Abstract: Both experiments and theory analysis proved that the Hardgrove grindability index(HGI) of mixed coal was nonlinear with its mixture ratio,which was explained by the theory of micro-grinding-ball effect.The HGI of 5 mixed coal samples was measured in lab.Because the HGI data of different mixed coal samples change in different ranges,they could not be directly compared with each other.Though normalizing by the relative grindability ratio(RGR),the comparison between these data was completed in the same range.The results show that different kinds of mixed coal samples with the same mixture ratio had the same RGR.The formula of RGR was obtained by partitioned least-square polynomial fitting.In conjunction with its definition,a method of calculating the HGI of mixed coal based on the nonlinear hypothesis was proposed.Practical applications indicate that the method is more accurate than that based on the linear hypothesis.
Abstract: The formation behavior of sulfides in free-cutting steel was investigated under unidirectional solidification.The relations of the dendrite arm spacing and sulfides' average diameter to solidification conditions were established.Experimental results show that the average diameter of MnS inclusions decreases with increasing temperature gradient around the solid/liquid zone and casting speed,but the number of MnS inclusions increases.The complete precipitation temperature of MnS is about 100℃ lower than the solidus temperature.The morphological changes of MnS are mainly effected by the activities of constituent elements,in other words,they are mainly influenced by interfacial energy.The relations of the dendrite arm spacing and sulfides' average diameter to solidification conditions were regressed,and the regression results are basically in agreement with the ones of previous researchers.
Abstract: The effects of quenching at 915℃ and tempering at 490~640℃ on the microstructure and mechanical properties of C-Mn-Mo-Cu-Nb-Ti-B based low-carbon microalloyed steel were investigated.The microstructure,the shape and distribution of precipitates,and the fractograph of the steel were observed by scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The volume fraction of retained austenite was measured by X-ray diffractometry(XRD).The results show that a multiphase microstructure with bainite,martensite and retained austenite is achieved after quenching and tempering.The bainite lath is 250 nm in width.The volume fraction of retained austenite decreases with the tempering temperature rising,and it is 2.1% after tempering at 520℃.The quantity of precipitates increases sharply after heat treatment,and the proportion of precipitates in a size range of 6 to 15 nm is above 70%.After quenching at 915℃ and tempering at 520℃,the test steel has a yield strength of 915 MPa,a tensile strength of 990 MPa and a-40℃ impact energy of 95 J.Fine precipitates and narrow lath bainite can enhance the strength,but the retained austenite existing between bainite laths can significantly improve the toughness.
Abstract: The effects of annealing processing on the mechanical properties and microstructure evolution of high strength and high ductility TRIP steels were investigated.The hot-rolled-and-annealed TRIP steel has remarkable strength and ductility due to the prior martensitic microstructure obtained in the as-hot-rolled condition and the retained austenite formed during intercritical annealing.The results show that the test steels have a tensile strength of over 1 000 MPa and an elongation of over 30%,and the product of ultimate tensile strength and total elongation exceeds 30 GPa·%.The mechanical properties are significantly influenced by intercritical annealing temperature and soaking time.When the TRIP steel is treated at an intercritical annealing temperature of 630℃ for 18h,the best mechanical properties are obtained.
Abstract: Weld thermal simulation experiments of F40 ship plates with 0.01% zirconium or not under different phase-change cooling time T8/5 were conducted on a Gleeble3500 thermal simulation test machine.The results show that the anti-large heat input welding performance is improved significantly for F40 ship plates containing titanium by adding trace amounts of zirconium,and the impact energy reachs 238J at-60℃ when T8/5 is 100s.The microstructure of the coarse grain heat affected zone(CGHAZ) in the F40 ship plates was studied by thermodynamic calculations and scanning electron microscopy.It is indicated that the size and mophyloy of original complex inclusions containing zirconium change with increasing T8/5.Therefore the number of the inclusions of 1 to 3 μm including zirconium which contribute to acicular ferrite nucleation non-monotonically decreases,leading to the toughness fluctuation of the CGHAZ with the welding heat input increasing.
Abstract: The filling and solidification processes of the primary coolant 90° bent pipes in pressurized water reactors(PWR) were simulated by ProCAST software.The simulation results show that molten steel can be filled smoothly,which demonstrates that the gating system plan meets the directional solidification principle.The locations of shrinkage and porosity in the bent pipes were predicted by using the solid fraction method.A series of technique optimizations were carried out in order to eliminate the shrinkage and porosity,so an optimized casting technique was finally obtained for the bend pipes.It is indicated that the casting yield of the bent pipes can be increased using ProCAST software analysis.
Abstract: Economic low-chromium steels show superior resistance to CO2 corrosion.The corrosion performance of 3%Cr pipeline steel was studied with a high-temperature and high-pressure autoclave.In a CO2 environment,X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy-dispersive spectrometry(EDS) were used to analyze the morphologies and characteristics of corrosion production scales on 3%Cr steel.The formation of the scales at different temperatures was also discussed.The results show that when the CO2 partial pressure is 0.8 MPa and the flow velocity is 1.0m·s-1 within the temperature range of 40 to 140℃,the average corrosion rate first increases and then decreases with increasing temperature,and its maximum can be obtained at about 100℃.For all the test conditions no localized corrosion was observed.There is a two-layer structure in the scales.The inner layer,which is mainly composed of Cr compounds and amorphous FeCO3,is denser and more stable because of Cr enrichment.The Cr content of the inner layer increases with increasing temperature and the mass ratio of Cr to Fe can reach 8/5.The outer layer is formed from the precipitation of crystalline FeCO3.
Abstract: In order to study the corrosion behavior of nickel-based alloy coatings in the winter precipitation of Chinese north old industrial city,Ni-P and Ni-Fe coatings were prepared by electrodeposition,and the phase structure and corrosion resistance of the nickel coatings were examined.Experimental results show that the corrosion resistances of different nickel coatings are different.The Ni-Fe coating has a nobler potential,a lower corrosion current density and a better corrosion resistance.Its corrosion rate is about half of 20 Steel's one.This is because that Fe in the nickel coating has a greater affinity with oxygen and can form a continuous oxide film quickly on the surface of the Ni-Fe coating.But the oxide film on the Ni-P coating forms slowly and its impedance resistance is lower than that of the Ni-Fe coating.Thus the Ni-P coating is not suitable to be used for outdoor decoration and corrosion protection in Chinese north old industrial city.
Abstract: Spherical Ti-6Al-4V(TC4) powders were prepared with irregular TC4 powders by a radio frequency(RF) plasma.The effect of spheroidization on the powder characteristics and the influence of feeding rate on the spheroidization ratio were studied.The morphology,particle size distribution and characteristics of the spherical powders were analyzed by scanning electron microscopy(SEM),laser micron sizer(LMS) and Hall flowmeter,respectively.The results show that TC4 powders after plasma processing have good sphericity and smooth surfaces,and their spheroidization ratio is almost 100%.The loose density,tap density and powder flowability significantly increases after the process,but the spheroidization ratio gradually decreases with the feeding rate increasing.
Abstract: A perovskite B-site ion oxide solid solution was synthesized by the citrate precursor route.The synthesized precursor was calcined with PbCO3 at 740℃ to prepare lead zirconate titanate(PZT) powders which are a pure metastable perovskite phase lacking of Pb in A-site.During sintering,both monoclinic and tetragonal phase ZrO2 nanoparticles were precipitated from the solid solution.X-ray diffraction,scanning electron microscopy and transmission electron microscopy were used to analyze the phase,composition and microstructure.When the amount of ZrO2 addition increased,the fracture mode changed from the coexistence of intergranular and intragranular fracture to intragranular fracture only.It is concluded that the intragranular type nanocomposite piezoelectric ceramics are successfully formed by the B-site citrate precursor route.
Abstract: Sr2Mg1-xAlxMoO6-δ(SMAM) anode materials were synthesized via citrate acid-complex combustion.X-ray diffraction and scanning electron microscopy were employed to characterize their lattice structure and microstructure,respectively.The effects of sintering conditions on the lattice structure and compactness were investigated.The results revealed that the reducing atmosphere is unfavorable for the densification of SMAM materials,but the oxidizing atmosphere can promote the densification process.The solution limit of Al ions in SMAM is relatively higher in the reducing atmosphere compared to the oxidizing atmosphere.For an SMAM sample prepared in the oxidizing atmosphere,reducing it at low temperature can increase the solubility of Al in SMAM.The conductivity of SMAM samples increases with increasing Al content.
Abstract: Since the temperature distribution and erosion of blast furnace hearth are directly affected by cooling system,a rational cooling water system is the assurance for long campaign life of large blast furnace.Combined with a 4 000m3 blast furnace,physical and mathematical models of temperature fields of blast furnace hearth and bottom were built according to heat transfer theory.Two different hearth cooling systems,namely "low water capacity and large temperature difference" and "large water capacity and small temperature difference",are both investigated by modeling and numerical simulation.Effects of different cooling systems on hearth temperature field,hearth erosion and blast furnace life are also analyzed.The results indicate that during the initial period with thicker brick lining,effects of different cooling systems on blast furnace temperature distribution are nearly the same.As the brick lining gradually becomes thinner,different cooling systems have much different effects on temperature distribution.When the brick lining is eroded to a certain level,even the best cooling system is of no use,but "large water capacity and small temperature difference" and enhanced cooling measures will slow down the erosion and prolong the campaign life.
Abstract: An asymmetrical bending control system of work rolls was designed to decrease the asymmetrical flatness defect of a cold-rolled strip.The influence function was adopted to calculate the deformation of the roll system and the effect of the lateral flow of metal in the roll gap on the transverse tension distribution of the strip at the exit side was taken into account.When different bending forces were exerted on both ends of work rolls,the contact pressure distribution between rolls,the lateral thickness distribution and the tension stress distribution of the strip at the exit side were calculated through the iterative method.The results of theoretical analysis show that the asymmetrical bending of work rolls can improve the pressure distribution between rolls,reduce the wear and the peeling off of rolls,and decrease the asymmetrical flatness defect of the strip at the edge.The application results prove that when the actual tilt is less than 10%,a higher accuracy of flatness is obtained with asymmetrical bending than work roll tilting.
Abstract: The general evolution rules of internal holes in aluminum alloy parts and the influence of process parameters on the internal holes in cross wedge rolling were studied by means of numerical simulation.The results show that the general evolution law of a single hole is firstly spherical,then ellipsoid,and finally a hole through the rolled piece at the axial direction.As for multi-holes,the evolution law of the center hole is similar to that of a single hole;however,holes lied in other positions finally become closed and have a positive effect on the center hole.The later segment of the knifing zone and the former segment of the stretching zone are the crucial evolution stage to the expansion of internal holes.Among the process parameters of cross wedge rolling,stretching angle is the most sensitive factor,followed by reduction in area and then forming angle.It is proved that the small forming angle,stretching angle and reduction in area are conducive to the expansion of internal holes.
Abstract: The polyacrylonitrile-based activated carbon fiber(PAN-ACF) is one kind of newer carbon material.Adsorption and removal experiments of SO2 in simulated flue gas by PAN-ACF were carried out.The influences of approach to adiabatic saturation temperature(AAST) on the desulfurization efficiency were investigated by changing the flue gas temperature and the volume fraction of vapor,respectively.The results show that PAN-ACF has effective desulfurization performance,AAST is the important influencing factor on the desulfurization efficiency,and the desulfurization efficiency increases at first and then decreases with increasing AAST.By comparison,the desulfurization efficiency of PAN-ACF at the same AAST by changing the flue gas temperature differs from that by changing the volume fraction of vapor,and their changing tendencies with AAST are also different.
Abstract: The artificial potential field method is a simple and efficient path planning algorithm for mobile robots.Aiming at a kind of goal unreachable problem in traditional artificial potential field methods,an improved algorithm which changes the angle of repulsion at the local minimum point and sets the virtual local minimum area was proposed for problem-solving.The genetic algorithm was also introduced to optimize the parameters,i.e.the revolved angle of repulsion and the radius of the virtual local minimum area for the improved artificial potential field algorithm.It is proved that the proposed algorithm can plan out a simple,smooth and safe optimum path connecting the start point and the end point by simulation experiments.
Abstract: The stability of a T-S model based fuzzy control system for both the discrete,linear time-invariant object and the nonlinear time-varying object is analyzed with the help of constructing a related virtual equivalent system.The purpose of adopting the virtual equivalent system is to reduce the difficulty of analyzing the stability of the fuzzy control system and to improve the conditions of existing stability criteria.The results indicate that the stability of the fuzzy control system depends on the precision of local models,the effectiveness of fuzzy rules,and the stabilizing characteristic of each local controller.
Abstract: A type of optimal preview control problem for time-varying discrete-time systems with state time-delay is investigated.The methodology is to first construct an augmented error system by introducing a difference operator,and then transform the system into a traditional control system without time-delay in form by using the lifting technique to solve the problem that the operator is not a linear operator.Finally,preview information of the vector containing the desired tracking is introduced to obtain the ultimate augmented error system.Beginning with this augmented error system,a controller with a preview function which can process the original system is designed by making use of the results on optimal control for time-varying systems.Later,matrix partition is employed to transform the high-order Riccati equation that needs to be solved into a low-order Riccati equation.The effectiveness of the proposed design method is demonstrated by a numerical simulation.
Abstract: The echo state network(ESN) is a novel kind of recurrent neural network and has recently become a hot topic for its easy and distinctive training method along with high performance.In ESN,the reservoir computing method is introduced,which is a completely new approach used to design a recurrent neural network.By comparing this novel model with existing recurrent neural network models,it can overcome the difficulty encountered in slow convergence and local minimum in the gradient descent based training algorithm.Currently,there is considerable enthusiasm for the research and application of ESN.A review on ESN is presented in this paper.The advantages and drawbacks of ESN and various improvements are analyzed.Finally,some future research directions are also discussed.
Abstract: Based on the reliability evaluating indicators of functional reliability and capability utilization,in combination with studies on the energy consumption states of steel manufacturing process systems,a new assessment system of energy reliability,process energy efficiency ratio and similar degree was established to describe the level of energy consumption reliability.The concept of contribution index was used to quantitatively analyze the influence of the two latter indicators on the energy reliability.Finally,the new assessment index was also applied to evaluating the energy consumption reliability of an EAF special steel plant.The evaluating result shows that the energy consumption reliability increases from 0.64 in the year 2008 to 0.72 in the year 2009;meanwhile,main reasons for the change of energy consumption reliability in the period of 2006 to 2009 were also discussed.
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
