongs and two bare bright circles with different sizes form in top liquid steel,which increases the erosion of the ladle wall refractory and reduce the mixing effect and cleanliness of liquid steel.
Abstract: Central segregation in high-carbon steel billets is one of the main causes of fracture in wire rod cold-drawing. Temperature stabilization in the tundish is an effective method to improve the quality of billets. Temperature control of 668 heats of high-carbon steel was analyzed by means of investigations on process capacity. Results show that the capability of temperature control in the converter process is low,and the ladle furnace process plays an important role in temperature control and in stabilizing the liquid steel temperature in the tundish. Furthermore,the capability of temperature control for the first casting furnace is not sufficient,so it should be improved. Some measures of improvement were proposed as the following:stabilize the tapping temperature of the converter,decrease the temperature drop of liquid steel from the ladle to tundish for the first casting furnace,and increase the liquid steel temperature before refining to meet the LF process.
Abstract: The minimal oxygen content in molten steel under the condition of[Al]-[O]equilibrium at atmospheric pressure condition as well as that under the condition of[C]-[O] equilibrium at various pressures was determined by thermodynamic analysis.Using aluminum as deoxidizer,the mass fraction of[Al]and[O] in molten steel shows U-type relationship at a fixed temperature.The mass fraction of[O]in molten steel cannot be effectively decreased when the mass fraction of[Al] in molten steel is greater or smaller than the lowest value of[Al]. Increasing temperature can reduce the minimal theoretics oxygen content in molten steel equilibrated with aluminum. It is well-known that decreasing the pressure or increasing the vacuum degree can largely improve the deoxidization ability of carbon. However,improving the mass fraction of[C]in molten steel is also an alternative method to decrease the mass fraction of[O]through[C]-[O]equilibrium at a fixed value of pressure or vacuum degree. The deoxidizing ability of carbon through[C]-[O]equilibrium will be greater than that of aluminum by[Al]-[O]equilibrium at 1873 K under conditions of the mass fraction of[C]greater than 0.0015% as well as the pressure is 100 Pa. Actual data is to used to test the minimum value theoretical formula of[Al]and[C]deoxidation which the results are well in agreement with that of the practical results.
Abstract: The corrosion behavior of rare earth(RE) heavy rail steel was studied by a cycle infiltration corrosion test and an electrochemical technique under simulated industrial atmosphere. The results show that RE heavy rail steel has more excellent anticorrosive property than the other none-RE heavy rail steel. In RE heavy rail steel,α-FeOOH phase quickly forms and content increase in rust layer due to the enrichment of RE alloy elements in the matrix,RE alloy elements improve the ability of rust layer to prevent erosion of corrosive agent penetration,which improves the corrosion resistance of the heavy rail steel in industrial atmosphere.
Abstract: The effect of Mn/S(mass ratio) on sulfide inclusions in non-quenched and tempered steel containing sulfur was studied by smelting with vacuum reduction furnace and forging in laboratory. It is found that the distributions of sulfides both in ingots and bars tend to be more dispersed with the increase of Mn/S; and it is beneficial to make the sulfides be globular or spindle with the increase of Mn/S because the percentage of sulfides whose length-width ratio is less than 3 is increased from about 5% to more than 25%. The recommended Mn/S ratio is about 40 under the experimental conditions.
Abstract: Large eddy simulation(LES) computational model was applied to investigate the transient turbulent flow in a continuous casting mold. Reynolds-averaged Navier-Stokes equations(RANS) model was also compared with LES to predict the turbulent flow features. The computation models were validated by ultrasonic doppler velocimetry(UDV) measurement in a liquid metal model,which indicates that the LES model predict much more accurate than RANS model. LES model can capture the large turbulent fluctuation near the jet region. A wobbling stair-step downward jet was simulated,which indicates that the small scale flow dominants this region. Due to the large scale flow structure in the lower velocity region,the asymmetrical flow pattern behavior always exists; the asymmetrical flow disappears with more time averaging.
Abstract: The surface cracks on the 300 mm×360 mm continuous casting bloom of low carbon and high manganese steel made by electric-arc furnace(EAF),ladle furnace(LF),and vacuum decarburization(VD) processes were found after cooling. The formation of surface crack was investigated by optical microscopy,scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The results indicated that surface crack was related to the chemical composition of the steel,the inclusions,the temperature of the steel,the mold fluxes,and the precipitates. Controlling the chemical composition of the steel,decreasing the amount of inclusions,controlling the temperature of the steel reasonably,and using special mold flux can promote the surface quality of the casting bloom in some degree.
Abstract: Using pyrite cinder with low melting point and bituminous coal as raw materials,carbonized pyrite cinder pellets were made and introduced to the reduction smelting process. The effects of basicity,roasting temperature,roasting time and C/O molar ratio on the iron recovery rate were investigated to search the optimum experimental parameters. It was found that iron nuggets with the iron recovery of 93.1% were obtained when the basicity was 1.2,the roasting temperature was 1450℃,the roasting time was 20 min and the C/O molar ratio was 1.2. Iron oxides and iron-bearing sulfides in pyrite cinder were reduced,thus a higher iron recovery rate was achieved. From X-ray diffraction analysis on the slag tailings,short smelting time caused high amount of iron in metallic state retained in the slag. Because of high sulfur in iron nuggets from pyrite cinder by reduction and melting separation,the iron nuggets can be used as raw materials to product sulfur-bearing free-cutting steel.
Abstract: A 3D steady numerical model of 1650 mm×220 mm slab mould was built,which was used to simulate the molten steel flow in the mould for with 3 schemes. The results showed that the width of the mould played an important role on the mould surface velocity. The velocity distribution became more and more non-uniform with the width increasing. The surface maximum velocity was affected by many factors,including the molten steel velocity at nozzle,nozzle angle,and the immersion depth of the nozzle,of which the molten steel velocity at nozzle had the most influence. The optimum scheme is as follows:mould width of 1100 mm,immersion depth of 120 mm,construction bottom structure of "E-lie-down" shape,nozzle outlet angle of 30°,flow rate of 11.6 m3·h-1,and inlet velocity of 0.8384 m·s-1.
Abstract: Alloy yield dynamic libraries were established based on self-learning of historical data and computer technology,through which accurate real-time alloy yield was obtained. Alloy charging optimization model was established for the First Steel-Making Plant of Tianjin Pipe Co. Ltd using the two-stage simplex method. As the operation of steelmaking is online,the alloy yields of different steel grades are obtained,and the accuracy of dosage of the alloy is improved. By optimizing alloy charging,average cost of alloy charging for each steel grade has been reduced. The maximum of the cost reduced is 54.96 yuan·t-1,and the minimum is 8.57 yuan·t-1.The cost of alloy charging per ton steel was reduced by 6.76%-11.40%,and the average cost was reduced by 9.74%.
Abstract: To solve the urgent problems in the thermal system at the initial stage of producing direct reduced iron(DRI) in a rotary hearth furnace(RHF) in China,thermal parameters in different sections of RHF were analyzed by systematic analysis,thermal simulation experiments,and numerical simulation. The RHF mathematical model and heat supply model were established with 83 variables and 20 parameters. The result of numerical simulation indicates that producing every 1 t metalized pellet needs 1213 kg iron ore fines,283 kg pulverized coal,and 615 kg coal gas. Based on the systematic analysis on different sections of the rotary hearth furnace,thermal simulation experiments on preheating,heating,and reducing sections were studied separately. Under different conditions(nC:nO=0.8~1.2),the real-time reduction progresses of carbon-bearing pellets in these sections were confirmed. According to the matching of the self-reduction decalescence of carbon-bearing pellets and thermal parameters,the fuel supply parameters of each section were determined. Fluent simulation software was used to verify the thermal parameters of the three sections. And the results show that the designed parameters are reasonable,and can effectively implement the functions of all the sections of a rotary hearth furnace,which provide the theoretical basis for the optimization design of the rotary hearth furnace.
Abstract: A water model of 1:2 scale was established to simulate the bottom blowing of N2 in a 3 t ferrovanadium electric arc furnace(EAF). The L25(56) orthogonal matrix was adopted to investigate the influence of different blowing positions and nitrogen blowing rates on the mixing time of liquid. Results show that the optimal bottom blowing conditions are as the following:the flow rate of bottom blowing is 1306 L/h and the positions of porous plugs are e(0.7R),d(0.6R),and e(0.7R) in the model. Both the position of porous plugs and the gas flow rate have significance on mixing time. The mixing time fitting result indicates that there is an exponential relationship between mixing time and gas flow rate,and the index value is- 0.5211.
Abstract: The reason of Si volatilization during the BOF steelmaking process using limestone for slagging was analyzed. After thermodynamic calculation,the temperature and atmosphere conditions that SiO exists stably near the surface of molten iron with high carbon concentration and low temperature were obtained. Results show that the SiO generation reaction only takes place in the "fire zone" in oxidation reactions between some elements in molten iron and CO2. At the temperature of 1400 to 2300 K,the value of pCO/pCO2 that makes SiO exist stably decreases gradually with the increase of temperature,which equals to 10-25~10-13 magnitude of the partial pressure of oxygen. Under the condition of adding limestone in 2 min,the partial pressure of SiO is about 10-2 magnitude when[Si]volatilizes,which is consistent with the practical production.
Abstract: The low melting point zone of CaO-Al2O3-SiO2-MgO inclusions was analyzed and calculated by thermodynamic software FactSage. It is found that the low melting point zone can be divided into two different areas by alkalinity,and the sulfur capacity of the two areas was calculated and compared by using the KTH model. Then combined with the requirements of critical hydrogen 12Cr2Mo1 R on compositions and desulfurization,its applicable low-melting region was discussed. The results show that if inclusions are controlled at the high alkalinity zone,the contents(mass fraction) of CaO,Al2O3,and MgO are about 30%,15%,and 10%,respectively,the content of SiO2 should be more than 40%,and it has a lager low melting point zone with higher SiO2 content. If inclusions are controlled at the low alkalinity zone,the contents of CaO,Al2O3,and MgO are about 50%,45%,and 5%,respectively,the content of SiO2 should be less than 5%. The sulfur capacity of the high alkalinity area is significantly less than that of the low alkalinity area. In both low melting point areas,the sulfur capacity is increased with the increase of alkalinity. The bigger the calcium/aluminum ratio is,the greater the sulfur capacity is increased with the increase of alkalinity. For the critical hydrogen 12Cr2Mo1 R,CaO-Al2O3-SiO2-MgO inclusions should be controlled in the low melting point zone with high alkalinity,and higher alkalinity and calcium/aluminum ratio are better.
Abstract: To study the effects of manganese and silicon contents on the microstructure and mechanical properties of medium manganese hot-rolled high-strength steel,different C-Si-Mn tested steels with different manganese and silicon contents were designed.The phase transformation point,microstructure,retained austenite content,and mechanical properties were measured and analyzed using dilatometric simulation,scanning electron microcopy,transmission electron microcopy,X-ray diffraction,and tensile testing.The obtained results indicate that the final microstructure of specimens can be greatly affected by the contents of manganese and silicon.The microstructure of low-silicon and high-manganese specimens consists of granular bainite. The microstructure of high-silicon and high-manganese specimens consists of bainite-ferrite,martensite,and retained austenite. The microstructure of high-silicon and low-manganese specimens consists of quasi-polygonal ferrite,bainite,martensite,and retained austenite. The results show that the best comprehensive mechanical properties of newly designed medium manganese hot-rolled high-strength steel are obtained in high Si and high Mn specimens. The ultimate tensile strength is in excess of 1200 MPa,the total elongation is 16%,and the product of tensile strength and elongation is about 20 GPa·%. The high strength and ductility of the tested high-silicon and high-manganese steel can be explained by the ultrafine grain microstructure and TRIP effect.
Abstract: To improve the mixing effect and inclusion removing during the ladle bottom blowing refining process at an electric furnace factory,the water modeling experiment was conducted. Results show that the distance of two gas columns is too close,so stacking and shifting of the gas columns occur when the gas flow rate is large,which make the flow field of molten steel unstable. According to the results,it is proposed that the bottom blowing position should be located at 0.5R-0.5R-135°(R is the ladle bottom radius),and the critical gas flow rate for slag entrapment is 0.24 m3·h-1.
Abstract: Effects of Zr on the solidification structure and hot ductility of Fe-36Ni invar alloy were investigated,and the corresponding mechanisms were also discussed. Results showed that a great amount of high-melting point compounds(ZrO2) formed in the alloy with the addition of 0.081% Zr(mass fraction). Based on the theory of lattice misfit,the lattice misfit between(001) surfaces of ZrO2 and the Fe-36Ni matrix is 0.77%,which is relatively low. Therefore,ZrO2 could serve as the effective core of heterogeneous nucleation,resulting in remarkably shorter and thinner columnar grains,which increases the proportion of equiaxed grains and refines the solidification structure. The alloy has a bad hot ductility below 1050℃,which is mainly attributed to weaker boundaries and grain boundary sliding. However,the hot ductility of the alloy is highly enhanced at 950~1000℃ because of the addition of 0.081% Zr,which could refine grain sizes to hinder grain boundary sliding,strengthen grain boundaries,and promote grain boundary movement.The alloy has a good hot ductility over 1050℃ for the existing of dynamic recrystallization.
Abstract: The influences of liquid steel temperature,nitrogen partial pressure,and carbon content on the nitrogen solubility in 316 L stainless steel under normal atmosphere and vacuum were studied by the Factsage thermodynamic calculation software and laboratory experiments. Results show that nitrogen solubility increases with decreasing the liquid steel temperature,increasing the nitrogen partial pressure,or decreasing the carbon content. The nitrogen partial pressure is the most important one among the three parameters.The thermodynamic calculation results are in coincidence with the measurement results in different nitrogen blowing processes. Producing 316 LN with the N content of 0.05%- 0.10%(mass fraction) could be conducted during oxygen blowing. Producing 316 LN with the N content of 0.10%- 0.40% should be carried out during charging(the nitrogen partial pressure must be over 30 kPa) and under atmospheric pressure.
Abstract: The influence of MgO content on liquid phase in CaO-SiO2-Al2O3-MgO slag system was simulated by Factsage software.The results show that,with increase of MgO content in CaO-SiO2-Al2O3-MgO slag,the low melting point liquid area moves forward ‘low CaO high SiO2’ area. 1500℃ liquid area ratio of phase diagram rises from 25.05% of 0% MgO(mass fraction) to 52.69% of 9% MgO,and drops to 46.70% of 15% MgO. 1400℃ liquid area ratio of phase diagram rises from 14.41% of 3% MgO to 34.39%of 11% MgO,and drops to 31.04% of 15% MgO. 1300℃ liquid area ratio of phase diagram rises from 5.57% of 5% MgO to 11.02% of 14% MgO,and drops to 10.05% of 15% MgO. 1200℃ liquid area ratio of phase diagram is 0 when MgO content during 0 to 6%,and rises from 0.88% of 7% MgO to 1.22% of 11% MgO,then changes to 0 when MgO content during 13% to 15%.Simulation results provide an effective guidance for composition selection of steelmaking slag with the CaO-SiO2-Al2O3-MgO components as the basic configuration.
Abstract: The characteristics and source of high SiO2 inclusions in IF steel slab were studied through a variety of methods,such as X-ray diffraction(XRD),scanning electron microscopy/energy dispersive spectroscopy(SEM/EDS),and non-destructive inclusion extraction. Results showed that many solid macro-inclusions existed in the IF steel slab,and the high SiO2 inclusions in irregular shape and large size(> 50 μm) occupied 60% of the total number. This kind of inclusions was mainly from the bad pre-melt mould power.High-melting-point solid oxides,such as SiO2 and Al2O3 existed inside the power particles,and these solid oxides were captured by the shell before dissolved completely during the casting,and finally formed inclusions in the slab. quality defects of the slab caused by high SiO2 inclusions can be reduced by improving the pre-melting performance of the mould powder.
Abstract: The morphology,size,and composition of inclusions were studied by scanning electron microscopy(SEM) in pipeline steel during refining process. The Ca-O equilibrium curve,Ca-S equilibrium curve,and the stability diagrams of inclusions(CaO and CaS) were discussed to explain the formation mechanism of CaO and CaS complex inclusions. The results show that the excessive addition of Ca-Si wireis the reason causing the formation of CaO and CaS complex inclusions.
Abstract: With different slag basicity and refining process,the total oxygen content,inclusion size,and composition were analyzed,and the morphological distribution of inclusions was studied in the spring steel. The results show that,high basicity slag is propitious to inclusion size control,but high basicity also results in the fragile inclusion in steel,low basicity slag can also cause the relatively high oxygen content and large inclusion in steel. In order to ensure the plastic inclusions in spring steel,the slag basicity should be controlled in 1.0-1.3,and at the same time,the soft blowing time should be prolonged properly to ensure the removal of large inclusion and decrease the oxygen content in steel.
Abstract: The composition of inclusions in low melting point area of CaO-SiO2-Al2O3-MgO system and CaO-SiO2-Al2O3-MnO system was analyzed by thermodynamic calculation,and the influence of Al2O3 content on inclusions in steel was studied. It is found that,at the Al2O3 content of 15wt%,the corresponding low melting point area of phase diagram takes the largest percentage. The angular Al2O3 inclusions increase by the increase of Al2O3 content,and the distribution of inclusions in steel becomes relatively concentrated.In the basicity of 1.2 and the Al2O3 content of 8wt%,the inclusions can be controlled in low melting point area of phase diagram,the corresponding shape of inclusions is spherical with the size of about 5 μm.
Abstract: Inclusions in hot rolled sheet of bearing steel and blockage in clogged submerged entry nozzle(SEN) were analyzed using scanning electron microscopy(SEM). It is found that the inclusions in hot rolled sheet are mainly TiN,MgO·Al2O3,MnS,and a little CaS,most of them are smaller than 20 μm. Besides,some large inclusions of MgO·Al2O3 and Al2O3 and the associated cracks are observed. By the detection on clogged nozzle,it is shown that the blockage is mainly MgO·Al2O3 spinel inclusions as well as some MgO-Al2O3-CaO system inclusions and solidified steel. The composition of blockage is consistent with that of inclusions in steel,thus it is indicated that the nozzle clogging is caused by the gathering and precipitation of solid oxide inclusions in molten steel on SEN during the continuous casting process. A possible reason for the existence of large inclusions in sheet may be the drop of blockage during casting.
Abstract: Effect of magnesium addition on the compositions of inclusion was studied in the different oxygen and sulfur contents at 1873 K. Under the present condition,magnesium deoxidation products of low-S content experiment steel can be changed in the order Al2O3→MgAl2O4→Mg-Al-O-S,and it is consistent with the results of thermodynamics calculation. But magnesium is preferred to react with oxide,comparing with sulfide. It reaches the reaction endpoint after 1 or 5 min,and it is faster than reacting with sulfide. When the content of all elements in high-S content experiment steel satisfy certain conditions,the oxide and sulphide can be modified simultaneously by magnesium. And the complex oxysulfides would be generated. The inclusions in experimental steel can be changed in the order Al2O3→MgO→MgO + MgAl2O4+ MgS,but the product layer of MgO-MgAl2O4depressed the further reaction. Sulphur in molten metal can be fixed in this way,and diameter of the inclusions is well under control at the same time.
Abstract: By thermodynamic calculations and analysis,the optimized slag composition(mass fraction) of ladle refining for low carbon low silicon Al-killed steel grades was optimized during compact strip production(CSP) process as CaO 50%-55%,Al2O3 30%-36%,SiO2 1%-6%. The equilibrium liquid steel composition is as[Si]0.2%-0.4%,a[O] lower than 4.5×10-6,[Ca]2×10-5-4×10-5when dissolved Al is approximating 0.03%. The optimized slag is more favorable for deoxidation,desulfurization and desiliconization. In addition,it is also with low melting point,quite well fluidity as well as the ability to absorb inclusions.Finally,both slag-steel equilibrium experiments in laboratory scale and industrial trials in plant scale verified that optimized slag can very control the steel composition as well as inclusion composition and improve steel cleanness quite a lot. After applied the optimized slag,the ratio of cold rolled strips that are degraded due to surface quality problems decrease from 1.23% to 0.8%,and the costs of LF refining reduce by 4.30 RMB per ton Fe,namely approximating 10%.
Abstract: In order to control liquid steel temperature accurately,forward and backward prediction models for liquid steel temperature in key strategic points of steelmaking process were proposed,based on the analysis of the main influencing factors and the control state of liquid steel temperature in actual steelmaking process. At the same time,to overcome the disadvantages of traditional prediction methods,a hybrid model method based ladle heat status and BP neural network was proposed. The method is based on the ladle heat status tracking model,and gives full consideration to the effects of ladle heat status on molten steel temperature,and combines with BP neural network,which can effectively improve the prediction precision.
Abstract: In order to present the operating principles and the appropriate control objectives for Nan Steel,according to dephosphorization theory and characteristics of double slag dephosphorization in combined blown converter,together with the conditions of molten iron in Nan Steel,the influences of silicon content,temperature and phosphorus content on dephosphorization were analyzed and the reasonable smelting solution was presented. The result shows that it can achieve the dephosphorization effect that phosphorus content is less than 4×10-5 and the dephosphorization rate is 97.3%,by using the optimizing process operation of slagging,oxygen blowing,first deslagging and end-point control,in Nan Steel 120 t combined blown converter. The need of ultra-low phosphorus steel produce can be met through the optimized solutions.
Abstract: The uniformity of a 7-stream tundish in a steel plant was studied by establishing a water model with the scale of 1:2.5.Experimental results show that the multi-stream tundish has poor uniformity with no flow control devices and the uniformity difference of each stream is obvious. The liquid steel flow of each stream in the tundish before optimization has a high dead zone proportion of 45.5%. It is found that the importance of flow control devices is U-type dams > turbulence suppressors > trapezium dams. After optimization,flow control devices have good applications in the steel plant,the uniformity of each stream improves greatly,and the proportion of the dead zone decreases to 23.1% from 45.5%.
Abstract: The surface tarnishing phenomenon was analyzed. The main inclusions are type A and type C determined by metallographic analysis. Serious intergranular corrosion was found in surface tarnishing 304 plate after annealing and pickling. After solution treatment and pickling test,the amount of ferrite decreases significantly,little carbide precipitation happens,and surface tarnishing phenomenon decreases. The result shows that the improper annealing results in carbide enrichment on the grain boundary and sensitization of material,which lead to intergranular corrosion when pickling,and then surface tarnishing of 304 pickling plate.
Abstract: A water model was established by the ratio of 1:2 to simulate bottom blowing of N2 in a 2t EAF in the CISC's ferrovanadium plant,the influences of different blowing positions and different blowing quantities to the mixing time and flow pattern were mainly investigated through orthogonal analysis. The result shows that the various bottom-blowing patterns and blowing quantities have greatly influence on the molten pool mixing. With orthogonal analysis on the experimental data,it is found that the mixing effect of the blowing gas to the bath is the strongest,the mixing time is the shortest and distribution of flow is reasonable,when the blowing holes is e-b-d and blowing quantity is 1092 L·min -1.
Abstract: In order to explore the metallurgical behavior of bottom blowing CO2 in ladle furnace, CO2 was used during the LF refining process, some thermodynamics calculation of bottom blowing CO2 was studied, and some exploratory experiments were conducted with different proportions of CO2 to Ar during the LF refining process in industry. The results show that it can cause the little oxidation of C in molten steel with the process of bottom blowing CO2, the average oxidation of C is from 0.3 to 0.8 kg. Compared with bottom blowing Ar, the types and composition of inclusions have less change and the equal yield density of inclusions decreases and the cleanness of steel is improved, it will not aggravate the erosion of ventilated bricks of LF. So it is possible to use CO2 in LF for refining.
Abstract: The effect of Mn/S(mass ratio) on sulfide inclusions in non-quenched and tempered steel containing sulfur was studied by smelting with vacuum reduction furnace and forging in laboratory. It is found that the distributions of sulfides both in ingots and bars tend to be more dispersed with the increase of Mn/S; and it is beneficial to make the sulfides be globular or spindle with the increase of Mn/S because the percentage of sulfides whose length-width ratio is less than 3 is increased from about 5% to more than 25%. The recommended Mn/S ratio is about 40 under the experimental conditions.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
