Abstract: The secondary oxidation caused by compositions of refining slag and Ca treatment on oxide inclusion was studied in TP347H stainless steel by EF+VOD+IC process. In industrial trials, the aluminum is used as the final deoxidation during VOD process. The FeO and SiO2 contents in refining are decreased and the quaternary basicity is higher than 1.3. Then the total oxygen content is below 0.003%. With Ca-Si wire feeding and soft blowing the hard Al2O3 and MgAl2O4 inclusions are transformed to CaO-Al2O3 inclusion. The amount of MgAl2O4 inclusion is reduced and the melting point of inclusion is below 1500℃. This kind of inclu-sion is liquid during steelmaking process and it is easy to coalescence and flotation. And in the following rolling and forging process the inclusions have a little deforming ability with the matrix deformed and prevent the ingot crack.
Abstract: The low carbon boron-bearing steel with 0.0045% boron and 0.0039% nitrogen was investigated, the thermodynamics and kinetics of precipitation and growth of BN during liquid steel solidification were studied. The effect of cooling conditions on the precipitation and growth of BN was experimentally investigated. The results show that BN can only precipitate at the solidifying front where the solid fraction is greater than the calculated critical value of 0.981 due to the segregation of boron and nitrogen. There is a serious segregation of boron and nitrogen with the increase of the solid fraction at the solidifying front. The diffusion of nitrogen in liquid steel is the rate-controlling step of BN growth because the boron content in the remaining liquid steel is much higher than that of nitro-gen when the solid fraction is close to 1. The change in cooling rate of liquid steel has negligible effect on the segregation of boron and nitrogen. However, the size of BN precipitates decreases greatly with increasing the cooling rate.
Abstract: To understand the characteristic of mixing in 210 t RH vacuum refining process,a 1:4 water model was established to investigate the effects of gas flow rate,snorkel immersion depth(SID),vacuum chamber pressure and number of blockage blowing air holeon the RH mixing time. The results show that the RH mixing time presents a decreasing trend with the increase of gas blowing andthe decrease of the vacuum chamber pressure. Furthermore,the mixing time first decreases then increases with the increaseof the snorkel immersion depth(SID) and the number of blockage blowing air hole,and the optimum SID is 480 mm. Using particle imagevelocimetry to measure the two-dimensional flow field of RH ladle in refining process,and then compared to the results of numerical simulation,the results show that the fluid movement in the ladle is mainly the circulation flow from down-leg to up-leg andthe back-flow around the down-leg. In addition,the inactive region is mainly located in the range of SID under the steel-slag interface.
Abstract: To investigate the feasibility of the transport of aluminum block to the slag-steel interface to suppress the oxygen trans-fer from slag to steel in the casting process, a mathematical model for the motion and melting of aluminum block was developed and it was solved in a coupled way. The effects of parameters such as the RH circulation flow rate and the initial size of aluminum block on the motion and melting of aluminum block were investigated based on this model. The results suggest that there are two melting routes for aluminum block. The difference between them lies on the internal melting of aluminum block. According to the results, for the sake of transporting the aluminum block to the slag-steel interface, the circulation flow rate should be larger than 100 t·min-1 and the origi-nal radius of aluminum block should be at least 10 mm.
Abstract: Based on the similarity principle, a water model with a scale of 1:4 of a 300 t RH unit was established to study the effect of different modes of nozzles blocking on the RH circulation flow rate. Results show that the deviation of gas volume is the main factor influencing the circulation flow rate in the case of nozzles blocking. In the situation of symmetrical blocking, the circulation flow rate is minimum when the angle of the attachment of the blocking position and circulation direction is 0o, on the contrary, the circula-tion flow rate is maximum when the angle is 90o. In the situation of concentrated blocking, with the increase of the number of blocked nozzles, the mechanism of bubble pump action shifts from the annular bubble pump mechanism to the cluster bubble pump mechanism and the circulation flow rate is increased.
Abstract: The morphologies and compositions of typical inclusions in liquid steel before and after calcium treatment were observed to study the evolution mechanism of non-metallic inclusions during calcium treatment. The process of calcium treatment could be modified by thermodynamic analysis. Results show that irregular solid inclusions finally change into spherical inclusions after calcium treatment. When the mass fraction of aluminum in liquid steel is 0.03% at 1873 K, the mass fractions of oxygen and calcium should be controlled in the range of 5×10-6~17×10-6 and 0.7×10-6~30×10-6, respectively. Inclusions in liquid steel can be modified effectively. When the mass fraction of sulfur in liquid steel at 1873 K is in the range of 6×10-6~19×10-6, liquid calcium aluminate inclusions can be formed via Al2O3, and the formation of CaS can be decreased.
Abstract: Taking the converter-refining procedure of a steel plant as an example,symbol exergy-economic model was established by the exergy-economic analysis method. Then the cost balance equation was constructed,and supplementary equations were established. The unit exergy price and thermal-economic cost of each exergy flow in the procedure were obtained on the converter-refining procedure through thermal-economic analysis. The results show that the thermoeconomic cost of per ton molten steel in the converterladle refine process is the lowest,which is 2243.12 RMB. The thermoeconomic cost of per ton molten steel in the converter-CAS refining process comes second,which is 2259.92 RMB. And the converter-RH refining process has the highest thermal-economic cost of per ton molten steel,which is 2270.16 RMB. From the standpoint of energy conservation and cost reduction,the converter-refining process is the reasonable process for SPHC steel production.
Abstract: The influence of superheat on internal structure of the bearing steel is researched by the macrostructure inspection tech-nology of dendrite corrosion and metallographic test method of bloom and wire with quenching and tempering heat treatment. The re-sults show that the equiaxed crystal ratio of the low superheat process increase. The secondary dendrite spacing decreases. Internal metallurgical defects such as segregation, shrinkage cavity improve. But there is little difference in the wire rod pickling macrostructure and carbide nonhomogeneity. Segregation control in the mixed crystal area is more serious than that in equiaxed crystal area. And there are a large numble of large size eutectic carbides.
Abstract: The surface fluctuation and slag entrapment involved in the wide slab continuous casting mold of 150 mmí1503 mm in a steel plant was caculated by FLUENT software. Surface velocity was set as the main measure to study about port angle and guide an-gular shape of the nozzle influence on flow field. The calculation results show that under the condition of original nozzle, the surface velocity was large, but the impact depth was small and the fluctuation was severe. Entrapment of slag was serious. After changed the angle of the outlet, the mold surface velocity remained large and severe entrapment of slag. When scheme 3 (outlet lead angle changed shape to tangent) was applied, surface velocity reduced from 0.6 m/s to 0.2 m/s, impact depth improved, flow field character became better, and problem of slag entrapment was resolved.
Abstract: The properties of hot rolled ribbed bars with different V contents are investigated. It is found that V can promote gain refinement. Contributions of different strengthening mechanisms to yield strength of bars are computed. The results show that V has a good effect on bar precipitation strength. Through thermodynamic calculations of V element precipitation in HRB400, the influence of V contents on the precipitating temperatures of V(CN) is demonstrated.
Abstract: Characteristics of flow field and stirring effects of top lance with various tilt angles(Tilt angles were 39°,41°,43°,45° and 47°,respectively) on the molten bath were studied using water experiment and Fluent software. It was found that appropriate tilt angle could improve dephosphorization process,and too large and too small reduced the impacting depth and impacting diameter,respectively,leading to decrease in dephosphorization rate. When injecting by the 43° oxygen lance,impacting depth and impacting diameter were medium,mixing time and volume of dead-zone were the minimum and average flow velocity of molten bath was the biggest. This is helpful to promote phosphorus dispersion in dephosphorization ladle furnace and improve the dephosphorization rate.Based on the results of industrial application research,the 43° oxygen lance could stir the molten bath better,increase the dephosphorization rate and reduce the consumption of hot metal and scrap.
Abstract: The varying characteristics of steel material consumption, oxygen consumption, and converter gas volume were studied when different ferrous materials and different proportions of limestone were used in 60 t converter. The results show that when liquid steel is used as raw material and mixture of slag-steel and lump ore as coolants, the steel material consumption per ton steel is the min-imum (only 1072.07 kg), and when liquid steel and scrap steel are used as raw materials and slag-iron by magnetic separation as coolant, the steel material consumption per ton steel reaches the maximum (1092.91 kg). Meanwhile, with the increase of the amount of limestone, the steel material consumption is increased, the oxygen consumption is slightly decreased, and the gas volume is im-proved. The results will provide a new method for optimizing the material structure and reducing the production cost in steelmaking process.
Abstract: Aiming at reducing the production cost of 82B steel and improving product quality,Shougang Iron & Steel Co. added vanadium titanium pellets as raw material in the blast furnace. The addition of vanadium titanium pellets led to several problems such as the low speed in the process of producing and slag melting in converter,the low efficiency of dephosphorization,and the non-ideal effects of slag splashing. In order to solve the above problems,taking the production process of 82B steel in converter in Shougang Iron& Steel Co. as the research object and using the Fluent software to conduct a numerical simulation in combined with high industrial test,this study optimizes the oxygen supply system when using high-V-high-Ti molten iron to smelt 82B steel in converter. In addition,the optimization of oxygen supply system serves as a guarantee for the enhanced ability in smelting 82B steel with high-V-high-Ti molten iron in convert. As a result,there exists increasing possibility for Shougang Iron & Steel Co. to produce high-quality and low-cost 82B steel.
Abstract: On the basis of analysis of limestone decomposing and slagging mechanism, the changing of surplus heat was studied using limestone instead of lime as the slagging agent during steelmaking process, which indicates that hot metal added ratio can reach approximate 86.1% if using lime entirely. If limestone is applied in the steelmaking process to replace all limes for slagging, the hot metal ratio can reach up to 97.0%. On this basis, the metallurgical results of using limestone instead of lime for slagging in 60 t con-verter were studied. The results show that the content of TFe in slag is 21.87% at 4 min and the basicity is 1.22 using limestone for slagging. With the blowing time increasing, the content of TFe reduces while the basicity increases to more than 3.0. Besides, the de-phosphorization process is much more stable and the dephosphorization ratio increases by 2.6%, and the average basicity of slag in the end is 3.52, meeting the demand of dephosphorization. Since the slag amount substantially reduces, which results in the decline of the consumption of steel material. The blowing time is prolonged and the temperature of liquid steel is kept constant. Furthermore, the re-sults also provide a new method and concept for optimizing the charging material structure and reducing the production cost.
Abstract: The effect of alkaline oxide content,optical basicity,total iron content in slag and temperature on the measured slag phosphate capacity was investigated through the calculation and analysis of the slag phosphate capacity during the converter dephosphorization process combined with previous study. The relationship between phosphate capacity and composition of slag was fitted according to the production data. In addition,different prediction models of phosphate capacity were compared and analyzed from previous studies. Based on the coexistence theory,the prediction model of phosphate capacity in slag system was established,and the error analysis shows that the prediction model is accurate and credible,which can provide a theoretical guidance for the field production.
Abstract: The effect of alkaline oxide content,optical basicity,total iron content in slag and temperature on the measured slag phosphate capacity was investigated through the calculation and analysis of the slag phosphate capacity during the converter dephosphorization process combined with previous study. The relationship between phosphate capacity and composition of slag was fitted according to the production data. In addition,different prediction models of phosphate capacity were compared and analyzed from previous studies. Based on the coexistence theory,the prediction model of phosphate capacity in slag system was established,and the error analysis shows that the prediction model is accurate and credible,which can provide a theoretical guidance for the field production.
Abstract: Scanning electron microscope and energy dispersive spectroscopy methods were used to investigate the inclusions of 55SiCr spring steel produced by WISCO,Baosteel and Nippon Steel. The result shows that aluminum deoxidization smelting process is used to obtain high level of cleanliness for Nippon Steel's spring steel. For Baosteel and WISCO's spring steel,non-aluminum deoxidization smelting process is used,but the control of the inclusion's plastic deformation capacity still needs to be improved. And then,the 55SiCr spring steel samples of smelting process were analyzed to study the evolution of inclusions' composition. Based on the results of thermodynamic calculation,a suggestion for the 55SiCr spring steel inclusion's plasticization was proposed,the[O]should be controlled from 0.0009% to 0.0020%,and the[Al] controlled from 0.0002% to 0.0008%.
Abstract: Plate products of DH36 high-strength ship plate steel,roll formed by a steelworks in China,were investigated. Analyzing by mathematical simulation method,a mathematical model was built for the connection between main chemical components and basic mechanical properties of DH36 high-strength ship plate steel. Based on the model,the impact of composition fluctuation of manganese on various mechanical properties was emphatically analyzed. The results show that the influence of manganese on impact energy mainly appears as the negative linear relationship. The impact of manganese on the yield strength,tensile strength and reduction of area also appears as the linear relationship,and the slope is impacted by other elements and needs further investigation.
Abstract: The mechanism of submerged entry nozzles (SEN) clogging with AISI 321 stainless steel billet was investigated by analyzing the structure and composition of the SEN deposits. The results of deposits dissection indicate that nozzle clogs consist of TiN, metal and slag. Then the thermodynamic model of TiN in the steel and solidification was established. The results show that the existence of TiO2 transition layer, high concentration product of titanium and nitrogen, and worse cleanness of the liquid steel have roles to play in the formation of deposits. Therefore the mechanism of clogging can be explained as follows. At first, a transition layer of TiO2 forms at the SEN refractory because of the reaction of[Ti] with the silicates in the SEN refractory during casting. Subsequently the good heat transfer properties of titanium oxide layer can cause a large drop in temperature of molten steel which makes it possible for the formation of the TiN deposits, additionally low cleanness deteriorates the cast-ability of molten steel. In the end, the growth of the deposits leads to the nozzle clogging.
Abstract: The slag detection system of hot metal is a set of slag grading system based on machine vision. Its main function is using a high resolution camera to observe the real-time situation in the molten iron tank, imaging through the industrial control comput-er and analyzing the thickness and the range of iron slag in the obtained image, judging the level of slag according to the standard data-base. This system can improve the automation level of the grade evaluation of online slag detection, further, not only reduce the influ-ence of the unstable factors of the workers' experience but realize the workers labor protection as well.
Abstract: The total oxygen,the contents of[H] and[Al],the inclusions and the compositions of slag by RH and VD refining treatment are compared under the other same conditions. The results show that dehydrogenation by RH is better than VD,while deoxidation by VD is better than RH. The final content of[Al] and the basicity of slag processed by VD increase and the compositions of inclusions deviate from the plastic zone. The content of Mg O in slag processed by RH increases obviously and the compositions of inclusions are dispersed. While the content of Mg O in slag processed by VD changes slightly and the compositions of inclusions are concentrated. The differences are ascribed to refractory shedding in the snorkel of RH unit which leads to the increase of external inclusions. The suggestions for vacuum refining are as follows:the quality of refractory should be improved and the gunning for snorkel should be reduced with the processing by RH. While the amount of lime and the basicity of slag should be decreased,and the treatment time should be increased with the processing by VD.
Abstract: A model for fluid and heat transfer of early stage of filling of a 19 ton ingot mould was built, and the flow and tempera-ture distribution characteristics during early stage of filling were investigated. Numerical simulations of mould filling with a series of en-trance nozzles with the different top diameters and bottom diameters were carried out, and the effects of entrance nozzle structure on mould powder entrapment during early stage of filling were investigated. The results show that level fluctuation in molten steel is strong and solidified shell grows fast so that mould powder can be entrapped easily. When top-end interior diameter is larger than bottom-end, the velocity of molten steel stream depends on the bottom-end interior diameter, and decreases with the increasing of op-end interior di-ameter. As for 19 ton steel ingot, the risk of mould powder entrapment can be greatly decreased when the bottom-end interior diameter is larger than 90 mm.
Abstract: The microscopic structures and inclusion in 42CrMoV bolt were investigated by SEM,STEM and software ASPEX. The results show that the matrix structure of 42CrMoV bolt is tempered sorbite,but still retains the original morphology of martensite. Carbides precipitate and arrange orderly in intracrystalline and lath boundaries,and the amount of precipitated carbides in grain boundaries are more than that in intracrystalline. Besides,the micro-hardness HV0.2 is 330 and the grain size(level) of austenitic is 9. The Mn S and aluminate are the main inclusion types in 42CrMoV bolt,and the size of inclusions are mostly less than 5 μm,the level of A,B,C,D and Ds inclusion was basically less than or equal to Level 0.5.
Abstract: Taking a 30 ton of LF as an investigated object, a gray-box model to predict the end-point temperature of molten steel in LF based on the mechanism model and the black-box model was established. The heat transfer mechanism model was firstly estab-lished according to the energy conservation law. In addition, the black-box model based on partial least squares was adopted to solve the problem that the regeneration of the ladle lining and thermal effects of the alloys are difficult to accurately calculate. Finally, the two models were combined to predict the end-point temperature of molten steel in LF. Simulation results show that the hit rate within the error range of ±5℃ by partial least squares for the regeneration of ladle lining refractory and thermal effects of the alloys reaches more than 97%, and the total hit rate within the error ranges of ±5, ±8 and ±10℃ by gray-box model reaches 88%, 96% and 99%, respectively. This means the grey-box model can accurately predict the end-point temperature of LF, which provides the guid-ance for the LF refining process in this factory.
Abstract: A New process for refining medium-low carbon ferrochromium (M-LCFeCr) from high carbon ferrochromium (HCFeCr) through converter was discussed. This technology is similar to argon oxygen decarburization process (AOD) with the differ-ence of carbon dioxide being introduced as mixing gas. The results show that, it is feasible to use CO2 for decarburization of high car-bon and medium carbon ferrochrome. Better decarburization effect is obtained by using high volume ratio CO2 at the initial stage of pro-ducing MCFeCr through HCFeCr, while at the last stage of refining, viz. low carbon content melt, higher O2 concentration is better for carbon removal. The optimal gas composition for decarburization is 25%CO2+75%O2 (volume ratio) in the current experiments. CO2 introduction is benefit for enhancing the yield of chromium, and higher CO2 leads to better Cr retention. It has positive effect of CO2 on desulfurization of HCFeCr melt.
Abstract: Slag skin formed in electroslag remelting (ESR) is obviously deposited in layers in the thickness direction. In this pa-per, the specimens of slag skin in the production process were taken for experiment and analysis. The detailed microstructure and chemical composition were obtained at different positions. Based on the mechanism of quenching layer formation, it is suggested that the composition of the quenching layer can be used to reflect the composition of the slag pool in the corresponding time. The composi-tion change of the slag pool in ESR process can be speculated by checking the slag skin quenching layer near the mold at different posi-tions (different heights of an ingot).
Abstract: The cleanliness evolution of SWRH82B steel produced by the BOFLFCC process was studied by systematic sampling and lab comprehensive analysis. The results show that the content of oxygen and the number of micro-inclusions significantly decrease after calcium treatment,while the content of nitrogen in molten steel slightly increases. Both the contents of oxygen and nitrogen sharply increase during the casting process. 97% of the micro-inclusions in casting billets are smaller than 5 μm. They mainly include trenchant angularity single Al2O3 inclusions,spherical complex inclusions of oxides with Ca S and Mn S,and complex inclusions of simple oxides or nitrides with Mn S. Calcium treatment after LF refining removes oxygen from molten steel efficiently,but increase the amount of Al2O3 inclusions in casting billets,which is harmful to the quality of SWRH82B steel. Due to serious lag entrapment,refractory erosion and reoxidation caused by unreasonable tundish structure,the cleanliness of liquid steel decreases.
Abstract: Based on the analysis of converter slagging and limestone slagging,the key point of smelting control and the operation strategies during the entire limestone steelmaking process were proposed in this paper,combined with the research of the double-slagging process by lime. According to the production practice in Shijiazhuang Iron and Steel Company,the entire limestone steelmaking of special steel was conducted. In the results,the average C content of the molten steel after converter tapping is 0.16%,and the average P content is 0.011%,which meet the requirements of special steel production. Compared with the entire lime steelmaking,the cost of entire limestone steelmaking is reduced by ￥2.32 per ton molten steel. The results of the industrial experiment show that the entire limestone steelmaking can make good economic benefits,and has some promotional values.
Abstract: To improve the effect of LF refining on SPHC steel, thermodynamics software FactSage was used to analyze the physi-cochemical properties of the LF refining slag system, and then the corresponding optimization scheme was verified by industrial verifi-cation. Experimental results show that at the end of LF refining, the total oxygen T[O] in steel decreases from 24×10-6 to 20×10-6, the total removal rate of micro inclusions increases from 56.67% to 71.54%, and the amount of large inclusions decreases to 42.45 mg/10 kg from 85.42 mg/10 kg by the optimization of the LF refining slag system.
Abstract: To study the source of inclusions in casting billets, 10% BaCO3, 10% SrCO3, and 10% La2O3 were used as tracers into the steel ladle, tundish covering flux, and tundish-coating refractories, respectively, during the production of non-oriented silicon steel. The steel and slag samples were taken from the related working procedure, and scanning electron microscopy (SEM) and a mi-croscope were used to analyze the morphology and composition of inclusions. Experimental results show that the large inclusions in non-oriented silicon steel are mainly SiO2, Al2O3, and aluminosilicate, resulting from the protecting slag and secondary oxidation.
Abstract: The changes of total oxygen(T. O.) and N contents,the evolution of non-metallic inclusions,and the characteristic of macro-inclusions in casting billets of 50 CrVA spring steel produced by the BOF-LF-CC process were studied by continuous sampling at different stages. Results show that the average contents of T. O. and N are 106×10-6 and 13×10-6 at LF-start,respectively,and they become 15×10-6 and 39×10-6 in billets,indicating that the deoxidization effect in the LF refining process is obvious. However,reoxidation phenomenon is obvious in the transportation and casting processes,so it is necessary to strengthen the steel stream protection from ladle to tundish. The CaO-Al2O3-MgO and CaO-Al2O3-SiO2 composite oxide inclusions are the main inclusions in billets,the Al2O3 content in those inclusions is as high as 60%-70%,and no low-melting inclusion is obtained. The low-melting inclusion can be obtained by increasing the slag basicity or feeding a proper content of Ca wire. Large-size inclusions are primarily composed of CaO and CaOAl2O3-SiO2-(MgO) spherical oxides as well as a certain proportion of pure Al2O3 inclusions. It is necessary to extend the soft stirring time in the ladle to make inclusions float fully.
Abstract: In order to control large calcium aluminate inclusions in bearing steel, the quantitative relationship between refining slag composition and inclusion type is discussed by calculating the formation thermodynamics of MgO·Al2O3 and CaO·6Al2O3 in this paper. The results show that MgO·Al2O3 can be reduced to CaO·6Al2O3 by dissolved aluminum with 0.10×10-6 Ca and less than 10×10-6 Mg in molten steel. When the basicity of refining slag is 7.04 and the content of (MgO) is 1.38%, the content of Mg in liq-uid steel is about 56% lower than the critical value, and the main inclusions is CaO-Al2O3, whose dimension is larger than 10μm. As the basicity of refining slag is 3.75 and the content of (MgO) is 3.14%, the content of Mg in liquid steel is about 14% lower than the critical value, and the main inclusions is MgO·Al2O3 surrounded by MnS, whose dimension is less than 8μm. Under the condition that the Ca/Al ratio is between 1.8 and 2.0, MgO·Al2O3 inclusions can be kept stable rather than reduced to CaO·6Al2O3 when the basicity of refining slag is between 4.5 and 5.5 and the content of MgO is between 3% and 5%.
Abstract: The effect of electroslag remelting(ESR) on nonmetallic inclusions in an optimal component 42 CrMo steel was studied by BX51 M optical microscopy and Image Pro-Plus software,and the continuous cooling transformation(CCT) curve was measured on a Gleeble3000 thermal simulation machine. These results show that ESR can reduce the number and size of inclusions in steel samples and the inclusions removal ratio reaches 71.90%. The CCT curve of 42 CrMo steel was plotted according to the thermal expansion curve and microstructure. When the cooling rate is lower,the microstructure is ferrite,pearlite and bainite; but when the cooling rate is higher,there are martensite and a small amount of bainite.
Abstract: High quality GCr15 steel produced by EAF-LF-VD-CC process was systematically studied by sampling in various sta-ges for a domestic factory. For the random characteristics of DS inclusions, the evolution rules of inclusions in bearing steel smelting process were investigated by ASPEX inclusion quick analysis equipment, which can scan the specimen surface in large enough area. The results indicate that the main inclusions are MgO-Al2O3-CaO and MnS, and there are also a small quantity of SiO2-Al2O3 and MgO-Al2O3. The size of the majority of inclusions is 3-8μm, few DS inclusions have a large size range, the biggest one can be more than 70μm, and the morphologies of the inclusions are round or nearly circular. Inclusions will be significantly removed by VD process and the content of CaO in inclusions increases after VD process. The content of Al2O3 in inclusions increases during the tundish to continuous casting process. Finally, the content of Al2O3 in inclusions is more than 80%, the content of MgO is less than 20%, and the content of CaO is less than 5% in the ternary system of MgO-Al2O3-CaO. The formation and removal behaviors of DS inclusions in bearing steel are of higher degree randomness.
Abstract: The mass transfer rate between steel and slag determines the reaction rates of elements in a molten bath(especially the reaction rates of desulphurization and dephosphorization),and has direct impact on the distribution ratios of elements between steel and slag. In this article,Hangang 250 t converter was taken as the research object. Factors such as gas flow,lance position and bottom blowing location were taken into consideration to study the mass transfer ability of the convertor by a water model whose similarity ratio was 1:9. The results show that increasing the top-blowing intensity and the bottom-blowing intensity can greatly improve the distribution ratios of elements in the molten bath between steel and slag. The mass transfer coefficient between steel and slag decreases obviously with the drop of bottom-blowing air flow,thus a bottom-blowing air flow not lower than 0.06 m3·t-1·min-1 is suggested. The more the bottom-blowing holes are,the larger the mass transfer coefficient between steel and slag gets. A distribution plan of bottomblowing air flow is presented,which is superior to the equal distribution plan of air flow.
Abstract: Based on the fact of high nitrogen pick-up, large nitrogen fluctuation and poor control in some steel works, the main aspects of nitrogen removal and nitrogen pick-up in an ultra-low-carbon Al-killed steel smelting process were summarized by analyzing the process data and sampling. The main sections for nitrogen removal are BOF decarburization period and vacuum treatment. High decarburization amount can lower the nitrogen content at the BOF endpoint. There is just a limited effect of switching between nitrogen and argon on the final nitrogen content at the BOF endpoint before the point of 70% oxygen blowing. Free oxygen is favorable for deni-trification by promoting the reaction of carbon and oxygen under the RH mode, in contrast under the VD mode. When free oxygen in liquid steel is controlled above 200×10-6, the nitrogen absorption during tapping can be controlled within 5×10-6. The nitrogen introduction of furnace charge is the important factor of nitrogen pick-up during the vacuum refining process, and it is up to 11×10-6. The minimum of nitrogen pick-up can reduce to 1×10-6 by adopting gasket sealing and argon blowing protection simultaneously.
Abstract: The formation conditions of shale gas in Wufeng-Longmaxi Formation of Yanjin-Gongxian area were analyzed on the basis of field observation and experimental data,and then the main factors for shale gas accumulation were discussed. Results show that black shale at the bottom of Wufeng-Longmaxi Formation is a deep-water shelf deposit product. The dessert shale gas from the first stage of Wufeng to the fourth stage of Longmaxi was complete. The organic carbon content is between 2.7%-6.0%. Mainly for the high organic carbon content,the thickness of black shale rich in organic matter is 30-50 m. In the high gas horizon,nanometer organic pores and pyrite intracrystalline pores are abundant,and the average rate of porosity is 2.28%-3.48%,providing a good reservoir space for the adsorbed gas and free gas. Structural strength in the research area is weak and large faults are less. There are good conditions of roof and floor. The pressure coefficient is more than 1,which reflects the suitable preservation condition. The main factors for shale gas accumulation are as follows:deep shelf sedimentary environment,high organic carbon content,abundant nanometer pores,high level porosity,and high pressure coefficient.
Abstract: Based on the characteristics of CO2 at high temperature, material and energy models for CO2 using in a dephosphoriza-tion converter were established to verify the feasibility of CO2 for oxidation reactions. Based on practical working conditions in a facto-ry, the effects of CO2 on the converter temperature and gas were studied. It is discovered that the CO2 ratio can be controlled within 28%, the oxygen consumption can be reduced by 16%, and the CO ratio in the gas can be increased by about 12% when the scrap ratio is 8% and the utilization ratio of CO2 is 85%. Besides, as the utilization ratio of CO2 increases, the semi-steel temperature of the converter gradually decreases, and the oxygen consumption also lowers.
Abstract: The effect of annealing time and cooling methods on the microstructure and mechanical properties of Fe-28Mn-2.8Si-2.2Al-TWIP steel was studied by optical microscopy and electron backscatter diffraction technology. It is found that when the annealing time is 5,10 and 20 min,the austenite grains grow quickly. At the same time,annealing twins in the austenite grains get long and thick,the tensile strength and yield strength decrease,but the change in elongation is little. Compared with air cooling,water cooling is more advantageous for the TWIP steel to obtain good mechanical properties,and the cooling rate has a certain effect on the grain orientation.
Abstract: A finite element model to describe the solidification and heat transfer process and the elastoplastic deformation in a mould is built by using the commercial software Thercast to study the thermomechanical behavior of the billet. Firstly, applying the heat flux on the billet shell surface, we obtain the solidification shrinkage and the shell temperature distribution of the billet, analyze the effect of molten steel static pressure, and propose the taper design principle of the mould to determine an appropriate mould taper profile. Then, applying the water cooling heat transfer coefficient on the cold side of the mould and considering the effect of casting slag and gap on the solidified shell, we study the solidification process of billet shell in the mould, and thus verify the rationality of taper design.
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
