2017年, 第24卷, 第8期　刊出日期：2017-08-15

  

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  Current status and development trends of innovative blast furnace ironmaking technologies aimed to environmental harmony and operation intellectualization

  Hong-tao Wang,Wei Zhao,Man-sheng Chu,Cong Feng,Zheng-gen Liu,Jue Tang

  中国钢铁期刊网. 2017, 24(8): 751-769.

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  Blast furnace (BF) ironmaking is dominant for reducing pollution emission and energy consumption in iron and steel industry. Under the increasingly strict environmental pressure, some innovative technologies of BF ironmaking for environmental protection have been developed and applied in actual operating facilities. The current state of BF ironmaking in Europe, America, Japan, and China were briefly overviewed. Moreover, some innovative BF ironmaking technologies aiming at environmental harmony and operation intellectualization in the world, such as waste gas recycling sintering, BF operation with coke oven gas injection, ferro-coke, lime coating coke, BF visualization and intellectualization, were roundly summarized. Finally, some discussion on the technologies was carried out and the development trends of BF ironmaking were pointed out. The review could provide references and supports for the progress of environment-friendly technologies of BF ironmaking, thereby promoting their practical applications and achieving sustainable development of BF ironmaking, especially for Chinese ironmaking industry.
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  Analysis of energy consumption for lump coal degradation in melting gasifier

  Qi-hang Liu,Xiao-ming Li,Jun-xue Zhao

  中国钢铁期刊网. 2017, 24(8): 770-777.

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  The volume hypothesis, a theory about the energy scale of comminution, was adopted to analyze the degradation behavior of lump coal under different heating time. The breakage energy of chars was determined by a compression test, and the results show that the ultimate strength of chars decreased at the early stage during the heating process, resulting in a decrease of the char breakage energy. At the late stage during the heating process, the char breakage energy increased with the increase of heating time. The power consumption coefficients CK of different chars were determined by a drum experiment, and then the char degradation behavior under different power consumptions was predicted. In addition, a gasification experiment was conducted to determine the gasification activation energy (with CO2) of lump coal heated for different time. The results show that the gasification activation energy increased greatly at the early stage during the heating process, which showed opposite change to the breakage energy of chars. Furthermore, the internal temperature and heat changes of the bonded coal briquette were calculated by using an unsteady heat conduction equation. The large difference between the surface and the center temperatures of coal and the large amount of heat absorption at the early stage during the heating process may have a negative effect on the breakage energy of chars.
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  Medium oxygen enriched blast furnace with top gas recycling strategy

  Wei Zhang,,Zheng-liang Xue,Ju-hua Zhang,Wei Wang,Chang-gui Cheng,Zong-shu Zou

  中国钢铁期刊网. 2017, 24(8): 778-786.

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  Top gas recycling oxygen blast furnace (TGR-OBF) process is a promising ironmaking process. The biggest challenge of the TGR-OBF in operation is the dramatic decrease of top gas volume (per ton hot metal), which once led to hanging-up and shutdowns in practice of the Toulachermet. In order to avoid this weakness, the strategy of medium oxygen blast furnace was presented. The maneuverable zone of the TGR-OBF was determined by the top gas volume, which should not be far from the data of the traditional blast furnace. The deviation of ±125% was used, and then the maneuverable blast oxygen content is from 030 to 047 according to the calculation. The flame temperature and the top gas volume have no much difference compared to those of the traditional blast furnace. The minimum carbon consumption of 357 kg per ton hot metal in the maneuverable zone occurs at the oxygen content of 030 (fuel saving of 14%). In the unsteady evolution, the N2 accumulation could approach nearly zero after the recycling reached 6 times. Thus far, some TGR-OBF industrial trials have been carried out in different countries, but the method of medium oxygen enriched TGR-OBF has not been implemented, because the accumulation of N2 was worried about. The presented strategy of medium oxygen enriched TGR-OBF is applicable and the strategy with good operational performance is strongly suggested as a forerunner of the full oxygen blast furnace.
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  Springback behavior of tailor rolled blank in U-shape forming

  Ri-huan Lu,Xiang-hua Liu,Shou-dong Chen,Lu Feng,Xian-lei Hu,Li-zhong Liu

  中国钢铁期刊网. 2017, 24(8): 787-794.

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  The springback of tailor rolled blanks with quenching and partitioning steels was investigated. In order to find out the springback behavior and related influence factors for the novel sheets, both experimental and simulation methods have been used to compare and analyze the springback characteristics of equal thickness blanks and tailor rolled blanks in U-channel forming. From the results, the overall springback angles of tailor rolled blanks at thin and thick sides are respectively 10679° and 99705°, which are both lower than those of the corresponding equal thickness blanks. Due to the existence of the thickness transition zone, the stress distribution in thin and thick sides of blanks is changed. The location of dangerous region in thin side of tailor rolled blanks is closer to the end of side, and the thick side moved to the middle of straight wall, which are different with the equal thickness blanks. Afterwards, the released quantitles of tangential stress and strain per unit section of blank are adopted to calculate relative springback angles and give novel evaluation criteria for qualitatively analyzing the amount of springback angles. By comparing the results, it shows that the tangential strain method is more suitable for the actual situation.
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  Robust multi-objective optimization of rolling schedule for tandem cold rolling based on evolutionary direction differential evolution algorithm

  Yong Li,Lei Fang

  中国钢铁期刊网. 2017, 24(8): 795-802.

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  According to the actual requirements, profile and rolling energy consumption are selected as objective functions of rolling schedule optimization for tandem cold rolling. Because of mechanical wear, roll diameter has some uncertainty during the rolling process, ignoring which will cause poor robustness of rolling schedule. In order to solve this problem, a robust multi-objective optimization model of rolling schedule for tandem cold rolling was established. A differential evolution algorithm based on the evolutionary direction was proposed. The algorithm calculated the horizontal angle of the vector, which was used to choose mutation vector. The chosen vector contained converging direction and it changed the random mutation operation in differential evolution algorithm. Efficiency of the proposed algorithm was verified by two benchmarks. Meanwhile, in order to ensure that delivery thicknesses have descending order like actual rolling schedule during evolution, a modified Latin Hypercube Sampling process was proposed. Finally, the proposed algorithm was applied to the model above. Results showed that profile was improved and rolling energy consumption was reduced compared with the actual rolling schedule. Meanwhile, robustness of solutions was ensured.
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  Surface microstructure control of microalloyed steel during slab casting

  Li-jun Xu,Shu-lan Zhang,Chun-gen Qiu,Sheng-tao Qiu,Xing-zhong Zhang

  中国钢铁期刊网. 2017, 24(8): 803-810.

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  Lots of work has been done to investigate slab surface microstructure evolution during continuous casting in order to improve hot ductility and avoid transverse cracks. The slab surface microstructure after continuous casting was characterized by optical microscopy, and the precipitation behavior was investigated by transmission electron microscopy. At the same time, the mechanical properties of the slabs were measured using a Gleeble 1500D thermal simulator and the transformation temperatures were examined by means of a thermal dilatometer. The experimental results show that homogeneous microstructure without film-like ferrites and chain-like precipitates at grain boundary can be obtained through surface intensive cooling and transverse cracks do not occur on the slab surface. For the experimental steel, fine ferrite can form at slab surface when the water flow rate is larger than 1560 L/min at vertical section. As the distance to surface increases, microstructure turned to ferrite and pearlite. Moreover, nano-size carbonitrides precipitated in the ferrite grain and the size was larger at the junction of the dislocations. The mechanical experiment results show that the hot ductility of the sample deformed at 650°C was better than that of the sample deformed at 750°C. The reason is that film-like ferrite formed at the grain boundary in the sample deformed at 750°C. Thus, the slab must be cooled quickly below Ar3 to prevent the occurrence of film-like ferrite and transverse cracks on the slab surface during casting.
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  Effect of α phase on fatigue crack growth of Ti-6242 alloy

  Hang-wei Zhou,,Hui-qun Liu,,Dan-qing Yi,,Yu Xiao,,Xiao-long Zhao,Jian Wang,Qi Gao

  中国钢铁期刊网. 2017, 24(8): 811-822.

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  Fatigue crack growth as a function of α phase volume fraction in Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy was investigated using fatigue testing, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The α+β annealing treatments with different solid solution temperatures and cooling rates were conducted in order to tailor microstructure with different α phase features in the Ti-6242 alloy, and fatigue crack growth mechanism was discussed after detailed microstructure characterization. The results showed that fatigue crack growth rate of Ti-6242 alloy decreased with the decrease in volume fraction of the primary α phase (αp). Samples with a large-sized α grain microstructure treated at high solid solution temperature and slow cooling rate have lower fatigue crack growth rate. The appearance of secondary α phase (αs) with the increase of solid solution temperature led to crack deflection. Moreover, a fatigue crack growth transition phenomenon was observed in the Paris regime of Ti-6242 alloy with 298% αp (typical bi-modal microstructure) and large-sized α grain microstructure, owing to the change of fatigue crack growth mechanism.
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  Tribological performance of uncoated and TiCN-coated D2, M2 and M4 steels under lubricated condition

  Luis Daniel Aguilera Camacho,Santos García Miranda,Karla Judith Moreno

  中国钢铁期刊网. 2017, 24(8): 823-829.

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  Hard coatings are used to improve the wear resistance of metals which largely depends on adhesion between substrate and coating. The wear and friction behavior of uncoated and TiCN-coated D2, M2 and M4 steels were evaluated by a pin-on-disk test under lubricated conditions. In order to evaluate the influence of lubricant on wear performance, dry friction tests were also performed. The results showed that friction coefficients were very similar for both uncoated and TiCN-coated steels. Under lubricated conditions, the uncoated D2 tool steel exhibited the lowest friction coefficient, but the TiCN-coated D2 steel presented the smallest wear rate. Abrasion was the main wear mechanism in all the tribocouples. Additionally, microhardness measurements were carried out, finding an influence of the steel substrate on the hardness of the coatings. Besides, adhesion test was conducted, suggesting a good adhesion of class 1 between substrates and TiCN coatings.
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  Thermal stability of retained austenite and mechanical properties of medium-Mn steel during tempering treatment

  Xiao-li Zhao,,Yong-jian Zhang,Cheng-wei Shao,Wei-jun Hui,Han Dong

  中国钢铁期刊网. 2017, 24(8): 830-837.

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  The thermal stability of retained austenite (RA) and the mechanical properties of the quenched and intercritical annealed 01C-5Mn steel with the starting ultrafine lamellar duplex structure of ferrite and retained austenite during tempering within the range from 200 to 500°C were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile testing. The results showed that there was a slight decrease in the RA volume fraction with increasing tempering temperature up to 400°C. This caused a slight increase in the ultimate tensile strength (UTS) and a slight decrease in the total elongation (TE); thus, the product of UTS to TE (UTS×TE) as high as 31 GPa·% was obtained and remained nearly unchanged. However, a portion of the RA began to decompose when tempered at 500°C and thus caused a ~35% decrease of the RA fraction and a ~16% decrease of the value of UTS×TE. It is concluded that the ultrafine lamellar duplex structure is rather stable and the excellent combination of strength and ductility could be retained with tempering temperature up to 400°C. Thus, thermal processes such as galvanization are feasible for the tested steel provided that their temperatures are not higher than 400°C.
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  Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment

  Min-qiang Gao,Ying-dong Qu,Guang-long Li,Jun-hua You,Rong-de Li

  中国钢铁期刊网. 2017, 24(8): 838-843.

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  Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated. Fractographies and microstructures of heat treated samples were observed using a scanning electron microscope and mechanical properties were measured by a universal tensile test machine. The results indicated that during isothermal annealing at 750°C, the tensile strength of pearlitic ductile cast iron was increased to a peak value at 05 h, and decreased gradually thereafter but the elongation was enhanced with the increase of annealing time. Moreover, the diffusion coefficient of carbon atoms could be approximately calculated as 056 μm2/s that could be regarded as the short-range diffusion. As the holding time was short (05 h), diffusion of carbon atoms was incomplete and mainly occurred around the graphites where the morphology of cementites changed from fragmentized shape to granular shape. In addition, the ductile cast iron with tensile strength of 740 MPa and elongation of 7% could be achieved after graphitization annealing heat treatment for 05 h. Two principal factors should be taken into account. First, the decomposition of a small amount of cementites was beneficial for increasing the ductility up to elongation of 7%. Second, the diffusion of carbon atoms from cementites to graphites could improve the binding force between graphites and matrix, enhancing the tensile strength to 740 MPa.
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  Evolution of microstructure, mechanical and magnetic properties of electrodeposited 50%Ni-Fe alloy foil after thermal treatment

  Hong-ru Ren,Jin-tao Gao,Zhe Wang,Chong Li,Fu-qiang Wang,Zhan-cheng Guo

  中国钢铁期刊网. 2017, 24(8): 844-851.

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  In order to expand the application of the electrodeposited Ni-Fe alloy foil, their mechanical and magnetic properties were studied after heat treatment. The development of grain growth during annealing was in-situ online investigated using a heating stage microscope, and the texture was analyzed via X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD). The results indicated that abnormal grain growth usually occurred during annealing at 1000-1050°C. The {111} oriented grains preferentially grew as the annealing temperature and holding time increased. The plasticities of the electrodeposited Ni-Fe alloy foils after heat treatment were better than those of the original samples. The excellent ductility was obtained without a loss in magnetic properties after annealing at 1100°C for 6 h.
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  Lower limit law of welding windows for explosive welding of dissimilar metals

  Chang-gen Shi,Xuan Yang,Yu-heng Ge,Jun You,Hong-bao Hou

  中国钢铁期刊网. 2017, 24(8): 852-857.

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  The influence of explosive charge thickness on the quality of explosive welding of dissimilar metals was investigated. The lower limit law should be followed in the course of explosive welding. Three welding experiments of stainless steel (410S) and steel (Q345R) were carried out in three different kinds of explosive charge thicknesses, namely 15, 25 and 35 mm. Interfaces of morphology and mechanical properties of three samples were observed and tested. It was found that micro and small wavy bonding is mainly formed for charge thickness of 15 mm whose strength is the highest with minor deformation and few defects in the interface; small and middle wavy bonding are mainly formed for charge thickness of 25 mm whose strength is comparatively mediocre; big wavy bonding is mainly formed for charge thickness of 35 mm whose strength is the lowest. The cause of high bonding strength of the micro and small wavy interface was analyzed and verified on the basis of the results of Electron Probe Micro-Analyzer (EPMA) tests of three selected samples.
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  Ripening behavior of M23C6 carbides in P92 steel during aging at 800°C

  Xu Yang,,Bo Liao,Fu-ren Xiao,Wei Yan,Yi-yin Shan,Ke Yang

  中国钢铁期刊网. 2017, 24(8): 858-864.

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  The rapid coarsening of the M23C6 carbides has been held responsible for the creep fracture in 9-12Cr martensitic heat resistant steels. A commercial P92 steel was subjected to thermal aging at a high temperature of 800°C to investigate the ripening behavior of the M23C6 carbides. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution, especially the ripening process of the M23C6 carbides. The new concept of the effective mean size, dependent on the critical radius, was introduced to correct the measured mean size and then the Ostwald theory was applied to describe the ripening behavior of the M23C6 carbides. The ripening of the M23C6 carbides was revealed to be grain boundary diffusion controlled.