Abstract: As a plastic fluid, the morphological features of internal structure in an unclassified tailing paste closely relate to its flow properties. Studies on the evolution characteristics of internal structure during the sheafing flow process have extremely important significance for analyzing flow behavior in pipeline transportation and paste preparation. In this paper, scanning electron microscopy was used to investigate the meso-structure images of the paste at different mixing time. The fractal dimensions of these meso-structure images were estimated by the image processing technology and fractal theory. A structure coefficient A was put forward to explain the morphological features of meso-structure, and a time-evolution mathematical model of meso-structure was built in the mixing process. Some related experiments were done for a lead-zinc tailing paste. It was found that the structure coefficient A flattened out gradually after a steep fall with mixing time, and finally reached an equilibrium state. The failure coefficient and restitution coefficient in the evolution model were obtained to be 0.171 and 0.491 respectively by fitting experimental data.
Abstract: The reduction reaction rate, reduction degree, surface microstructure and weight loss of composite pellets with different components under biomass syngas atmosphere were investigated to illustrate the effects of biomass addition in pellets on the reduction behavior and reaction kinetics. The porosity of pellets with the addition of biomass is higher than that without the addition of biomass, which is favorable to heat and mass transfer of the reduction process, increases the reduction degree of products and decreases the apparent activation energy of reaction. The reduction of pellets was carried out in the manner of a shrinking core model. In the range of 1123 to 1323 K, the rate-controlling mechanism of reduction for these two kinds of pellets is inteffacial chemical reaction. The addition of biomass in pellets can improve the inteffacial chemical reaction, and thus the apparent activation energy of reaction decreases from 95.448 kJ. mol-1 to 68.131 kJ. mol-1.
Abstract: This article is focused on the reduction law of Indonesia ironsaud oxidized pellets by hydrogen. Reduction experiment was performed with a thermogravimetric analyzer. The hydrogen reduction mechanism of the oxidized pellets was studied by the phase change, thermodynamic and kinetic analyses of the reaction process. It is found that the final products are FeTiO3 at 800℃ and 850℃, and the restrictive step of reduction is composed of two different stages, which are chemical reaction in the early stage of reduction and the mixed-control of chemical reaction and intraparticle diffusion in the subsequent reaction. Titanium oxide appears at 900, 950 and 1000℃, and the restrictive step of reduction is composed of three stages, which are chemical reaction, the mixed-control of chemical reaction and intraparticle diffusion, and intraparticle diffusion.
Abstract: The isothermal hydrogen reduction kinetics of FeO powder at 773-1273 K was investigated by thermogravimetry. Above 873 K, there was a turning point in the kinetic curve, which indicated that the reduction mechanism changed. An unusual temperature effect that the reduction rate decreased with increasing temperature was observed from 973 K to 1073 K. To discuss the effect of product structure on the reduction rate of iron oxide, the morphology of samples reduced at different temperatures and for different reaction time was observed by scanning electron microscopy. It was shown that holes on the sample surface increased gradually, the dendritic characteristic appeared with increasing temperature, and the sintered phenomenon was obvious at 973 K and 1023 K. At a certain temperature, holes on the sample surface increased and the sintered phenomenon appeared gradually with prolonging reaction time. At 973 K and 1023 K, the sample kept fairly the original shape, but at 1173 K, just reacted for 2 rain, a large number of dendritic products appeared and sintered gradually. Combining the morphology and kinetic curves, it can be summarized that interfacial chemical reaction is the rate-limiting step in the initial stage of hydrogen reduction. But as the reaction proceeds, the reduced iron sinters and the compact structure of the reduced product hinders the outward diffusion of produced gas. The rate-limiting step changes to the outward diffusion of produced gas, which leads to the decrease of the reduction rate of iron oxide by hydrogen.
Abstract: Medium carbon non-quenched and tempered steels with different S contents were smelted with a vacuum induction furnace. Several experiments were conducted to study the effect of S content on the morphology of sulfides and microstructure in the steels. The results show that with the increase of S content from 0.025 wt% to 0.065 wt%, the number of sulfide inclusions increases, and the aggregation of sulfide inclusions is promoted, while the microstructure becomes finer due to the increasing area ratio of intragranular ferrite. Thermodynamic calculations and phase diagram information were employed to explain the transition of MnS from type Ⅱ to type m. The angular type Ⅲ MnS is resulted from divorced eutectic reaction before the solidification completes, and the rod-like type Ⅱ MnS is derived from normal eutectic reaction at the end of the solidification process. Both MnS and MnS-V (C, N) complex inclusions are found to act as effective nucleation sites to improve the formation of intragranular idiomorphic ferrite.
Abstract: The microstructural refinement effect of alloying elements Nb, Ti and S was investigated by analyzing austenite grain growth behavior and hot-rolled microstructure in a non-quenched steel for crankshafts. The results show that the austenite grain coarsening temperature increases by 100℃ when the heating time is 30 min, and the microstructure in the hot-rolled bar edge is significantly refined after 0.027% Nb-0.012% Ti microalloying and an increase of S from 0.029% to 0.046% in the steel investigated. The undissolved second phase particles MnS and (Nb, Ti) (C, N) have a pinning effect on austenite grain boundaries, and then retard the austenite grain growth. Besides, the microstructural refinement effect of the alloying elements needs a suitable deformation schedule.
Abstract: The microstructures of La deoxidized steels obtained at different cooling rates were investigaled by optical microscopy and scanning electron microscopy coupled to an energy dispersive X-ray spectrometer. The continuous cooling transformation diagram of the tested steel was also drawn in this paper. It is found that in the cooling rate range of 4 to 10℃·s-1, intragranular ferrite can form in the steel. While at the cooling rate of 8℃·s-1, the microstructure mainly consists of fine and dispersed intragranular acicular ferrite (IAF). The lattice disregistry between lanthanum-containing inclusions and α-Fe is small; especially, this value of La2O2S is 0.2%. These kinds of inclusions can induce IAF nucleation and sympathetic nucleation, and also make grains refined.
Abstract: In order to develop a new generation cold-rolled ultra-high strength low-alloy steel, continuous annealing experiments of a Ti-0.12%, Nb-0.076% cold-rolled ultra-high strength low-alloy steel were done on a continuous annealing test machine. The influence of annealing temperature on the phase composition, grain size, and mechanical properties of the steel was investigated at four dif-ferent annealing temperature ranges from 760℃ to 830℃. The final composition is ferrite and a small amount of bainite under 800℃ annealing and 400℃ over-aging conditions, the ferrite grain size is about 1.4 μn, and the yield strength reaches up to 700 MPa. A large number of nanometer size sub-crystal structures, a small number of dislocations, and nano-Ti and Nb precipitates are observed by scanning electron microscopy and transmission electron microscopy. Those microstructures improve the strength a lot.
Abstract: The effect of heat treatment on the high temperature ductility of 00Cr24Ni13 austenitic stainless steel casting billets was investigated by heat treatment experiment, therma-compression test and thermal tensile test. The result showed that δ ferrite morphology in the casting billet could be significantly changed through the heat treatment process. After air cooling from 1200℃ for 3 h, large area of continuous reticular δ ferrite in the casting billet completely changed into dispersed granular phases. Compared with the casting billet before heat treatment, heat-treated samples which are composed of granular δ ferrite had a higher value of deformation resistance at different compression temperatures, but there was no sharp deterioration in deformation resistance, the thermal simulation tensile strength remained almost the same and the reduction of area (Z) at the same temperature increased obviously. The temperature region of Z ≥ 60% extended from 1150-1280℃ to 1050-1300%, and the high plasticity (Z ≥ 80%) range is about 150% (1150-1300℃).
Abstract: The stress corrosion cracking growth behavior of 316L stainless steel, which is used as nuclear auxiliary pipelines, was continuously monitored by a direct current potential drop method under a constant stress intensity factor K of 33 MPa·m1/2. By comparing the cracking behavior of this material at 200, 250, 280 and 325℃ in 2 mg·L-1 oxygenated water and deoxygenated water, we found that the crack growth rate is faster in the oxygenated water than in the deoxygenated water. Experimental results also show that there is a peak of the crack growth rate of this material in the deoxygenated water at 250℃, while the crack growth rate increases with the rise of temperature in the oxygenated water.
Abstract: The texture and room-temperature formability of rolled Mg-1.5Zn alloys containing different contents of Ce were inves-tigated by experiment, it is indicated that during the same hot rolling and annealing processes, Ce addition can effectively modify and weaken the texture. When 0.2wt% Ce is added, the Mg-1.5Zn alloy has excellent room-temperature formability, and its maximum texture intensity is only 2.20. This alloy exhibits the transverse direction split texture, whose basal pole is tilted by about ±35° from the normal direction toward the transverse direction. At room temperature, the Erichsen value reaches 5.46, and the ultimate elonga-tion in the rolling direction is 23.2% with a low planar anisotropy value of 0.01. However, 0.5% and 0.9% Ce additions promote the formation of huge secondary phase particles, resulting in an increase in the intensity of the basal texture, a decrease in the Erichsen value, and deterioration in the room-temperature stretch formability.
Abstract: Microstructure and texture evolution in Ti-6Al-4V alloy under different hammer forging processes were investigated by electron backscattered diffraction and scanning electron microscopy. The results showed that the inicrostructure became more and more uniform along with the frequency of forging, and the directionality turned more and more invisible; after heat treatment, the distribu-tion uniformity of α and β phases and the micro-texture were both increased to somewhat extent because of the release of deformation energy and the tilting of α and β phases, especially highlighted in the forging modes of uniaxial 3 times and cross upsetting and stretching 3 times. As for the texture distribution of this alloy, the close-packed hexagonal structured α phase was more sensitive to hot working modes than the body centered α phase. For raw materials and one-time axial upsetting and stretching, the texture of α phase mainly consisted of the {0001 } basal texture; with the increase of frequency and deformation energy, the {1010} and {1120} prismatic slip and the {1011} and {1212} pyramidal slip were strengthened, accordingly inducing the more uniform of orientation because of the texture components and the dispersion of texture distribution.
Abstract: A thermodynamic analysis was performed on possible reactions of Fe3O4 in sediment material, intermediate product FeO, Fe, and other matters. In combination with the predominant area phase diagram of the Fe-Si system under different carbon mon-oxide partial pressures and excess carbon and silicon dioxide as well as the thermodynamic parameter state diagram of the Fe-O-N system, it is found that Fe finally exists in the form of Fe3Si, which provides a thermodynamic theoretical basis for using sediment to synthesize O'-Sialon-SiC-Fe3Si (Fe-Sialon) composites. These Fe-Sialon matrix composites made from sediment were prepared by carbothermal reduction-nitridation on the basis of thermodynamic analysis. X-ray diffraction and scanning electron microscopy resuhs in-dicate that plentiful O'-Sialon phase and a small quantity of SiC and Fe3Si phases appear in samples, and the crystalline grains are fi-ber-, cotton-, or short column-shaped, which is consistent with thermodynamic analysis results.
Abstract: The grouting technology is a very important maintenance method of the blast furnace stack. In China, the grouting process is completed by experience, so the furnace shell is always burnt and the mud material sometimes permeates into hot metal through the furnace lining, leading to accidents. In this paper, a stress calculation model of the furnace lining in the grouting process is set up with ANSYS software based on the finite element method and the theory of elastic mechanics. By using this model, the stress distribution of the furnace lining in the grouting process is calculated under different conditions of grouting pressure, grouting area and grouting location. It is found that the maximum stress in the furnace lining increases along with the increase of grouting pressure, but the stress concentration locates at the same place, and therefore the grouting pressure can be increased under certain conditions. The increase of single-hole grouting quantity causes the stress concentration location of the furnace lining to move towards the hot surface, so the guiding principle of "small quantity and more holes" should be insisted. The probability of lining cracking at the hot surface increases when grouting at the thinnest area of the furnace lining, so grouting at this area should be avoided. An application of the model shows that the simulation results are reasonable and effective.
Abstract: Three-dimensional temper rolling processes are simulated by nonlinear elastoplastic finite element software called ABAQUS. In this simulation, the initial flatness defects of steel strips are modeled by the temperature field, and the adjustment effect of flatness control methods on the support roll gap shape is comprehensively expressed by the contour change of rigid work rolls. Based on the above mechanical model, flatness defects after temper roiling and their dependency on initial flatness defects and temper rolling conditions are numerically studied for steel strips with initial flatness defects, and moreover, the heredity and evolution laws of flatness defects in the temper rolling process are presented. Simulation results show that the support roll gap shape is the most important factor deciding the heredity and evolution of flatness defects, and the initial flatness defect level of entry strips has some effect on the flatness of exported strips.
Abstract: A radial flow pressure swing adsorption (PSA) unit with two-tower configuration was designed for oxygen production. The influences of gas flow pattern, outer flow channel width and channel structure on oxygen production were studied by experiment. The result indicates that it is an optimal choice to use centripetal flow in the radial flow adsorber for oxygen production with PSA. Un-der the experimental condition, when the outer flow channel width decreases to 13 mm, the separation of oxygen from nitrogen is the best. A R-shaped channel structure can better improve the utilization efficiency of molecular sieves and oxygen production compared with a Z-shaped channel. This research result provides a foundation for the application and research of a radial flow adsorber in the PSA unit for oxygen production.
Abstract: Heat-pipe-cooled thermal protection is an effective thermal protection method with embedded high heat transfer capacity materials or structures. A numerical model of a heat-pipe-cooled thermal protection structure with an embedded high thermal conduc-tivity C/C material was proposed in the present paper. Contact thermal resistance was tested between the high thermal conductivity C/C material and the heat-resisting three-dimensional braid C/C material. The effects of several key parameters on the thermal protection results were also numerically investigated. The results show that it is an effective method to decrease the stagnation temperature by reducing the thickness of the heat-resisting material, but the resulting strength problem should also be taken into account. Interface contact thermal resistance has a significant influence on the thermal protection effect, and in order to achieve effective thermal protection the interface contact thermal resistance should be lowered through fabrication processing.
Abstract: A tracker using the method of minimum cost flow was designed to solve the problems of object occlusion, lighting effects and clutter disturbance. This tracker combines integer programming with the minimum cost flow model, and converts the prob-lem of object tracking into a linear programming problem. Compared with other similar trackers, this tracker has a better tracking accu-racy. Simulation results show that the tracker in this paper has strong robustness and better tracking stability in complex environments.
Abstract: A recommendation algorithm is proposed by introducing the universal law of gravitation into a recommendation system. This new algorithm is named as the gravitation-based personalized recommendation (GBPR) algorithm. In the algorithm, social tags used by users are regarded as particles that made up of their preference objects, social tags marking on items are considered as parti-cles that made up of item objects, and the user preference objects and item objects are taken as a user preference object model and an item object model, respectively. Gravitation exists between the user preference objects and item objects, and its strength obeys the universal law of gravitation. The strength of gravitation between the user preference objects and the item objects is computed, and it is regarded as their similarity. The bigger the strength is, the more similar they are, and the corresponding item objects are more proba-ble to be liked by users. Experimental results show that the proposed algorithm can get good performance.
Abstract: The impact-resistant performance of steel-reinforced concrete beams with a rigid-flexible composite structure was ana-lyzed based on our earlier research outcomes. The focus was to disscuss the influence of constraint forms on the crashworthy perform-ance of reinforced concrete beams with composite laminates. In the process of numerical simulation, the observed beam with four dif-ferent measures incluing the unprotected, the rigid protective, the flexible protective and the proposed one was considered separately. Meanwhile, three considered constraint forms of the beam ends were as follows:fixed at both ends; hingled at both ends; fixed at one end and hingled at the other end. Protective effects of the different measures were compared and analyzed by observing the strain, the displacement, the acceleration and the impact force of the target beam. Numerical results show that, under the same impact conditions the composite system can obtain the optimal protective effect, but constraint forms may have significant impact on suppression of the dynamic response of the beam. Especially, for the beam fixed at both ends the best protective effect may be obtained.
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
