2018年, 第25卷, 第1期　刊出日期：2018-01-15

  

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  Interfacial reaction between.oxide inclusion and.steel matrix deoxidized by.Si and.Mn at.1473.K

  Xue-liang .Zhang, · Shu-feng . Yang , · Cheng-song Liu · Jing-she Li, · Qing Liu, · Gang .Liu,

  . 2018, 25(1): 1-8.

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  An improved di.usion couple method was used to simulate the dynamic process of the solid-state reaction at the interface between oxide inclusions and a steel matrix deoxidized by Si and Mn during heat treatment at 1473.K. Experimental results indicated that good contact between the oxide and steel matrix was attained after pre-treatment at 1673.K. In addition, the reaction between the oxide and steel matrix at 1673.K was suppressed, and the e.ect of this reaction on the di. usion couple experiments at 1473.K was minimized. In the di.usion couple experiments, the di.usion of oxygen from the oxide to the steel matrix resulted in the precipitation of .ne oxide particles and a decrease in the Mn content in the steel matrix near the interface after heat treatment at 1473.K. With increasing heat treatment time, the widths of the particle precipitation zone (PPZ) and Mn-depleted zone (MDZ) gradually increased. In addition, the solid-state reaction at the interface between the oxide and steel matrix was intense, and the widths of the PPZ and MDZ increased rapidly during the 0–20.h stage of heat treatment, especially during the 0–5.h stage. The interfacial reaction was retarded, and the rates of width expansion of PPZ and MDZ decreased with increasing heat treatment time.
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  Effect of.superheat on.quality of.central equiaxed grain zone of.continuously cast bearing steel billet based on.two-dimensional segregation ratio

  Wei . Wang · Zi-bing Hou · Yi Chang · Jiang-hai Cao

  . 2018, 25(1): 9-18.

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  The quality of central equiaxed grain zone (CEGZ) of GCr15 bearing steel billets was investigated at di. erent superheats (20, 25 and 35.°C) by experimental observations and a . nite element model in order.to optimize superheat in continuous casting process. Several GCr15 billets were collected from the continuous casting shop, and the same CEGZ was chosen for comparison of internal quality of GCr15 billets. Considering the limitation of segregation index at some points, two-dimensional segregation ratio in CEGZ was introduced. Firstly, the segregation ratio and the area of center large dark points in CEGZ obtain the minimum at 25.°C superheat, which indicates that the quality of CEGZ at 25.°C superheat is improved compared with those at 20 and 35.°C superheats for corresponding continuously cast billets. The highest superheat and the lowest superheat are not bene. cial for improving the central zone quality in the billets. Secondly, the quality of CEGZ of GCr15 billets increases with a decrease in the secondary dendrite arm spacing of CEGZ. Finally, according to the established .nite element model, it is deduced that the secondary dendrite arm spacing of CEGZ is closely related to its later solidi. ca-tion time at solid fraction of 0.5–1.0, and the former will be decreased when decreasing the latter.
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  Effect of.metallurgical dust on.NO.emissions during.coal combustion process

  Zhi-fang Gao , · Hong-ming Long , · Tie-jun .Chun · Zhao-jin . Wu · Zheng-wei . Yu

  . 2018, 25(1): 19-27.

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  NO emissions from coal combustion are receiving signi. cant attention in recent years. As a solid waste generated from metallurgical industry, metallurgical dust (MD) contains a large amount of metal oxides, such as Fe2O3, CaO, SiO2 and Al2O3, as well as other rare metal oxides. The in.uence of MD on the NO emissions and the mechanism of the coal com-bustion systems were analyzed. The results show that the peak values of NO emission decrease with the increase in MD mass percent, and the curve of NO emission can be divided into two stages including rapid generation (400.600.°C) and slow release (800.900.°C). The reduction of NO is signi. cantly a.ected by temperature, volatile components, O2 and CO. CO has a signi.cant catalytic action which can deoxidize NO to N2. The results obtained by X-ray di.raction and scanning electron microscopy indicate that multiple components in MD, such as Fe9TiO 15, Fe2O3 and TiO 2, can react with NO to produce TiN. Besides, the alkali metals in MD, such as Na, K and Ca, may catalyze NO precursor to inhibit NO emission. These results indicate that MD is cheap and highly e.cient in controlling NO emissions during coal combustion processes.
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  Numerical simulation and.experimental measurement of.transport phenomena for.coherent jet with. CH4 +.N2 mixed fuel gas

  Shao-yan Hu, · Rong Zhu, · Run-zao Liu, · Kai .Dong, · Fu-hai .Liu, · Guo-hong .Ma, · Rong-fang Su

  . 2018, 25(1): 28-36.

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  Coherent jet technology has been widely used in EAF steelmaking process because of the longer potential core length and stronger impacting power of the supersonic oxygen jet. However, more oxygen and fuel gas are consumed to achieve excel-lent characteristics of coherent jets, which causes the increase in steelmaking cost. Computational .uid dynamics simulation and experimental measurement of the coherent jets with CH4 +.N2 mixed fuel gas were carried out aiming at reducing the consumption of fuel gas. The numerical simulation results showed good agreement with the experimental data. As a result, high proportion of N2 negatively a.ects the combustion of CH4, which is not good for the protection of oxygen jets. While the gas composition is 75% CH4 + 25% N2, the N2 addition to the CH4 leads to an expanding of CH4 combustion zone, and the energy generated by the combustion reaction could be delivered to the molten bath more e. ciently, which is one control scheme with high performance–price ratio.
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  Thermodynamic evaluation of reaction abilities of structural units in Fe–C binary melts based on atom–molecule coexistence theory

  Xue-min Yang . Jin-yan Li . Dong-ping Duan . Fang-jia Yan . Jian Zhang

  . 2018, 25(1): 37-56.

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  The reaction abilities of structural units in Fe–C binary melts over a temperature range above the liquidus lines have been evaluated by a thermodynamic model for calculating the mass action concentrations Ni of structural units in Fe–C binary melts based on the atom–molecule coexistence theory (AMCT), i.e., the AMCT-Ni model, through comparing with the predicted activities aR,i of both C and Fe by 14 collected models from the literature at four temperatures of 1833, 1873, 1923, and 1973 K. Furthermore, the Raoultian activity coef.cient c0C of C in in.nitely dilute Fe–C binary melts and the standard molar Gibbs free energy change DsolGH;%of dissolved liquid C for forming w[C] as 1.0 in Fe–C binary m;Cdis: elT!.Cw.C.1:0 melts referred to 1 mass% of C as reference state have also been determined to be valid. The determined activity coef.cient ln cC of C and activity coef.cient ln cFe of Fe including temperature effect for Fe–C binary melts can be described by a quadratic polynomial function and a cubic polynomial function, respectively.
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  Central composite design for.optimization and.formulation of.desulphurization of.iron ore concentrate using atmospheric leaching process

  Ali Mostafavi · Hassan Rezvanipour , · Dariush Afzali · Tayebeh .Shamspur · Amir Hajizadehomran

  . 2018, 25(1): 57-64.

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  Owing to the negative e.ects of sulphur in iron ore on steelmaking process and environment, a tank leaching process was performed in atmospheric conditions to remove the sulphur from the iron ore concentrate and simultaneously to transform sulphide minerals into useful by-products. To achieve desirable sulphur removal rate and e. ciency, central composite design was adopted as a response surface methodology for the optimization and evaluation of the process. A full-quadratic polynomial equation between the sulphur removal and the studied parameters was established to assess the behaviour of sulphur removal as a function of the factors and to predict the results in various conditions. The optimum conditions were obtained based on the variance tests and response surface plots, from which the optimized ranges for each factor resulting in the best response (corresponding to the highest percentage of desulphurization) could be then achieved. The results show that most desirable conditions are atmospheric leaching in 1.39.mol/dm 3 nitric acid and 0.88.mol/dm 3 sulphuric acid for 47.h. The designed process under the optimized desulphurization conditions was applied to a real iron ore concentrate. More than 75% of the total sulphur was removed via the leaching process. In addition to the desulphurization, the conversion of sulphide-bearing minerals into useful by-products, extraction of valuable metals, and executing the process under atmospheric conditions are the other advantages of the proposed method.
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  Thermodynamic analysis of.improvement of.converter gas by.injecting pulverized coal into.vaporization cooling fl ue

  Jian-an Zhou, · Xue-kai .Jiang, · Jian-bo Xie, · Hua Zhang, · Lei .Li · Bao Wang , · Hong-wei .Ni,

  . 2018, 25(1): 65-71.

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  In order to improve the calori.c value and the recovery yield of converter gas during the steelmaking process, a novel and thermodynamically admissible process was proposed. This method involved injecting pulverized coal into the vaporization cooling .ue of a converter, and the approach was developed based on an industrial 30 t converter. The e.ects of temperature, O2 content, and the volumetric ratio of CO to CO2 on the conversion of the mixed components of gas were analyzed using thermodynamic calculations. Furthermore, the e.ect of the injection rate on the quality and quantity of gas was investigated. The results show that the O2 and CO2 components of .ue gas decrease as the injection rate increases, whereas the CO and H2 components synchronously increase. With the injection rate of 30.kg min .1, the O2 and CO2 components of the gas decreased by 64.12 and 41.19%, respectively, while the CO and H2 increased by 20.09 and 236.84%, respectively, and the recovery time of gas increased by 11.61%, compared to non-injection.
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  Effect of.vacuum level on.microstructure and.mechanical properties of.titanium–steel vacuum roll clad plates

  De-han . Yang · Zong-an .Luo · Guang-ming Xie · Ming-kun . Wang · R. D. . K. . Misra

  . 2018, 25(1): 72-80.

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  Vacuum roll cladding (VRC) was used to bond pure titanium (Ti) plate to a plain low carbon steel (Q345) with the aim of obtaining a high-quality Ti–steel clad plate. The e.ect of interfacial compound on the microstructure and mechanical properties of Ti–steel clad plate was studied by electron probe microanalysis, scanning electron microscopy, X-ray di.raction and shear test. The clad plates were heated at 850.°C for 120.min and welded at di.erent levels of vacuum. The results indicated that the cracked zone of the bonded interface decreased signi.cantly with the increase in the level of vacuum during welding. Welding at atmospheric pressure, the randomly distributed TiN damaged the continuity of TiC and the uniformly di.used region of Ti and Fe at the bonded interface, while welding in vacuum of 1.×.10 .2 Pa, maximum shear strength of 298.MPa was obtained because of the decrease in TiN content.
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  Influence of.austempering process on.microstructures and.mechanical properties of.V-containing alloyed ductile iron

  Jun-jun Cui , · Li-qing .Chen

  . 2018, 25(1): 81-89.

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  The in.uence of austempering time and vanadium addition on microstructure and mechanical properties of the alloyed ductile iron has been investigated. The 0.30.wt% V-containing and V-free alloyed ductile irons were .rstly austenitized at 850.°C for 1.h and then austempered in a salt bath at 300.°C for 2, 3 and 4.h, respectively. For the 0.3.wt% V-containing alloyed ductile iron, the transformation product (ausferrite) was .ner, and a small amount of martensite and a large amount of stable austenite were obtained after austempering for 2.h, while higher hardness and compressive strength of 62.8 HRC and 3000.MPa were achieved. For the V-free alloyed ductile iron, lower hardness and compressive strength were measured to be 56.8 HRC and 2320.MPa. As the austempering time increases, the amount of stable austenite decreases in the V-containing ductile iron, typically for the start of the second stage formation (retained austenite (γ r).→α + carbide). Based on this, it is assumed that the optimal processing window (OPW) was narrowed due to the addition of 0.30.wt% V as compared to the V-free ductile iron. When the hardness of 0.30.wt% V-alloyed ductile iron was higher than 59 HRC, the highest wear resist-ance was obtained. The mechanical cutting plays a dominant role in abrasive wear process.
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  Fabrication of.Al foam without.thickening process through.melt-foaming method

  Dong-hui Yang , · Jian-qing .Chen · Lei . Wang · Jing-hua Jiang · Ai-bin Ma

  . 2018, 25(1): 90-98.

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  By using calcium carbonate (CaCO 3) powder as the blowing agent, Al foams with porosities of.~.60 to 85% and pore size of.~.1.5.mm were fabricated via melt-foaming method. Instead of adding a thickening agent to increase Al melt viscosity, a small amount of Mg ingot (5.0.wt%) was added .rst, and then Al melt was foamed by adding calcium carbonate via the impellor stirring. The e.ect of Mg addition on the gas release behavior of calcium carbonate in the Al melt was investigated. The compression behavior of fabricated Al foams was examined. The results show that the blowing gas is possibly from the reaction between Mg and calcium carbonate, and this reaction can produce solid oxides with micrometer level size, which leads to increasing the Al melt viscosity and is bene. cial for inhibiting pores coarsening. Besides, the micrometer level cracks in the cell walls make the strength of Al foam decrease.
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  Morphology and.distribution of.precipitates and.their eff ects on.compression cracks in.Fe-6.5Si-0.02B electrical steel

  Zhi-hao Zhang · Jun-li Wang · Hua-dong .Fu

  . 2018, 25(1): 99-107.

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  Morphology and distribution of precipitates in the Fe-6.5Si-0.02B alloy were characterized, and these e.ects on room-temperature compression cracks were investigated. The results showed that the precipitate in the Fe-6.5Si-0.02B alloy is Fe2B with body-centered tetragonal structure, and its nano-hardness is 15.0.GPa which is higher than that of the matrix (~.8.5.GPa). In the as-cast alloys, most of the intragranular precipitates are coarse lath-like with the length of 5–15.μm and width of 2–5.μm, and the precipitates formed at the grain boundaries are of about 2–3.μm in width. After oil quenching followed by heat treatment at 1100.°C for more than 30.min, the precipitates inside grains are re.ned with a size of several hundred nanometers and the precipitates at the grain boundaries are re.ned with a size of <.1.μm. After compression test, transgranular and intergranular cracks occur in the as-cast alloys with coarse precipitates. For the quenched alloys with .ne precipitates, the number of cracks decreases signi.cantly, and no transgranular cracks happen because some cracks are blocked or the propagation direction is changed by grain boundary.
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  Effect of.laser shock peening on.combined low- and.high-cycle fatigue life of.casting and.forging turbine blades

  Cao .Chen · Xiao-yong .Zhang,,, · Xiao-jun . Yan ,,, · Jun Ren · Da-wei .Huang · Ming-jing .Qi

  . 2018, 25(1): 108-119.

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  Laser shock peening (LSP) is a novel e.ective surface treatment method.to improve the fatigue performance of turbine blades. To study the e.ect of LSP on combined low- and high-cycle fatigue (CCF) life of turbine blades, the CCF tests were conducted at elevated temperatures on two types of full-scale turbine blades, which were made of K403 by casting and GH4133B by forging. Probabilistic analysis was conducted to .nd out the e.ect of LSP on fatigue life of those two kinds of blades. The results indicated that LSP extended the CCF life of both casting blades and forging blades obviously, and the e.ect of LSP on casting blades was more evident; besides, a threshold vibration stress existed for both casting blades and forging blades, and the CCF life tended to be extended by LSP only when the vibration stress was below the threshold vibra-tion stress. Further study of fractography was also conducted, indicating that due to the presence of compressive residual stress and re.ned grains induced by LSP, the crack initiation sources in LSP blades were obviously less, and the life of LSP blades was also longer; since the compressive residual stress was released by plastic deformation, LSP had no e.ect or adverse e.ect on CCF life of blade when the vibration stress of blade was above the threshold vibration stress.
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  Corrosion behavior of.low alloy steel for.cargo oil tank under.upper deck conditions

  Hao Li · Feng .Chai · Cai-fu . Yang · Chao Li · Xiao-bing .Luo

  . 2018, 25(1): 120-128.

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  A simulated corrosion test apparatus was used to investigate the corrosion behavior of a low alloy steel under simulated upper deck conditions in a cargo oil tank. The estimated corrosion loss of conventional E36 class ship plate steel is 4.27.mm, which is clearly inadequate compared with the standard adopted by International Maritime Organization. Outer rust layer of specimens starts to peel o. after 77.days and becomes fragmented after 98.days. X-ray di.raction, scanning electron micros-copy, and Raman spectroscopy revealed that the resulting rust is composed of σ-FeOOH (the main protective phase), Fe2O3, FeS, elemental S, and FeSO4. FeSO4 in the interface of the base and rust layer leads to localized corrosion. Elemental sulfur forms on the surface of σ-FeOOH, and the quantity and size thereof increase with increasing corrosion time. Furthermore, layered elemental sulfur promotes fracture and peels o. the rust layer.