Abstract: Direct reduction iron was prepared by adding dephosphorization agents during a direct reduction roasting-magnetic separation process,and the effects of reductants on the direct reduction process of high-phosphorus oolitic hematite were studied.Experimental results and SEM analysis show that the aggregation and growth of iron crystals,the increase of iron crystals' amount and the index of the reduced iron with a reductant can be influenced by the contents of fixed carbon and volatile in the reductants.When the reductant is coke or anthracite,iron crystals and gangue minerals are more closely combined in the roasting products,thus it is difficult to achieve monomeric liberation during the grinding process.When lignite is used as a reductant,the obvious connection and growth of iron crystals appear,coarser iron crystals form,and the boundary between iron crystals and gangue minerals is clear in the roasting products.Thus the liberation of iron crystals from gangue minerals is easier and the recovery of iron is higher than that obtained with other reductants.
Abstract: Dissimilatory metal reducing bacteria were domesticated with MnO2 in acidic conditions,and then the MnO2 color changed from black to white,even colorless.X-ray diffraction analysis indicated that dissimilatory reductive microbes could reduce MnO2 effectively after domestication.Manganese leaching from pyrolusite was investigated by using dissimilatory metal reducing bacteriaunder acid conditions,with the effluent of bio-hydrogen production as a reducing agent.Single-factor experiments were employed to examine the effects of anaerobic conditions and pH values on the leaching rate of Mn.The removal rate of chemical oxygen demand(COD) and the mechanism were also studied.It was shown that dissimilatory metal reducing bacteria reduced pyrolusite using the effluent of fermentative hydrogen production.The leaching rate of manganese under anaerobic conditions was higher than that under aerobic conditions,and it could reach 98% under the conditions of pH 3.0-3.5 and the leaching time of 3d.For degrading the effluent of bio-hydrogen production under subacid conditions,the COD removal rate could reach 84% when COD in the effluent of bio-hydrogen production was 2612mg·L-1,and it would be higher with more pyrolusite.
Abstract: Ozonation was used to degrade residual BK809 in flotation wastewater and the degraded products in different stages were identified and quantified by gas chromatography-mass spectrometry(GC-MS).The results showed that the COD removal rate of 68.68% could achieve at an ozone flow rate of 300mg·h-1 for 20min and pH 9-11.It was indicated from GC-MS analysis that BK809 was firstly oxidized to azobenzene and then converted to nitrobenzene.With the deepening of ozonation,the benzene was broken and further decomposed into C15-C25 carbon-chain alkanes and gaseous substances,including nitrogen oxides and carbon oxides.Finally the residual mass percentage of total organic compounds(TOC) reduced from 100.00% to 17.18%.Meantime,the chroma of the wastewater increased from 5.02 to 471.71 and then decreased to 28.75;in macroscopic view,the color of the wastewater turned from colorless to brown,and then from brown to milky.
Abstract: A feasible conductivity method of measuring the crystallization temperature of mold flux was proposed to solve the limitations of the existing measuring methods.At first,the relationship between the activation energy and compositions of precipitates as well as the ratio of crystallization was analyzed theoretically.Then a simple measuring method was developed based on the former theoretical analysis.The measuring results were verified by differential thermal analysis(DTA),polarizing microscopy and X-ray diffraction analysis.It is shown that this measuring method has high accuracy and low cost,and the determination of main precipitates is basically right,indicating that this method can be a new means studying the crystallization temperature of mold flux.
Abstract: Equilibrium precipitated phases in switch K2 spring steel in the temperature range of 400 to 1600℃ and the solubilities of Nb and V in austenite were calculated by using the thermodynamic software Thermo-Calc to investigate the effect of alloying element content on the equilibrium precipitated phases.Then,the effect of Nb content on the precipitated phases was analyzed by carbon extraction replica and transmission electron microscopy(TEM).It is shown that the main equilibrium precipitated phases in switch K2 spring steel are MX,M7C3,M3C2 and AlN,and the stability of MX phase can be significantly improved by adding Nb.TEM results reveal that the precipitated phases are spherical or disc-shaped,and their sizes range from several nanometers to more than 100nm.With the content of Nb increasing,the proportion of fine particles which precipitated from low-temperature phase ferrite increases dramatically,and the proportion of undissolved carbonitride also increases,overall the average particles size is refined.The large precipitates are Nb-rich carbides,while the small ones are V-rich carbides,which is in accordance with the results of thermodynamic calculations.
Abstract: An automatic measurement system for silicon steel and an X-ray diffraction meter were used for measuring the magnetic property parameters and texture of ex-processed samples and processed samples.It is shown that under the condition of a lower voltage,9Hz,a longer processed time and an annealing temperature of 650℃,the decrease rate of iron loss can be increased;a lower voltage,a higher frequency and an annealing temperature of 650℃ are in favor of improving the increase rate of magnetic induction.The best test parameters for improving the magnetic properties are the frequency of 9Hz,the voltage of 500V,the processing time of 6min and the annealing temperature of 650℃.Through texture analysis,it is verified that the change in magnetic induction of oriented silicon steel depends on the {110} 001 orientation degree and the {110} 001 orientation degree can be regarded as a comprehensive value which reflects the situation of the overall average angle of divergence.
Abstract: Optical microscopy,electron microscopy and electrolytically extracted phase analysis,in combination with thermodynamic calculations,were used to study precipitates and their precipitation behavior in Ti-microalloyed high strength steel produced by CSP process.It is found that many micron-sized cubic TiN particles and a large number of nanometer precipitates exist in the steel.The mass fraction of MX phases(M=Ti,Mo,Cr;X=C,N) in the steel is 0.0927%,in which particles smaller than 10nm account for 26.9%.Thermodynamic calculations show that titanium nitride has been almost completely precipitated from the steel during or before soaking,but titanium carbide hardly precipitates before tandem rolling.Decreasing the contents of nitrogen and sulfide and controlling the coiling temperature can increase the volume fraction of titanium carbide,and decreasing the γ→α transformation temperature can prevent fine carbides from growing.These results indicate that the precipitation hardening resulting from nanometer particles is about 156MPa and the effect can be raised through controlling the chemical composition and rolling parameters.
Abstract: XRD analysis was used to compare the textures of tire cord steel produced from four different steel works at home and abroad.The results show that the textures of wire rods produced at domestic and foreign works are obviously different.The strength of {111} texture in the axis of wire rods produced at domestic works is stronger than that at foreign works,however {111} texture in the axis of wire rods has strong orientation,which is adverse to wire drawing.The strength of {111} texture can be obviously decreased by prolonging the heating time of heating furnaces and increasing the heating and laying temperature.
Abstract: A low-alloy high-strength steel Q960 for construction machinery was designed.Under the condition of homogeneous composition,homogeneous rolling and quenching techniques,a mechanism was researched to describe the influence of tempering temperature on low angle grain boundaries in Q960 steel.It is shown that with the rising of tempering temperature,the frequency of low angle grain boundaries as well as the tensile strength and yield strength of Q960 steel gradually decreases,but the tensile ratio increases.At different tempering temperatures,the peak value of the frequency of low angle grain boundaries is about at a misorientation of 5°,so the misorientation is small.Because of the small misorientation,the low angle grain boundaries are quite stable and the atomic mobility ratio is also very small.According to the calculation of bond order integrals(BOI),B element can strengthen low angle grain boundaries in Q960 steel.
Abstract: The effects of inclusions in two kinds of low carbon micro-alloy steels on the phase transformation of welding heat affected zone were analyzed and compared.Inclusion distribution and size were observed and the selected area diffraction patterns(SADP) of inclusions were analyzed by transmission electron microscopy(TEM).The continuous cooling transformation curves(CCT) and isothermal cooling transformation curves(TTT) of the test steels were built by thermal expansion method and metallographic analysis.It is shown that the main inclusions in Ti-deoxidized steel are globular TixO-MnS compounds with the size smaller than 3μm,and the TixO cores have two types,Ti2O3 and Ti3O5.These inclusions have the effect of inducing the nucleation of intragranular acicular ferrite.The acicular ferrite prefers to nucleate on the surface of TixO-MnS compounds in Ti-deoxidized steel,therefore,compared with that in Al-deoxidized steel,the bainite transformation temperature is increased and the transformation time is advanced obviously.
Abstract: The electrochemical behavior of 00Cr12Ti with different heat treatments in a 0.1mol·L-1 H2SO4+0.0001mol·L-1 KSCN solution was investigated by Cu-CuSO4-16%H2SO4 tests,double-loop electrochemical potentiokinetic reactivation(DL-EPR) tests and dynamic electrochemical impedance spectroscopy(DEIS).It was found that specimens treated at 1000℃ for 2h sensitized but specimens treated at 650℃ for 2h did not.The different heat treatments mainly affected the reactivation behavior,but had almost no effect on the activation behavior.During reactivation process,for specimens treated at 1000℃ for 2h,the capacity loop decreased dramatically and then increased gradually,meanwhile it showed a negative value at the low frequency capacitive loop,indicating the breakdown and repair of passive films.For specimens treated at 650℃ for 2h,there were not the breakdown and repair of passive films,meaning that the passive films were stable comparably.After the occurrence of intergranular corrosion,the charge transfer resistance(Rct)of specimens treated at 1000℃ for 2h is much less than the passive film's resistance(Rp) of specimens treated at 650℃ for 2h due to local corrosion in specimens treated at 1000℃ for 2h.
Abstract: Scanning Kelvin probe(SKP) was used for measuring the corrosion behavior of carbon steel with a defected epoxy coating after neutral salt spray test,and the volta potential changes of carbon steel at different stages of neutral salt spray test were analyzed.It is shown that the defect formed by the damaged epoxy/carbon coating provides a way for the corrosive medium to contact the carbon steel matrix.The potential of carbon steel is more negative at the defect point than that under the coating,resulting in anodic dissolution at the defect point.After some time of neutral salt spray test,insoluble corrosion products can cover the bare defect,leading to the potential at this part shifting to more positive values.Consequently,the defect becomes a cathode,while its vicinity under the coating exists as an anode.Meanwhile,the potential difference between the new cathode and the new anode offers a driving force for continuous corrosion under the coating.Therefore,with the corrosion developing,there would be a considerable corrosive medium and corrosion products aggregating at the interface,which destroy the binding between the epoxy coating and carbon steel,leading to the appearances of bubbling and peeling.
Abstract: The stable phases and composition of FGH97 powder metallurgy(P/M) superalloy with different contents of hafnium were calculated by JMatPro software.The effects of hafnium content on the equilibrium phases and composition were studied.Meanwhile,the stable phases were analyzed and checked by physical and chemical phase analyses and microstructure observations.Then,the behaviors of phase precipitation and the character of hafnium partition in different phases were revealed and the effects of hafnium on FGH97 P/M superalloy were summarized.It is shown that the stable phases at 750℃ include γ matrix,γ' phase,MC carbide,M23C6 carbide,M3B2 boride,and μ phase.Hafnium mainly exists in γ' phase and MC carbide,and increasing the hafnium content causes the different distribution of hafnium between γ' phase and MC carbide.
Abstract: The effects of sintering temperature and rare element Nd on the phase structures,morphology,pressure-composition-temperature(PCT) curves and hydrogen absorption/desorption kinetics characteristics of Mg2-xNdxNi(x=0,0.1,0.2,0.3)alloys prepared by spark plasma sintering(SPS) were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM) and PCT experiments.The structures and hydrogen storage properties of the Mg-based alloys prepared by SPS and vacuum induction melting were compared.It is shown that Mg2-xNdxNi alloys prepared by SPS exhibit a multiphase structure,demonstrating better hydrogen absorption/desorption kinetics performances but deterioration in hydrogen storage capacity with increasing Nd content,and Mg alloying is prompted by Nd.Sintering temperature has an obviously effect on the hydrogen storage capacity and the plateau properties of PCT curves.When Mg2-xNdxN alloys contain Mg or NdMg12 phase,their PCT curves exhibit two platforms.Compared with the alloys prepared by casting,the Mg1.7Nd0.3Ni hydrogen storage alloy prepared by SPS has better absorption/desorption kinetics properties but awful hydrogen storage capacity,hydrogen desorption rate and platform properties of PCT curves.
Abstract: A ceramic with stable and good performances was synthesized by designing the composition of the CaO-MgO-SiO2 system with steel slag as one of ceramic raw materials.Its bending strength can reach up to 99.84MPa.The ceramic samples were tested and analyzed by scanning electron microscopy(SEM),electron probe microanalysis(EPMA) and X-ray diffraction analysis(XRD).The results show that when the content of steel slag is 40% the dominated crystal phase in the ceramic is a solid solution of diopside and ferric diopside,but when the content of steel slag is higher than 65% the dominated crystal phases are akermanite and diopside.It is indicated that synthesizing a ceramic with steel slag is a promising technology for the utilization of steel slag with high added values.
Abstract: Ti-B-N nanocomposite coatings with different B contents were deposited on Si(100) and high speed steel(W18Cr4V) substrates by reactive magnetron sputtering.The microstructures of the coatings were characterized by X-ray diffraction(XRD) and high-resolution transmission electron microscopy(HRTEM).Meanwhile the nanohardness and elastic modulus values were measured by nano-indention method.It is indicated that Ti-B-N nanocomposite coatings can be prepared by changing the power of TiB2 targets and Ti targets.The deposited Ti-B-N coatings mainly consist of TiN nanocrystals.With the B content increasing,the sizes of TiN nanocrystals become smaller,and the amorphous component increases.When the B content is very high,the sizes of TiB2 nanocrystalline phase in the Ti-B-N coatings are very small and the coatings' properties are poor.When the TiN grain size is about 5nm,the Ti-B-N coatings have the best mechanical properties,with the nanohardness of 32.7GPa and the elastic modulus of 350.3GPa.
Abstract: In order to study the generation mechanism and deformation law of warping(cross bowing,lengthwise bowing and twisting) in thin steel strips during temper rolling,strip warping models with tension on-line and without tension off-line were established using ANSYS software.The mechanical mechanism of warping deformation under the two states and the influence mechanism and law of factors were analyzed.According to the analysis results,it is indicated that the warping deformation is caused by the uneven distribution of plastic deformation(mainly vertical extension) along the thickness direction during temper rolling,not the uneven distribution in width.Under the guidance of simulation data,serious cross bowing after temper rolling in a continuous annealing process line was investigated,and a good result was gotten after improving the rolling process.
Abstract: An automatic gauge control(AGC) secondary loop control system was added to a monitor AGC system.A cascade control scheme was proposed for the AGC system based on the Smith prediction control model.Generalized predictive control(GPC) was used in the monitor AGC main control loop and a PID control strategy was applied to the secondary loop.Due to the secondary loop control system,disturbances added in the secondary loop are rejected,thus the influence of disturbances on the main control loop is weakened,the ability of rejecting disturbances is increased,and the control precision is improved.Simulation results show that the control strategy is effective and has a better control performance.
Abstract: The robust control problem was studied for variable speed-constant frequency(VSCF) wind energy conversion systems based on doubly fed induction generators(DFIG).Using vector transformation a state space model of DFIG was established when the synchronous frame was linked to the stator flux.The dynamic model was simplified reasonably to reduce the order of the controller to be actualized easily in fact.Aiming at the influence of modeling error and gust in maximum power points tracing(MPPT) control,a robust rotor voltage controller was designed by using H∞ robust control method,which makes the system have the robust performance of restraining external disturbances.Simulation results validate that the conversion system with the controller proposed above can trace the reference command exactly and achieve the maximum energy from wind even if with the uncertainty of parameter variety and unmodeled dynamic and external disturbances.
Abstract: Aiming at analyzing the tunnel excavation problem in representative silty clay stratum in Beijing,triaxial consolidation drainage tests were carried and the mechanical characters under different stress paths were analyzed.Then,a two-dimensional numerical tunneling model with general engineering parameters was established.The stress of grid points and Gauss points was calculated,and the stress changes of typical points were tracked.After that,the action zones of the stratum were classified,and the final ground settlements which consider action zones were calculated by turning the test results of strength into the corresponding action zone model.At last,a centrifuge test model was constructed,and the final surface settlement value was recorded.By contrasting test results with simulation results,the correctness of action zoning in silty clay stratum was verified.
Abstract: Wind pressure distribution characteristics of the Phoenix Media Center flexible roof,in non-large deformation,were analyzed by wind tunnel tests of the rigid model.Meanwhile,the average wind pressure coefficients on the surfaces of the outer shell and the atrium with a suspended cable-membrane structure in different wind direction angles were obtained.It is shown that the wind effects of the majority of the outer shell are suction,except that positive wind pressure distributes on the main windward side of the outer shell and a small portion of the windward side of the insider shell,but the effects of wind pressure on the atrium with a suspended cable-membrane structure are mainly suction.
Abstract: Six concrete filled square steel tubular(CFSST) columns were tested under low cyclic loads for studying their accumulate energy dissipation performance.The effects of test parameters,such as slenderness ratio,axial compression ratio and sectional steel ratio,on the hysteretic curves,strength deterioration,and accumulate plastic deformation were analyzed.It is indicated that these columns have a better energy dissipation capacity.The energy dissipation capacity improves with the sectional steel ratio increasing,but it reduces when the axial compression ratio and the slenderness ratio increase.
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
