Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method

A new method called mixed Lagrangian and Eulerian (MiLE) method was used to simulate the continuous casting process in a mold of free-cutting steel 38MnVS. The simulation results are basically in agreement with experimental data in the literature, achieving the three-dimensional visualization of temperature distribution, melt flow, shell thickness, and stress distribution of blooms in a mold. It is shown that the flow velocity of steel melt becomes smaller gradually as the casting proceeds. When the flow reaches a certain depth, two types of flow patterns can be observed in the upper zone of the mold. The first flow pattern is to flow downwards, and the second one is to flow upwards to the meniscus. The corner temperature is higher, and the thickness is thinner than those in the mid-face. The effective stress in the corner area is much bigger than that in the mid-face, indicating that the corner area is the dangerous zone of cracking.     

Study on pitting process of 316L stainless steel by means of staircase potential electrochemical impedance spectroscopy

Pitting corrosion of 316L stainless steel in NaCl solution was investigated by means of staircase potential electrochemical impedance spectroscopy (SPEIS). The investigation focused on the transition of stainless steel from the passive state to pitting corrosion. Based on the evolution of electrical parameters of the equivalent electrical circuit, it is suggested that the most probable mechanism of pit creation is the film breaking model. The result demonstrates that staircase potential electrochemical impedance spectroscopy is an effective method for the investigation of pitting corrosion.     

Crystallization characteristics of iron-rich glass ceramics prepared from nickel slag and blast furnace slag

The crystallization process of iron-rich glass-ceramics prepared from the mixture of nickel slag (NS) and blast furnace slag (BFS) with a small amount of quartz sand was investigated. A modified melting method which was more energy-saving than the traditional methods was used to control the crystallization process. The results show that the iron-rich system has much lower melting temperature, glass transition temperature (T_g), and glass crystallization temperature (T_c), which can result in a further energy-saving process. The results also show that the system has a quick but controllable crystallization process with its peak crystallization temperature at 918℃. The crystallization of augite crystals begins from the edge of the sample and invades into the whole sample. The crystallization process can be completed in a few minutes. A distinct boundary between the crystallized part and the non-crystallized part exists during the process. In the non-crystallized part showing a black colour, some sphere-shaped augite crystals already exist in the glass matrix before samples are heated to T_c. In the crystallized part showing a khaki colour, a compact structure is formed by augite crystals.     

Comparative stability analyses of traditional and selective room-and-pillar mining techniques for sub-horizontal tungsten veins

The stability and productivity concerning a modification on the traditional room and pillar for a new selective technique at the Portuguese Panasqueira Mine have been described. The traditional room-and-pillar stoping uses 5.0-m wide rooms with 3.0 m×3.0 m pillars, while the selective room-and-pillar mining technique consists in stoping with rooms of 4.0 m wide and pillars of 4 m×4 m with a subsequent selective cutting of the quartz veins at the mid pillar of approximately 0.5 m high, to obtain a pillar section with an area of 3.0 m×3.0 m. The stability and productivity analyses indicate that the selective technique obtains smaller average pillar safety factor, more rock mass displacement, more extraction and selectivity ratios, and ore grade improvement, compared with the traditional technique. These results show that the selective technique is also more convenient. This proposed selective room-and-pillar mining technique is applicable to any sub-horizontal narrow quartz veins with wolfram, gold, etc. such as the famous La Rinconada gold mine in the Peruvian Andes.     

Existence of multiple solutions for the laminar flow in a porous channel with suction at both slowly expanding and contracting walls

The asymptotic behavior of solutions of a similarity equation for the laminar flow in a porous channel with suction at both expanding and contracting walls has been obtained by using a singular perturbation method. However, in the matching process, this solution neglects exponentially small terms. To take into account these exponentially small terms, a method involving the inclusion of exponentially small terms in a perturbation series was used to find two of the solutions analytically. The series involving the exponentially small terms and expansion ratio predicts dual solutions. Furthermore, the result indicates that the expansion ratio has much important influence on the solutions.     

The large sample properties of the solutions of general estimating equations

This paper develops the large sample properties of the solutions of the general estimating equations which are unbiased or asymptotically unbiased or with nuisance parameters for correlated data.The authors do not make the assumption that the estimating equations come from some objective function when we establish the large sample properties of the solutions.So these results extend the work of Newey and McFadden(1994) and are more widely applicable.Furthermore,we provide some examples to justify the importance of our work.     

Finding the topology of implicitly defined two algebraic plane curves

An algorithm is given for computing in a very efficient way the topology of two real algebraic plane curves defined implicitly.The authors preform a symbolic pre-processing that allows us later to execute all numerical computations in an accurate way.     

Kinetics and mechanism of titanium hydride powder and aluminum melt reaction

Based on the measurement of the released hydrogen gas pressure (P_H2), the reaction kinetics between TiH₂ powder and pure aluminum melt was studied at various temperatures. After cooling the samples, the interface of TiH₂ powder and aluminum melt was studied. The results show that the 2 H P_H2-time curves have three regions; in the first and second regions, the rate of reaction conforms zero and one order, respectively; in the third region, the hydrogen gas pressure remains constant and the rate of reaction reaches zero. The main factors that control the rate of reaction in the first and second regions are the penetration of hydrogen atoms in the titanium lattice and the chemical reaction between molten aluminum and titanium, respectively. According to the main factors that control the rate of reaction, three temperature ranges are considered for the reaction mechanism:(a) 700-750℃, (b) 750-800℃, and (c) 800-1000℃. In the first temperature range, the reaction is mostly under the control of chemical reaction; at the temperature range of 750 to 800℃, the reaction is controlled by the diffusion and chemical reaction; at the third temperature range (800-1000℃), the dominant controlling mechanism is diffusion.     

Mechanical properties of Mn-doped ZnO nanowires studied by first-principles calculations

First-principles calculations were performed to investigate the mechanical properties of ZnO nanowires and to study the doping and size effects. A series of strains were applied to ZnO nanowires in the axial direction and the elastic moduli of ZnO nanowires were obtained from the energy versus strain curves. Pure and Mn-doped ZnO nanowires with three different diameters (1.14, 1.43, and 1.74 nm) were studied. It is found that the elastic moduli of the ZnO nanowires are 146.5, 146.6, and 143.9 GPa, respectively, which are slightly larger than that of the bulk (140.1 GPa), and they increase as the diameter decreases. The elastic moduli of the Mn-doped ZnO nanowires are 137.6, 141.8, and 141.0 GPa, which are slightly lower than those of the undoped ones by 6.1%, 3.3%, and 2.0%, respectively. The mechanisms of doping and size effect were discussed in terms of chemical bonding and geometry considerations.     

Effect of deep cryogenic treatment on the properties of 80CrMo12 5 tool steel

The effect of deep cryogenic treatment on the mechanical properties of 80CrMo12 5 tool steel was investigated. Moreover, the effects of stabilization (holding at room temperature for some periods before deep cryogenic treatment) and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribution and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tempering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogenically treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness.