2017年, 第24卷, 第2期　刊出日期：2017-02-15

  

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  Development of Chinese duplex stainless steel in recent years

  Zhi-gang Song*,Han Feng,Shaomei Hu

  中国钢铁期刊网. 2017, 24(2): 121-130.

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  The development in research, production, applications, and national standards of Chinese duplex stainless steel (DSS) in recent years was introduced in light of the worldwide development in the field of DSS. The results showed that the output of Chinese DSS increased greatly, and at the same time its grade gradually evolved into a collaborative developing series including the main grade type 2205 and other DSS types in recent years. Economical DSS and super DSS underwent rapid development, especially after 2010. In recent years, the application of Chinese DSS has been expanded further not only in traditional application areas such as the petrochemical industry, but also in diverse new fields such as oil and gas transportation, chemical tanker manufacturing, nuclear power plants, and construction. Moreover, due to the increase in output and improvement in quality, as well as applications in Chinese projects, Chinese DSS has also been exported to the Middle East, Eastern Europe, and other regions.
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  Recovery of boron from high-boron iron concentrate using reduction roasting and magnetic separation

  Jian-wen Yu*,Yue-xin Han**,Peng Gao,Yan-jun Li

  中国钢铁期刊网. 2017, 24(2): 131-137.

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  The comprehensive utilization of abundant highboron iron concentrate is of particular significance to China, and the highboron iron concentrate has not yet been utilized as a source for boron at an industrial scale due to its complex mineralogy and fine mineral dissemination. An innovative method was proposed for recovery of boron and iron from highboron iron concentrate by reduction roasting and magnetic separation. The effects of reduction temperature and roasting time were investigated and their optimum conditions were determined. The mineralogical changes during roasting were characterized by Xray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the pyrrhotite (FeS) contained in the highboron iron concentrate and the newformed FeSFe solid solution softened or melted at high temperatures owing to their low melting points, and then decreased the metallic iron ratio and accelerated the growth of metallic iron particles. Meanwhile, the magnetite and szaibelyite were converted into metallic iron and suanite, respectively. Consequently, boron was readily enriched into the nonmagnetic product and the metallic iron was aggregated to the magnetic concentrate by magnetic separation. Boron recovery of 886% with corresponding B2O3 content of 145% and iron recovery of 951% with an iron grade of 927% were achieved when highboron iron concentrate was reduced at 1125°C for 150 min. Besides, the boron reactivity of the boronrich nonmagnetic product was up to 808%.
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  Characteristics of metal flow in cold extrusion under electric-hydraulic chattering

  Zhi-heng Wang, Wei-tao Zhan,Xiao-xiao Hong,Guan-jun Bao,Qing-hua Yang*

  中国钢铁期刊网. 2017, 24(2): 138-146.

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  An experimental setup for cold extrusion process with electrichydraulic chattering was developed and its working principle was introduced. The finite element (FE) model for a kind of cup part (material: 20Cr) was built by using the software Deform3D. FE simulation experiments with and without electrichydraulic chattering were carried out to analyze the velocity fields and the metal grid flow lines. The extrusion experiments of the cup part were also performed under different conditions. The difference of metal flow lines with and without electrichydraulic chattering was discussed via a scanning electron microscope (SEM) and the Keyence superdepth threedimensional microscopic system. The results showed that with the electrichydraulic chattering, the velocity of material flow increases, whereas deformation resistance decreases. Electrichydraulic chattering results in easy metal flow, small bending degree of metal flow lines, slender and dense metal grains, and thereby an improved quality of the deformed parts.
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  Iron recovery and rare earths enrichment from Bayan Obo tailings using Coal-Ca(OH)2-NaOH roasting followed by magnetic separation

  Qiang Zheng,Xue Bian,Wen-yuan Wu*

  中国钢铁期刊网. 2017, 24(2): 147-155.

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  The recovery of iron and enrichment of rare earths from Bayan Obo tailings were investigated using CoalCa(OH)2NaOH roasting followed by magnetic separation. The influences of roasting temperature, roasting time, coal content, milling time, Ca(OH)2 dosage and NaOH dosage on the iron and rare earths recovery were explored. The results showed that the magnetic concentrate containing 7001 wt% Fe with the iron recovery of 9434% and the tailings of magnetic separation containing 1146 wt% rare earth oxides (REO) with the REO recovery of 9819% were obtained under the optimum conditions (ie, roasting temperature of 650°C, roasting time of 60 min, coal content of 20%, milling time of 5 min, and NaOH dosage of 20%).The Ca(OH)2 dosage had no effect on the separation of iron and rare earths. According to the mineralogical and morphologic analysis, the iron and rare earths of Bayan Obo tailings could be utilized in subsequent ironmaking process and hydrometallurgy process.
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  Effects of embedding direct reduction followed by magnetic separation on recovering titanium and iron of beach titanomagnetite concentrate

  Chao Geng,Ti-chang Sun*,You-wen Ma,Cheng-yan Xu,Hui-fen Yang

  中国钢铁期刊网. 2017, 24(2): 156-164.

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  Embedding direct reduction followed by magnetic separation was conducted to fully recover iron and titanium separately from beach titanomagnetite (TTM). The influences of reduction conditions, such as molar ratio of C to Fe, reduction time, and reduction temperature, were studied. The results showed that the TTM concentrate was reduced to iron and irontitanium oxides, depending on the reduction time, and the reduction sequence at 1200°C was suggested as follows: Fe275Ti025O4→Fe2TiO4→FeTiO3→FeTi2O5. The reduction temperature played a considerable role in the reduction of TTM concentrates. Increasing temperature from 1100 to 1200°C was beneficial to recovering titanium and iron, whereas the results deteriorated as temperature increased further. The results of Xray diffraction and scanning electron microscopy analyses showed that low temperature (≤1100°C) was unfavorable for the gasification of reductant, resulting in insufficient reducing atmosphere in the reduction process. The molten phase was formed at high temperatures of 1250-1300°C, which accelerated the migration rate of metallic particles and suppressed the diffusion of reduction gas, resulting in poor reduction. The optimum conditions for reducing TTM concentrate are as follows: molar ratio of C to Fe of 168, reduction time of 150 min, and reduction temperature of 1200°C. Under these conditions, direct reduction iron powder, assaying 9028 mass% TFe and 173 mass% TiO2 with iron recovery of 9085%, and titanium concentrate, assaying 4624 mass% TiO2 with TiO2 recovery of 9115%, were obtained.
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  Optimization of magnetic separation process for iron recovery from steel slag

  Yuan-pei Lan,Qing-cai Liu,*,Fei Meng,De-liang Niu,Heng Zhao

  中国钢铁期刊网. 2017, 24(2): 165-170.

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  To improve the efficiency of iron recovery from steel slag and reduce the wearandtear on facilities, a new method was proposed by adding a secondary screen sizer to the magnetic separation process according to grain size distribution of magnetic iron (MFe) in the slag. The final recycling efficiency was evaluated by calculating the percentage of recycled MFe to the maximum amount of MFe that could be recovered. Three types of slags, namely basic oxygen furnace slag, desulfurization slag, and iron ladle slag, were studied, and the results showed that the optimized recovery efficiencies were 9320%, 9248%, and 8582% respectively, and the recycling efficiencies were improved by 958%, 711%, and 624% respectively. Furthermore, the abrasion between the mill equipment and the remaining slags was significantly reduced owing to the efficient recovery of larger MFe particles. In addition, the using amount of grinding balls was reduced by 046 kg when every 1 t steel slag was processed.
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  Phase-field simulation of tip splitting in dendritic growth of Fe-C alloy

  Yong-sheng Kang,Yu-chun Jin,Yu-hong Zhao*,Hua Hou,Li-wen Chen

  中国钢铁期刊网. 2017, 24(2): 171-176.

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  Two types of dendrite tip splitting including dendrite orientation transition and twinnedlike dendrites in FeC alloys were investigated by phasefield method. In equiaxed growth, the possible dendrite growth directions and the effect of supersaturation on tip splitting were discussed; the dendrite orientation transition was observed, and it was found that the orientation regions of anisotropy parameters were reduced from three to two with increasing the supersaturation, which was due to the effect of interfacial anisotropy controlled by the solute in front of S/L interface changing with the increase of supersaturation. In directional solidification, it was found that the twinnedlike dendrites were formed with the fixed anisotropy couples and no seaweed dendrites were observed; these were concluded from the results of competition between process anisotropy and inherent anisotropy. The formation process of twinnedlike dendrite was investigated by tip splitting phenomenon, which was related to the changes of dendrite tips growth velocity. Then, the critical speed of tips splitting and solute concentration of twinnedlike dendrites were investigated, and a new type of microsegregation in FeC alloys was proposed to supplement the dendrite growth theories.
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  Effects of Ni on austenite stability and fracture toughness in high Co-Ni secondary hardening steel

  Chen-chong Wang,Chi Zhang*,Zhi-gang Yang

  中国钢铁期刊网. 2017, 24(2): 177-183.

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  Three kinds of high CoNi secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by OlsonCohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr′s circle methods, respectively. Simulation and mechanical test results showed that the decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt%, the Ni content in γ phase would be lower than 20 wt%. And the simulation value of Mσs (stressinduced critical martensite transformation temperature) would be up to 80°C, which was about 60°C higher than room temperature. Based on the analysis, the Ni content in the overall composition of high CoNi secondary hardening steels should be higher than 8 wt% in order to obtain a good fracture toughness.
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  Tribological properties of FeCoCrNiAlBx high-entropy alloys coating prepared by laser cladding

  Dan-yang Lin,Nan-nan Zhang,*,Bin He,Guang-wei Zhang,,Yue Zhang,De-yuan Li

  中国钢铁期刊网. 2017, 24(2): 184-189.

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  FeCoCrNiAlBx (x=0, 025, 050, 075) coatings were prepared by laser cladding to study the effects of boron on the structure and properties of highentropy alloys coatings. The microstructure, microhardness, and wear resistance properties of the samples were investigated by scanning electron microscopy, Xray diffraction, metallographic microhardness test, and frictionwear test, respectively, and the mechanism of the wear behavior was also analyzed. The results showed that the highentropy alloys consisted of BCC phase and eutectic structure, which contained FCC phase and M2B. With boron addition, the content of BCC phase increased while that of eutectic structure decreased. The wear resistance of the highentropy coatings was considerably improved with increasing addition of boron, and accordingly, the FeCoCrNiAlB075 coating showed the best wear resistance.
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  Thermodynamic modeling of Fe-C-Mn-Si alloys

  Wei-sen Zheng,,Xiao-gang Lu,,*,Yan-lin He,,Lin Li,

  中国钢铁期刊网. 2017, 24(2): 190-197.

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  The thermodynamic database of the FeCMnSi system has been developed in the framework of the CALPHAD approach. The subternary systems have been carefully evaluated and revised based on available experimental data. A satisfactory description of the liquid phase in the FeCSi system has been obtained. The CMnSi system was assessed treating the liquid phase as a substitutional solution. Phase equilibria in the CMnSi system, especially those involving the liquid phase, can be well described. Based on the extrapolation of the experimental data in the quaternary system, the FeMnSi system has been modified to agree well with experimental data at high temperatures. The comparison between the calculated and measured phase transformation temperatures confirms the reliability of the present quaternary database. Additionally, the solidification process of Fe016C15Mn15Si (wt%) alloy was simulated by using the thermodynamic database developed.
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  Hydrogen storage thermodynamic and kinetic characteristics of PrMg12-type alloys synthesized by mechanical milling

  Jin-liang Gao,*,Yan Qi,Ya-qin Li,Hong-wei Shang,Dong-liang Zhao,Yang-huan Zhang

  中国钢铁期刊网. 2017, 24(2): 198-205.

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  To improve the hydrogen storage performance of PrMg12type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMg11Ni+x wt% Ni (x=100, 200) alloys were prepared via mechanical milling. The phase structures and morphology of the experimental alloys were investigated by Xray diffraction and transmission electron microscopy. The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amorphous structure. The gaseous hydrogen storage properties of the experimental alloys were determined by differential scanning calorimetry (DSC) and Sievert apparatus. In addition, increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5572 wt% for the x=100 alloy and 5829 wt% for the x=200 alloy, respectively. The enthalpy change (ΔH), entropy change (ΔS) and the dehydrogenation activation energy (Edek) markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.
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  Comparison of microstructure and property of high chromium bearing steel with and without nitrogen addition

  Hai-feng Xu,,*,Feng Yu,Chang Wang,Wan-li Zhang,Jian Li,Wen-quan Cao

  中国钢铁期刊网. 2017, 24(2): 206-213.

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  Microstructure and property of bearing steel with and without nitrogen addition were investigated by microstructural observation and hardness measurement after different heat treatment processing. Based on the microstructural observation of both 9Cr18 steel and X90N steel, it was found that nitrogen addition could effectively reduce the amount and size of coarse carbides and also refine the original austenite grain size. Due to addition of nitrogen, more austenite phase was found in X90N steel than in 9Cr18 steel. The retained austenite of X90N steel after quenching at 1050°C could be reduced from about 60% to about 7% by cold treatment at -73°C and subsequent tempering, and thus finally increased the hardness up to 60 HRC after low temperature tempering and to 63 HRC after high temperature tempering. Furthermore, both the wear and corrosion resistance of X90N steel were found much more superior than those of 9Cr18 steel, which was attributed to the addition of nitrogen. It was proposed at last that nitrogen alloying into the high chromium bearing steel was a promising way not only to refine the size of both carbides and austenite, but also to achieve high hardness, high wear property and improved corrosion resistance of the stainless bearing steel.
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  Mechanical and fatigue properties of selfpiercing riveted joints in high-strength steel and aluminium alloy

  Chun-yu Zhang,Rui-bin Gou,Min Yu,*,Ya-jing Zhang,Yin-hu Qiao,Shu-ping Fang

  中国钢铁期刊网. 2017, 24(2): 214-221.

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  Static tensile and fatigue tests were performed on shear and tensile selfpiercing riveted aluminiumsteel structures to evaluate their mechanical and fatigue properties. The influences of the thickness and the strength of the highstrength steel on mechanical and fatigue performances were investigated based on the tensile and FN curves of the joints. The results show that mechanical and fatigue properties of the shear selfpiercing riveted joints are much better than those of the tensile selfpiercing riveted joints. Mechanical and fatigue performances of the two joints were significantly influenced by the thickness and strength of the steel sheet, and were markedly improved when the thickness of steel sheet increased. The steel strength showed significantly different effects on shear and tensile riveted structures, ie, when the steel strength increased, the strength of the shear structure greatly increased while the tensile structure just had a slight increase in the strength. Fatigue failure generally occurred in the sheet materials and the fatigue crack location changed with increasing the sheet thickness and the sheet strength.
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  Static recrystallization behavior of 25CrMo4 mirror plate steel during two-pass hot deformation

  Peng Zhou,,Qing-xian Ma,,*

  中国钢铁期刊网. 2017, 24(2): 222-228.

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  The static recrystallization behavior of 25CrMo4 mirror plate steel has been determined by hot compression testing on a Gleeble 1500 thermal mechanical simulation tester. Compression tests were performed using double hit schedules at temperatures of 950-1150°C, strain rates of 001-05 s-1, and recrystallization time of 1-100 s. Results show that the kinetics of static recrystallization and the microstructural evolution were greatly influenced by the deformation parameters (deformation temperature, strain rate and prestrain) and the initial austenite grain size. Based on the experimental results, the kinetics model of static recrystallization has been generated and the comparison between the experimental results and the predicted results has been carried out. It is shown that the predicted results were in good agreement with the experimental results.
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  New bainite kinetics of high strength low alloy steel in fast cooling process

  Xuan-wei Lei,Ji-hua Huang*,Shu-hai Chen,Xing-ke Zhao

  中国钢铁期刊网. 2017, 24(2): 229-233.

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  Based on KolmgorovJohnsonMehlAvrami analysis, a new bainite kinetics of high strength low alloy steel in fast cooling process was developed by utilizing different experimental methods. Upper bainite transformation morphological evolutions at a cooling rate of 83 K/s were directly observed by laser scanning confocal microscopy. This qualitative analysis suggests that bainite packet is more suitable to give a onedimensional growth model if it is considered as a transformation unit. The nucleation rate of bainite packets in fast cooling process is assumed to give an a priori item. Onedimensional growth model with constant growth rate which is assumed as a function of cooling rate is adopted as well. Thus, the developed new bainite kinetics is simple in expression and contains an adjustable parameter and an empirical parameter. Experimental results show upper bainite and lower bainite transformations in fast cooling processes. Their referential phase volume fractions are calculated by the expanded lever rule on the first derivative dilatometer curves. For the similar transformation mechanisms, upper bainite and lower bainite are considered to give the same kinetics. With considering the Nakamura′s equation, the bainite kinetics is fitted with experimental data. Results show that bainite volume fractions and bainite transformation rates can be expressed precisely by the newly developed bainite kinetics.