2021 Vol. 42, No. 5

Technical Review
Global vanadium industry development report 2020
Wu You, Chen Donghui, Liu Wuhan, Sun Zhaohui, Zhang Bangxu
2021, 42(5): 1-9. doi: 10.7513/j.issn.1004-7638.2021.05.001
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The overall situation of the global vanadium industry was elaborated and analyzed from the global vanadium resources and the production capacity, the output, supply and demand, import and export, as well as the market prices of vanadium pentoxide, ammonium metavanadate, ferrovanadium and vanadium-nitrogen (VN) alloys in 2020. The major events in the global vanadium battery field are also introduced. Based on the current operating situation of the vanadium industry at home and abroad, the outlook for the market is forecasted, and it is believed that the global vanadium expansion situation will not be greatly changed in the short term, and the oversupply will bring about the price fluctuation of vanadium products in the specific range. The Chinese market under the background of “efforts to achieve carbon peak and neutrality goals” is still the main focus for global vanadium demand, and VN alloys will also be the trend of vanadium products in the near and mid-term. Collaborative innovation between vanadium enterprises will promote the vanadium industry to gradually show a positive “competition and cooperation” situation.

Separating and Extracting of Vanadium and Titanium
Study on the regulation mechanism of valuable elements in the reduction process of vanadium-titanium magnetite marine placer
Hu Peiwei, Hu Chao, Hu Bing, Xie Zhicheng, Zheng Fuqiang, Liu Chen
2021, 42(5): 10-17. doi: 10.7513/j.issn.1004-7638.2021.05.002
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In this paper, a marine placer from Indonesia is used as the testing material. Its chemical composition and mineral composition were analyzed by XRD, and the reduction characteristics and the regulation mechanism of the valuable elements of the ore are discussed on the basis of thermodynamics. The reduction and grinding experiments of marine placer were carried out by microwave heating with biochar as the reducing agent for direct reduction. Microwave heating is beneficial to strengthen the reduction process of marine placer. The results show that the reduction product with 98.28% metallization rate can be obtained with the C/Fe ratio of 0.6 and the reduction temperature of 1 200 ℃ for 150 min. Under the conditions of 50% pulp concentration, 40 min grinding time and 0.08 T magnetic field intensity, the refined powder with iron grade of 85.1% and iron recovery of 94.01%, tailings powder with TiO2 grade of 28.95% and recovery of 71.98%, V2O5 grade of 2.14% and recovery of 56.82% can be obtained. The separation and enrichment of iron and vanadium-titanium are effectively realized.
Effects of phase structure of vanadium slags with different calcium content on calcified vanadium extraction
Yu Tangxia, Wen Jing, Sun Hongyan, Li Fangfang, Jiang Tao
2021, 42(5): 18-23. doi: 10.7513/j.issn.1004-7638.2021.05.003
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In this paper, the vanadium slags with different calcium contents were obtained by remelting and crystallizing the mixture of CaO and Xichang vanadium slag with low-CaO contents. The changes of phase and micromorphology of vanadium slags with different calcium contents were observed by XRD and SEM-EDS. Furthermore, the law of phase changing of roasted samples and the impact on vanadium leaching rate were explored. The results showed that as the CaO mass fraction in vanadium slags rose, the spinel size gradually increased, and the olivine phase Fe2SiO4 gradually changed to Ca2SiO4. When the CaO content rose to 9.7%, part of Ti began to transfer from spinel to CaTiO3. When the CaO content further rose to 13.7%, the spinel shape became irregular, and the silicate was gradually complicated. V was produced as Ca2V2O7 for low-calcium contents in vanadium slags after calcification roasting. As the calcium content rose to 3.7%, Ca3V2O8 gradually generated. The highest vanadium leaching rate was 87.52% when the calcium content was 2.7%. As calcium content increased further, the vanadium leaching rate decreased slightly. The calcium contents in vanadium slags would influence the amount of calcium salt additives during the calcium roasting process and the vanadium leaching rate at this point.
Experimental study on vanadium extraction from alkaline vanadium-containing powder
Wu Zhenxiu
2021, 42(5): 30-33. doi: 10.7513/j.issn.1004-7638.2021.05.005
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In this study, the alkaline powder is mainly sodium sulfate, containing 3.4% V2O5, which can not be dissolved in acid or alkali. If vanadium is directly roasted and then extracted, vanadium and a large amount of sodium sulfate will enter the solution and form a low vanadium solution with low vanadium and high sodium, and the subsequent recovery of vanadium from the solution is more difficult. With the alkaline low vanadium powder used as the raw material for extracting vanadium, 87.94% vanadium can be separated into the filter residue after water dissolution and filtration, and the filter residue contains V2O5 34%. Exploratory tests on vanadium extraction from vanadium-rich filter residue by direct acid dissolution, alkali dissolution and sodium roasting were carried out. The sodium roasting-water leaching process was selected for vanadium extraction technology research on the filter residue. The experimental results showed that the extraction rate of vanadium could reach 97.96% and the total yield of vanadium could reach 86.15%, according to the dry weight of 100 g with 30 g sodium carbonate, calcination at 780 ℃ for 90 min and water leaching of the roasted residue. The study of this technology provides a new approach for extracting vanadium from this kind of alkaline low vanadium powder.
Research progress on comprehensive recovery of chromium in vanadium bearing mother liquor
Song Yue, Wu Guixuan, Ying Ziwen, Wei Qifeng, Ren Xiulian
2021, 42(5): 34-41. doi: 10.7513/j.issn.1004-7638.
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This paper introduces five common recovery methods including chemical precipitation, ion exchange, adsorption, electrolysis and solvent extraction, expounds their process routes and basic principles, and analyzes and summarizes their advantages and disadvantages. According to the characteristics of vanadium precipitation mother liquor, it is pointed out that enterprises should reasonably select the corresponding recovery methods under different needs. Through comprehensive comparison, it is considered that the solvent extraction method with the advantages of strong selectivity, low energy consumption, easy regeneration of extractant and high degree of mechanization has better application prospects, and it is worth investing more energy to develop new extractants.
Effects of Ti element on phase stability of σ(FeV)
Xie Yi, Xian Yong, Feng Long
2021, 42(5): 42-46. doi: 10.7513/j.issn.1004-7638.2021.05.007
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In order to study the effect of large-size transition-metal element Ti on σ(FeV). FeV alloys with different Ti contents were prepared by arc melting, and phase identification and microhardness testing were conducted. The results show that with the increase of Ti concentration from 5% to 15%, the phase of the alloy gradually changes from complex structure σ(FeV) into simple bcc phase α(FeV). It shows that microhardness increases first and then decreases due to the solid solution strengthening of Ti atoms and subsequent σα phase transition. The introduction of Ti reduces the phase stability of σ(FeV), and inhibits the formation of σ(FeV) phase. With the increase of Ti content, Ti decreases the dominating d-d electron covalent bonding in σ phase and promotes the formation of coordination polyhedron with coordination number of 16, which does not meet the geometric requirements for the formation of σ phase.
Application of Vanadium and Titanium
Preparation and properties of Ti4AlN3 by powder metallurgy
Guo Hui, Li Xikun, Song Yuanyuan, Sun Qian, Huang Yiwen
2021, 42(5): 47-53. doi: 10.7513/j.issn.1004-7638.2021.05.008
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The ternary layered cermet of Ti4AlN3 was prepared by powder metallurgy. The effects of raw powder, sintering temperature and holding time on the purity of Ti4AlN3 ceramic were studied. The samples were qualitatively analyzed by X-ray diffraction (XRD) and quantitatively analyzed by TOPAS based on Rietveld method. The microstructure and micro area composition of Ti4AlN3 were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results show that high purity Ti4AlN3 bulk can be prepared from Ti, Al and TiN powders. With the holding time of 2 h and the sintering temperature of 1 400 ℃, high purity Ti4AlN3 can be obtained (wTi4AlN3=98.03%). Compared with other Max phases, the hardness of Ti4AlN3 is lower. With the increase of load, the hardness of Ti4AlN3 is close to 2.8 GPa.
Microstructure and high temperature tensile properties of (TiC+TiB) reinforced titanium matrix composites by vacuum induction suspension melting
Wang Zhenling, Yu Yucheng, Li Ruizhi, Li Qiang, Han Jiaping, Ma Lan
2021, 42(5): 54-61. doi: 10.7513/j.issn.1004-7638.2021.05.009
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(TiC+TiB)/Ti-6Al-4Sn-8Zr-0.8Mo-1.5Nb-1W-0.25Si titanium matrix composites were prepared by vacuum induction suspension melting, with the reinforcement composition volume ratio respectively at 0%, 2% and 4%. The microstructure and high temperature tensile properties of the composites were investigated by metallographic microscope, SEM, XRD, TEM and high temperature tensile testing machine. The results show that the titanium alloy is mainly composed of α-Ti phase and Ti2ZrAl phase, and the Ti2ZrAl phase is distributed at the junction of α-Ti flakes. In addition, there also exist polygonal bulk TiC and long TiB whiskers. The microstructure of the titanium alloy is typical widmandgren structure, and the α-Ti phase presents long needlelike shape with nearly parallel arrangement in the β-Ti grains. In titanium matrix composites, with the increase of reinforcement composition, the length to diameter ratio of α-Ti significantly decreases, and the grain size of β-Ti is refined. The strength of titanium matrix composites is increased significantly at 650~700 ℃. The best strengthening effect appears at 650 ℃ for the composites with 2% reinforcement composition while at 700 ℃ for the composites with 4% reinforcement composition. When the temperature exceeds 700 ℃, the strengthening effect of the reinforcement composition is weakened. The plasticity of the composites is generally low. The strengthening mechanism of the titanium matrix composites are attributed to the grain refinement, solid solution strengthening and load transfer strengthening. The fracture mode of the titanium matrix composites is brittle fracture under high temperature tensile conditions.
Research on numerical simulation method for dynamic tensile performance of laser tailor-welded joints of different thickness
Zheng Bangzhi, Tian Xiaolin, Wang Zelong, Tang Xinxin
2021, 42(5): 62-68. doi: 10.7513/j.issn.1004-7638.2021.05.010
Abstract(3427) HTML (22) PDF(47)
The laser tailored welding process of HC340LA and HC260LA low-alloy high-strength steels with different thicknesses was studied, and the welded joints were tested and analyzed by X-ray flaw detection, static tensile, metallographic structure and microhardness. The results show that the low-alloy high-strength steel with different thickness can get well-formed welds through the laser tailor welding process, and the weld structure is mainly columnar martensite. After flaw detection, the welds showed no obvious defects such as pores and slag inclusions. The fracture position of the tensile specimen was on the side of the base material of the thin blank, and the hardness of the weld fusion zone was significantly higher than that of the base material. For laser tailor-welded joints, dynamic tensile test and numerical simulation analysis are carried out, and the difference between common node model and test, regional effect and thickness effect on stress and strain are studied. The research shows that the strain values of the dynamic tensile simulation using the common node numerical model are much higher than those measured in the experiment. The area of the base metal associated with the weld can directly affect the distribution of stress and strain, the strain can be regulated by the regional effect, and the stress can be regulated by the thickness effect.
Effect of crystallographic orientation on globularization during the rolling of a near α titanium alloy tube
Zhu Wensha, Pan Mingyan
2021, 42(5): 69-73, 98. doi: 10.7513/j.issn.1004-7638.2021.05.011
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The dynamic globularization of a near α titanium alloy tube during hot rolling was studied by observation of different regions of the pipe using metallographic analysis and electron backscatter diffraction (EBSD) technology. The results showed that the fraction of globularized α phases near the outer surface of the tube was very high. After globularization, the large-angle grain boundaries increased and the small-angle grain boundaries decreased. The globularization of the α phases in the middle part was greatly affected by the crystal orientation. The Schmidt factor of α phase in different crystallographic orientations is calculated. It was found that the α phases were more prone to be globularized when the basal slips and prism slips have a larger Schmidt factor (> 0.3) in the rolling direction (RD) and transverse direction (TD), respectively. The globularization would be difficult when the α phase has only one slip system and the Schmidt factor was high only in one direction.
Application of sub-micron α phase alumina powder in PE membrane coating of lithium ion battery
Luo Jinhua, Zhao Neng
2021, 42(5): 74-78. doi: 10.7513/j.issn.1004-7638.2021.05.012
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In this paper, sub-micron α-alμmina powders were prepared by physical mechanical milling of α-alumina powder with D50 = 1.08 μm, and then applied to lithium-ion battery separator coating modification. The sub-micron α-alumina powder was applied to the PE membrane coating of lithium-ion battery. The results show that the coating is compact and flat, and the alumina particles are evenly distributed on the surface of PE film. The thickness of the film is 2.5 μm. After the coating, the density increases by 4.0 g/m2, the air permeability increases by 48.2 s, the thermal shrinkage decreases by 1.3% and 0.3%, and the tensile strength increases by 26.4 MPa and 3 MPa, respectively.
Effects of vanadium on microstructure and properties of high strength automobile steel
Yang Yaqin, Sun Xianchao
2021, 42(5): 79-83. doi: 10.7513/j.issn.1004-7638.2021.05.013
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The microstructure, wear resistance and tensile properties of high-strength steel were tested and analyzed by adding different content of vanadium in high-strength automobile steel. The results show that the addition of vanadium is beneficial to refine the internal structure of the steel and improve the wear resistance and tensile properties of the high-trength steel. With the increase of vanadium content from 0 to 0.24%, the wear volume of the high-strength steel first decreases and then increases, the tensile strength and yield strength increase gradually, the elongation after fracture increases first and then decreases, and the wear resistance and tensile property of the high-strength steel first increase and then decrease. Compared with that without vanadium, the wear volume of the high-strength steel with 0.16% vanadium decreases by 29.6%, while the tensile strength, yield strength and elongation after fracture increase by 14.4%, 20.9% and 12.8% respectively.
Physical Testing and Chemical Analysis
Application of laser induced fluorescence technology in mixing effect analysis of oxidation furnace at titanium dioxide via chloride process
Sun Hongtao, Ni Xiaomin, Wang Yue, Xie Weiqing, Yang Guoqiang
2021, 42(5): 84-91. doi: 10.7513/j.issn.1004-7638.2021.05.014
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Titanium dioxide (TiO2) through chloride process is the mainstream production technology of titanium dioxide industry in the world nowadays, and the structure design of oxidation reactor is a key technology for the production of titanium dioxide by chlorination. The mixture of TiCl4 and O2 plays a decisive role in the properties of TiO2, such as particle size, distribution and crystal shape, and then affects the quality of the product. Therefore, it is of great significance to monitor the mixing effect of two kinds of material airflow under different working conditions for the design of oxidation reactor and the optimization of practical operation parameters. However, the existing research shows that the traditional measurement technology is difficult to adapt to the characteristics of high speed and instability of complex flow field, so the modern diagnosis technology with high precision is urgently needed. Herein, using the undisturbed non-contact laser induced fluorescence (LIF) the gas concentration distribution in different location of the reactor was measured by simulation under different working condition. The mixing effect and its variation law of the two gases in different oxidation furnace structure and different materials were studied, and the key factors influencing the mixing effect were found out. This study provides necessary reference for the structure design of the oxidation furnace and the control of the operation process conditions, as well as important experimental parameters for the relevant theoretical model and numerical simulation. It shows important scientific and practical significance to promote the development of TiO2 production process in China.
Study on analytical method of V, Cr and Si in the process of extracting V from vanadium slag by sub-molten salt
Zhang Wei, Wang Baohua, Liu Chao, Liu Liying, Lv Hui, Zhu Jianyan
2021, 42(5): 92-98. doi: 10.7513/j.issn.1004-7638.2021.05.015
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The analysis method of vanadium, chromium and silicon in the process of vanadium extraction from vanadium slag by sub-molten salt was studied. The content of vanadium and chromium was determined by ammonium persulfate oxidation and ammonium ferrous sulfate titration. At 15%~20% sulfuric acid acidity, ammonium persulfate oxidizes vanadium to a pentavalent state, while Cr(VI) is reduced to Cr(III) to eliminate chromium interference and determine the amount of vanadium. In 4%~6% sulfuric acid acidity, add silver salt and ammonium persulfate at the same time for oxidization of vanadium and chromium, in order to determine the amount of vanadium and chromium, and the amount of chromium is calculated by difference subtractive method. The concentration of silicon in the crystallization solution was determined by silicon molybdenum blue photometric method. Add sodium sulfite to reduce vanadium and chromium and eliminate the interference of vanadium and chromium. With phenolphthalein as indicator, sulfuric acid was added to adjust the acidity of silicon molybdenum yellow to 0.3 mol/L. The absorbance of the color solution was determined at the wavelength of 660 nm, and the working curve was drawn to calculate the silicon concentration. At the same time, the method precision and standard addition recovery tests were carried out, and the results were satisfactory.
Resources Environment and Energy Saving
Current situation of resource utilization of waste acid from titanium dioxide production
Gao Guangyan, Gao Likun, Rao Bing, Wang Feiwang, Shen Hairong
2021, 42(5): 99-108. doi: 10.7513/j.issn.1004-7638.2021.05.016
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Waste acid after processing titanium dioxide contains valuable resources. The reprocessing and value-added of waste acid is gradually becoming the focus of titanium pigment industry. In this paper, the current situation of recovery and utilization of waste acid from titanium dioxide have been reviewed, mainly focusing on the application of waste acid in extracting metal elements, leaching metal elements, recovering sulfuric acid and industrial production. And then the future development of resource utilization of waste acid from titanium dioxide have been discussed.
Influence of temperature on dephosphorization of recycling converter gasification dephosphorization slag
Tong Shuai, Li Chenxiao, Wang Shuhuan, Xue Yuekai, Guo Ruihua, Zhou Chaogang, Sun Huakang
2021, 42(5): 109-114. doi: 10.7513/j.issn.1004-7638.2021.05.017
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In this paper theoretical analysis and experimental verification are combined in order to study the dephosphorization ability of the converter gasification dephosphorization slag when it is recycled and reused. Gasification dephosphorization slag had been prepared by using coke powder to reduce converter slag. The influence of different reduction temperatures on the phosphorus capacity and phosphorus distribution ratio of gasification dephosphorization slag has been theoretically analyzed. According to theoretical analysis, with the increase of reduction temperature, the phosphorus capacity and phosphorus distribution ratio of the slag after reduction both increase. In the laboratory, gasification dephosphorization slag is used to conduct hot metal dephosphorization experiments, and a single temperature variable is set to study the dephosphorization effect of gasification dephosphorization slag when it is reused. The results show that converter gasification dephosphorization slag has new dephosphorization, significant dephosphorization effect during the early stage of the reaction. With the increase of temperature, the dephosphorization capacity of gasified dephosphorization slag decreases, and the dephosphorization speed becomes slower, which is in agreement with thermodynamics law.
Analysis of causes of blockage of waste acid concentration heat exchanger in sulfuric acid process titanium dioxide
Wang Haibo, Wang Kui, Sun Ke, Ma Weiping
2021, 42(5): 115-119, 125. doi: 10.7513/j.issn.1004-7638.2021.05.018
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The blockage of the waste acid heat exchanger of sulfuric acid process titanium dioxide had been investigated through chemical composition analysis and XRD analysis, and caused by a mixture of calcium sulfate, ferrous sulfate monohydrate and meta-titanic acid. These mixture is derived from calcium sulfate, ferrous sulfate and titanyl sulfate in 20% waste acids. The influence of waste acid temperature and concentration on the concentration of calcium sulfate, ferrous sulfate and titanyl sulfate was studied in the laboratory. The results showed that when the waste acid temperature was 107 ℃ and the waste acid concentration increased from 18.41% to 49.93%, the concentration of calcium sulfate, ferrous sulfate and titanyl sulfate decreased from 1.26 g/L, 126.29 g/L and 10.76 g/L to 0.19 g/L, 13.23 g/L and 0.16 g/L, respectively. The concentration changing rule and data of calcium sulfate, ferrous sulfate and titanium oxysulfate in concentrated waste acid at all levels are basically consistent with those of laboratory research. The research results provide important data and theoretical support for the solution of heat exchanger blockage.
Test on the hot utilization of stainless steel refining slag in EAF
Zhao Haiquan
2021, 42(5): 120-125. doi: 10.7513/j.issn.1004-7638.2021.05.019
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Based on the analysis on hot utilization of stainless steel refining slag, considering the characteristics of electric furnace which it is primary steelmaking process and using electric power, a test on hot pouring residual utilization in electric furnace had been carried out. It is found out that hot pouring residual utilization in electric furnace can not only promote the rapid formation of high basicity slag and improve desulfurization efficiency, but also recycle waste heat and reduce power consumption. After hot utilization, the consumption of lime is reduced by 3 kg/t and lightly burned dolomite by 1.2 kg/t and fluorite by 1.8 kg/t as well, meanwhile electricity consumption is reduced by 5~10 kWh. Electric furnace conditions is improved significantly, where oxidation loss of molten steel is reduced, the consumption of ferrosilicon is reduced by 1.5~2 kg/t and smelting time is shortened by 3~5 minutes per heat. From the aspects of utilization of steel slag, energy conservation and emissions reduction, this research results can be helpful for the development of refining slag utilization.
Ferrous Metallurgy and Materials
FEM analysis and experimental study of microwave assisted separation of vanadium-titanomagnetite
Zhou Yufeng, Qian Gongming, Cheng Xiangyu
2021, 42(5): 126-131. doi: 10.7513/j.issn.1004-7638.2021.05.020
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Taking vanadium-titanomagnetite (VTM) from Panxi zone as the investigation object, the feasibility of microwave selective separation of VTM was analyzed theoretically through finite element simulation, and the effects of microwave power and treatment time on its dissociation were investigated. The influence of microwave treatment on the separation characteristics of VTM were studied by using scanning electron microscope (SEM), X-ray diffraction (XRD), BET specific surface area detection method (BET), particle size analysis and other methods. The results showed that the ore can be rapidly heated up to 600 ℃ under the condition of microwave power of 3 kW and treatment time of 40 s. After microwave treatment, many obvious cracks appeared in the ore, and the specific surface area and pore volume of VTM increased by 46.04% and 83.45%, respectively. The fractions of product with size of −0.160 mm and −0.074 mm in the grinding products increased by 21.47% and 16.68%, respectively, while the Bond grinding work index decreased by 8.13%. The magnetite separation test shows that the iron grade and recovery of concentrate can be increased by 2.34% and 1.13% respectively after microwave treatment. It is demonstrated that microwave treatment is positive to the selective separation of VTM and improve the separation effect.
Experimental study on decarbonization of Fe -C-Mn thin strips in Ar-H2O-H2 atmosphere
Meng Fanjun, Ai Liqun, Hong Lukuo, Zhou Yuqing, Zhou Meijie, Liu Xinliang
2021, 42(5): 132-137. doi: 10.7513/j.issn.1004-7638.2021.05.021
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In order to study the influence of Mn content and decarburization temperature on decarburization effect of ferromanganese carbon alloy thin strip in Ar-H2O-H2 atmosphere, the ferromanganese carbon alloy thin strip in 1mm thickness with initial carbon content of 3.90% and manganese content of 0, 0.30% and 0.49% was used to conduct decarburization experiment in the weak oxidizing atmosphere of Ar-H2O-H2. XRD analysis was done on the surface of thin strip after decarburization under different atmosphere conditions. It is indicated that the decarbonization atmosphere PH2O/PH2 should not exceed 0.53. Decarburization was carried out at 1 293, 1 353 and 1 413 K for 5, 10, 20 and 30 min, respectively. The results show that the amount of decarburization increases obviously with increasing Mn content. The increase of decarburization temperature significantly increases average decarburization amount of thin strip.
Numerical simulation on interfacial behavior and mixing phenomena in three-phase argon-stirred ladles
Yang Yadi, Zhao Jing, Cui Jianzheng
2021, 42(5): 138-148. doi: 10.7513/j.issn.1004-7638.2021.05.022
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A three-phase flow mathematical model of argon/liquid steel/slag for a 180 ton ladle was established by using the multi-phase flow volume method according to design parameters of ladle. The interface behavior and mixing phenomena of three-phase flow in the process of bottom blowing argon in the ladle were simulated by CFD software Fluent. Based on the theory of hydrodynamics, the effects of arrangement of double permeable bricks and flow rate of bottom argon blowing on the velocity field, behavior of steel-slag interface and mixing time in ladle were calculated and analyzed. The results show that in the process of bottom argon blowing, the arrangement of double permeable bricks has a great influence on flow field in ladle, and the flow rate of bottom argon blowing has a great influence on behavior of steel slag interface and mixing time. When the angle between two permeable bricks is 135°, the distance from ladle bottom center is 0.6R, and argon flow rate is 600 L/min, flow field distribution in the ladle is better, which is beneficial to improve stirring efficiency of molten steel.
Review of continue casting slab electromagnetic stirring technology
Yang Bao, Zhang Hui, Wang Minglin, Wang Xuebin, Liu Bin, Liu Shuai
2021, 42(5): 149-157. doi: 10.7513/j.issn.1004-7638.2021.05.023
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The development process and existing problems of electromagnetic stirring technology for continuous casting slabs were briefly described, focusing on the working principle and technical characteristics of electromagnetic stirring in the mold and the secondary cold zone during the production of continuous casting slabs. The installation position of the electromagnetic stirrer and the research status of electromagnetic stirring in the slab mold as well as electromagnetic stirring in the secondary cold zone were summarized. The factors affecting the electromagnetic stirring effect of slab and their primary and secondary relationships were discussed, and the electromagnetic stirring support roll used in the secondary cold zone was summarized. The role of slab electromagnetic stirring technology and the direction to be further explored were analyzed. The influence of slab electromagnetic stirring technology on the element distribution and equiaxed grain gap ratio in the cast slab was analyzed.
Effect of annealing temperature on microstructure and mechanical properties of vanadium microalloyed 780 MPa cold rolled dual phase steel
Yu Cansheng, Zhang Longchao, Zheng Zhiwang, Gong Hui, Zhang Dafu
2021, 42(5): 158-163. doi: 10.7513/j.issn.1004-7638.2021.05.024
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The vanadium microalloyed tested steel was heated to 780 ℃, 800 ℃, 820 ℃ and 840 ℃, respectively and then held for a few minutes, followed by different cooling modes such as slow cooling, rapid cooling, simulated galvanizing, and air cooling to room temperature. Microstructure observation by SEM shows that microstructure uniformity is poor during annealing at 780 ℃ and undissolved carbides are found, leading to a weak combination of strength and plasticity. With the increase of annealing temperature, the size and fraction of ferrite gradually decrease, the volume fraction of mid-low temperature transformation products gradually increases and its size becomes coarser. When the annealing temperature was 800 ℃, the fraction of martensite reaches the maximum. When the annealing temperature further increases, the fraction of martensite decreases, while the fraction of bainite increases, resulting in a relatively stable tensile strength when annealing temperature of 800 ~840 ℃ range, however, the elongation firstly increases and then decreases. When the annealing temperature was 820 ℃, the steel strip obtains better mechanical properties. The yield strength, tensile strength, yield ratio, elongation after fracture A80 and hole expansion rate are 486 MPa, 835 MPa, 0.58, 16.0% and 27%, respectively.
Transformation of the spine in Mg-treated non-quenched and tempered steel
Li Zhiwei, Zeng Zhiqi, Xie Jianbo, Tian Qianren, Fu Jianxun
2021, 42(5): 164-169. doi: 10.7513/j.issn.1004-7638.2021.05.025
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Based on the characteristics and formation of the Mg-treated inclusions in non-quenched and tempered steel, the misfit degrees of MgAl2O4+MnS was calculated to reveal the best growth surface and main action forces between the MgAl2O4 inclusions. For Mg free steel, the sulfide in slab edge mainly precipitate in chain shape along grain boundary, while the sulfide in center slab is mainly in rod or angle shape. When Mg is added to the steel, the inclusions at the edge and center of slab are mainly spherical or chain like, and their size are small. The average area of inclusions in center area is reduced from 14.33 μm2 to 8.78 μm2, while in the edge area it is reduced from 3.17 μm2 to 2.99 μm2. Mg addition reduces the equivalent area of inclusions in the steel. The misfit degree between crystal face (110) of MnS and (110) of MgAl2O4 was 7.65%. The main acting force for the attachment of MgAl2O4 was cavity-bridge force of 1×10−8 N.
Study on the microstructure of superalloy GH4065A solidified under high pressure
Li Jing, Shui Lang, Zhou Yang, Zhang Shucai
2021, 42(5): 170-174. doi: 10.7513/j.issn.1004-7638.2021.05.026
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OM and SEM were used to observe the microstructure of GH4065A under two solidification modes: normal pressure and pressure (under 2 MPa) to analyze the effect of high pressure on the structure. The results show that the as-cast GH4065A structure under normal pressure has a large number of loose shrinkage cavities, the main precipitated phase in the microstructure is γ' phase, and the most severely segregated element is Nb. Solidification at 2 MPa can eliminate a large number of loose shrinkage cavities, increase the density of castings, and greatly reduce the residual segregation index of Nb element. At the same time, the pressure solidification can make the secondary dendrite spacing of alloy GH4065A lower than that of the normal pressure ingot. This is because the pressure increases the phase transition temperature, thereby increasing the phase transition driving force of the melt and refining the crystal grains. These results demonstrate that the great advantages and application prospects of pressurized solidification in superalloys, and it can be extended to other superalloy grades in order to exert the important value of pressurized solidification.
Thermodynamic control of pearlite lamellar sheet spacing and its effect on mechanical properties of steel
Mo Wenfeng
2021, 42(5): 175-179. doi: 10.7513/j.issn.1004-7638.2021.05.027
Abstract(179) HTML (8) PDF(22)
A pearlite steel was prepared via laboratory steelmaking, and then after rolling and heat treatment to obtain two different samples with different pearlite lamellar spacing. The mechanical properties and microstructures of the materials were observed by scanning electron microscopy and universal testing machine. Results show that the reciprocal Sp−1(μm−1) of pearlite lamellae and transformation super cooling degree of pearlite ∆T(℃) satisfy the linear relationship of Sp−1=9.0201+0.03358∆T. This indicates that the theoretical minimum pearlite lamellae spacing(~61 nm) can be obtained by isothermal treatment at 550 ℃. With the thinning of the spacing between the very fine pearlite lamellar( from 105 to 72 nm), the strength increases but ductility will deteriorate significantly, and the ultimate deformation strain will decrease from 0.18 to 0.12. This result conflicts with the traditional grain refinement strengthening theory. The reason is that the refined pearlite lamellar restrains the free movement of dislocations.
Effect of oxidizing atmosphere on scale formation of weathering steel containing Si
Mei Peng, Bao Siqian, Gong Li, Lu Weina, Cao Shuwei, Sun Guanghui, Wan Guoxi
2021, 42(5): 180-185. doi: 10.7513/j.issn.1004-7638.2021.05.028
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To simulate the influence of oxygen deficient and air conditions on the scale formation in the production process, the experimental steel was heated in 1150 ℃ and 1200 ℃ with oxygen content of 3% and 21% by tubular furnace to study the scale formation. The cross-section morphology of the scale was observed and analyzed by SEM and EPMA. The results show that when the temperature is higher than 1150 ℃, the oxidation weight gain curve under different oxidation atmospheres is more close to linear relation, and the oxidation weight gain and oxidation rate increase obviously with the increase of oxygen content in the oxidation atmosphere. Compared with the traditional scale structure, there are more Fe2SiO4 layers between the scale and the matrix. Fe2SiO4 does not undergo liquid phase transformation at 1150 ℃ except for 3% oxygen content. Liquid phase transformation occurs under other conditions. The permeability of liquid Fe2SiO4 increases with the increase of temperature and oxygen content in the oxygen atmosphere. Combined with the experimental results, the residual oxygen content in the heating furnace at high temperature (above 1150 ℃) was reasonably controlled, and no obvious red scale defect was found in the finished product.
Industrial practice of deep dephosphorization technology with less slag in converter
Wang Duogang, Guo Peimin, Cheng Nailiang, Xia Yunjin
2021, 42(5): 186-191. doi: 10.7513/j.issn.1004-7638.2021.05.029
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In this paper, the industrial practice of deep dephosphorization with less slag in dephosphorization period was carried out on 250 ton converter of Meigang. The effects of smelting temperature, slag composition and blowing system on phosphorus content in molten steel were studied. The practice shows that at the end of the dephosphorization period of converter smelting, the appropriate bath temperature is 1370~1420 ℃, the basicity of slag is 1.3~1.8, and the FeO content in slag is 18%~28%; The suitable oxygen blowing amount in the dephosphorization period of converter smelting is 24%~28% of the total oxygen flow, the scrap ratio is controlled at 12%~16%, and the number of bottom blowing holes is more than 8. Through above parameters optimization, average dephosphorization rate in converter smelting dephosphorization period of Meigang was increased from less than 50% to 63.2%, and finally achieved stable operation of the less slag process. During period from year 2012 to 2019, the less slag smelting proportion was increased from 0 to 83.7%, and the lime consumption per ton of steel was reduced from 53.3 kg to 23.2 kg, decrease by 56.5%.
Microstructure and mechanical properties of titanium magnesium alloy for automobile frame
Gui Lin, Li Qiangjun
2021, 42(5): 192-196. doi: 10.7513/j.issn.1004-7638.2021.05.030
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The microstructure and mechanical properties of Mg-8Al-1Zn-xTi(x=0.05,0.15,0.3) magnesium alloy containing titanium with different titanium contents were tested and analyzed, and the microstructure and mechanical properties of Mg-8Al-1Zn alloy without titanium were compared. The results show that the addition of alloy element Ti can refine the alloy grain and improve the mechanical properties of the alloy. The average grain size of the alloy first decreases and then increase, and the mechanical properties first improves and then declines. Compared with Mg-8Al-1Zn alloy without Ti, the average grain size of Mg-8Al-1Zn-0.15Ti alloy containing Ti decreases by 7.2 μm, tensile strength increases by 32 MPa, yield strength increases by 33 MPa, the elongation after fracture increases by 3.8%, and the tensile fracture mode changes from mixed fracture to plastic fracture.
Research progress of notched specimen fatigue
Chen Lifei, Luo Yunrong, Fu Lei, Li Xiulan, Zhang Yingqian, Li Hui
2021, 42(5): 197-204. doi: 10.7513/j.issn.1004-7638.2021.05.031
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In this paper, the effects of environmental factors, loading mode, workpiece geometry and technological treatment on fatigue behavior of notched parts are summarized, and the methods of fatigue life analysis of notched parts and the technological methods of strengthening fatigue performance of notched parts are introduced. The application of finite element software on studying the fatigue behavior of notched parts at home and abroad is briefly introduced. Stress and strain distribution of the dangerous position can be obtained through finite element simulation, and the fatigue life of notched parts can be effectively predicted by combining simulation results with the life prediction model. Finally, the current research progress are summarized and the research direction and prospect of notched parts are proposed.