1,721,036 research outputs found
NEAR-CRACK-TIP DEFORMATION IN COPPER SINGLE-CRYSTALS
No full textCracked Cu specimens, made by diffusion bonding two halves of a single crystal, were 3-point bend tested, and the surfaces near the crack tips were examined by an optical microscope and a stylus profilometer. The plastic zone developed as assembled fan-shaped sectors, the details of which depended on the crystal orientation. A sector was often characterized by a family of dominant slip lines, and operations of slips on coplanar slip planes (CSP) were mutually exclusive. The through-thickness displacement changed gradually across sector boundaries but its gradient did not, suggesting a constant plastic strain within a sector but strain discontinuites at sector boundaries. The degree of necking depended mostly on the operation of slips on non-CSP, but operation of CSP caused either local necking or protrusion depending on the crystal orientation
Infiltration of Slag Film into the Grooves on a Continuous Casting Mold
No full textAn analytical model is developed to clarify the slag film infiltration into grooves on a copper mold during the continuous casting of steel slabs. A grooved-type casting mold was applied to investigate the infiltration of slag film into the grooves of a pitch of 0.8 mm, width of 0.7 mm, and depth of 0.6 mm at the vicinity of a meniscus. The plant trial tests were carried out at a casting speed of 5.5 m min(-1). The slag film captured at a commercial thin slab casting plant showed that both the overall and the liquid film thickness were decreased exponentially as the distance from the meniscus increases. In contrast, the infiltration of slag film into the grooves had been increased with increasing distance from the meniscus. A theoretic model has been derived based on the measured profile of slag film thickness to calculate the infiltration of slag film into the grooves. It successfully reproduces the empirical observation that infiltration ratio increased sharply along casting direction, about 80 pct at 50 mm and 95 pct at 150 mm below the meniscus. In the model calculation, the infiltration of slag film increases with increasing groove width and/or surface tension of the slag. The effect of groove depth is negligible when the width to depth ratio of the groove is larger than unity. It is expected that the developed model for slag film infiltration in this study will be widely utilized to optimize the design of groove dimensions in continuous casting molds.open1155sciescopu
The effect of chemical composition on grain structure and texture evolution of hot rough rolled carbon steels
No full textCombination of thin slab casting and direct hot rolling to obtain thin steel plate products is an energy efficient process in commercial steel plants. Generally, cracking near the surface is the most serious problem especially during rough rolling of as cast thin slabs. Therefore, it is highly recommended that the microstructure near the surface should be controlled to have enough ductility to withstand the strain. In this study the effect of chemical composition on microstructure evolution and texture has been investigated for the steel plates rough rolled from 70 to 25 mm at a commercial plant. In low carbon content of 0.05 wt%, the micrograph was seen to comprise mainly ferrites with minor pearlite islands which changed to ferrite-pearlite structure with increasing carbon to 0.17 wt%. A detailed investigation was carried out to examine the behavior of the grain structure formed in rough rolled steels, using high resolution SEM microscope fitted with EBSD camera. In all investigated steel plates, a fine grain structure was observed in the plate top surface due to development of rapid static recrystallization after rough rolling which gradually coarsened in mid-section region. Investigation was carried out to understand the effect of alloying elements such as Mn on the texture. Mainly fiber textures of both ND and RD directions were observed after transformation showing inhomogeneity with increasing distance from the plate surface towards the depth. Massive ferrite (bcc) grains transforming from austenite (fcc) has been detected during the rough rolling process. Therefore, tensile test was carried out at 600 degrees C in order to investigate the failure mechanism of ferrite as the work roll chilling has a significant effect on temperature reduction in the plate surface which may lead to lower ductility of massive ferrites and thus formation of crack at the surface during rough rolling process. (C) 2014 Elsevier B.V. All rights reserved.1111sciescopu
In-Depth Study of Mold Heat Transfer for the High Speed Continuous Casting Process
No full textMold heat transfer during the commercial high speed continuous casting up to 7 m/min was investigated in order to clarify the influence of various operating conditions such as casting speed, mold flux, mold thickness, thickness and height of mold coated layer and so on. A simple, but practical formula of heat flux has been derived in terms of those operating conditions by analyzing the heat flux data obtained in CEM (R) (Compact Endless Casting and Rolling Mill) caster based on simplified one dimensional heat transfer model. Especially, impact of mold parameters such as mold thickness, mold coated layer thickness and its height on the heat flux can be linearly expressed in the empirical formula derived. Heat flux ratio (HR), the ratio of the narrow face heat flux to the wide face one, is one of the important indicators to evaluate whether the solidified shell is evenly robust or not. Averaged HR in CEM (R) caster is around 0.87, which varies according to the caster specifications and operating conditions. It is suggested that the mold taper should be adjusted to maintain the HR as close to 0.87 as possible.1111sciescopuskc
Fluoride evaporation and crystallization behavior of CaF2–CaO–Al2O3–(TiO2) slag for electroslag remelting of Ti-containing steels
No full textTo elucidate the behavior of slag films in an electroslag remelting process, the fluoride evaporation and crystallization of CaF2-CaO-Al2O3-(TiO2) slags were studied using the single hot thermocouple technique. The crystallization mechanism of TiO2-bearing slag was identified based on kinetic analysis. The fluoride evaporation and incubation time of crystallization in TiO2-free slag are found to considerably decrease with decreasing isothermal temperature down to 1503 K. Fish-bone and flower-like CaO crystals precipitate in TiO2-free slag melt, which is accompanied by CaF2 evaporation from slag melt above 1503 K. Below 1503 K, only near-spherical CaF2 crystals form with an incubation time of less than 1 s, and the crystallization is completed within 1 s. The addition of 8.1wt% TiO2 largely prevents the fluoride evaporation from slag melt and promotes the slag crystallization. TiO2 addition leads to the precipitation of needle-like perovskite (CaTiO3) crystals instead of CaO crystals in the slag. The crystallization of perovskite (CaTiO3) occurs by bulk nucleation and diffusion-controlled one-dimensional growth.1121Nsciescopu
Controlling the shear thinning property of calcium silicate melts by addition of Si3N4
No full textCalcium silicate melts at high temperature are valuable as a lubricant for continuous casting of steel. They are limited by the contradictory situation in that high viscosity is required under low shear rate whereas low viscosity is needed under high shear rate. To resolve such problem, we conducted a rheological study to generate a strong shear thinning behavior of a calcium silicate melts which is an ideal thermal property for continuous casting of steel. We found that a small amount of silicon nitride leads to a strong shear thinning property, allowing a high viscosity at low shear rate without significant changes in the viscosity at higher shear rates. Such trend is completely opposite to the one previously suggested with a borate additive. This improvement of the shear thinning property arises because each additive enables these calcium silicate melts to have a shear thinning favorable structure in thoroughly different manner. (C) 2015 Elsevier B.V. All rights reserved.1143sciescopu
Stabilized edge-to-edge aggregate flow control
No full textIn this paper, we present a distributed flow control scheme which achieves weighted max-min fair bandwidth allocation among all source-destination pairs on a per-aggregate basis within its network. The motivation behind the scheme is the absence of per-aggregate flow control in the current Internet, resulting in inability to enforce a certain fairness on source-destination flows. In our scheme, the distributed algorithm to compute weighted max-min fair rates is based on PI control in feedback control theory. We mathematically prove the asymptotic stability of the algorithm in presence of aggregate flows with heterogeneous round-trip delays. Through simulations we demonstrate the effectiveness of the proposed scheme in controlling per-aggregate flows
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