2011年, 第18卷, 第12期　刊出日期：2011-12-15

  

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工艺
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  Improvements on Calculation Model of Theoretical Combustion Temperature in a Blast Furnace

  WU Sheng-li,LIU Cheng-song,FU Chang-liang,XU Jian,KOU Ming-yin

  中国钢铁期刊网. 2011, 18(12): 1-5.

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  On the basis of the existing originally modified calculation models of theoretical combustion temperature (TCT), some factors, such as the combustion ratio of pulverized coal injection (PCI), the decomposition heat of PCI and the heat consumption of SiO2 in ash reduced in high temperature environment, were amended and improved to put forward a more comprehensive model for calculating TCT. The influences of each improvement on TCT were studied and the results were analyzed compared with those of traditional model and originally modified model, which showed that the present model could reflect the thermal state of a hearth more effectively.
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  Cleanliness of Alloying Structural Steel

  YU Hui-xiang,WANG Xin-hua,ZHANG Jing,LI Hai-bo,WANG Wan-jun

  中国钢铁期刊网. 2011, 18(12): 6-11.

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  Alloying structural steel used for mechanical structures has a high requirement for cleanliness because its failures are greatly affected by non-metallic inclusions and total oxygen content in steel. It has been reported by some steelmaking plants to have some problems in controlling total oxygen content and inclusions during alloying structural steel production. For this purpose, cleanliness control in 02C-03Si-06Mn-1Cr-02Mo steel was investigated. Firstly, low melting temperature zone (≤1873 K) of CaO-Al2O3-MgO system and formation condition of low melting temperature inclusions were investigated through thermodynamic equilibrium calculation. On this basis, industrial tests were carried out. Through sampling at different stages, transformation of oxide inclusions and change of total oxygen content in steel were studied. The results show that: in order to form CaO-Al2O3-MgO system inclusions with low melting temperature, mass percent of Al2O3, MgO and CaO in inclusions should be controlled from 376% to 708%, 0 to 174% and 255% to 606%; For the condition of 1873 K and 005% (mass percent) dissolved aluminum in steel, the activities of dissolved oxygen, magnesium and calcium should be controlled as 0298×10-4-2×10-4, 01×10-5-40×10-5 and 08×10-8-180×10-8 respectively. With secondary refining proceeding, average total oxygen content and inclusion amount decrease, the type of most inclusions changes from Al2O3 after tapping to Al2O3-MgO after top slag is formed during ladle furnace refining and finally to CaO-Al2O3-MgO after RH treatment. In the final products, average total oxygen content was 127×10-6 and most inclusions were in spherical shape with size less than 5 μm.
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  Effect of MgO Critical Particle Size on Properties of MgO-C Continuous Temperature-Measuring Sensor for Liquid Steel

  ZHAO Shu-mao,MEI Guo-hui,XIE Zhi

  中国钢铁期刊网. 2011, 18(12): 12-21.

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  MgO-C continuous temperature-measuring sensors for liquid steel were made of fused magnesia with different critical particle sizes from 05 to 20 mm, thus the effects what magnesia′s particle size affect sensors′ properties and lifetime were studied. The result shows that the MgO-C continuous temperature-measuring sensor has good aggression resistance to basic tundish powders and meets the requirement for response time of temperature measuring practice in tundish. The sensor′s service life, which is affected by multi-properties of material and operating environment, reached its maximum when the critical particle size of magnesia was 10 mm. The average lifetime of sensors was 43 or 40 h when served for casting SPHC or Q195 steel.
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  Phosphorous Enrichment in Molten Adjusted Converter Slag: Part II Enrichment Behavior of Phosphorus in CaO-SiO2-FeOx-P2O5 Molten Slag

  WANG Nan,LIANG Zhi-gang,CHEN Min,ZOU Zong-shu

  中国钢铁期刊网. 2011, 18(12): 22-26.

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  The enrichment behavior of phosphorus in CaO-SiO2-FeOx-P2O5 slag was studied by making an investigation on the distribution of phosphorous content in the CaO-SiO2-FeOx-P2O5 molten slag. The research results showed that the 2CaO·SiO2 solid particles existing in molten slag were the condensation sites for the phosphorus enrichment. The enrichment process of phosphorus in the molten slag can be recognized as three substeps: mass transfer of phosphorus from bulk slag to the surface of 2CaO·SiO2 particle, superficial solid solution reaction of phosphorus around the 2CaO·SiO2 particle, and diffusion of phosphorus through the product layer of 2CaO·SiO2-3CaO·P2O5 solid solution to the inner of 2CaO·SiO2 particle. Moreover, higher temperature is favorable to the phosphorous enrichment from molten bulk slag to the 2CaO·SiO2 particles.
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  Theoretical Foundation of Carbonation Pellet Process for Ferrous Sludge Recycling

  HU Chang-qing,,HAN Tao,,ZHANG Yu-zhu,,ZHANG Zhi-xia,

  中国钢铁期刊网. 2011, 18(12): 27-31.

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  For the recycling of ferrous sludge from steel industry, the carbonation pellet process should be considered as a “green” process, since no impurities are added as well as CO2 can be sequestrated and consumed. Through the thermodynamic calculation, the carbonation reaction can occur spontaneously and is an exothermic reaction. Based on the kinetic analysis through unreacted core model, the interfacial chemical reaction was the rate controlling step in the initial fast stage of carbonation, and the CO2 diffusion through the CaCO3 product layer was the rate controlling step in the following extremely slow stage. For the carbonation bonded mechanism, the pellet strength was gained by the formation and growing of CaCO3 product layer. Since the interfacial chemical reaction was the critical stage of the entire carbonation process, the emphasizes should be focused on the improvement of sorbent activity and the optimization of process parameters, such as pore structure, pore surface area, and total pressure, CO2 partial pressure, reaction temperature, etc to accelerate the reaction rate and to improve the quality of carbonation pellets.
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  Process of Re-Resourcing of Converter Slag

  GAO Jin-tao,LI Shi-qi,ZHANG Yan-ting,ZHANG Yan-ling,CHEN Pei-yu,,SHEN Ping

  中国钢铁期刊网. 2011, 18(12): 32-39.

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  The process of “re-resourcing of converter slag” was put forward based on the analysis of the existing steel slag treatment process. The converter slag obtained from Jinan steel plant was studied. After grinding, the slag contained 33% of iron particles, 5484% of magnetic part (wTFe=20%), and 4184% of non-magnetic part, which could be used for making cement directly. At a temperature below 1000 ℃, the non-magnetic Fe2O3 in the slag could be efficiently reduced to magnetic iron by pure H2 and CO. The slag after precise reduction had high degree of dispersion and did not get sintered, which provided an optimum condition for the separation of iron and impurities. To separate the slag and enrich the iron after reduction, the laboratory-scale device of magnetic separation was designed and made. The process of slag re-resourcing, which included magnetic sorting, precise reduction, magnetic separation, and removal of free calcium oxide (f-CaO), was proposed to obtain iron-rich magnetic materials and cement adulterant materials. Through this process, 33 kg iron particles, 150 kg iron-rich material and 700 kg cement could be obtained in each ton slag. Besides, this process to recycle converter slag had a lower energy and material consumption and no pollutant emission.
材料
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  Three-Dimensional Microstructures and Tensile Properties of Pure Iron During Equal Channel Angular Pressing

  YANG Gang,YANG Mu-xin,LIU Zheng-dong,WANG Chang

  中国钢铁期刊网. 2011, 18(12): 40-44.

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  Commercial pure iron billets having diameter of 60 mm and length of 180 mm were subjected to equal channel angular pressing (ECAP) at 350 ℃ for 1 to 4 passes via route Bc. Microstructural evolutions on three planes (X, Y, Z planes) were characterized by optical microscopy and transmission electron microscopy (TEM). It was found that after four passes an ultrafine microstructure could be formed on the X plane, but a band structure remained on the Z plane. Accordingly, the mechanical properties exhibited apparent dependence on the orientations. The strength in the x and y directions was higher than that in the z direction. The microstructural refinement and mechanical properties were discussed in terms of experimental results.
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  Microstructure and Mechanical Properties of Hot-Rolled Fe-Mn-C-Si TWIP Steel

  ZHANG Li,LIU Xiang-hai,SHU Kang-ying

  中国钢铁期刊网. 2011, 18(12): 45-48.

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  Mechanical properties and microstructural evolution of the hot-rolled Fe-Mn-C-Si TWIP steel were investigated and the deformation mechanism was analyzed. The results showed that the tensile strength and elongation were about 1050 MPa and 60%, respectively. The hot-rolled steel had high specific energy absorption and impact toughness between -120 ℃ and 20 ℃. Some inhomogeneous dislocation zones were observed in the undeformed steel. Lots of deformation twins and twin-dislocation interactions were observed in the deformed steel. TWIP effect was the major deformation mechanism for the excellent mechanical properties.
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  Effect of Multi-Step Tempering on Retained Austenite and Mechanical Properties of Low Alloy Steel

  Hamid Reza Bakhsheshi-Rad,Ahmad Monshi,Hossain Monajatizadeh,Mohd Hasbullah Idris,Mohammed Rafiq Abdul Kadir,Hassan Jafari,

  中国钢铁期刊网. 2011, 18(12): 49-56.

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  The effect of multi-step tempering on retained austenite content and mechanical properties of low alloy steel used in the forged cold back-up roll was investigated. Microstructural evolutions were characterized by optical microscope, X-ray diffraction, scanning electron microscope and Feritscope, while the mechanical properties were determined by hardness and tensile tests. The results revealed that the content of retained austenite decreased by about 2% after multi-step tempering. However, the content of retained austenite increased from 36% to 51% by increasing multi-step tempering temperature. The hardness and tensile strength increased as the austenitization temperature changed from 800 to 920 ℃, while above 920 ℃, hardness and tensile strength decreased. In addition, the maximum values of hardness, ultimate and yield strength were obtained via triple tempering at 520 ℃, while beyond 520 ℃, the hardness, ultimate and yield strength decreased sharply.
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  Parameters Optimization of Plasma Hardening Process Using Genetic Algorithm and Neural Network

  LIU Gu,WANG Liu-ying,,CHEN Gui-ming,HUA Shao-chun

  中国钢铁期刊网. 2011, 18(12): 57-64.

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  Plasma surface hardening process was performed to improve the performance of the AISI 1045 carbon steel. Experiments were carried out to characterize the hardening qualities. A predicting and optimizing model using genetic algorithm-back propagation neural network (GA-BP) was developed based on the experimental results. The non-linear relationship between properties of hardening layers and process parameters was established. The results show that the GA-BP predicting model is reliable since prediction results are in rather good agreement with measured results. The optimal properties of the hardened layer were deduced from GA. And through multi optimizations, the optimum comprehensive performances of the hardened layer were as follows: plasma arc current is 90 A, hardening speed is 22 m/min, plasma gas flow rate is 60 L/min and hardening distance is 43 mm. It concludes that GA-BP mode developed in this study provides a promising method for plasma hardening parameters prediction and optimization.
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  Effect of Heat Treatment Process on Mechanical Properties and Microstructure of Modified CNS-Ⅱ F/M Steel

  YANG Ying,YAN Qing-zhi,MA Rong,GE Chang-chun

  中国钢铁期刊网. 2011, 18(12): 65-70.

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  Ferritic/martensitic (F/M) steels have been recommended as one of the candidate materials for supercritical water cooled reactor (SCWR) in-core components use for its high thermal conductivity, low thermal expansion coefficient and inherently good dimensional stability under irradiation condition in comparison to austenitic steel. CNS-Ⅱ F/M steel which has good mechanical properties was one of the 9-12Cr F/M steels designed for SCWR in the previous work. In this study a modified CNS-Ⅱ F/M steel was used and it′s ultimate tensile strength was 925 MPa at room temperature and 483 MPa at 600 ℃ after optimizing heat treatment parameter. The ductile to brittle transition temperature of modified CNS-Ⅱ F/M steel is -55 ℃. Those are at the same level or even higher than that of CNS-Ⅱ and some commercial F/M steels nominated for SCWR in-core component use. The transmission electron microscope (TEM) results showed that the mechanical properties of the tempered martensite was closely related to the decomposition stage of the martensite.
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  Workability Studies in Forming of Sintered Fe-035C Powder Metallurgy Preform During Cold Upsetting

  S Narayan,A Rajeshkannan

  中国钢铁期刊网. 2011, 18(12): 71-78.

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  An experimental investigation on the workability behaviour of sintered Fe-035C steel preforms under cold upsetting, have been studied in order to understand the influence of aspect ratio and lubrication condition on the workability process. The above mentioned powder metallurgy sintered preform with constant initial theoretical density of 84% of different aspect ratios, namely, 04 and 06 respectively were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1200 ℃. Each sintered preform was cold upset under nil/no and graphite frictional constraint, respectively. Under the condition of triaxial stress densification state, axial stress, hoop stress, hydrostatic stress, effective stress and formability stress index against axial strain relationship was established and presented in this work. Further more, attained density was considered to establish formability stress index and various stress ratio parameters behaviour.