Abstract: The sticking during reduction of iron ore fines under different atmosphere conditions was studied by using a thermal state visible fluidized bed from 973 to 1173 K.It is found that when defluidization occurs the influences of temperature and reducing atmosphere on the metallization rate of iron ore fines are limited if the superficial gas velocity is constant.At the same time,the surface microstructure of particles when defluidization happens is strongly dependent on reducing gas types and reduction temperature,but it is less dependent on the volume fraction of reducing gas.In addition,with the volume fraction of reducing gas increasing,the fluidization time of iron ore fines gradually decreases,and the mathematical relationship between them was obtained by linear fitting at different temperatures.
Abstract: The influence of coke reactivity on the ferric burden reduction of the lumpy zone in a blast furnace was studied by using five kinds of coke with different reactivities.The pressure drop and CO volume fraction of the burden layer as well as the burden reduction degree were also analyzed.It is found that the coke gasification rate,CO volume fraction of the burden surface,and burden reduction degree increase with the increase of coke reactivity.When the CO volume fraction(only considering CO and CO2) of the original gas is 72.22%the burden reduction degree increases from 33.18%for low-reactivity coke to 53.83%for high-reactivity coke.When the CO volume fraction of the original gas is 66.67%,which is slightly lower than the CO theoretical equilibrium volume fraction of FeO reduction at 900℃, metallic iron can be obtained by means of high-reactivity coke.Therefore,appropriately increasing the coke reactivity in a blast furnace can promote the coupling reaction between coke and ferric burden,improve the CO volume fraction of the burden layer,and increase the burden metallization rate before going into the cohesive zone.
Abstract: The product composition under different conditions and the reduction behavior of Fe and Ni in the Fe-Ni-0 system were studied by electric resistance furnace experiments and thermogravimetric analysis.The order of difficult degree for reducing Fe/Ni oxides in five systems is NiOFe2O3+NiFe2O3+NiONiFe2O4Fe2O3.The existence of Ni can promote the reduction of iron oxides,while the contribution degree depends on its initial state,and the order tends to be metallic NiNiONi released from NiFe2O4.As the temperature increases,the reduction products of NiFe2O4 are in order of Fe3O4,Ni,(Fe,Ni),Fe,and Fe0.64Ni0.36.Based on these experimental results,the reduction processes and the kinetics such as activation energy and rate-controlling step for reducing the five oxides were analyzed and discussed.
Abstract: To find out the origin of 20Mn2 axle crack defects during rolling round pipes to square pipes,the formation mechanism and influencing factors of the crack defects were studied by optical microscopy,scanning electron microscopy,and O/N automatic analyzer.It is shown that cracks all appear at the corners of square pipes,where the mass fraction of nitrogen is more than 70×10-6.Upper bainite is found in the microstructure of cracked specimens and there are non-metal inclusions at the cracks.The crack defects can be effectively decreased through reducing the nitrogen content of liquid steel,enhancing the cooling speed of quenching,reducing inclusions in the steel.
Abstract: Based on the double-sublattice model,the mass fractions of Nb,Ti and Al precipitates in two high-grade pipeline steels were calculated at different temperatures.The sizes of austenite grains in the two steels were determined at different heating temperatures after different soaking time.Two models were built to describe the austenite grain growth.It is found that the complete-solution temperature increases with the addition of Nb.The amount of small carbonitrides at the sides of grain boundaries,which hinder the austenite grain growth,also increases due to the drop of temperature.Austenite grains in the high-Nb steel remarkably coarsen when the soaking temperature is 1250℃,the prediction model is different from those used between 1050 and 1200℃,but the austenite grain size is obviously smaller than that of the low-Nb steel at the same soaking temperature.Based on the data-fit method,the austenite-growth activation energy of the high-Nb steel is calculated,which is much larger than that of the low-Nb steel.It is again proved that austenite grains are greatly refined in the high-Nb pipeline steel soaked at temperatures no more than 1200℃.The prediction models show good agreement with experimental data.
Abstract: 22Si2MnCrNi2MoA drill steel was tested by optical microscopy,scanning electron microscopy and energy dispersive spectroscopy to study its dynamic continuous cooling phase transformation law and annealing process optimization,analyze the effect of cooling rate on its continuous cooling transformation(CCT) curves and transformation microstructure,and find out the cause of banded structure formation and measures for quality improvement.It is shown that the steel has high hardenability,and a bainite and martensite duplex microstructure is obtained when the hot rolled material is cooled in air after deformation.The optimal annealing process is at 710℃for 5 h.The composition inhomogeneity of the banded structure in the steel cannot be eliminated by isothermal annealing.The banded structure is caused by the segregation of the alloy elements of Si,Mn,Cr,Ni and Mo,and can be weakened by improving the crosssection deformation uniformity of bars.However,the homogeneous distribution of alloy elements in the metallurgical process is the critical way to reduce or eliminate the composition inhomogeneity of the banded structure.
Abstract: A kind of TRIP steel without Si was heat-treated on a Gleeble3500 thermal simulation testing machine. Its mechanical properties,microstructure,and phase transformation were studied by tensile machine,scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and thermal dilatometer.The effects of bainite transformation temperature and time on the mechanical properties and retained austenite in the Si-free TRIP steel were analyzed.It is found that the Si-free TRIP steel has excellent overall mechanical properties with the tensile strength of 740 to 810 MPa and the elongation above 25%,which can reach up to 32%.The best comprehensive mechanical properties can be achieved when the isothermal bainite transformation temperature is 420℃.At this temperature,the tensile strength decreases and the elongation increases with the increase of bainite transformation time, but the yield strength has no significant change.The size of ferrite grains in the Si-free TRIP steel is 3 to 4μm,smaller than that in the Si-containing TRIP steel.The volume fraction of retained austenite is 8%to 10%,about 3%lower than that in the Si-containing TRIP steel.Bainite transitions in the Si-free TRIP steel almost complete at 420℃for 300 s, but the diffusion of C still continues.Compared to the Si-containing TRIP steel,bainite transitions in the Si-free TRIP steel are much faster and the bainite transformation amount is bigger.
Abstract: A series of Fe-Mo-C steels with the Mo mass fraction of 0.1%to 0.8%were designed to study the high-temperature strengthening mechanisms of fire-resistant steels with Mo addition.Two heat treatments were carried out on the Fe-Mo-C steels to investigate the strength contributions of Mo addition from solid-solution strengthening and bainite strengthening.It is found that Mo can remarkably increase the high-temperature strength of the Fe-Mo-C steels.The dominant strengthening mechanism is solid-solution strengthening.The contribution of Mo addition to strengthening the Fe-Mo-C steels shows a rapid increase with the mass fraction of Mo no more than 0.5%,and the yield strength at 600℃ goes up by a significant 13.71 MPa per 0.1%Mo addition.But the high-temperature strength slowly increases when the mass fraction of Mo is more than 0.5%.Bainite strengthening also has great effect on the high-temperature strength of the Fe-Mo-C steels,and the strength increases remarkably when the volume fraction of bainite exceeds 20%.
Abstract: The corrosion behavior and mechanism of 304 stainless steel exposed for different time periods in the marine atmosphere of Xisha islands were studied by scanning electron microscopy,energy dispersive spectra,electrochemical impedance spectroscopy,and Raman spectroscopy.Pitting corrosion is the main corrosion type of the steel in the atmospheric environment.The main compositions of the corrosion products areβ-FeOOH,γ-Fe2O3,and Fe3O4. With the exposure time prolonging,the stability of the passive film deteriorates,the pitting number and depth increase, and the coverage of the surface corrosion products also enlarges.The pitting initiates more easily at scratches on the surface.The increase in machining precision of the surface will improve the pitting corrosion resistance.
Abstract: The influenced corrosion behavior of Q235 carbon steel was investigated in the presence of Penicillium by using the surface analysis method,mass loss method,and electrochemical method.It is demonstrated that dense biofilms and depositing films of corrosion products form on the surface of Q235 carbon steel in the presence of Penicillium. Corrosion of Q235 carbon steel is evidently promoted and the corrosion morphology of Q235 carbon steel is pitting in Penicillium systems.The films on the surface of Q235 carbon steel changes through a complex process,from free state to solid state and single-layer to multilayer.The effect of the biofilm depends on bacterial activity,and the corrosion promotion of the biofilm decreases as the bacterial activity weakens.
Abstract: Calcium oxide(CaO) was prepared by directly pyrolyzing the precursor called calcium carbonate (CaCO3),which was synthesized by solid-state ball milling reaction between NH4HCO3 and CaSO4·2H2O,the byproduct generated during the preparation of MnSO4.The effects of NH4HCO3-to-CaSO4·2H2O molar ratio,milling time,and ball-to-feed mass ratio on the conversion of CaSO4·2H2O were investigated respectively.The product was analyzed by X-ray diffraction and chemical analytical method.The reaction mechanism was also discussed.When the NH4HCO3-to-CaSO4·2H2O molar ratio is 3.5:1,the milling time is 40 min,and the ball-to-feed mass ratio is 5:1,the conversion rate of CaSO4·2H2O reaches 99.8%.Calcium oxide,whose purity is 99.2%,can be prepared by pyrolyzing the precursor at 1000℃for 1 h.The effectiveness of the solid-state reaction is improved by refining the reactant size, increasing the contact area,and providing necessary energy during the ball-milling process at ambient temperature.
Abstract: Coarse and spherical tungsten powders were prepared by wet hydrogen reduction.Ammonium tungstate solutions with the additives of Li,Na and K alkali metal salts were used as raw materials.The effects of the type and content of the alkali metal salts as well as reduction time on the microstructure,chemical composition,phase composition, and particle size of ammonium paratungstate(APT) and coarse tungsten powders were investigated by scanning electronic microscopy,energy dispersive spectroscopy,X-ray diffraction,and test sieves.It is shown that ideal tungsten powders with good fluidity,sphericity,integrity and even distribution can be obtained by using the ammonium tungstate solution with 3 g·L-1 NaCl,KCl and Li2CO3 and reducing at 1000℃for 180 min in wet hydrogen atmosphere.The average particle size of the obtained tungsten powders is 67μm,the maximum particle size is 150μm,the biggest loose density is 13.41 g·cm-3,and the best powder flowability is 9 s for 50 g tungsten powders.
Abstract: Existing methods are not accurate enough to apply in the solution of shaping curves for narrow steps in cross wedge rolling.In order to solve this problem and explore the shaping essence,the curve solution was described as the initial value problem of a differential equation by improving the previous geometric model and analyzing the relationships among various factors in shaping processes.A numerical method by mathematical programming software was used to solve the discrete results of the shaping curves.Through simulation and practice experiments,the calculated results were compared with data in literatures.The comparison of step size obviously shows that this method is not only able to be established,but also better than previous methods on the shaping accuracy of narrow steps.
Abstract: A algorithm was proposed to distinguish the initial vibration of rolling mills in tandem rolling.Firstly, a new morphological un-decimated wavelet(MUDW) based on a multi-scale average filter is developed according to the MUDW's general structure.Then the relationship between the new MUDW scale and real frequency is found by simulation experiment.Finally the time information of fault frequency from rolling mill vibration signals is extracted using the algorithm based on the new MUDW and S-transform.
Abstract: A multi-objective scheduling model was developed to solve the steelmaking-continuous casting scheduling problem of a special steel plant.Static scheduling and dynamic scheduling were investigated in the solving process of the model.The production modes in static scheduling were classified and the corresponding solving methods were formulated in combination with the running principles of steelmaking workshops and on the basis of the operation cycles of steelmaking furnaces and casters,while time-adjusting methods based on scheduling rules were described for the process of dynamic scheduling.A case in a BOF special steel plant,in which three casters are producing at the same time,was used to test the methods,and the scheduling plans of three casts were calculated and compared with actual production data.The comparison result indicates the validity of the methods.
Abstract: To solve contradictions between market demands and productivity,the problem how to arrange the production,which not only meets the needs of many customers for all types of products,but also gives full play to productivity was discussed under the premise of smooth running in iron and steel plants.A domestic special steel plant, which produces long products,was chosen as an example,and the reasonable proportion of different type of products was analyzed in combination with the concepts of product structure and productivity.The relationship between product structure and productivity was studied from three aspects of the equipment,the processes and the steelmaking plant. Finally,a method was proposed to calculate the reasonable product structure and productivity.
Abstract: A preview tracking control method based on tracking reconciliation error and switch rules was provided to deal with the preview tracking control problem of time-limited objective trajectories in continuous-time systems.This method consists of the following steps.First,the trace reconciliation error,the position tracking error,and the derivative of the state variable are combined into a new system state variable,which transforms the tracking problem into a regulator problem and builds a tracking control system with an objective value preview based on reconciliation error.Second,by means of switching systems,the problem of complicated objective trajectories crossing over different coordinate axes is solved.This leads to the global preview tracking control of objective trajectories.In addition,the paper is also a typical example whose subsystem is a time-varying switching system.Numerical simulation results demonstrate the effectiveness of the suggested method.
Abstract: A strength reduction method(SRM) based on the generalized Hoek-Brown yield criterion was used to analyze the stability of tunnel surrounding rock.The program code of SRM was compiled by FISH language embedded in the finite difference software FLAC3D,and the safety factor was determined according to the criteria including the convergence of numerical computation and the mutagenicity of feature points' displacement.Regarding to four basic input parameters in the generalized Hoek-Brown yield criterion,σci,mi,GSI and D,the equivalent approach index was introduced to discuss the rationality of seven strength reduction paths.It is concluded that the rationality of strength reduction paths depends on specific engineering parameters.This conclusion is verified by an engineering case.The global stability of tunnel surrounding rock decreases with the increase of D values,and the stability judging method combining the convergence of numerical computation with the mutagenicity of feature points' displacement is more reasonable than either of them.
Abstract: According to the characteristics of a buried sewage treatment system,the start-up of high concentration microbial agents in dealing with analog household sewage was studied in a biofilm reactor.When the chemical oxygen demand,ammonia nitrogen,and total phosphorus are 750,48 and 7.5 mg·L-1,the removal rates of them are 85%,58%, and 35% after operation for 10 d,respectively.Optical microscopy and environmental scanning electron microscopy observations show that with the system removal rate increasing,the microbial species gradually changes.The results of polymerase chain reaction-denature gradient gel electrophoresis(PCR-DGGE) demonstrate that the microbial species on volcanic rocks and suspended fillers are abundant,and the microbial community changes under different conditions, but the whole system of microorganisms maintains relatively stable.
Abstract: An early warning method for the risk of crowd gathering based on the bi-directional flow ratio of the section was proposed according to the characteristics of the opposite movement of pedestrian flow at the business street. Its error was analyzed in theory and verified by an example.It is found that using this method as a criterion of crowded events is feasible.Whether the measured values are greater or less than the true values,the error of the ratio between the inward and the outward flow across the section is less than that from a pedestrian flow statistic system,so the method is helpful for improving the accuracy of crowd statistic tools to some extent.In addition,the method can be used as a reference in selecting the type of a pedestrian flow statistic system according to requirements for the measuring accuracy of actual applications.
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
