Functional and Functionally Structured Materials III

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Authors: Xi Cheng, Yan Feng Li, Guo Jie Huang, Xiang Qian Yin, Yong Zhen Li, En Dong Yao, Xiu Ling Ma, Xiang Sheng Xie, Shan Long Qi, Zi Ming Li
Abstract: Under the condition of controlling the relevant electrolysis process parameters, 12μm-thick electrolytic copper foils were prepared by adjusting the electrodeposition time under different current densities. The surface morphology, mechanical properties and textures of the electrolytic copper foil at different current densities were studied using SEM, XRD, EBSD and universal testing machines. The fracture mechanism of the copper foil at different current densities was also analyzed in this paper. The results show that as the current density increases, the surface of the copper foil become larger and sharper. The main orientation of the crystal surface is {220}, and the preference firstly increases and then decreases. The high preference of the {220} crystal surface of the copper foil reduces its tensile strength. When the current density is from 8 to 14 A/dm2, the preferential degree of {111} decreases with the increase of current density, while the preferential degree of {220} increases, and the tensile strength of copper foil decreases. When the current density is from 14 to 26 A/dm2, the preferential degree of {111} and {311} increases with the increase of current density, while the preference of {220} crystal surface decreases, and the tensile strength of copper foil increases. The elongation of copper foil is affected by the fracture mechanism. When the current density is 8 A/dm2, the copper foil is plastically fractured and has high elongation. When the current density is 14A/dm2, the copper foil is brittle fracture and the elongation is low. When the current density is 26 A/dm2, the copper foil is plastically fractured but the effect of hydrogen evolution at high current density reduces the plasticity of the copper foil.
205
Authors: Hai Nan He, Xiao Chen Wang, Quan Yang
Abstract: The hot-rolled yoke steel plate is used in the manufacture of motor rotors for core components of large generators, which is required to ensure high strength and high-precision plate profile, especially the control of the thickness difference. High-precision cross-section control technology from rough rolling to finishing rolling for high-strength yoke steel is designed. First, through the varying contact backup roll technology and optimization of load distribution in the roughing stand, the profile of transfer bar is improved, which provides the basis for the strip shape control in the finishing mills. Secondly, the approximate rectangular section of a hot strip is obtained by high-precision shape setting and control model for finishing rolling, symmetrical variable taper work roll technology and smart shifting technology in the downstream stands. These methods solve the problem that the shape of the high-strength strip is difficult to control, and significantly enhance the shape regulation ability and control accuracy of the hot-rolled yoke. In addition, this technology has been applied to hot rolling mills with remarkable results and economic benefits.
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Authors: Yu Zhang, Er Jun Guo, Li Ping Wang, Yi Cheng Feng, Si Cong Zhao, Mei Hui Song
Abstract: Ductile iron was prepared through Sandwich Process and annealing treatment was carried out. The effects of annealing treatment on the microstructure, mechanical and damping properties of ductile iron were studied by means of metallographic microscope, scanning electron microscope, transmission electron microscope, universal test machine and dynamic thermal mechanical analyzer. The results show that annealing treatment has little effect on the morphology and distribution of graphite cast iron, but it will lead to the decrease of pearlite content in the matrix, the increase of ferrite content and the disappearance of cementite. Annealing transforms the fracture form of ductile iron from cleavage fracture to quasi-cleavage fracture, which greatly increases the ductile fracture area of the matrix compared with the as-cast, and tends to develop ductile fracture. The annealing treatment results in a decrease in the tensile strength of the ductile iron, but it can increase the plasticity and increase the elongation after fracture to 7.5 times that of the as-cast state. The damping value of as-cast ductile iron increases first and then decreases with the increase of temperature, and peaks at 190 °C when Q-1 is 0.025. The damping value of annealing ductile iron decreases with increasing temperature. The damping value increases with increasing strain amplitude before and after annealing. Annealing treatment will reduce the sensitivity of the damping property of ductile iron to strain amplitude.
222
Authors: Guo Qing Wu, Zi Yun Chen, Ming Huang, Yuan Qin, Alimjan Ablat, Han Lu Jiang, Sen Yang
Abstract: In order to get optimal grain boundary character distribution (GBCD) and grain boundary properties, thermomechanical processing (TMP) is usually adopted in grain boundary engineering. However, the mechanism behind the TMP treatments and GBCD optimization is still unclear. The present study has conducted a series experiments involving low-strain TMPs to study the relationship between TMP parameters and the behind microstructural evolution. The experimental results indicate that in the scope of low-strain TMP, strain induced boundary migration (SIBM) is the most effective process for GBCD optimization. Besides, SIBM and grain growth would gradually transfer to recrystallization with the increase of pre-deformation level and annealing temperature. Further quasi in-situ EBSD results infer that SBIM is activated locally in some region with high stored energy, and further gradual initiation of SIBM from one region to another contributes to the gradual increase of special boundaries with annealing time.
229
Authors: Guang Yi Song, Xiao Chen Wang, Quan Yang, Jian Wei Zhao
Abstract: The hot-rolled strip skin-pass mill is the important technological equipment of finishing process in the hot rolling plant, and its role is to apply a slight thickness reduction of approximately 1% - 4% to the finished products cooled to room temperature to repair flatness defects and improve the surface quality and mechanical properties. In this study, the initial flat roll contours were optimized to solve some problems such as the serious and non-uniform wear of work rolls and the poor shape control abilities of the strip. A three-dimensional rolls–strip coupling model of hot-rolled strip skin-pass mill was established using the nonlinear finite element software ABAQUS. The effects of the roll contours on the contact pressure between rolls and the control effect of bending forces were analyzed, and a variable contact-length backup roll (VCR) contour configured with a positive crown contour for work rolls was proposed. Compared with the initial flat roll contours, the average replacement cycle of work rolls for the optimized roll contours increased from 465.4 tons to 701.3 tons, the non-uniform wear amount was reduced by nearly 15%, and the adjustment ratio of the negative bending forces decreased from -100% to -40% by industrial experiments in the 1580 mm single-stand four-high hot-rolled strip skin-pass mill.
237
Authors: Jian Wei Zhao, Quan Yang, Xiao Chen Wang
Abstract: In order to provide an accurate prediction of the flow stress during the thermal deformation process, a physical model is established. In the model, it is assumed that the flow stress is mainly composed of short-range stress and long-range stress. The short-range stress is a friction stress needed to be overcome when dislocations pass short-range obstacles and through the lattice, and the long-range stress is athermal stress caused by the interaction of dislocation substructure. The model is established mainly based on the evolution of dislocation density which is described as a competitive process of work hardening and recovery. Meanwhile, the interaction between vacancies and dislocations is also taken into account. The effect of solutes and precipitation on stress is quantified. In addition, some experiments have been performed using two steels containing different amounts of Nb under various deformation conditions. The experimental results indicate the prediction accuracy of the model is satisfactory.
247
Authors: Yao Huang, Lei Gang Wang, Xiang Ma, Lei Liu
Abstract: Sheet forming of galvanized metals presents a great challenge for automobile industry. This is partially caused by a significant induced plastic deformation and high contact friction during forming, which results in pulverization, flaking and failure seen in the zinc layer. Cupping tests is used to study the formability of the galvanized sheets, for a better understanding of microscopic failure mechanisms of the zinc layer. The results show that during the cupping of the galvanized sheet, the zinc layers of each deformed zone encounter varying degrees of failure behaviors. The regions next to the fillets of the punch and the blank holder ring are more serious. In these severe failure areas, the residual stresses in the zinc layer are shown as tensile in nature; and increase with the degree of deformation increasing. The galvanized layers rupture prematurely prior to any damage seen in the steel substrate; thus leading to chalking, flaking and final failure. The results provide a theoretical guidance for improving formability of galvanized sheets.
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Authors: Wan Jun Zhu, Chun Feng Wang, Jiang Hua Qi, Yi Qang Sun, Zhen Cai, Chen Qiu
Abstract: In order to evaluate the feasibility of 9SiCr alloy tool steel produced by thin slab casting, the high temperature mechanical properties of 9SiCr alloy tool steel were investigated by Gleeb-1500 thermal simulator. The morphologies of the tensile fracture at different temperatures were observed by scanning electron microscope (SEM), together with analysis of fracture mechanisms in different regions. The results showed that there were two brittle zones in the temperature range from 600 °C to 1200 °C. A melting fracture was characterized in the high temperature brittle zone of above 1170 °C, whereas a typical cleavage fracture was exhibited in the low temperature brittle zone from 820 °C to 600 °C, Meanwhile, a good hot ductility behavior characterized by typical dimple fracture was demonstrate at the temperature range from 1170 °C to 820 °C.Thus, the 9SiCr alloy tool steel with the final gauge of 1.5mm was produced by CSP, based on the optimal process parameters.
259
Authors: Yun Long Wang, Yin Li Chen, He Wei, Yi Na Zhao, Ze Sheng Liu
Abstract: The effects of final rolling temperature, cooling rate and deformation on phase transition point, the duration of the phase transition and the pearlite laminar layer of non-quenched and tempered steel 45MnSiV were studied by simulating the process of rolling and post-rolling cooling on Gleeble-3500 thermal simulator and thermal expansion tester. The results show that: the ferrite and pearlite transformation temperature ranges from 510 °C to 700 °C, and the bainite transformation temperature ranges from 400 °C to 500 °C when the steel is continuously cooled at a final rolling temperature of 950 °C, and the martensite transforming temperature is 300 °C under high cooling rate (> 10 °C/s); The pearlite laminar spacing decreases with the decrease of final rolling temperature. It can be seen that the rolling deformation increases the temperature at which the test steel undergoes a phase change at each cooling rate by comparing the results of deformation and no-deformation test at 950 °C. The effect of time advance on the phase transition zone of ferrite and pearlite is particularly obvious, but the effect on the phase transition temperature and time of the bainite and martensite phase transition is not obvious. When the final rolling temperature remains constant, the Rockwell hardness value of the test steel gradually increases, and the pearlite layer spacing decreases with the decrease of ferrite transformation temperature gradually and the increase of the cooling rate.
265
Authors: Mao Lin Jiang, Wei Yu
Abstract: Complete the composition design and laboratory smelting of high strength weathering steel for railway freight car body of grade 500MPa. The actual continuous cooling transformation curve (CCT curve and cold speed of 0.5-50 °C/s) was measured through the Gleeble3500 thermal simulation test machine with expansion method and alloy phase method, observing the microstructures by optical microscope and SEM. The hardness of the samples under different cooling rates were measured by Vivtorinox hardness tester. Study on the effect of cooling rates on the microstructures and hardness of the steels.
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