Abstract: Based on Euclidean distance, the hierarchical cluster method was adopted to analyze the unit normal vectors converted from the dip angle and dip direction of Bayan Obo East Iron Mine on the premise that the rectangular coordinates system was construc-ted. A proper distribution model was chosen to describe each joint group, and its validity was verified by chi-square test. It is found that the hierarchical cluster method can analyze the joint attitude accurately and provide reasonable classification of joint attitude without any uncertainty caused by human judgment. Based on the hierarchical cluster result of rock mass joints and slope design parameters, the most probable slope instability mode is determined by the stereographic horizon projection technique, which provides a basis for ad-justing slope design parameters and controlling slope disaster.
Abstract: Taking underground mine stope as the object of study, a fill-rock seepage model was established and the seepage pres-sure and flow formula of water in backfill-rock were deduced according to the practical situation which confirmed the initial and boundary conditions. Based on that, the seepage laws and influencing factors were analyzed. The results show that in backfill, the flow increases rapidly in the initial stage, then reaches a peak and gradually declines; the seepage pressure decreases gradually and tends to be stable;the larger the permeability, the larger the flow and pressure drop;the higher the height, the smaller the flow and the larger the pressure drop;the smaller the porosity, the higher the pressure. Porosity has different effects on the flow in different stages. In the rock, seepage pressure has no relationship with the permeability but greatly affected by the seepage of back-fill and declines with time. The flow only relates to the rock mass permeability.
Abstract: The lowest assimilation temperature is usually used as a terminal system index to characterize assimilation reactions between iron ores and CaO. However, this characterization does not take into account assimilation speed and heating rate. In order to adopt several indexes to evaluate the characteristics of the assimilation reactions, this article introduces an assimilation characteristic parameter by adopting the Van't Hoff's law and making full use of data obtained in the high temperature assimilation process of iron ores. The characteristic parameter, which considers assimilation speed, heating rate, assimilation temperature and the effect of temperature on assimilation speed, can characterize assimilation reactions between iron ores and CaO, including assimilation starting temperature, assimilation time, assimilation finishing temperature, etc. Moreover, it is based on the practical production temperature of sintering ores. Because of integrating much more important information in the assimilation process of iron ores, this parameter can comprehensively reflect the assimilation properties of iron ores. Although the same or similar results are obtained by the two methods, com-pared with the conventional method by only considering the lowest assimilation temperature, the new method can find out assimilability differences of different iron ores in further analysis.
Abstract: Orthogonal experiments of control device arrangement in different slab casting tundishes were carried out to study the influence of the reactor's structure on the flow characteristic of molten steel. The optimal arrangement rule of control devices and its effect on the flow characteristic of molten steel and inclusion removal were mainly analyzed. A quantificational relation of control devices, dead volume and the structure factor D was determined. The results indicate that the steel cleanness can be reflected by dead volume while the piston flow volume is disadvantageous to inclusion removal. There is a great influence of outlet pumping action on the fluid flow pattern, so the best distance between the dam and outlet is 1000 to 1300 mm, which results in the decrease of nozzle blocking rate to 7.5%. The relation between the flow characteristic of molten steel and the dam's relative location is obtained at normal casting speed when 0.0035 < D < 0. 0055. As the relative speed of inclusions to molten steel reaches to 6 ×10-5m·s-1, the floating speed of inclusions becomes faster.
Abstract: The contents of tramp elements Cu, As and Sn as well as P in A105 continuous casting billets were analyzed by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectrometry (EDS). Main precipitates in the steel and the variation of P content in molten steel with solid fraction were calculated by Thermo-Calc thermodynamic software. The hot ductility of the steel was measured by using a Gleeble 1500 thermal simulator. It is found that P segregation is the main reason for transverse cracking of the steel. The segregation of tramp elements Cu, As and Sn at grain boundaries promotes the formation of cracks. Straightening in a lower temperature zone accelerates crack propagation. AlN precipitation may have nothing to do with the formation of cracks due to little AlN.
Abstract: The microstructure and mechanical properties of a low-carbon Mn-Si multiphase steel treated by two different thermal-mechanical processes, the hot-rolling process for TRIP steel based on dynamic transformation of undercooled austenite and the process based on bainitic isothermal treatment, were investigated by hot uniaxial compression tests on a Gleeble-1500 hot simulator, in combination with optical microscopy, scanning electron microscopy, X-ray diffraction and tensile testing. A comparison was carried out to analyze the influence of multiple-phase microstructure states by the two processes on the work-hardening behaviors of the steel. The multiple-phase microstructure consisting of fine-grained ferrite matrix, bainite, and retained austenite is formed by the hot-rolling process for TRIP steel based on dynamic transformation of undercooled austenite, but the multiple-phase microstructure which is composed of lath bainite matrix and retained austenite is formed by the process based on bainitic isothermal treatment. The volume fraction of retained austenite and the mass fraction of carbon in retained austenite in the former are higher than those in the latter. The yield strength and tensile strength of the steel with the multiple-phase microstructure consisting of lath bainite matrix and retained austenite are higher;but the steel has lower uniform elongation and total elongation, which should be attributed to its lower work-hardening capability resulting from the lower stability of retained austenite.
Abstract: Experiments were performed to investigate the effect of austenitizing temperature on the mechanical properties of quenched and tempered Ti-V microalloyed steel. Metallographic and transmission electron microscopy (TEM) observations reveal the variation of austenite grain size with austenitizing temperature. Within the temperature range of 850 to 1200℃, the austenite grain size experiences three phases, which are stable, rapidly increased, and stable again. Tensile strength and impact toughness tests show that, when the austenitizing temperature rises, the tensile strength Rm increases gradually, but the impact toughness undergoes a process of stabilizing, decreasing and then increasing. At a certain temperature, coarsening of precipitated particles leads to the sudden increase of austenite grain size. The increase of diffuse precipitates resulting from continuous solutionizing of microalloying elements with temperature rise and the effective pinning of precipitated particles are the main reasons for the increase of tensile strength, while abnormal grain growth and grain size uniformity at a certain temperature are the key factors that influence the toughness of the steel.
Abstract: The compressive deformation behavior of a new microalloyed high-strength steel containing 1.79% Al was investigated at temperatures from 900 to 1100℃ and strain rates from 0.01 to 30 s-1 on a Gleeble-1500 thermo-simulation machine. A hyperbolic sine equation with strain-dependent constants was developed for the steel. The predicted flow stress curves by the constitutive equation well agreed with experimental results, indicating that the constitutive equation can give a relatively accurate estimate of flow stress for the steel. According to processing map analysis, the dynamic recrystallization zone of the steel was determined as 1000 to 1100℃ and 0.01 to 1 s-1. Microstructure observation showed that dynamic recrystallization occurred in this dynamic recrystallization zone, and in the instability zone, flow localization and necklace structure was observed. Finally, a combination of the constitutive equation and processing map provided a method for comprehensively investigating the hot deformation behavior of the steel under different conditions.
Abstract: The effects of two different processes, normalizing with air cooling + tempering and normalizing with controlled cooling+ tempering, on the retained austenite and mechanical properties of medium-carbon low-alloy martensitic ultra-high strength steel were investigated to improve its plasticity and toughness. The microstructure of the steel was observed by scanning electron microscopy (SEM). The volume fraction, shape and distribution of retained austenite in the steel were measured by X-ray diffraction (XRD) and electron back-scattering diffraction (EBSD). The results show that lath martensite and retained austenite (M+RA) are obtained by the two processes and a uniform distribution of retained austenite is located between lath martensites. The volume fraction of retained austenite varies from 3% to 10% with treatment parameters. Normalizing with controlled cooling can significantly refine lath martensite while the yield strength and tensile strength increase more than 100 MPa and the impact energy decreases by 4 J. When the quenching temperature rises, the volume fraction of retained martensite increases firstly and then decreases. Normalizing with controlled cooling can also act as a method for improving the microstructure and properties of martensitic steel.
Abstract: Transversal pre-strain experiments were carried out to investigate the effect of transversal hole enlargement on the tensile strain behavior of multi-phase pipeline steel. Experimental results indicate that the work hardening behavior after pre-strain treatment has directional characterization. When the pre-strain direction parallels to the final tensile strain direction, the work hardening rate is very high. Only when the pre-strain rate is lower than 2%, the yield ratio can keep below 0.95. When the tensile strain direction is perpendicular to the pre-strain direction, the strain-stress curves can maintain a continuous yield character, which has low yield ratio (below 0.75) and high uniform elongation rate. In addition, strain aging treatment was carried out to investigate the effect of anti-corrosion thermal coating treatment on the tensile strain behavior of multi-phase pipeline steel. It is shown that the multi-phase pipeline steel has excellent anti-aging stability.
Abstract: Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the corrosion resistance of 904L stainless steel welding joints in concentrated sulfuric acid, and the corrosion mechanisms were analyzed in brief. Experimental results show that there are no significant changes in cathodic polarization curves of the weld zone and the substrate, both of them are hydrogen reduction reaction process while an opposite trend is seen upon the anodic polarization curves. Compared with the substrate, the corrosion potential of the wilding zone decreases while the anode current increases. Welding contributes to the anode reaction. The corrosion of the substrate and the weld zone is mainly controlled by the electrochemical step. Both Nyquist graphs are similar, which are composed of a single capacitive reactance arc, having a time constant. The corrosion resistance of the substrate is superior to the weld zone.
Abstract: The microstructure characteristics and recrystallization mechanism of GH720Li alloy deformed in the bi-model phase region and then air cooled or annealed were investigated by metalloscopy, scanning electron microscopy and transmission electron microscopy. It is found that the main softening mechanism after hot deformation at 1100℃ and air cooling is recovery and recrystallization occurs only in a limited portion of grains with the subgrain growth and merging mechanism due to a great content of gamma prime phase in the alloy. During the annealing process, the nucleation of static recrystallization may occur in dislocation pile-up areas located at the juncture of several grains or by strain-induced boundary migration (SIBM) but the whole recrystallizing process is restrained by the retained percentage of primary gamma prime phase. It must be pointed that the retained primary gamma prime phase in GH720Li can also be somewhat deformed during hot working and then also softened to some extent by recovery and recrystallization during the annealing process.
Abstract: A fusion measuring method proposed in this paper by using the soil mechanical granular accumulation theory is a new concept for computing the burden line shape in blast furnaces. This method offers a powerful solution to compute the burden line shape directly in comparison with the traditional way in which the contact force model is adopted to compute the burden line shape in blast furnaces from the bottom up. With the multiloop distributing accumulation property of blast furnaces and the advantage of 6-point array radar on the top, the boundary conditions of the burden line shape can be easily calculated. Under the boundary conditions, the estimated values gotten by cross temperature and mechanical sounding rods can be compensated. Taking into consideration the distributing discipline of blast furnaces and the particle accumulation method, this method adopts Bayes data fusion and sectional triple Hermite interpolation under the boundary conditions to finish the combination of theoretical calculation and measurement correction. Measurement results indicate that compared with the traditional method, the measurement accuracy rises by 4.8% and the resolution of the burden line increases by 27.2%, which make the control of burdening more precise and more targeting.
Abstract: The gas jet of swirl-type oxygen lances and the liquid steel velocity in vanadium extraction converters were simulated using Fluent software. The stirring effects and impact characteristics of conventional oxygen lances and various swirl-type oxygen lances (swirl angles of 5o, 8o, 10o and 13o) on the molten pool were studied on the basis of simulated results. It is found that the gas jet of swirl-type oxygen lances has a relative dispersed distribution and the flows have a less disturbance. When the injecting area of swirl-type oxygen lances increases, the area surrounded by isovelocity is larger in the molten pool. Injecting with the 10o swirl-type oxygen lance makes the area surrounded by isovelocity get the largest, about 75% of the longitudinal section of the molten pool, and the liquid steel velocity is the highest. This is helpful to promote vanadium dispersion in the vanadium extraction converter and improve the vanadium extraction efficiency.
Abstract: Based on the lubricating and unsteady properties of rolling processes and hydrodynamic analysis, a film distribution model of the deformation zone which concerns the steady and unsteady conditions is set up and the film wave coefficient is proposed which is used to study the absolute fluctuation of unsteady film thickness. The von Karman equation is used to describe the stress distribution of rolling interfaces under the steady and unsteady conditions. According to the stress distribution under the steady condition, the stress wave coefficient is proposed which is used to study and describe the absolute fluctuation of unsteady stress. It is found that large reduction results in a thinner film thickness and a larger hydrodynamic pressure and shear stress in the deformation zone under the steady condition. Under the unsteady condition, as the fluctuation of disturbance factors such as inlet strip thickness intensifies, the film wave coefficient increases, indicating that the absolute fluctuation of film thickness gets larger. The position and value of the pressure stress peak change with time under the unsteady condition. The absolute fluctuation of unsteady film thickness has a greater impact on the hydrodynamic pressure than on the shear stress. When the absolute fluctuation of film thickness is 6.33%, the pressure stress and the shear stress have a 1.17% and a 0.24% absolute fluctuation, respectively.
Abstract: Based on the lubrication principle of rolling process and the mechanical vibration theory, a vertical vibration model of single-stand aluminum cold rolling mills was established with the consideration of dynamic friction state in roll gap to study vertical vibration phenomena in high speed rolling of thin strips. This model includes the geometric model of roll gap, the dynamic friction model of the roll-strip working interface, the distribution model of principle rolling stress and friction stress, and the two-degree-of-freedom vertical structure model which is coupled with the former three models. In order to analyze the vertical vibration mechanism and system stability under dynamic friction state in roll gap, the rolling force curve and normal rolling stress distribution curve were simulated separately on Matlab/Simulink platform for validating this model, with the actual data of a single-stand aluminum cold rolling mill. Moreover, the dependences of the system stability on strip entry thickness, mixed friction state and rolls-strip surface roughness were dis-cussed in this article.
Abstract: A design scheme of triple-redundancy transmission systems was presented in which three groups of power units parallel input and backup each other. A compound gear train transmission system coupling with input movement and power makes sure continuous power output by automatically switching to another mode while part of the input unit fails. Based on the analysis of the design scheme, a structure design scheme was introduced, and the matching relationship of gear teeth was derived to meet the requirement of transmission ratio. Then a multidisciplinary design optimization model of the triple-redundancy transmission system was established, in which the system is discomposed into two subsystems:differential gear train and fixed axis gear train. The multidisciplinary variable couple design optimization method of discrete variables was used in the optimal design of the triple-redundancy transmission system and the optimal comprehensive scheme was obtained which meets the matching relationship of gear teeth, strength requirements and kinetic requirements.
Abstract: An approach, whose hardcore is a classification of charges by determining whether the charge starts at the time of disturbance occurrence, of making a re-plan was proposed to solve the problem of multi-constrained steelmaking-continuous casting re-planning. The constraints of the re-planning problem are divided into hard and soft constraints. A hybrid algorithm based on time forward inferring and genetic algorithm is designed for the processing charges, and another hybrid algorithm based on time backward inferring and genetic algorithm is designed for the un-processing charges. The feasible solution of the re-planning problem is solved with the hybrid algorithm and hard constraints, and the optimal solution is searched with the soft constraints in the feasible solution. The feasibility and effectiveness of the method were verified with the help of simulation experiments by production data in a steel plant.
Abstract: A constraint satisfaction optimization model was presented to deal with the optimization decision problem about the steel tube location. Through the analysis of stack height and the piling rules of steel tubes, a two-stage algorithm was given based on clustering and constraint satisfaction technology. In the first stage, steel tubes to be put into storage are grouped by clustering-based approach according to their multiple attributes. In the second stage, by using constraint satisfaction technology, the specific location of steel tubes in each group is assigned, and the search space of the problem is dynamically shrunk through constraint propagation. Finally, this algorithm was compared with the classical BFD (best fit deceasing) algorithm through experiments. Experimental results demonstrate that, in the premise of minimizing stacking operations, the algorithm can effectively reduce the quantity of stacks and achieve a well-performed utilization rate of stacks. And thus the results verify the feasibility and effectiveness of the model and algorithm.
Abstract: The seismic responses of a single steel-pipe pile built in the frozen crust and the liquefiable sand soil were studied by shaking table tests. A flexible soil container was designed and used to construct the soil profile in order to minimize the boundary effect. The frozen crust was simulated through the mortar which was made of cement, sand and water by the mixture ratio. Liquefaction can occur in the saturated sand soil beneath the frozen crust. A lumped mass was exerted at the top of the pile to satisfy the inertia conditions. During the tests, several amplitude-scaled ground motions were chosen as input seismic waves. The liquefying levels of the saturated sand soil and the dynamic responses of the pile can be analyzed via the measured real-time data including strains of the pile, dis-placements between the pile and the frozen crust and pore water pressures in the sand. Experimental results show that before liquefaction occurs, the frozen crust can provide a lateral constraint, and thus improve the load bearing capacity of the pile and suppress its lateral deformation. It is also found that once liquefaction occurs, the frozen crust may further strengthen this tendency and deteriorate the performance of the pile.
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
