2017年, 第24卷, 第7期　刊出日期：2017-07-15

  

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  Two-phase sink vortex suction mechanism and penetration dynamic characteristics in ladle teeming process

  Da-peng Tan,Ye-sha Ni,Li-bin Zhang

  中国钢铁期刊网. 2017, 24(7): 669-677.

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  At the late stage of continuous casting (CC) ladle teeming, sink vortex can suck the liquid slag into tundish, and cause negative influences on the cleanliness of molten steel. To address this issue, a two-phase fluid mechanical modeling method for ladle teeming was proposed. Firstly, a dynamic model for vortex suction process was built, and the profiles of vortex flow field were acquired. Then, based on the level set method (LSM), a two-phase 3D interface coupling model for slag entrapment was built. Finally, in combination with high-order essentially non-oscillatory (ENO) and total variation diminishing (TVD) methods, a LSM-based numerical solution method was proposed to obtain the 3D coupling evolution regularities in vortex suction process. Numerical results show that the vortex with higher kinetic energy can form an expanded sandglass-shape region with larger slag fraction and lower rotating velocity; there is a pressure oscillation phenomenon at the vortex penetration state, which is caused by the energy shock of two-phase vortex penetration coupling.
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  Oxidation kinetics of ilmenite concentrate by non-isothermal thermogravimetric analysis

  Ying-yi Zhang,Wei Lv,Xue-wei Lv,Chen-guang Bai,Ke-xi Han,Bing Song

  中国钢铁期刊网. 2017, 24(7): 678-684.

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  The non-isothermal oxidation experiments of ilmenite concentrate were carried out at various heating rates under air atmosphere by thermogravimetry. The oxidation kinetic model function and kinetic parameters of apparent activation energy (Ea) were evaluated by Málek and Starink methods. The results show that under air atmosphere, the oxidation process of ilmenite concentrate is composed of three stages, and the chemical reaction (G(α)=1-(1-α)2, where α is the conversion degree) plays an important role in the whole oxidation process. At the first stage (α=0.05-0.30), the oxidation process is controlled gradually by secondary chemical reaction with increasing conversion degree. At the second stage (α=0.30-0.50), the oxidation process is completely controlled by the secondary chemical reaction (G(α)=1-(1-α)2). At the third stage (α=0.50-0.95), the secondary chemical reaction weakens gradually with increasing conversion degree, and the oxidation process is controlled gradually by a variety of functions; the kinetic equations are G(α)=(1-α)-1 (β=10 K·min-1, where β is heating rate), G(α)=(1-α)-1/2 (β=15-20 K·min-1), and G(α)=(1-α)-2 (β=25 K·min-1), respectively. For the whole oxidation process, the activation energies follow a parabolic law with increasing conversion degree, and the average activation energy is 160.56 kJ·mol-1.
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  Precipitation behavior of titanium nitride on a primary inclusion particle during solidification of bearing steel

  Liang Yang,,Bryan A. Webler,Guo-guang Cheng

  中国钢铁期刊网. 2017, 24(7): 685-690.

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  Titanium nitride precipitation on a primary inclusion particle during solidification of bearing steel has been tracked by varying temperature in a confocal scanning violet laser microscope. Upon precipitation, an obvious growth of titanium nitride on a primary inclusion particle was observed due to the rapid solute diffusion in liquid steel. The onset of titanium nitride precipitation did not change with primary inclusion particle size, but the time of growth was greater for a smaller primary inclusion particle. Meanwhile, the particle size displayed little influence on the total precipitated amount of titanium nitride on it under the same conditions. At the later period of solidification, almost no change occurred in inclusion size, but the inclusion shape varied from circle to almost square in two-dimension, or cubic in three-dimension, to attain the equilibrium with steel.
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  Niobium and phosphorus behavior during melting-separation process of pre-reduced niobium ore concentrate

  Yu-bao Liu,,Zhi-hong Zhang,,Er-xiong Zhao,,Xian-heng Zhang,,Xiao-qing Wang,, Guo-hua Chen,

  中国钢铁期刊网. 2017, 24(7): 691-696.

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  The pre-reduced Bayan Obo ferroniobium (FeNb) ore concentrate block was taken as raw materials for studying the physical properties of niobium-enriched slag and changes in niobium recovery rate. In addition, the dephosphorization rate of the slag under different melting-separation conditions was investigated using the melting-separation test. The research results demonstrate that (i) the niobium recovery rate and dephosphorization rate of the slag decrease with the increase in melting-separation temperature; (ii) the niobium recovery rate of the slag initially increases and then decreases with increase in basicity and time; and (iii) the dephosphorization rate of the slag increases with the increase in basicity and time. When the test was performed under the conditions of basicity of 0.6-0.7, time of 7-10 min, and temperature of 1400-1450°C, the niobium recovery rate and dephosphorization rate are over 96% and 95%, respectively. By scanning electron microscopy, it is observed that niobium mainly exists in the form of calcium and titanium silicate within the slag phase, with uneven distribution.
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  Sintering of solid waste generated in iron and steel manufacturing process in Shougang Jingtang

  Yuan-dong Pei,,,Sheng-li Wu,,Shao-guo Chen,Zhi-xing Zhao,Gang An,Zheng-ming Cheng, Yao-sheng Luo

  中国钢铁期刊网. 2017, 24(7): 697-704.

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  It is important to make full use of waste generated in the iron and steel manufacturing process for energy saving, emission reduction, low carbon production and a circular economy. Based on research on different kinds of industrial solid wastes from Shougang Jingtang, wastes have been optimized for use in sintering. At first, basic tests for all kinds of solid wastes that may be used in sintering were carried out, including chemical composition, calorific value of a fuel, holding time at high temperatures, the sintering pot test, etc. The results show that the appropriate solid waste ratios for current sintering conditions are: steel slag ＜5%, scale 2.0%, environmental ash 2.0%, and cyclone ash 1.0%; blast furnace dry ash, sintering electric field ash, and steelmaking ash should not be circulated in sintering. As for the fuel structure, both coking ash and nut coke should be below 15%. By optimizing the addition of solid wastes, the damage of harmful elements to sintering and blast furnaces has been significantly reduced, which satisfies the demands for blast furnace materials and earns benefits. The utilization of solid wastes has made a contribution to the circular economy and sustainable development.
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  Effects of tantalum on austenitic transformation kinetics of RAFM steel

  Jian-guo Chen,Yong-chang Liu,Chen-xi Liu,Bi-yu Yan,Hui-jun Li

  中国钢铁期刊网. 2017, 24(7): 705-710.

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  The RAFM (reduced activation ferritic/martensitic) steels containing different tantalum contents (0 wt.%, 0.027 wt.%, 0.073 wt.%) were designed and cast. Differential scanning calorimetry and optical microscopy were employed to explore the influence of tantalum content on the austenitic transformation of RAFM steels. The austenitic transformation kinetics was described by a phase-transformation model. The model, involving site saturation nucleation, diffusion-controlled growth and impingement correction, was established based on the classical Johnson-Mehl-Avrami-Kolmogorov model. The phase-transformation kinetics parameters, including D0 (pre-exponential factor for diffusion) and Qd (activation energy for diffusion), were calculated by fitting the experimental data and the kinetic model. The results indicated that the average grain size is decreased with the increase of tantalum. The values of Ac1 and Ac3 (onset and finish temperature of austenitic transformation, respectively) are increased by increasing the tantalum content. The increase of tantalum caused the decrease of D0. However, Qd is increased with the increase of tantalum. In addition, as a carbides forming element, tantalum would reduce the carbon diffusion coefficient and slow down the austenitic transformation rate.
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  Influence of cooling rate on magneto-structural transition and magnetocaloric effect of Ni30Cu8Co12Mn37Ga13 alloy

  Zhu-jun Jiang,Yu-ye Wu,,Jing-min Wang,Cheng-bao Jiang

  中国钢铁期刊网. 2017, 24(7): 711-717.

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  The influence of heat treatment with different cooling rates on phase transition behaviors and magnetocaloric effect is systematically studied. Difference in atomic order is induced by changing cooling rates, where ordered phase is obtained in the furnace cooled (FC) sample while disordered phase is reserved in the water quenched (WQ) sample. The coupled magneto-structural transition is detected in both samples but the characteristic temperature significantly shifts to lower temperatures with increasing atomic order. Giant magnetic entropy change (ΔSmag) derived from magnetic field induced martensitic transformation is confirmed for both samples, and can be remarkably enhanced by the atomic ordering. The largest ΔSmag of 20.9 J/(kg·K) is obtained at 307.5 K under 5 T in the FC sample.
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  Microstructure characteristics of segregation zone in 17-4PH stainless steel piston rod

  Jia-long Tian,,Wei Wang,,Wei Yan,,Zhou-hua Jiang,Yi-yin Shan,,Ke Yang

  中国钢铁期刊网. 2017, 24(7): 718-723.

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  The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment. Further investigation showed that the segregation zone was composed of three layers, namely the fine grain martensitic layer, the coarse grain martensitic layer and the coarse grain austenitic layer from the matrix to the crack surface. Three button ingots with the same chemical compositions as those three layers have been prepared to evaluate the grain size distribution, microstructure and mechanical properties. The effects of Cu and Ni segregation on the microstructures of those three layers have been explored by thermodynamic calculation. Based on the microstructure and mechanical properties results, an intensive understanding of the cracking in the segregation zone was therefore reached.
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  Dynamic mechanical behavior of ultra-high strength steel 30CrMnSiNi2A at high strain rates and elevated temperatures

  Qiu-lin Niu,,Wei-wei Ming,Ming Chen,Si-wen Tang,,Peng-nan Li,

  中国钢铁期刊网. 2017, 24(7): 724-729.

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  During high speed machining in the field of manufacture, chip formation is a severe plastic deformation process including large strain, high strain rate and high temperature. And the strain rate in high speed cutting process can be achieved to 105 s-1. 30CrMnSiNi2A steel is a kind of important high-strength low-alloy structural steel with wide application range. Obtaining the dynamic mechanical properties of 30CrMnSiNi2A under the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining. The dynamic compressive mechanical properties of 30CrMnSiNi2A steel were studied using split Hopkinson pressure bar (SHPB) tests at 30-700°C and 3000-10000 s-1. The stress-strain curves of 30CrMnSiNi2A steel at different temperatures and strain rates were investigated, and the strain hardening effect and temperature effect were discussed. Experimental results show that 30CrMnSiNi2A has obvious temperature sensitivity at 300°C. Moreover, the flow stress decreased significantly with the increase of temperature. The strain hardening effect of the material at high strain rate is not significant with the increase of strain. The strain rate hardening effect is obvious with increasing the temperature. According to the experimental results, the established Johnson-Cook (J-C) constitutive model of 30CrMnSiNi2A steel could be used at high strain rate and high temperature.
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  Interface associativity and energy absorption capability of anti-vibration porous Al-MM alloy core with iron alloy skin structures

  Xu Ran,Hong-wei Sun,Li-dong Wang,Yao-ming Wu

  中国钢铁期刊网. 2017, 24(7): 730-736.

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  The interface associativity and energy absorption capability of composite structure with anti-vibration porous Al-MM (cerium-rich mischmetal) alloy core and iron alloy skin were investigated. Porous aluminum core/iron alloy skin structures were fabricated considering an iron alloy tube as its shell and closed-cell porous Al-MM alloy as its core. A peeling experiment was carried out to calculate the capacity of interfacial bonding and a compression test was carried out to determine the energy absorption capability. The results showed that the addition of MM significantly enhanced both the interfacial bonding and the energy absorption capacity.
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  Microstructures and mechanical properties of ferrite-based lightweight steel with different compositions

  Reng-chong Xu,,Yan-lin He,,Hu Jiang,,Hua Wang,,Na-qiong Zhu,,Xiao-gang Lu,, Lin Li,

  中国钢铁期刊网. 2017, 24(7): 737-742.

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  The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermodynamic calculation (TC). It was shown that the ferrite-based lightweight steels with 5 wt.% or 8 wt.% Al were basically composed of ferrite, austenite and κ-carbide. As the annealing temperature increased, the content of the austenite in the steel gradually increased, while the κ-carbide gradually decomposed and finally disappeared. The mechanical properties of the steel with 5 wt.% Al and 2 wt.% Cr, composed of ferrite and Cr7C3 carbide at different annealing temperatures, were significantly inferior to those of others. The steel containing 5 wt.% Al, annealed at 820°C for 50 s then rapidly cooled to 400°C and held for 180 s, can obtain the best product of strength and elongation (PSE) of 31242 MPa·%. The austenite stability of the steel is better, and its PSE is higher. In addition, the steel with higher PSE has a more stable instantaneous strain hardening exponent (n value), which is mainly caused by the effect of transformation induced plasticity (TRIP). When the κ-carbide or Cr7C3 carbide existed in the microstructure of the steel, there was an obvious yield plateau in the tensile curve, while its PSE decreased significantly.
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  Precipitated phases of superaustenitic stainless steel 654SMO

  Zhi-gang Song,En-xiang Pu,

  中国钢铁期刊网. 2017, 24(7): 743-749.

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  The phase diagram of superaustenitic stainless steel 654SMO was calculated by thermodynamic software and the precipitated phases in the specimens aged at 800-1100°C for 1 h were studied by methods of physicochemical phase analysis, scanning electron microscopy and transmission electron microscopy. The results showed that the size of precipitated particles increased with increasing the temperature. The amount of second phases reached the maximum value at 900°C, but decreased above 900°C. There were about eight kinds of precipitated phases in 654SMO including σ phase, Cr2N, μ phase, χ phase, Laves phase, M23C6, M6C and M3C, in which the σ phase and Cr2N were the dominant precipitated phases.