Abstract: Key technologies for the control of sulphur, phosphorus, nitrogen, oxygen, hydrogen, inclusions, slab quality, and narrow composition refining are assembled on studies by systematic sampling, process, and technologies analyzing about high grade pipeline production in various Chinese steel groups. Systematical process optimization of hot metal pretreatment, converter refining, secondary refining and continuous casting, and the assemble of special controlling technologies for various components against their characterizations and requirements are two important aspects of impurity and inclusion controlling for high grade pipeline steel. The application of the new inclusion modification standard on calcium treatment, and the improvement of process and technologies for unsteady casting are keys for the control of inclusions' harm on pipeline properties. While, the coordination of the optimized continuous casting process, perfect equipment management, and the appropriate refining process are keys for no defect slab production.
Abstract: Numerical simulation and physical simulation on the arrangement of 50 t LF with a bottom argon blowing nozzle were made by the commercial software FLUENT and a water simulation instrument. The effects of three different bottom argon blowing nozzle arrangement ways (haplopore, binocular central symmetry, and binocular rotational symmetry) on molten steel blending time and entrapped slag were studied. The results show that, with the same amount of argon, bottom blowing argon with binocular rotational symmetry gets the shortest blending time;the homogeneous and steady flow velocity in the surface and internal of the molten steel ladle is attained in the same arrangement ways, which can eliminate the stirring dead zone, avoid slag entrapment in molten steel, and provide favorable dynamic conditions for the removal of inclusions.
Abstract: The effects of basicity (R) and the (FeO+MnO) content of the refining slag on the deoxidation of A36 and 45A steels were investigated during the refining process, and the influences of basicity (R) and the (FeO) content of the slag on desulfurization were also analyzed. The results show that the desulfurization efficiencies are increased to 61.3% and 64.3%, respectively. In addition, the changes of[P],[H], and[N] contents were studied. And the results show that the average removal rate of inclusions is 70.27%, and the maximum is 85.62%.
Abstract: Before putting the scrap steel into the electric arc furnace (EAF), using the high-temperature exhaust gas generating from EAF to preheat it can bring obvious energy-saving effect. Continuous scrap preheating EAF is different from the ordinary EAF in the way of the scrap steel continuous feeding, continuous preheating and melting, electric arc heating molten pool and then the molten pool melting scrap. In order to achieve high efficiency and energy-saving, ensure operating the equipment smoothly in the process and optimize the operating parameters, based on the technology features of the continuous scrap preheating EAF the research results indicate that more attention should be paid to the building of EAF lining, power supply, oxygen jet decarburization, slagging dephosphorization and so on;As the whole "flat molten bath", once the electric power is supplied, the electric arc heats the molten steel and at the same time the slag line is radiated by the high temperature electric arc, so the slag line must be protected and therefore full-time submerged arc operation by foaming slag is required;full-time "flat molten bath" and "change slag line" phenomenon need the thickness of magnesia-carbon brick on slag line increase about 300 mm, thus the resistance of slag line change can be increased;To determine the transformer parameters of the continuous preheating EAF, the following requirements should be considered:the scrap steel melting (voltage to be higher), the flat molten pool heating and heat preservation (voltage to be lower) by the electric arc. The selection of the voltage should based on the arc shielding state (scrap, or slag shelter state);in order to maximize energy-saving and environmental protection, the re-use technology of the waste heat must be applied, the pollution of dioxin deserves attention and research.
Abstract: A new concept named "non-carbon metallurgy by solar energy photovoltaic technology" was put forward through the analysis of the iron source usage and the carbon metallurgy process. The main study included smelting at high temperature, no-carbon reduction, and melting-reduction. The experimental system with 1-kg capacity was designed and manufactured. Three kinds of experiments were carried out. It shows that the concept of "non-carbon metallurgy by solar energy photovoltaic technology" is feasible and the system can meet the needs of smelting. The conversion rate of the photovoltaic cell is 9.8% and the steel enthalpy accounts for 5% of the total energy consumption in the high temperature smelting experiment. The current efficiency is 85.1% with the highest being 97.6% during the electrolysis process. The decrease order of influence on the reduction degree of Fe2O3 is atmosphere temperature, time, and particle size in the hydrogen reduction process. According to the results, further study is needed to get better economy, stability, and operability of this system.
Abstract: The crystallization capability at high temperature and devitrification properties of glassy films in annealing of routine and optimized high-speed casting mold flux were studied. The results show that the optimized mold flux with high basicity has a higher crystallization temperature and a lower devitrified temperature;also, its crystal-forming abilitiy is much stronger in the same conditions. The main crystal phase of the optimized mold flux is Cuspidine(3CaO·2SiO2·CaF2) and it has larger crystalline particles. Moreover, there are a great number of gaps in the solidification structure, which can increase the roughness on the surface of flux films. Consequently, it can enhance the heat resistance of flux films and will be more suitable for high-speed casting.
Abstract: In order to study the oxygen jet in BOF steelmaking, the software FLUENT was used to simulate the characteristic of coherent jet oxygen lance and common oxygen lance. The advantage of coherent jet oxygen lance was proved by comparing the characteristic of the two lances. In a 35 t converter, coherent jet oxygen lance carried out a preliminary industrial test. The results demonstrated that the coherent jet oxygen lance solved the behavior of high phosphorus successfully, and the consumptions of steel stuff and oxygen were declined.
Abstract: The fluid flow of four-strand tundishes under two different control devices was studied by water model experiments and numerical simulation. The results show that the formation of short-circuit flow in the original tundish makes liquid steel have short residence time in the middle outlet, and have large difference of residence time compared with the edge outlet. The improved tundish can homogenize the residence time of molten steel between different outlets, decrease the dead volume fraction, and increase the removal rate of inclusions. The plant trial shows that the macroinclusion content and the microinclusion number in billet decrease by 44.9% and 2.7%, respectively, compared with those of the original tundish.
Abstract: Recycling reducing gas was heated to 1 100℃ with blast furnace gas, fuel gas from garbage power, low caloric value gas or with heat from hot coke, hot direct reduced iron (DRI), or other heat in a hot-blast stove. Then, the recycling reducing gas was input to a reductive shaft kiln to heat iron ore-coal briquette to produce DRI. Sulfur and CO2 were recovered from the top gas, and the purified gas was used as the recycling reducing gas. The carbocoal and coke from coal carbonization in the briquette acted as skeleton, which was different from coke in the blast furnace. The coal consumption of DRI was reduced through using the afterheat of reducing gas to preheat and carbonize briquette, using the high surface area of iron concentrate and coal powder, and using coal carbonization and gasification to accelerate carbon gasification reaction and direct reduction reaction at low temperatures. If the temperature of the top gas drops to 150℃, 218 kg coal is blended, and blast furnace gas of about 947 m3 is consumed, the energy consumption will be about 333 kg/t coal. Compared with the blast furnace process, this process can economize 52% energy and reduce about 83% CO2 emission;it will save about 84 kg standard coal than MIDREX process. This technical process is abbreviated to DRI-NHQ.
Abstract: An intensified purification control during tapping of converter was introduced. The results show that the[O] and (FeO) can be decreased effectively within a short period of time through this new process;based on the good dynamics condition during tapping, better refining effect and molten purity are obtained. By optimizing the process, some kinds of steel grades can be produced without LF treatment, which relieves the burden of LF.
Abstract: A carbon-oxygen reaction model was developed to simulate actual reactions in the RH process, and the calculation results were in good agreement with the measurement results. It was found that the initial carbon content had no influence on the carbon content at the end of decarburization in RH. The carbon-oxygen reaction nearly reached equilibrium due to 14 minutes' reaction at a decarburization rate of less than 1.5×10-6 min-1. The ratio of ΔO/ΔC of decarburization in the RH process decreased with the increase in the TFe content of ladle slag, and the ratio was near the theory ratio when the TFe content was 8%.
Abstract: In the process of molten steel casting, outflow slag must be detected when liquid steel in a ladle flowing into a tundish. After lots of investigations on the slag detection technology and experiments in the Steelworks internal and external, a kind of high-sensitive slag detection system has been put forward. It alters the traditional single detective mode in hardware, meanwhile makes the software of feature extraction simple. The results testing in the Steelworks proved the effectiveness of the slag detection system, which can control the slag flowing into a tundish and create benefit for Steelworks evidently.
Abstract: Deoxidization reaction of high grade pipe steel refining in LF was calculated and analyzed in thermodynamics. The reasonable deoxidizer dosage was obtained. The effects of oxides in slag and the slagging process on desulphurization were investigated by comparing the different factors in industrial experiments. A better slag system and indexes were recommended to increase the desulphurization efficiency. The results indicate that the first 20 min during the LF process is the most important period of desulphurization. The new method can shorten the melting time by nearly 8 min.
Abstract: The influences of liquid steel temperature and nitrogen partial pressure on the nitrogen solubility in 316 L stainless steel under normal atmosphere and vacuum were studied. The nitrogen solubility increased with decreasing the liquid steel temperature or increasing the nitrogen partial pressure. A thermodynamic model was developed to calculate the nitrogen solubility in 316 L stainless steel, and the calculated results were in coincidence with the measurement results under different nitrogen blowing processes. At 1 773 to 1 873 K, the nitrogen partial pressure must be over 6-28 kPa to produce 316LN (N:0.05%-0.10%, mass fraction, so as the follows), and must be over 22-101 kPa to produce 316 LN (N:0.10%-0.40%). The nitrogen content was over 0.01% in the condition of nitrogen blowing for 10 min under normal atmosphere.
Abstract: In order to control the total oxygen at an appropriate level, investigations on deoxidation and purification were carried out in ultra-low carbon and low carbon steels by means of the RH vacuum degasser in the General Steelmaking Mill, Wuhan Iron & Steel Co. Ltd. The results show that influential factors of total oxygen removal in the order from main to subordinate are the free oxygen level in the tapping molten steel, interaction between the free oxygen and slag, slag in the ladle, and the vacuum treatment time, respectively. The clean molten steel with a total oxygen content of 10×10-6 and nonmetallic inclusions less than 10 μm in size was produced by the optimizing process. A new equation involving the change of total oxygen concentration via the ladle with time is approved, which considers the influences of apparent oxygen equilibrium content, circulation, and diffusion mass transfer on the removal rate of oxide inclusions.
Abstract: One type of premelted refining slag was developed in this article. This new type refining slag has the characteristics of high basicity and low melting point. Under laboratory conditions, the average desulfurization rate reached to 84.5%. During the industrial experiment, the charging schemes of steel grades were distinct. The experimental results indicated that using the new type refining slag the slag-melting rate was 100% at the end of tapping and the refining time was shortened by 11 min. By comparison with original refining slag, oxygen content and nitrogen content in steel reduced respectively by 7×10-6 and 12×10-6 before VD refining and by 5×10-6 and 15×10-6 after VD refining. The desulfurization rate was also increased sharply. The results showed that the desulfurization rate was 92% from EAF tapping to craning ladle of VD, and the lowest sulphur content in steel was 30×10-6.
Abstract: The 150 t EAF steelmaking of Tianjin Pipe Group Co., Ltd uses four furnace charges for a long time, its average furnace charge is scrap of 46.2%, pig iron of 9.1%, hot molten iron of 26.4%, and DRI of 18.3%, the material and energy consumptions in the EAF steelmaking process were analyzed through the material and energy balance calculations. The influence of unit furnace charge on the material and energy consumptions in research process was obtained, as well as the input scope of electric power required by the compositions change of four furnace charge is 153~744 kW. Based on the stepwise regression analysis to the mass production data, it is found that the influence of RDRI is most remarkable. If it increases 1.0% every time, the electric power consumption per ton steel probably increases 1.4 kWh. Next impact factor is RHM. If it increases 1.0% every time, the electric power consumption per ton steel probably reduces 2.0 kWh.
Abstract: Based on the experiment of adding nitrogen in nitrogen-containing stainless steels by blowing nitrogen gas, the influencing factors including chemical compositions, temperature, superficial active elements and nitrogen-flow rate to molten steel's nitrogen absorbing were studied. The experimental results show that some alloy elements such as Mn and Cr can raise the nitrogen solubility in the molten steel;the temperature of molten steel increases, the rate of absorbing nitrogen increases correspondingly;the oxygen content in molten steel keeps molten steel from absorbing nitrogen;the nitrogen flow rate increases, the rate of absorbing nitrogen increases correspondingly. And the production process was discussed, which provides reference for adding nitrogen in nitrogen-containing stainless steels steelmaking process by blowing nitrogen gas.
Abstract: Based on the test of 1 kg molten iron in molybdenum-wound furnace and 10 kg molten iron in induction furnace, the influences of slag basicity, temperature of molten iron on simultaneous desiliconization and removing Mn and Ti were studied, and the removal behavior was systemically analyzed. The results show that the temperature of molten iron and the slag basicity do not contribute to desiliconisation and removal of Ti in molten iron, but affect demanganization very much, lower temperature and lower slag basicity are available to demanganization. When the hot metal temperature T=1 280℃ and the slag basicity R=0.44, the final content of[Si],[Ti] and[Mn] can reach 0.011%, less than 0.005%, and 0.024%, respectively, which meet the requirement of Mn content in high-pure pig iron.
Abstract: Thermodynamics on the formation and transformation of spinel inclusions in gas cylinder steel and the effect of calcium treatment on the compositions of molten steel and inclusions were studied by using Factsage 6.0 software. The results show that spinel inclusions will be produced even through the content of magnesium is very low, and the spinel inclusions will transform to liquid complex inclusions when the content of dissolved Ca in the molten steel exceeds 1×10-6. With the increase of calcium, on one hand, the contents of Al2O3 and MgO in the complex inclusion keep decreasing, and the content of CaO increases, but the content of SiO2 changes a little. On the other hand, the content of oxygen decreases, while the content magnesium increases.
Abstract: The relationship between calcium activity (α[Ca]) and aluminum content was analyzed by thermodynamic calculation to guarantee inclusions in liquid region after calcium treatment for X80 pipeline steel, and the α[Ca] ranges were determined to obtain liquid calcium-aluminates inclusions. The effect of relationship between[Al] and[S] on the forming of CaS and the effect of temperature on the precipitation of CaS were calculated quantificationally. The results show that when the mass percent of sulfur is 20×10-6, the CaS solubility in calcium-aluminates can reach 0.18%.
Abstract: Molten 430 stainless steel deoxidized by complex deoxidizers was studied in a MoSi2 furnace and an MgO crucible. The SiCaBa, SiAlBaCa, SiCaBaAl, SiCaBaMg and SiCaBaAlSr alloys were used as the deoxidizers, and Al and FeSi were used as the deoxidizers for contrasting. The total oxygen content in steel, the distribution, size and morphology of deoxidation products were studied. The results show that when deoxidized by SiCaBa alloy, a lower total oxygen content of 430 stainless steel can be obtained, the deoxidation products can easily float out from the steel and the size of inclusions in the steel can be significantly decreased, the morphology of which is changed to spheric shape.
Abstract: The inclusion removal rate in molten steel is influenced by molten steel flow and the bubble/inclusion size. As the research results shown, the upward movement of molten steel is in favor of the inclusion floatation, and almost all of the inclusions can float up. Inclusion and bubble flotation is hindered by the downward molten steel flow. Bubbles whose diameters are smaller than 1 mm can not float up when the molten steel flows downward. In the ladle refining process, small gas injection rate should be used to avoid forming excessive big bubbles, which will reduce the gas-injection efficiency, and to reduce the molten steel velocities, which is good for the bubble/inclusion flotation. But the gas injection rate also should not be too small, which ensures that bubbles in molten steel maintain a certain size to fully float up. In the ladle refining process, both the molten steel velocity and the bubble size should be considered when choosing the gas injection rate.
Abstract: The deoxidation experiments of liquid iron were carried out in the high temperature molybdenum wire furnace by adding SiMg alloy, Al and combination of both. At the same time, the additional sequence of SiMg and Al was changed in the experiments. The contents of dissolved and total oxygen and residual magnesium were measured and change of inclusions in molten iron over time was investigated. The results indicate that the limit of deoxidization by the combination of 0.02% (mass fraction) SiMg and 0.03% (mass fraction) Al is comparable with 0.05wt% SiMg only and the yield of Mg in the molten iron treated by the combination is improved greatly at 1 873 K. In the case of SiMg/Al deoxidation, the change of inclusions amount in samples over time is consistent with that obtained by only SiMg. The change of inclusions amount in samples over time in case of Al/SiMg deoxidation is consistent with that obtained by only Al.
Abstract: Based on the industrial experiments of VD treatment at HZSteel, the effect of slag on[Al]s was studied as well as the effects of vacuum holding time and vacuum degree on the total oxygen content. The results show that the higher the basicity, the less the[Al]s reduction in the steel in the basicity range of 2.5~4.5, while the reduction trend of CaO is increased;The longer the vacuum processing, the lower the total oxygen content in the steel, but not obviously decreases after 16 min;When vacuum is more than 67 Pa, the total oxygen content in steel drops with the decrease of the vacuum;However, when vacuum is less than 67 Pa, the total oxygen content in steel rises instead of decreases.
Abstract: According to the operating parameters of Jiuquan Iron & Steel Group, the factors, which affect the collision of inclusions and removal rate by coagulation, have been studied through the theoretical analysis and calculation. Increasing stirring energy and temperature of liquid steel is helpful for coagulation between inclusions. In the process of coagulation between inclusions, turbulent collision plays a main role. Inclusion removal by collision is suitable for inclusions having a radius of 1 to 13 μm, whose removal rates are 41.2%-87.8%.
Abstract: The influence of RH vacuum processing time on the total oxygen content and micro inclusion removal of bearing steel GCr15 was discussed. The results show that total oxygen content and micro inclusion amount will be decreased further by prolonging vacuum processing time, deoxidization during the RH process is caused by micro inclusion removal, and the relationship between the total oxygen content and RH vacuum processing time is in agreement with the relationship between the micro inclusion amount and vacuum processing time. After 25 min of the RH vacuum process, total oxygen content and micro inclusion amount are decreased by about 60%, which is 13% less than those after 14 min of the RH vacuum process. It is found that the deoxygenation coefficient is -0.036 min-1 under the RH production condition of bearing steel GCr15 in Xingtai Iron & Steel Corporation. The average total oxygen content of 147 heats bearing steel is 6.7×10-6 after process optimizing.
Abstract: A systematic investigation was carried on the variations of total oxygen content and inclusion types in 39Mn2V steel before and after calcium treatment.The modification mechanism of Al2O3 and MnS was analyzed by thermodynamics.The results show that Al2O3 can be wholly modified into 12CaO·7Al2O3 and 3CaO·Al2O3 inclusions which are liquid at steelmaking temperature,while MnS just can be modified partially into CaS under the present amount of Ca-Si wire fed.
Abstract: The formation and transformation of MgO·Al2O3 based inclusions in the gas cylinder steel produced by EAF-LF-VD-CC process flow have been studied. The three-dimensional inclusions were observed by SEM. The results show that after LF refining for 30 min, the content of Mg decreases and that of Ca increases in the inclusions, and MgO·Al2O3 inclusion disappeares;at the end of LF refining, the content of Mg in the inclusions has little changes, the content of Ca in the inclusions decreased, and no MgO·Al2O3 inclusion exists;during VD refining, the content of Mg in the inclusions increases, the content of Ca in the inclusions has little changes, and MgO·Al2O3 inclusion appears again;MgO·Al2O3 inclusion can be modified during refining, but to avoid forming MgO·Al2O3 inclusions again, the content of Ca in the molten steel have to reach a certain value.
Abstract: The experimental samples were the marine crank steel S34MnV produced by the EAF-LF(VD)-VC production process, including the electric period, LF-VD refining period, casting period, and forging ingots from a heavy machinery factory in north China to solve the difficulty of being rejected by ultrasonic flaw detection for crank shaft. These samples were analyzed by the methods of metallographic observation, energy spectrum, and the electrolysis. The obtained results indicated that there was a large number of inclusions during the refining stage, and the proportion of inclusions with the size bigger than 15 μm accounting to total inclusions were within 1.65%-10.34% after VD process. Furthermore, the probability of inclusions captured by columnar crystal in the steel ingot cross-section was found changed obviously in different locations of ingot cap. The content of large inclusions in the center of the beginning of the ingot cap was 5.81 mg/10 kg, with increasing the distance from the center to the edge, whereas this value decreased to only 25.9 mg/10 kg in the rear center of ingot cap, with decreasing the distance form the center to the edge. In addition, large numbers of inclusions was found to exist in the forging ingot with the biggest inclusion of a 140 μm DS category, which were difficult to be cut off completely and would be the main reason of being rejected by ultrasonic flaw detection for crank shaft.
Abstract: A statistical analysis on the compositions of inclusions in high carbon wire rod produced by one steel company was conducted. And the compositions of low melting point inclusions of Al2O3-SiO2-MgO-CaO-MnO system in a high carbon wire rod steel with Al-Si-Mn deoxidization were calculated and analyzed by the thermodynamic software FactSage. In the low melting point zone of the Al2O3-SiO2-MgO-CaO-MnO system for a high carbon wire rod steel, the Al2O3 content should reach 56%, and CaO 20%~30%.
Abstract: Based on the theoretical analysis of TiN inclusion precipitation in bearing steel, the saturation solubility curves of TiN inclusion precipitation under different solidification rates was calculated. The control range for[Ti] and[N] is proposed to prevent TiN inclusion precipitation, and control measures for[Ti] and[N] are raised in the production process.
Abstract: The formation thermodynamics of the existed TiN inclusion and the control theory of titanium and nitrogen in bearing steel were studied. Then based on the theoretic calculation results, the industrial trials of GCr15 bearing steel were carried out in a steel plant. The results showed that the higher the titanium or nitrogen content in steel is, the higher the precipitation temperature of TiN, and the bigger the size of precipitates;the use of low-Ti alloy materials can effectively reduce the Ti content;using low-Ti molten iron and reducing the TiO2 content to less than 1.0% in furnace slag can control the Ti content effectively. The use of low-titanium synthetic slag can make Ti content of the steel drop from the original 37×10-6 to 30×10-6. Optimized and improved refining processes protective casting process can reduce the N content of 33×10-6. With the degree of solidification segregation decreases, the precipitation of TiN inclusion is reduced.
Abstract: The morphology and sizes of inclusions after liquid steel Ca treatment,in the slab and in the plate were researched by SEM for high strength and low alloy (HSLA) steel containing 0.065%Ti.The composition of inclusions was studied by EDS.The results show that most of inclusions in the slab and plate are CaO-Al2O3-TiOx-CaS inclusions,and few of them are TiN inclusions. The inclusions have been modified well by Ca treatment.The precipitations of TiN and CaS have been analyzed by thermodynamic calculation.
Abstract: A computational fluid flow model was applied to investigate the effects of electromagnetic brake (EMBr) field strength on flow in the mold cavity. The three-dimensional, steady k-ε model of the nozzle and liquid cavity in the mold applied for the magnetic induction method in FLUENT to add the localized-type static EMBr field which was measured at a steel plant. The 3-D fluid flow, heat transfer, and inclusion removing on top free surface in a continuous casting strand with EMBr were investigated. It is found that EMBr effectively slows the speed of molten steel exiting from the nozzle outlet, reduces impingement impact of the jet on the narrow face, and shortens the penetration depth of the lower recirculation zone. It is also helpful to increase the temperature of molten mold flux at the meniscus by 2-5℃. Larger inclusions are easy to be entrapped by mold slag. The inclusion removing fraction increases with an increase in magnetic field strength when the diameters of inclusions exceed 30 μm.
Abstract: The effect of solidification structure on the centerline segregation and flow of molten steel has been studied based on the steel production and the solidification structure.The interface of solidification goes ahead regularly and the solutes concentrate on the center of slabs,which cause the segregation.But if the columnar crystals are developed and the solutes rest on the interspace of columnar crystals,the centerline segregation can be improved.The solidification interface of equiaxed grains can spread the solutes around it,which can improve the centerline segregation,but when the phenomena of molten steel complementing the solidification shrinkage happens in the region of equiaxed grains,it will worsen the centerline segregation.
Abstract: The temperature distribution and solidification heat transfer process of round billet in different drawing blank technics were studied by means of solidification/melting models of Fluent software and pin shooting jointly, taking round billet horizontal continuous casting process as the research object. By this studies, the liquid steel temperature field distribution in the mold was obtained, and effects of casting process on steel temperature field inside of the mold was achieved. The results show that, through nailing experiment and numerical simulation using Fluent software, the solidification heat transfer model can be established, liquid solidification in continuous casting steel heat transfer process can be effectively analyzed, and the quality of molten steel can be improved.
Abstract: With the investigation of continuous slab casting factory, the slab broadening phenomenon of different degrees in the continuous casting process was found, and the broadening amount could not be corrected through the adjustment of process parameters. According to the correlation between the mould size and slab broadening, the mould setting formulas for correcting the broadening amount were obtained;combined with the width of slab measured at the exit of caster, the mould setting data for correcting the broadening amount could be obtained to control the width of the slab. A specific application is shown combined with the parameters of the secondary continuous slab caster in Ma'anshan Iron and Steel Co., Ltd.
Abstract: Surface network cracks that often appear in bloom casting can cause severe longitudinal cracks during the rolling process. Through micro-examination and hot tensile tests, several results were obtained. The surface network cracks are obviously intergranular located at the boundaries of abnormally large prior-austenite grains. It has been recognized that network cracks are associated with large prior-austenite grains, residual Cu element, precipitation of carbides and nitrides (AlN, BN, Nb(C, N)), and ferrite films. The main precondition for crack formation appears to be a coarse microstructure, which leads to critical concentrations of segregated solutes and precipitates along the austenite grain boundaries. This may lead to a combined effect of region Ⅱ-and Ⅲ-embrittlement for network cracking. The cracks occur mostly at the locations where bulging or surface depression appears. The study has shown that the abnormally large prior-austenite grains are caused by higher superheat and uneven cooling.
Abstract: Based on the theories of Ostwald ripening, the coarsening law of Ti(C, N) in 20CrMnTi gear steel was calculated at 930℃. The results show that when the holding time is 1, 2, 4, 8, 16 h, with the increase of holding time, the coarsening of Ti(C, N) particles would occur to some extent. While the coarsening rate coefficients m of second phase is greater, the coarsening is more serious. The range of dt which is the average size of the second phase at t time is 2.64-16.2 nm and 3.33-20.4 nm when the holding time is 8 h and 16 h respectively with the maximum deviation 13 nm and 17 nm apart. So Ostwald ripening has little effect on the particle size of second phase Ti(C, N), and it is the original size of the particles that has the main influence on pinning the grain boundaries and preventing austenite grain growth.
Abstract: The influences of microalloy element niobium (Nb) on the stacking fault energy and mechanical properties of Fe-22Mn-0.4C alloy were analyzed. The stacking fault probability of Fe-22Mn-0.4C alloys with different Nb contents was determined by X-ray diffraction (XRD) profile analysis. The result shows that, with the increase of the Nb content, stacking fault probability decreases and the stacking fault energy of the alloy increases. During tensile deformation, the dominated deformation mechanism turns from transformation induced plasticity (TRIP) gradually into twinning induced plasticity (TWIP). Different deformation mechanisms play roles in the alloys with different Nb contents, which lead to changes in mechanical properties and stacking fault probability.
Abstract: The 00Cr13Ni4Mo ultra low-carbon martensitic stainless steel was decarbonization refined by a 40t VOD.The vacuum degree,temperature,supplying oxygen intensity,and argon intensity were controlled as about 260660 Pa, 1600℃, 570 Nm3·h-1, and 48.4 NL3· min-1, respectively,during inputting oxygen by regulating the optimal parameters in the furnace.However,after finishing blowing oxygen,these four parameters changed to 7998 Pa, 1750 to 1800℃, 550 Nm3·h-1,and 117.5NL3· min-1, respectively.The height of oxygen lance was controlled as 75mm.It should be pointed that the increase of supplying argon intensity at the same stage can expedite the circular speed of molten steel in the ladle.
Abstract: Effect of precipitation and solid-solution on slab's quality and product's mechanical properties is very important. Based on studying effect of carbon content, nitride content, niobium content and temperature on solid-solution of carbonitride, the following laws were obtained. Firstly, solid-solution temperature will rise when content of carbon, nitride and niobium increases. Secondly, effective activity of NbN goes upwards with increases of content of nitride, and amount of solid-solution of niobium reduces. Quantity of NbN rises with increase of content of niobium from 800℃ to 1 100℃. The same laws can also be used for effect of carbon content. Niobium ratio between solid-solution amount and total content rises with increase of temperature, the ratio value lies from 30% to 70%.
Abstract: Banded structure is one of the main defects which influence inner quality of medium-and low-carbon pinion steels. In this paper, the banded structures of industrial pinion steel samples of 20CrMnTiH and SAE8620H were observed by optical microscope, and the results of EPMA analysis showed obvious banded segregation of alloying elements, such as chromium, manganese and silicon in these two types of samples. However, the results revealed that element segregation is, not a sufficient, but a necessary condition of forming banded structures, since in some examples even the banded segregation of elements was observed while the banded structures did not exist. In addition to micro segregation, other properties of alloying elements, such as their effect trend on the transition temperature from austenite to ferrite (Ar3), their solubility or content in steel, their effect on the carbon activity and CCT curves, also give significant influence on the formation of banded structures. In order to weaken or eliminate banded structures, several possible ways were suggested for the industrial practice.
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
