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Wang H.-Q.,University of Science and Technology Beijing | Wang H.-Q.,Hunan Valin Lianyuan Iron and Steel Co. | Bao Y.-P.,University of Science and Technology Beijing
Beijing Keji Daxue Xuebao/Journal of University of Science and Technology Beijing | Year: 2012

A continuous casting mould with a cross section of 1400 mm×230 mm was simulated by software Fluent 6.3, and the effects of casting speed, immersion depth and submerged nozzle (SEN) opening-angle on its flow field were investigated. It is shown that with the increase of casting speed, the maximum horizontal and vertical velocities of the liquid surface increase, and the position of the impact point on the narrow side does not change. With the increase of distance to the liquid surface, the velocity of the narrow side first increases and then decreases, till near to zero. When the casting speed is greater than 1.2 m·min -1, the horizontal velocity of the liquid surface obviously increase. With the increase of SEN immersion depth, the maximum horizontal velocity of the liquid surface decreases, and the maximum vertical velocity increases. SEN immersion depth has little effect on the impact point on the narrow side. When the SEN immersion depth is greater than 140 mm, the change of the maximum horizontal velocity is small. With the increase of SEN downward opening-angle, the maximum horizontal velocity of the liquid surface first decreases and then increases. When the SEN downward opening-angle is 12.5°, the maximum horizontal velocity of the liquid surface is the smallest, but the minimum velocity at the impact point on the narrow side can be obtained when the SEN downward opening-angle is 10° to 12.5°. Source


Yang G.,Kunming University of Science and Technology | Yang G.,Control Iron and Steel Research Institute, China | Sun X.,Control Iron and Steel Research Institute, China | Li Z.,Control Iron and Steel Research Institute, China | And 4 more authors.
Materials and Design | Year: 2013

The precipitation behavior of vanadium-rich carbides formed during the reheating processes and its influence on the microstructure and mechanical properties have been systematically investigated in a high strength low alloy martensite steel. It was found that the nano-sized (Ti, V)C particles mainly precipitated during reheating rather than soaking at the austenitization process. For their pinning effect on grain growth, ultra-fine austenite grain with the average size of 3.5. μm formed during holding at 880. °C for 1. h. As the austenitization temperature increased, the prior nano-sized (Ti, V)C coarsened and its volume fraction decreased, which led to increment of austenite grain size. Excellent combined mechanical properties such as tensile strength 1670. MPa, yield strength 1460. MPa, elongation 10% at room temperature and impact energy (Akv) 57. J at -40. °C were obtained in the ultra-fine grained steels. In particular, the low-temperature toughness was improved by grain refinement. The strengthening mechanisms were also investigated by comparing the experimental results with theoretical calculation. The variation of yield strength with the condition of heat treatment was discussed in detail. © 2013 Elsevier Ltd. Source


Hou Z.,Chongqing University | Chen H.,Chongqing University | He X.,Hunan Valin Lianyuan Iron and Steel Co. | Wang W.,Chongqing University | And 2 more authors.
Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015 | Year: 2015

Over the years, many works have been done about the defect formation and the methods for controlling equiaxed grains ratio in order to improve the internal quality, but there are few investigations about the related solidification-structure compactness degree of central equiaxed grains. The authors ever performed a special study about the compactness degree of central equiaxed grains based on the numerical modeling, and it is found that the compactness degree of central equiaxed grain zone in the billet is closely related to the centre solidification time (i.e., it decreases with the increase of the centre solidification time). However, the previous study was only based on numerical modeling. Consequently, Confocal Laser Scanning Microscope (CLSM) is used to conduct hot-model experiments in this paper, and change mechanism of compactness degree of central equiaxed grains is investigated based on the influences of cooling rate in different stages and superheat on the compactness degree. Firstly, cooling rate of solidifying stage is found to have a great influence on the compactness degree, which is consistent with the previous result by using numerical modeling. Secondly, cooling rate of eliminating superheat also has an influence on the compactness degree. Moreover, it is shown that, at to the compactness degree, the influence abilities of cooling rates in different stages are different. From strong to weak, the order of the ability is cooling rate of earlier solidifying stage, cooling rate of eliminating superheat stage and cooling rate of later solidifying stage. Finally, under some certain conditions, the influencing ability of cooling rate on compactness degree is stronger than that of the superheat. Source


Tian F.,Hunan Valin Lianyuan Iron and Steel Co. | Wang Z.-R.,Hunan Valin Lianyuan Iron and Steel Co. | Li Z.-D.,Hunan Valin Lianyuan Iron and Steel Co. | Li Z.-D.,Control Iron and Steel Research Institute, China
Kang T'ieh/Iron and Steel | Year: 2015

Two series of cold rolled low-alloy and high-strength automotive steel, i.e. Mn-Si series and Nb microalloyed series, have been investigated to study the microstructure and mechanical properties through industrial trial with the same process, including batch annealing. The strengthening mechanism of the Nb microalloyed steel has been investigated by comparing with Mn-Si series cold rolled batch annealed low-alloy and high-strength steel. The microstructures of the hot-rolled and cold-rolled annealed sheets of those two kinds of steels were characterized by means of OM, SEM and TEM. The mechanical properties were also measured by tensile testing machine. The results were compared and showed that the sizes of the ferrite grains and nano precipitates of the two kinds of cold rolled annealed sheets were larger than those of the hot rolled sheets, which led to the reduction of the strength. Comparing with the Mn-Si steel, the sizes of ferrite grains and nano precipitates of hot-rolled and cold-rolled annealed sheets of Nb microalloyed steel were smaller, and the amount of the nano precipitates was larger. Thus the strength of the Nb microalloyed steel was higher with similar elongation. The strengthening mechanism analysis of cold rolled batch annealed sheet indicates that, the main strengthening method for Nb microalloyed low-alloy and high-strength steel is grain refinement strengthening and NbC precipitation strengthening. In the present study, grain refinement strengthening is stronger under 0.025% Nb microalloying. ©, 2015, Chinese Society for Metals. All right reserved. Source


Dong X.-x.,University of Science and Technology Beijing | He A.-r.,University of Science and Technology Beijing | Sun W.-q.,University of Science and Technology Beijing | Liu Z.-b.,Hunan Valin Lianyuan Iron and Steel Co. | Hong B.,Hunan Valin Lianyuan Iron and Steel Co.
Heat Transfer - Asian Research | Year: 2015

Slab heating plays an important role in the production of iron and steel materials. However, it is a very complex process involving physical and chemical change. In this study, we built a numerical heat transfer model to predict the three-dimensional transient temperature field of a slab based on the implicit finite difference method. The model takes the growth of the oxide layer into account, as well as the impact on heat transfer. Slab temperature and oxide layer thickness were calculated in each step. The model considers three kinds of boundary conditions. It displays the temperature variation of each part of the slab in the furnace at all time, the heating curve, and the growth in the thickness curve of the oxide layer. This model can be used to control heating time, optimize the heating curve, and improve production efficiency, thereby reducing cost. The model is also useful for calculation of rolling force, as well as the control of carbon isolation and product microstructure. © 2015 Wiley Periodicals, Inc. Source

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