19 June 2020, Volume 32 Issue 6
    

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    Reviews
  • Research progress on high entropy alloys by selective laser melting
    LIN Hui-xian1,WANG Kai1,DING Dong-hong1,LIU Jie1,YANG Jing-wei1,YI Jiang-long2
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 437-451. https://doi.org/.10.13228/j.boyuan.issn1001-0963.20190276
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    Abstract： In recent years, highentropy alloys have attracted great attention in various fields due to their multiple principal components, unique structures, and many excellent properties. This new type of alloy based on “configurational entropy” design is expected to break the performance limit of traditional alloys and has become one of the new hotspots and directions in the development of materials science. The traditional arc melting technology has limited the production and industrial application of hig entropy alloy complex structural parts. The emerging additive manufacturing technology has become one of the most promising manufacturing methods in the preparation of complex metal components. It summarized the latest advances in selective laser melting of highentropy alloys, including processes, optimization, and applications. And the industrial application of highentropy alloys in the future was prospected.
    • Smelting and Working
  • Effects of alkali metal enrichment on structure and gasification reactivity of blast furnace tuyere coke
    ZENG Zhi-hao1,ZOU Chong1,SHE Yuan1,2,YANG Jun1,MA Cheng1,HE Jiang-yong1
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 452-461. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190265
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    Abstract： Taking the furnace coke and tuyere coke taken from the same blast furnace for two wind breaks as the research objects, XRD, SEMEDS, N2 adsorption, thermal analysis and other methods were used to compare and analyze the carbon chemical structure, alkali metal enrichment degree, pore structure, CO2 gasification reactivity of different samples, and to explore the degree of coke reactivity in blast furnace and its influencing factors.The results show that compared with the furnace coke, the tuyere coke has a significantly higher gasification reactivity, an increase in specific surface area, an increase in the degree of ordering of carbon structure, and an increase in alkali metal content.The presence of metallic potassium on the edge of the tuyere coke is mainly composed of soluble salts, and interior of the coke is mainly potassium nepheline.The differences in different parts of furnace coke are small, the gasification reactivity and structural properties of the tuyere coke in edge, middle and core are significantly different, which indicate that the gasification reaction processes for different parts of the tuyere coke in the blast furnace are different.The alkali metal content in tuyere coke is the most important factor affecting gasification reactivity, and the secondary influencing factors are carbon chemical structure and pore structure.
  • Treatment of vanadiumtitanium magnetite based on fluxed green ball composite agglomeration process
    MA Li-ming,ZHANG Jian-liang,WU Sheng-li,LIU Zheng-jian,WANG Yao-zu,XU Chen-yang
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 462-469. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190263
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    Abstract：The composite agglomeration process is one of the important ways to deal with lowgrade complex symbiotic ore. The traditional composite agglomeration process is generally a high basicity matrix material with acid green balls. In this experiment, the composite agglomeration treatment with fluxed green balls was used to treat vanadiumtitanium magnetite. The fritting quicklime was finely ground and then added to the vanadium titanomagnetite concentrate to prepare fluxed green balls. The basicity of the pellets was controlled between 06 and 12, and the comprehensive basicity of the sinter was 176. The results show that as the basicity of the fluxed green ball increases, the strength of the green ball increases, the permeability of the mixture layer improves, and the sinter yield increases. After finely grinding the coke powder for sintering and adding vanadiumtitanium magnetite to prepare carboncontaining green balls，the amount of coke powder should be controlled at about 04 mass%. When the green ball basicity is 09, the sintered drum has the highest intensity. The analysis results show that, as the basicity of the fluxed green ball in the sinter increases, the degree of embedding of the pellets in the matrix of the finished sinter is higher, the boundary between the pellets and the matrix gradually narrows, the content of composite calcium ferrite and silicate at the boundary increases, and a small amount of perovskite is generated.
  • Simulation of sintering shuttle distribution based on discrete element method
    ZHAO Shi-qi1,2,WANG Chun-lai3,FAN Zheng-yun1,2,ZHOU Ji-liang1,2,YIN You-hao1,2,QIU Suo-chao4
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 470-475. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190232
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    Abstract：Sintering shuttle distribution plays an important role in the uniform distribution along the width direction of sintering trolley. A threedimensional model was established according to the actual size of shuttle distributor of sintering machine in an iron and steel enterprise, and the shuttle distribution process with front baffle was simulated by EDEM software. The results show that when the angle of the front baffle of the shuttle distributor is 90°, the residence time of the shuttle distributor on both sides of the silo should be the same as possible. When the residence time is 7 s, the shape of the material surface is flat, and the particles mass fraction standard deviation in different areas is 0001. However, the difference of the mass fraction of the particles on both edges of the silo is still large, which may lead to the uneven distribution of materials. When the angle of the baffle in the front of the shuttle distributor is 60°, the particles mass fraction standard deviation in different regions is 0006, the flatness of the material surface is the highest, and the proportion of the smallest particle at both ends of the silo is the largest, which could effectively reduce the “edge airflow effect” and improve the sintering uniformity.
  • Formation mechanism of scale in iron ore slurry filtration backwater pipe
    FAN Jian-jun1,ZHENG Fu-qiang2,GUO Yu-feng2,ZANG Long3,WANG Lei3,YAO Hong-guo2
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 476-482. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190235
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    Abstract： The scale was accumulated in the backwater pipe of iron ore slurry filtration, when the sulfuric acid was replaced by R31 filter aid for filtrating iron ore slurry in a domestic beneficiation plant.In order to reveal the chemical reaction mechanism of scale formation, the mineral phase of scale was confirmed to be calcium carbonate by Xray diffraction analysis. The fluorescence analysis method was used to quantitatively analyze the elemental composition of different filtrates. The simulation experiment of calcium carbonate formation was investigated. The results show that the CO2-3 reacted with Ca2+ to generate the CaCO3 precipitate after mixing the R31 filtrate with sulfuric acid filtrate. The CO2-3 was produced by the dissolution of CO2 in water, and the CO2 was formed from decarboxylation of carboxyl (-COOH) in the filter of R31 filter aid in alkaline solution. The Ca2+ ions were formed by the reaction of sulfuric acid and calciumbearing mineral in iron concentrate during filtration process. Finally, the chemical reaction mechanism of the scale formation in backwater pipe of iron ore slurry filtration was revealed.
  • Effect of microporous MgO refractories on steel cleanliness
    YAN Xue-qiang1,2,ZHENG Wan1,2,WANG Guo-wei1,2,YAN Wen1,LI Guang-qiang1,2
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 483-490. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190268
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    Abstract： Interaction between three kinds of magnesiabased refractories (compact magnesia, microporous MgO, and magnesiacarbon) and ultralowcarbon steel (1560℃) was investigated by immersion experiments. The changes of O, N, C and Al, Si, Mn content and the composition, quantity and distribution of inclusions in steel at different immersion time (0-35min) were investigated, and observation and analysis of the interface layer between refractory and steel were carried out. The results show that with the extension of the immersion time, the oxygen content in the three kinds of steels first increases and then decreases, which causes some pollution to the molten steel, the number of inclusions in the steel increases, and the type of inclusions gradually changes from Al2O3-MnO to Al-Mg-Si-Mn-O composite inclusions. Compared with dense magnesium refractory materials, a continuous MgO spinel layer and a dense MgO layer can be formed at the interface between microporous MgO and magnesium carbon refractory materials and steel, which helps reduce the erosion of the refractory material and contamination of molten steel. In addition, compared with magnesiumfree refractory materials without carbon, magnesiumcarbon refractory materials have severe carbon addition to molten steel. Therefore, the microporous MgO refractory material not only has little secondary pollution to the molten steel and does not add carbon to the molten steel, but also can absorb alumina inclusions in the steel, which is more conducive to the production of ultralow carbon clean steel.
  • Study on investment casting process of K4002 cover plate based on laser sintering rapid molding technology
    LI Pei-jia1,XU Zhen-nan2,LIANG Chao2,ZHANG Ya-yan1,CHEN Xing-fu2,WU Jian-tao2
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 491-496. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200054
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    Abstract： The wax model of plate or arc surface casting which is prepared by rapid prototyping manufacturing technology has a large volume expansion during dewaxing, resulting in cracking of shell mold, deformation of the casting size. The cover plate casting is a largescale thinwalled casting with an outline size of 350mm × 260mm × 10mm, and the distance between the lowest point of arc and the highest point is 23mm. The wax model of cover plate prepared by rapid prototyping manufacturing technology increases the difficulty of investment casting process. Pasting a wax plate on the wax mold prepared by rapid prototyping manufacturing technology, with the melting point difference and volume allowance between the two, shell mold cracking is improved. With side pouring system, proper sand filling molding and smelting parameters, casting with qualified metallurgical quality and dimensional accuracy is produced.
    • Materials Research
  • Effect of sample thinning on DWTT property of heavy wall X80 steel
    SHAO Chun-juan,ZHEN Fan,ZHANG Ji-ming,QU Jin-bo,ZHANG Lei
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 497-504. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190208
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    Abstract： The effect of thinning style on DWTT properties of X80 pipeline steel was investigated by means of DWTT testing, and facture morphology and microstructure were observed using optical microscope (OM) and scanning electron microscope (SEM). The results show that with the decrease of test temperature, the properties of DWTT of singleside thinned sample are better than that of doubleside thinned sample. From the surface to center of the doubleside thinned sample, the bainitic volume fraction gradually decreases, the polygonal ferrite volume fraction gradually increases, the grain size increases gradually, the morphology of MA islands are changed from a single fine granular into a large particle chain, and microstructure in the center is accompanied by severe segregation and inclusions. However, the microstructure of the singleside thinned sample has little change from the surface to the center of sample. Due to the crack initiation preferentially along the sites with the lowest energy consumption, therefore the brittle cleavage and reverse cleavage fracture are worse in the center of the doubleside thinned sample than that of the singleside thinned sample.
  • Effect of carbide evolution on Lüders behavior of cold rolled ART 0.1C-7Mn steel
    TIAN Ya-qiang1,BI Wen-qiang1,PAN Hong-bo2,LI Hong-bin1,ZHENG Xiao-ping1,CHEN Lian-sheng1
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 505-511. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190209
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    Abstract：Through SEM, XRD and tensile test, the carbide evolution of a cold rolled mediumMn steel (0.1C-7Mn) during austenite reverted transformation at different intercritical temperatures, and its effect on Lüders strain were investigated.The results show that the carbides precipitate first and then dissolve completely when annealing at higher temperature than 640℃.Highest PSE of 25GPa·% is achieved due to the moderate stability of reverted austenite at 640℃.The stability of austenite is high when annealing at lower temperature, and the carbides retard the dislocation motion, which result in the significant yield point elongation.When annealing at moderate temperature, the high density dislocation starts to recover, continuous TRIP effect will harden the matrix during deformation, and enhance the mechanical properties.The dissolution of carbides at high annealing temperature leads to the elimination and rearrangement of dislocation, and the Lüders strain disappears.The stability of austenite decreases, strain induces the formation of martensite rapidly, resulting in higher ultimate tensile strength and lower uniform elongation.
  • Evolution of microstructure and properties of thickness section of wearresistant steel
    HE Ya-yuan,LI Li-wei,YIN Yun-yang,DENG Zhao-jun
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 512-518. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190200
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    Abstract： By means of OLYMPUS GX71 optical microscope, field emission scanning electron microscope (FESEM) Quanta450 and JEM2100F transmission electron microscope (TEM), the evolution of microstructure and properties of thickness section of 60mm thick wear resistant steel at quenched and quenched + tempered state was studied. The results show that the hardness of quenched wearresistant steel is gradient distribution with high hardness on the surface and low hardness in the core. After tempering, the hardness ratio of core to surface increases from 70% to 93%, and the impact energy at 1/4 and center of the section decreases. The difference of thickness crosssection microstructure and precipitation phase has great effects on solution strengthen and precipitation strengthen, which is the main reason of performance evolution. Increasing quenching cooling rate and improving the uniformity of quenched thickness section are the fundamental methods to improve uniformity and optimize application performance.
  • Study on high temperature thermoplasticity of medium manganese steel
    CHEN Ming-xin1,YANG Xiao-jiang2,MENG Qing-yong2
    JOURNAL OF IRON AND STEEL RESEARCH　. 2020, 32(6): 519-524. https://doi.org/10.13228/j.boyuan.issn1001-0963.20190252
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    Abstract： After smelting medium manganese steel in vacuum induction furnace, there were a lot of micro cracks in the ingot directly cooled to room temperature in the casting iron mold. The results show that the hot temperature thermoplasticity of medium manganese steel is very poor. However, when the ingot reaches 700℃ and is placed in a Muffle furnace at 700℃, the internal micro cracks disappear when the ingot is cooled to room temperature. But the high thermoplasticity of medium manganese steel was also very poor. The results show that the main reasons for the poor thermoplasticity are the development of columnar crystals in ingots and the micro cracks in the solidification process. The thermal stress caused by the rapid cooling of the cast iron die and the transformation stress after the ingot has completely solidified 700℃ are the main reasons for the internal cracks. In the production process, it is recommended to adopt the relative weak cooling process of mould and secondary cooling section to reduce the risk of slab crack.
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