2018年, 第25卷, 第4期　刊出日期：2018-04-15

  

• 全选
  |

• Select
  Application status and comparison of dioxin removal technologies for iron ore sintering process

  Hong-ming Long, ? Qi Shi ? Hong-liang Zhang ? Ru-fei Wei ? Tie-jun Chun ? Jia-xin Li

  . 2018, 25(4): 357-365.

  摘要 ( )   可视化   收藏

  The emission of dioxins from the iron ore sintering process is the largest emission source of dioxins, and the reduction in dioxin emission from the iron ore sintering process to the environment is increasingly important. Three approaches to control the emission of dioxins were reviewed: source control, process control, and terminal control. Among them, two terminal control technologies, activated carbon adsorption and selective reduction technology, were discussed in detail. Following a comparison of the reduction technologies, the terminal control method was indicated as the key technology to achieve good control of dioxins during the sintering process. For the technical characteristics of the sintering process and flue gas, multiple methods should be collectively considered, and the most suitable method may be addition of inhibitors + ultra-clean dust collection (electrostatic precipitation/bag filter) + desulphurization + selective catalytic reduction to sufficiently remove multiple pollutants, which provides a direction for the cooperative disposal of flue gas pollutants in future.
• Select
  Behavior of molten steel flow in continuous casting mold with different static magnetic field configurations

  Zhuang Li, ? En-gang Wang, ? Yu Xu,

  . 2018, 25(4): 366-377.

  摘要 ( )   可视化   收藏

  A three-dimensional mathematical model was established to investigate the behavior of molten steel flow and steel/slag interface with different processes and electromagnetic parameters under two different static magnetic field configurations [ruler-type electromagnetic brake (EMBr ruler) and vertical electromagnetic brake (V-EMBr)] in a continuous casting mold. The results showed that the brake effect of EMBr ruler is significantly influenced by its configuration parameters, the distance between the pole and bottom of the submerged entry nozzle (SEN), and the port angle of the SEN outlet; therefore, it is not helpful to depress the diffusion of jet flow along the thickness direction of mold. For a constant SEN depth and port angle, there is a reasonable pole position (P = 0 mm) where the pole simultaneously covers three key zones, i.e., the jet flow impact zone and the upward and downward backflow zones. For V-EMBr, the magnetic field can simultaneously cover the three key zones and depress the diffusion of jet flow along the casting and thickness directions of the mold. Both the meniscus height and the impact intensity of the jet flow can be obviously depressed by V-EMBr even if the SEN depth and port angle have changed in the continuous casting process.
• Select
  Coking properties of thermal soluble constituents of coals by N-methyl-2-pyrrolidone solvent

  Hai-bin Zuo ? Si-yang Long ? Jing-song Wang ? Wen-tao Guo

  . 2018, 25(4): 378-386.

  摘要 ( )   可视化   收藏

  Four types of coals, KL, XB, ZS and GD with different coal ranks, were dissolved with the organic solvent N-methyl-2-pyrrolidone at 350 °C and around 3.0 MPa pressure to obtain thermal soluble constituents (TSCs). The yield, component and maceral group were investigated as well as their coking properties, including caking index and thermoplasticity. The results indicated that the yields of the four coals were of the following order: KL > XB > ZS > GD. Based on the yield and the vitrinite content, coals were ranked from high to low. The ash contents of TSCs were significantly less than that of raw coals, and the TSCs contain more light components, leading to an increase in volatile matter. The patterns of Fourier transform infrared spectroscopy indicated that carbonyl was enriched in TSCs. Regarding the maceral group, TSCs were mainly composed of vitrinite which is the main reactive material and converts into binder phase in cokemaking process. Higher caking index values and fluidity were obtained in TSCs compared with the raw coals. The coking experiments with different amounts of TSCs addition were carried out. The results demonstrated that the proper TSCs addition could enhance the coke strength due to its high caking index and good fluidity.
• Select
  Combustion performance of nozzles with multiple gas orifices in large ladles for temperature uniformity

  Fei Yuan, Hong-bing Wang Pei-ling Zhou An-jun Xu,

  . 2018, 25(4): 387-397.

  摘要 ( )   可视化   收藏

  In order to improve the baking temperature uniformity of the large ladle in steelmaking plants, the flame combustion characteristics of nozzles with different inner structures were numerically simulated with the finite volume method code Fluent. The flow field and premixed combustion reaction inside and outside the nozzle with multiple gas orifices were exhibited. Meanwhile, the influences of the gas injecting angle and the number of gas orifices on temperature, velocity, and pressure fields were studied. The results show that the flame length and width at the rear of flame temperature field reach the maximum values in the nozzle with the gas injecting angle of 20° and 4 gas orifices for the control of premixed combustion inside the nozzle, which could provide better temperature uniformity in ladles. The length of the 1273 K isothermal surface is 4.89 m, and the cross-section area at 4 m away from the outlet of the nozzle is 0.13 m2. The pressure losses of different types of nozzles range from 112.2 to 169.4 Pa and decrease with the decrement in gas injecting angle and the number of gas orifices. The ladle bottom preheating temperature is increased by 320–360 K for the optimized nozzle. The inner surface temperature differences between wall and bottom of the ladle are less than 10%. There is good baking temperature uniformity after the application of optimum structurally designed nozzles.
• Select
  Numerical model establishment and verification of cold pilgering on cycle feed rate

  Zhi-bing Chu, ? Dong Wei ? Lian-yun Jiang ? Duo Zhang ? Qing-xue Huang, ? Yu-gui Li,

  . 2018, 25(4): 398-408.

  摘要 ( )   可视化   收藏

  A numerical model was established to calculate the cycle feed rate through studying the case of a cold pilger mill with the 304 stainless steel pipe. Firstly, the precise constitutive equation of 304 stainless steel was obtained through nonlinearly fitting the true stress–strain data from unidirectional tensile test. Then, the numerical method to calculate the equivalent deformation was determined according to the plastic deformation feature of the steel tube during cold rolling and the incremental theory. Finally, the cycle feed rate of cold rolled 304 stainless steel pipe was extracted when formulating springback through utilizing above results comprehensively and unloading law. Stress state, metal flow, finished pipe size and distribution of residual stress were obtained by finite element method to calculate the whole rolling process when the cycle feed rate was 10 mm, and the optimized model was verified through finished pipe size.
• Select
  Model for Ruhrstahl–Heraeus (RH) decarburization process

  Dong-ping Zhan, ? Yang-peng Zhang ? Zhou-hua Jiang ? Hui-shu Zhang

  . 2018, 25(4): 409-416.

  摘要 ( )   可视化   收藏

  A mathematical model was established to predict the carbon content of ultralow carbon steel in the Ruhrstahl–Heraeus (RH) process. The model was solved using the fourth-order Runge–Kutta method and assumed that the volume of steel partaking in the reaction depends on the decarburization mechanism. After analyzing the decarburization process using the proposed model, the following conclusions were drawn. First, the initial carbon and oxygen contents in the RH degasser should be stabilized in the range of (200–350) ? 10-6 and (500–700) ? 10-6, respectively. Second, in the initial stage, the pressure should be reduced as quickly as possible. Third, oxygen blowing should begin as early as possible when the forced decarburization is needed and the minimum oxygen flow rate should be 0.1923 m3/(t min). Finally, expanding the diameter of the snorkel tube from 480 to 600 mm clearly enhances the decarburization rate.
• Select
  Experimental study on smelting reduction of carbon-bearing manganese briquettes in slag bath

  Bo Zhang, ? Da-ping Wang ? Bin Chen ? Zhen-jian Su ? Zheng-liang Xue

  . 2018, 25(4): 417-425.

  摘要 ( )   可视化   收藏

  The reduction of carbon-bearing manganese briquettes in a slag bath was experimentally investigated at temperatures ranging from 1550 to 1650 °C. Both the internal temperature and the microstructure evolution of the briquettes were analyzed by differential thermal analysis, scanning electron microscopy and energy-dispersive spectrum analysis, and the smelting reduction mechanism of the carbon-bearing manganese briquettes in the slag bath was further elaborated. The results indicated that the smelting reduction of the briquettes in the slag bath could be divided into three stages, and the aggregation and growth of the metallic particles during the reduction were significantly affected by the slag temperature. Under the experimental conditions, the reduction speed at the initial stage of the carbon-bearing manganese briquettes smelting reduction was controlled by the chemical reaction, whereas the reaction speeds at both the middle and following stages were limited by gaseous diffusion.
• Select
  Effect of two-step cooling process on mechanical properties of TRIP steel with high performance

  M.L. Li, ? H. Jiang, ? Y.L. He, ? L.B. Chen, ? G.T. Zhang ? H. Wang ? X.G. Lu, ? L. Li,

  . 2018, 25(4): 426-432.

  摘要 ( )   可视化   收藏

  A novel two-step cooling experiment was established to simulate the slow cooling process of continuous annealing production line for transformation-induced plasticity (TRIP) steel. The microstructures and mechanical properties of TRIP steel soaked at 700 °C for different time were investigated by tensile test, scanning electron microscopy, X-ray diffraction, and thermodynamic and kinetic calculation. It is shown that the steel soaked for 15 s exhibits the optimal product of strength and elongation (PSE > 30,000 MPa%) due to the transformation of austenite to proeutectoid ferrite, which delays the bainite transformation and improves the stability of retained austenite. In addition, the mechanical properties of TRIP steel soaked over 30 s are much lower, resulting from the precipitation of cementite, which decreases the stability of retained austenite and weakens the TRIP effect.
• Select
  Effect of Mg addition on formation of intragranular acicular ferrite in heat-affected zone of steel plate after high-heat-input welding

  Long-yun Xu, ? Jian Yang ? Rui-zhi Wang ? Wan-lin Wang ? Yu-nan Wang

  . 2018, 25(4): 433-441.

  摘要 ( )   可视化   收藏

  The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite (IAF) nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO–Al2O3–Ti2O3–MnS inclusions with size around 2 lm are effective nucleation sites for IAF, whereas Al2O3–MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain (PAG) size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 lm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 lm. Therefore, the nucleation of IAF can hardly be observed.
• Select
  Effects of annealing temperature and cooling rate on microstructures of a novel titanium alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si manufactured by laser additive manufacturing

  Guo-chao Li ? Xu Cheng ? Xiang-jun Tian

  . 2018, 25(4): 442-452.

  摘要 ( )   可视化   收藏

  The microstructure changes of Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si alloy manufactured by laser additive manufacturing (LAM) are systematically investigated with statistical analysis of primary α phase (α p) and secondary α phase (α s) under different annealing conditions. Results indicate that, with the increase in holding temperature, the content of α p lamellas decreases with the increasing as content, maintaining the total α phases concentration stabilized. The width of α p lamellas and the nominal specific surface area of α phase both exhibit positive correlation with the temperature, while the increment of α p and the widths of α s lamellas show an increase–decrease tendency. Besides, with the decrease in cooling rate, the total content of α and the width of α p lamellas increase, while the nominal specific surface area of a phase shows no significant change. The results indicate that, in the annealing process, the holding temperature determines the surplus and growth interfaces of α p lamellas, and the cooling rate influences the nucleation quantity of α s in unit time. During the cooling stage, the α p lamellas grow initially, and then, the nucleation and crab-like structure growth occur followed by those of the α s lamellas. The time intervals among them are influenced by cooling rate. The mechanism of microstructure formation of the LAMed titanium alloy during annealing stage was discussed, which would guide for the heat treatment method to achieve required microstructure.
• Select
  Microscopic damage mechanism of SA508 Gr3 steel in ultra-high temperature creep

  Zhi-gang Xie, ? Yan-ming He ? Jian-guo Yang ? Xiang-qing Li ? Chuan-yang Lu ? Zeng-liang Gao

  . 2018, 25(4): 453-459.

  摘要 ( )   可视化   收藏

  The lower head of reactor pressure vessel (RPV) will endure a great temperature gradient above the phase transition temperature, and the creep and fracture will be the primary failure mode for the RPV material in such a situation. The interrupted creep tests were performed on a typical RPV material, SA508 Gr3 steel, at 800 °C. The microstructure of different creep stages was examined by scanning electron microscopy and transmission electron microscopy. The results showed that the microscopic damage is mainly induced by creep cavities and coarse second-phase particles. Furthermore, the volume fractions of creep cavities and coarse second-phase particles show a linear relationship with the extended creep time. The second-phase particles are determined to be MoC in the second creep stage and Mo2C in the third creep stage, according to the results of selected-area electron diffraction pattern. Combined with energy-dispersive spectrum analysis, the segregation of precipitates caused by the migration of atoms is finally unveiled, which leads to the coarsening of the particles.
• Select
  Effect of N and Zr on as-cast microstructure and properties after annealing of a high-speed steel

  Hao-ran Cui ? Jian-ping Lai ? Qing-lin Pan ? Xiang-dong Wang

  . 2018, 25(4): 460-468.

  摘要 ( )   可视化   收藏

  Effects of N and Zr on the as-cast microstructure and properties after annealing of high-speed steel (HSS) were investigated by using electronic probe micro-analysis, Rockwell hardness test, X-ray diffractometry and differential scanning calorimetry with combination of microstructure analysis. The results indicate that the addition of N and Zr will refine the eutectic structures and enhance the stability of carbides which are mainly MC, M2C and M7C3. The coarse dendritic structures decrease significantly and most of the carbides are distributed in the microstructure uniformly. Moreover, a kind of Zr–Si compound which only exists in VC is discovered, and this new phase is speculated to be related with the spheroidization of VC. The annealing process is set up to 6 different time periods which are 1, 3, 6, 10, 15 and 20 h, respectively. In different annealing processes at 750 °C which is lower than austenitizing temperature, the addition of N and Zr makes the decrease of hardness more obvious and restrains the precipitation of secondary carbides with the extension of time. Moreover, when the annealing time reaches 20 h, some clusters appear in the matrix of the two samples, and the density of clusters in HSS1 is lower, but the matrix of HSS1 contains more C and alloying elements which indicate more carbides precipitate.
• Select
  Impacts of multiple laser shock processing on microstructure and mechanical property of high-carbon steel

  Yi Xiong,? Tian-tian He ? Yan Lu ? Han-sheng Bao ? Yong Li ? Feng-zhang Ren, ? Wei Cao,5 ? Alex A. Volinsky6

  . 2018, 25(4): 469-475.

  摘要 ( )   可视化   收藏

  Multiple laser shock processing (LSP) impacts on microstructures and mechanical properties were investigated through morphological determinations and hardness testing. Microscopic results show that without equal channel angular pressing (ECAP), the LSP-treated lamellar pearlite was transferred to irregular ferrite matrix and incompletely broken cementite particles. With ECAP, LSP leads to refinements of the equiaxed ferrite grain in ultrafine-grained microduplex structure from 400 to 150 nm, and the completely spheroidized cementite particles from 150 to 100 nm. Consequentially, enhancements of mechanical properties were found in strength, microhardness and elongations of samples consisting of lamellar pearlite and ultrafine-grained microduplex structure. After LSP, a mixture of quasi-cleavage and ductile fracture was formed, different from the typical quasi-cleavage fracture from the original lamellar pearlite and the ductile fracture of the microduplex structure.