2016年, 第23卷, 第9期　刊出日期：2016-09-15

  

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Metallurgy and Metal Working
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  Chromium Recycling from Argonoxygen Decarburization Dust in Hot Metal Predephosphorization Process

  Dongping ZHAN,Yangpeng ZHANG,Zhouhua JIANG,Dewei WANG,Huishu ZHANG

  中国钢铁期刊网. 2016, 23(9): 867-873.

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  The chromium recycling from the stainless steel dust of an argonoxygen decarburization (AOD) furnace during a hot metal pretreatment process was investigated. Experiments at different temperatures or with different amounts of AOD dusts were carried out in a laboratory furnace equipped with MoSi2 heating elements and subsequently industrial experiments were conducted in a stainless steelmaking factory, in order to study the thermodynamic mechanism of C and Si reacted with Cr2O3 to get Cr from AOD dust. The results showed that the reaction between C and Cr2O3 occurred below 157218 K. Although its reducing ability was weaker than that of Si, C enabled the Cr in Cr2O3 in the AOD dust to be recycled using the Si in the slag. By combining the AOD dust added in an earlier stage, the hot metal pretreatment slag added in a later stage could not only recycle Cr from AOD dust but also remove Si, S, and P. Higher hot metal temperatures resulted in higher Cr content and lower remained P concentration in the molten iron.
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  Direct Reduction of Highphosphorus Oolitic Hematite Ore Based on Biomass Pyrolysis

  Dongbo HUANG,Yanbing ZONG,Rufei WEI,Wei GAO,Xiaoming LIU,

  中国钢铁期刊网. 2016, 23(9): 874-883.

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  Direct reduction of highphosphorus oolitic hematite ore based on biomass pyrolysis gases (CO, H2, and CH4), tar, and char was conducted to investigate the effects of reduction temperature, iron orebiomass mass ratio, and reduction time on the metallization rate. In addition, the effect of particle size on the dephosphorization and iron recovery rate was studied by magnetic separation. It was determined that the metallization rate of the hematite ore could reach 9935% at iron orebiomass mass ratio of 1∶06, reduction temperature of 1100 ℃, and reduction time of 55 min. The metallization rate and the aggregation degree of iron particles increase with the increase of reduction temperature. The particle size of direct reduced iron (DRI) has a great influence on the quality of the iron concentrate during magnetic separation. The separation degree of slag and iron was improved by the addition of 15 mass% sodium carbonate. DRI with iron grade of 8911%, iron recovery rate of 8347%, and phosphorus content of 028% can be obtained when ore fines with particle size of -10 μm account for 7815%.
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  Preparation and Metallurgical Analysis of High Activity Burnt Lime for Steelmaking

  Huaqiang HAO,,Yuzhu ZHANG,,Suju HAO,Chaofa ZHANG,Wufeng JIANG,Penghui CUI

  中国钢铁期刊网. 2016, 23(9): 884-890.

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  Burnt lime is an important material in steelmaking and its activity degree is a key factor for liquid steel quality. The burnt lime was made by the calcination of limestone in a high pressure electric furnace. The burnt lime mineralogical phases and micromorphologies were characterized by Xray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The burnt lime activity degree was determined by acidbase titration, the burnt lime pore distribution was measured by mercury intrusion porosimetry (MIP), and the thermal effect of a mixture of burnt lime and slag was measured by differential scanning calorimetry (DSC). The results showed that the CaO grain size and pore size of burnt lime made under high pressure were larger than those of burnt lime made under atmospheric pressure. The CaO grain size and pore size increased and the laminate phenomenon also occurred clearly under high pressure. The activity degree of burnt lime made under high pressure was greater than that made under atmospheric pressure. The maximum activity degree was 437 mL for burnt lime made under a pressure of 04 MPa. For the same ratio of CaO to SiO2, the melting temperature, hemisphere temperature and fluidity temperature of slag decreased with increasing burnt lime activity degree. The higher the activity degree the burnt lime had, the better the slag forming occurred. It was advantageous for 2CaO·SiO2 and 3CaO·SiO2 forming at lower temperatures if the burnt lime activity degree was increased.
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  Microstructure Characteristic and Phase Evolution of Refractory Siderite Ore during Sodiumcarbonateadded Catalyzing Carbothermic Reduction

  Shaojun BAI,,Meng WU,Chao L,Shuming WEN,

  中国钢铁期刊网. 2016, 23(9): 891-899.

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  Thermodynamic analysis of refractory siderite ore during carbothermic reduction was conducted. Microstructure characteristics and phase transformation of siderite ore during sodiumcarbonateadded catalyzing carbothermic reduction were investigated. Xray diffraction (XRD), scanning electron microscopy and energydispersive analysis of Xrays were used to characterize the reduced samples. Results indicate that the solid reaction between FeO and SiO2 is inevitable during carbothermic reduction and the formation of fayalite is the main hindrance to the rapid reduction of siderite. The phase transformation of present siderite ore can be described as: sideritemagnetitemetallic iron, complying with the formation of abundant fayalite. Improving the reduction temperature (≤1050 ℃) and duration is helpful for the formation and aggregation of metallic iron. The iron particle size in the reduced ore was below 20 μm, and fayalite was abundant in the absence of sodium carbonate. With 5% Na2CO3 addition, the iron particle size in the reduced ore was generally above 50 μm, and the diffraction intensity associated with metallic iron in the XRD pattern increased. The Na2O formed from the dissociation of Na2CO3 can catalyze the carbothermic reduction of the siderite. This catalytic activity may be mainly caused by an increase in the reducing reaction activity of FeO.
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  Dynamic Response of Mold Oscillator Interacting with Steel Slabs

  Yonghui PARK,Hyunchul PARK

  中国钢铁期刊网. 2016, 23(9): 900-909.

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  A mathematical model to show the dynamic response of the mold oscillator was suggested. The model considered a frictional interaction between the mold oscillator and slab as several connected nodes. The governing equation considered the slab as a multidegreeoffreedom (DoF) system, and included a hysteresis model to describe elasticplastic behavior of the slab; the mold oscillator was given two DoF by utilizing pressure and displacement experiment data. Simulations indicate that the mold and slab execute various vibrations, and that mold oscillation marks are caused by a stickandslip phenomenon during intervals, in which the slab contacting the mold moves downward compared to the other slab (negative strip time). The slab shows the formation of mold oscillation marks to previous formation criterion equally when the mold velocity is faster than the casting speed about downward. The oscillation mark will grow up over 2 Hz exciting frequency with constant 4 mm stroke in simulations. Finally, the negative strip time was compared to the frictional force, hysteresis variable, and plastic force to investigate formation mechanism of the oscillation marks.
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  Effect of Rolling Process on Microstructure and Properties of 95CrMo Drill Steel

  Wei YU,Baosheng XIE,Ban WANG,Qingwu CAI,Shixin XU

  中国钢铁期刊网. 2016, 23(9): 910-916.

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  In order to improve the strength and toughness of 95CrMo steel and explore a short flow process, a direct rolling process was employed, and the effect of finishing rolling process on microstructure and mechanical properties was investigated. The results show that, with the decrease of finishing rolling temperature, interlamellar spacing increases, the strength as well as hardness has a general increase, and secondary cementite is distributed uniformly but represents a remarkable decrease in size. Based on HallPetch type equation, an effective relationship of yield strength and pearlite structure parameters was established. The correlation coefficients between the measured and calculated strength were more than 095, which indicated a high reliability of the relationship. By analyzing the individual strength contributions of pearlite structures, yield strength was found to have a more great dependence on pearlite interlamellar spacing than colony size.
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  Thermal Behavior and Kinetics of Raw/Pyrolytic Wood and Coal Blends during Cocombustion Process

  Jian DING,Qingcai LIU,Lijun JIANG,Guoqing LIU,Shan REN,Jian YANG,Lu YAO,Fei MENG

  中国钢铁期刊网. 2016, 23(9): 917-923.

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  The thermal properties of raw wood (RW) biomass, corresponding pyrolytic wood (PW) biomass, and their blends with anthracite coal (AC) were evaluated under combustion conditions with a thermogravimetric analysis (TGA) method. The blending ratios of the biomass with AC ranging from 0 to 100 mass% were taken into consideration to investigate the thermal behavior and kinetics of these blends during their cocombustion. For blends with different ratios of the RW to AC and 100% AC (100 AC), two distinct mass loss peaks related to the release or combustion process of the volatiles and the combustion of the char were noted. The addition of a higher ratio of RW or PW into AC can improve the combustion process of the blends. The thermal behavior of the RW/AC or PW/AC blends could not be characterized by a simple linear correlation of their pure material thermal behavior. With the RW/PW addition ratios varying from 25 mass% to 80 mass%, the apparent activation energy of the blends gradually decreased from 4846 to 3493 kJ/mol and from 8274 to 3781 kJ/mol for the RW/AC and PW/AC blends, respectively, with high correlation coefficient (R2) values ranging from 09956 to 09984.
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  Oxidation and Induration Characteristics of Pellets Made from Western Australian Ultrafine Magnetite Concentrates and Its Utilization Strategy

  Congcong YANG,Deqing ZHU,Jian PAN,Binzhi ZHOU,Hu XUN

  中国钢铁期刊网. 2016, 23(9): 924-932.

  摘要 ( )   可视化   收藏

  Western Australian magnetite concentrates normally have ultrafine granularity and much higher specific surface areas than Chinese magnetite concentrates owing to the significant pregrinding and beneficiation for saleable iron grade. Such characteristics will inevitably affect the subsequent pelletization process. However, very few investigations have been done before. Thus, the oxidation and induration characteristics of pellet made from a Western Australian ultrafine magnetite concentrate were revealed by conducting routine preheatingroasting tests in an electric tube furnace and investigating the microstructure of fired pellets under an optical microscope in comparison with that of pellets made from typical Chinese magnetite concentrate. The liquidus regions of CaOSiO2Fe2O3 and CaOSiO2Al2O3 ternary systems in air at various temperatures were calculated by FactSage software to explain the importance of liquid phase in the consolidation of fired pellets. The results show that pellet made from ultrafine magnetite concentrate possesses better oxidability and preheating performance than that made from Chinese magnetite concentrate. However, it has inferior roasting performance, usually requiring conditions of roasting at 1280 ℃ for at least 30 min to acquire sufficiently high compressive strength, which are attributed to higher temperature sensitivity caused by its smaller particle size and less formation of liquid phase because of low impurities like CaO and Al2O3 in raw materials. Correspondingly, its roasting performance can be significantly improved by blending with Chinese magnetite concentrates or increasing the pellet basicity (wCaO/wSiO2). By comprehensive evaluation, blending with Chinese iron ore concentrates is an appropriate way to utilize Western Australia ultrafine magnetite concentrates.
Material
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  Mechanical Properties and Fracture Behavior of CuCoBe Alloy after Plastic Deformation and Heat Treatment

  Yanjun ZHOU,,Kexing SONG,,Jiandong XING,Zhou LI,Xiuhua GUO,

  中国钢铁期刊网. 2016, 23(9): 933-939.

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  Mechanical properties and fracture behavior of Cu084Co023Be alloy after plastic deformation and heat treatment were comparatively investigated. Severe plastic deformation by hot extrusion and cold drawing was adopted to induce large plastic strain of Cu084Co023Be alloy. The tensile strength and elongation are up to 4766 MPa and 18%, respectively. The fractured surface consists of deep dimples and microvoids. Due to the formation of supersaturated solid solution on the Cu matrix by solution treatment at 950 ℃ for 1 h, the tensile strength decreased to 2719 MPa, while the elongation increased to 42%. The fracture morphology is parabolic dimple. Furthermore, the tensile strength increased significantly to 5802 MPa after aging at 480 ℃ for 4 h. During the aging process, a large number of precipitates formed and distributed on the Cu matrix. The fracture feature of aged specimens with low elongation (46%) exhibits an obvious brittle intergranular fracture. It is confirmed that the mechanical properties and fracture behavior are dominated by the microstructure characteristics of Cu084Co023Be alloy after plastic deformation and heat treatment. In addition, the fracture behavior at 450 ℃ of aged Cu084Co023Be alloy was also studied. The tensile strength and elongation are 3836 MPa and 112%, respectively. The fractured morphologies are mainly candyshaped with partial parabolic dimples and equiaxed dimples. The fracture mode is multimixed mechanism that brittle intergranular fracture plays a dominant role and ductile fracture is secondary.
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  Constitutive Model of Warm Deformation Behavior of Medium Carbon Steel

  Hongbin LI,,Yunli FENG,Tao YAN,Enlin YU

  中国钢铁期刊网. 2016, 23(9): 940-948.

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  The compressive behaviors of medium carbon steel specimens were investigated over a wide range of temperatures and strain rates using a Gleeble3500 thermosimulation machine. The results show that the flow stress increased with strain at first, and then gradually decreased after reaching a peak value. The flow stress softening rate at a high strain rate was larger than that at a low strain rate. The effects of deformation heating and friction on flow stress were analyzed. A new friction correction method, wherein the effect of strain on frictional coefficient was considered, was established here. The stresses revised by the new method deviated from the measured stresses with increasing strain. Meanwhile, the apparent frictional coefficient variation law with strain was obtained. The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value. The stress was corrected by considering deformation heating. The accuracy of the temperature correction method was verified using a special experiment. The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating. A constitutive model considering strain was proposed here to describe the deformation behaviors. Compared with experimental data, the modified constitutive model exhibited a good accuracy as to constitutive correlation.
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  Tailoring of Mechanical Properties of Indirect Hot Stamping Steel Tubes by Laser Assisted Local Rapid Heating

  Mahmudun Nabi CHOWDHURY,Juri KIM,Sungtae HONG,Jinwook JUNG,Heungnam HAN,Sangwoo SO

  中国钢铁期刊网. 2016, 23(9): 949-954.

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  The effect of laser assisted local heating on the mechanical properties of a hot stamping steel tube was investigated. A heated region with a spiral shape was generated on the surface of the tube by combining the linear movement of the laser and the rotation of the tube. The results of axial crush tests show that the laser assisted local heating can be effectively used to modify the mechanical performance of the tube. A microstructural analysis confirms that the laser locally induces a martensitic phase transformation in the heated region and results in inhomogeneous microstructures along the length of the tube.
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  Corrosion Behavior of Welded Joints for Cargo Oil Tanks of Crude Oil Carrier

  Jinshan WEI,Yanchang QI,Zhiling TIAN,Yun PENG

  中国钢铁期刊网. 2016, 23(9): 955-962.

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  E32 grade corrosion resistant steel was welded with welding wires with three different S contents. The microstructure, mechanical properties, inclusions, and corrosion behavior of welded joint were investigated. The joint coupon corrosion test and potentiodynamic polarization test were carried out under the simulated corrosion environment of the inner bottom plates of cargo oil tanks. The pitting initiation and propagation mechanism of the weld metal were studied by scanning electron microscopy and infinite focus. The results indicated that the microstructures of three kinds of weld metals are all composed of acicular ferrite, ferrite sideplate and proeutectoid ferrite. The microstructure of heataffected zone is composed predominantly of bainite. Joint welded with low S filler wire has good mechanical properties. S can decrease free corrosion potential and increase the corrosion tendency. The pitting initiation is oxide inclusion or sulfideoxide inclusion complex. S can induce the formation of occluded area and promote the corrosion propagation. The chemical compositions of weld metal is similar to base metal, which can limit the galvanic corrosion between weld metal and base metal, and avoid formation of corrosion step.
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  Tensile Deformation Behavior of FeMnAlC Low Density Steels

  Xiaofeng ZHANG,,Hao YANG,Deping LENG,Long ZHANG,Zhenyi HUANG,Guang CHEN

  中国钢铁期刊网. 2016, 23(9): 963-972.

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  Room temperature tensile tests of FeMnAlC low density steels with four different chemical compositions were conducted to clarify the dominant deformation mechanisms. Parameters like product of strength and elongation, as well as specific strength and curves of stressstrain relations were calculated. The microstructures and tensile fracture morphologies were observed by optical microscope, scanning electron microscope and transmission electron microscope. The tensile behavior of low density steel was correlated to the microstructural evolution during plastic deformation, and the effects of elements, cooling process and heat treatment temperature on the mechanical properties of the steels were analyzed. The results show that the tensile strength of steels with different cooling modes is more than 1000 MPa. The highest tensile strength of 28Mn12Al alloy reached 1230 MPa, with corresponding specific strength of 18916 MPa·cm3·g-1, while the specific strength of 28Mn10Al alloy was 17898 MPa·cm3·g-1, and the excellent product of strength and elongation of 28Mn8Al alloy was over 692 GPa·%. A large number of ferrite reduced the ductility and strain hardening rate of the alloy, while the existence of κ carbides may improve the strength but weaken the plasticity. Some fine κ carbides appeared in the waterquenched specimen, while coarse κ carbides were observed in the aircooled specimen. High temperature heat treatment improved the decomposition kinetics of γ phase and the diffusion rate of carbon, thus speeded up the precipitation of fine κ carbides. The dominant deformation mechanism of low density steel was planar glide, including shearbandinduced plasticity and microbandinduced plasticity.
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  Effects of Thermal Gradients and Rotational Flows on Grain Growth in 22 t Steel Ingots

  Zheng CHEN,,Qijie ZHAI,Jieyu ZHANG,Honggang ZHONG

  中国钢铁期刊网. 2016, 23(9): 973-980.

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  Heavy ingots are widely used in many industrial fields. The coarse grains formed during the process of ingot solidification influence the properties and fracture behaviors of the final products. The coarse grain growth was simulated under different thermal gradients. A 30Cr2Ni4MoV steel ingot was melted in a cubic crucible with dimensions of 15 cm×10 cm×23 cm, and the cooling conditions on each side of the crucible were controlled by different thermal curves. The influences of thermal gradients and rotational flows on grain growth in heavy steel ingots were then investigated both numerically and experimentally. The results showed that when the amplitude of the rotation angle was 60°, the metal was solidified under a reciprocating horizontal rotational condition when the angular velocity was 10 (°)/s or 20 (°)/s. As the thermal gradient increased, the lengths of the primary columnar grains increased, and the diameters of equiaxed grains decreased. When the direction of flow rotation was perpendicular to the direction of grain growth, the columnar grain zone was nearly eliminated, and the average diameter of equiaxed grains was 05 mm.
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  Magnetic Properties of Thermally Aged FeCu Alloys with Predeformation

  Yi LI,,Yuanfei LI,Ben XU,Qiulin LI,Guogang SHU,Wei LIU,

  中国钢铁期刊网. 2016, 23(9): 981-987.

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  Magnetic properties of thermally aged FeCu alloys with predeformation have been evaluated to improve the understanding of using magnetic technology for the nondestructive evaluation (NDE) of irradiation embrittlement in reactor pressure vessel (RPV) steels. FeCu alloys with and without predeformation were thermally aged at 500 ℃ and the changes in microstructure, mechanical properties and magnetic properties were determined. It is found that the straininduced dislocations recover and the Curich particles precipitate during the aging process, and the magnetic properties variation depends on the combined influence of these two factors. From the point of view of NDE, a fully tempered or annealed microstructure is favorable before RPV is put into service. These results improve the understanding of magnetic property evolution in actual RPV steels and help to develop NDE theory for irradiation embrittlement.
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  Unexpected Effect of Nb Addition as a Microalloying Element on Mechanical Properties of δTRIP Steels

  Sajad Gholami SHIRI,Seyed Ahmad Jenabali JAHROMI,Yahya PALIZDAR,Majid BELBASI

  中国钢铁期刊网. 2016, 23(9): 988-996.

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  The concept of microalloying was applied to the δTRIP (transformationinduced plasticity) steel to investigate the feasibility of increasing the mechanical properties and understanding the effect of microalloying on the morphology and structure of the steel. A hot rolled δTRIP steel with three different contents of Nb (0, 003, 007 mass%) was subjected to the microstructural and mechanical examination. The high Al and Si concentration in these steels guaranteed the presence of the considerable δferrite phase in the microstructure after the casting and the subsequent hot rolling. The obtained results showed that Nb dramatically affects the microstructure, the dynamic recovery and recrystallization behavior, as well as the grain shape and thus the stability of austenite after the thermomechanical process of hot rolling. The results also revealed an unexpected effect of Nb on the mechanical properties. The addition of Nb to the δTRIP steel led to a significant decrease in the ultimate strength (from 1144 to 917 MPa) and an increase in ductility (from 24% to 28%). These unconventional results could be explained by the change in the steel microstructure. The workhardening behaviors of all samples exhibit three stages of the workhardening rate evolution. At the stage 2, the workhardening rate of the studied steels increased, being attributed to the TRIP effect and the transformation of austenite to martensite.