25 September 2021, Volume 33 Issue 9
    

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  • LIU Weidong1, CAI Wenhe2, ZHAO Yong1, SUN Yue1, YUAN Yongliang1
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 891-900. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210013
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    Abstract: Based on the new heated surface tube materials for servicing 630℃ doublereheat power generation units, the comprehensive property of three alternatives,Sanicro25, CHRA5 and SP2215,was researched. The properties included chemical composition, microstructure, mechanical properties, impact property after aging at high temperature, steam oxidation resistance, corrosion resistance and economy. Compared with traditional steels, Super304H and HR3C, those are currently used for 600-620℃ units, the comprehensive property of these new materials are superior. They can be used as the heated surface tube materials for 630-650℃ units.
  • Smelting and Working
  • SHEN Zhongmin1,2, GUO Jing1,2, DUAN Shengchao1,2,GUO Hanjie1,2, DUAN Ran3, LI Lianpeng4
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 901-910. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210091
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    Abstract: In order to reduce the nonuniform distribution of Al and Ti elements in the large Fe-Ni-based alloy ingot during the electroslag remelting(ESR) process, the thermodynamic model for the burning loss of Al and Ti in the GH4706 alloy was established based on the ion and molecule coexistence theory(IMCT). The activity of Al and Ti in Fe-Ni-based alloy can be calculated by using the firstorder activity interaction coefficient in the Wagner formula. Taking Fe and Ni as the matrix and ignoring the influence of Ni element on the activity interaction coefficient for other elements in the alloy, a more accurate calculation result can be obtained. In the CaO-MgO-Al2O3-TiO2-CaF2 slags system, the burning loss of Al and Ti elements can be effectively inhibited by controlling the content of TiO2 between 2%-6% in the slags system. GH4706 electroslag ingot with  1100mm was successfully smelted by using the calculated results for the slags composition, and the content of burning loss of Al and Ti elements was less than 10%.
  • CHEN Chang1, 2, 3, LI Yang1, 2, 3, GAN Wenliang1, FENG Hao1,HE Huanyu1, 2, 3,NI Hongwei1, 2, 3
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 911-919. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200261
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    Abstract:Spinel Ni-ZnFe2O4 was synthesized directly by hydrothermal method using Zn2+ extracted from EAFD, Fe3+ extracted from iron scale and nickel chloride hexahydrate (NiCl2·6H2O ) as raw materials. The effects of roasting temperature, NaOH/EAFD mass ratio and roasting time on the extraction rate of Zn2+ from EAF dust and the concentration of HCl on the leaching rate of Fe3+ from iron scales were discussed, respectively. Then, the influences of synthesis conditions on the magnetic properties of prepared Ni-ZnFe2O4 were investigated. The results show that the extraction rate of zinc from EADF is 88.77% when the mass ratio of NaOH to electric furnace dust is 1∶1, the roasting temperature is 450℃, and the roasting time is 1h. When the concentration of HCl was 1.75mol/L, the dissolution rate of Fe3+ from iron scales is 96.89%. Meanwhile, spinel Ni-ZnFe2O4 could be synthesized successfully when the mole ratio of Zn2+ extracted from EAFD and Fe3+ extracted from iron scale to NiCl2·6H2O is controlled at 1∶20∶9. Moreover, the magnetic properties of synthesized Ni-ZnFe2O4 could be improved significantly after heat treatment. When the heat treatment temperature is increased from 150℃ to 450℃, the saturated magnetic induction intensity of prepared spinel NiZnFe2O4 increases from 13.35(A·m2)/kg to 40.06(A·m2)/kg.
  • ZHANG Jixin1, LI Qiuju1, ZHOU Cang2, LI Chonghe2, WANG Dan3
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 920-928. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200236
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    Abstract: Stainless steel pickling sludge is a hazardous waste, but it contains a lot of valuable heavy metals, so it is of great significance how to resource utilization of stainless steel sludge. The interaction and transformation of iron, chromium, nickel and other elements in the process of carbothermal reduction reaction were studied, and the influencing factors of iron, chromium as well as nickel elements distribution in the sludge were explored. The phase of sludge and its reduction samples were analyzed by XRD, and metallographic microscope and SEM-EDS were used to analyze the morphology and migration behavior of metal particles in sludge reduction process. The results show that NiO combines with Fe2O3 to form NiFe2O4 spinel phase, which is reduced to form Ni-Fe metal phase during sludge carbon reduction process. FeO combines with Cr2O3 to form FeCr2O4, which forms FeCrC metal solid solution with carbon reduction. Ni-Fe-Cr-C alloy particles containing carbon are lower melting point which can transfer and grow up through convergence. There will form a micro molten pool as the reduction temperature is 1300℃, which provides better migration and growth conditions for the metal droplets. The nonmetallic elements form slag pellets with [Si-O] network structure, which is composed of Ca2Al (AlSiO7).
  • ZHOU Jin, ZHOU Cunlong, DUAN Jingjing
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 929-935. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200246
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    Abstract: The bonding characteristics between oxide scale and steel substrate determine the setting accuracy of process parameters for environmental friendly acid free descaling. In order to analyze the mechanism of debonding between the low carbon steel matrix and the surface oxide scale, FeO/Fe was taken as the research object, and molecular dynamics software was used to simulate the growth behavior of the interface cracks of the FeO/Fe under tensile load. The local normal stress distribution and displacement at constant stage and propagation stage of crack and were analyzed. The local normal stress and displacement under the condition of steadystate crack growth were used to fit the traction separation curve, and compared with the exponential, bilinear and cubic polynomial cohesion models, and the sum of squared deviations was 24586, 22202, and 40610, respectively. The results show that this method can predict the debonding mechanism of FeO and Fe quickly and accurately, which is helpful to reveal the debonding mechanism of oxide scales and steel matrix, as well as to promote the technology of acid free descaling.
  • YIN Huifang1, YANG Gang1, ZHAO Jiqing1, BAO Hansheng1, HU Ri2
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 936-942. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200193
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    Abstract:The effect of tempering on microstructure and mechanical properties of COST-FB2 rotors steel was investigated by SEM and TEM. The results show that the bar-shaped Fe3C and the fine particle-shaped MX precipitate in martensitic lath, and few particle-shaped carbides precipitate at lath boundaries after the first tempering at 570℃. After the second tempering at 700℃, the rod-like Fe3C and granular carbides disappear or transform to the fine and dispersive M23C6 carbides. The sample of COST-FB2 rotors steel has higher strength and lower impact energy after the first tempering at 570℃. The strength of COST-FB2 rotors steel decreases slightly, and the impact energy improves significantly after the second tempering at 700℃. The better strength and toughness match of COSTFB2 rotor steel is obtained during the different temperature tempering.
  • LI Erlong1,2, FENG Kongfang3, GUO Hairong3, SUN Jipeng1,2, ZHANG Jieyu1,2, WANG Bo1,2
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 943-951. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200247
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    Abstract:The transition piece is an intermediate metallurgical reactor that connects the tundish to the mold in the thin strip casting process. The study of the flow of molten steel in the transition piece and the temperature distribution at outlet is of great importance for the thin strip continuous casting process. For a multistrand transition piece, it was proposed to add the dam and weir combination to optimize the flow pattern and temperature distribution of molten steel in the transition piece. The numerical simulation and physical simulation methods were adopted to study the flow pattern and temperature distribution of molten steel under the different flow control devices in the transition piece. The uniformity of molten steel was investigated by the average residence time and temperature at each outlet. The results show that the dam and weir combination can stabilize and unify the flow and temperature distribution of molten steel in the transition piece, and the optimal scheme is that the height of dam is 30mm, the height of weir is 30mm, the distance between dam and weir is 120mm, and the distance between weir and nozzle is 253mm, and its average residence time variance is 82% less than that of the original model; the temperature range in the outlet is 67% lower than that of the original model. The numerical simulation results are in good agreement with the physical simulation results.
  • YI Chengxin1, LI Weigang1,2, L Lihua3, ZHAO Yuntao1
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 952-959. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200187
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    Abstract:Continuous and real-time prediction of strip temperature is the key to improve the performance of hot strips. The high-dimensional data of hot strip rolling process are not conducive to the rapid and accurate prediction of slab temperature. To address this problem, an RFLSTM model was proposed to predict the strip rough rolling exit temperature. Firstly, the improved random forest algorithm was used to select the input variables, and the contribution degree of the characteristics was measured by analyzing the change in the predicted results of the strip rough rolling exit temperature, and then the feature selection evaluation function reflecting the process data characteristics and strip temperature was constructed. Then, in view of the time series characteristics of the hot continuous rolling process data, the Long-Short Term Memory (LSTM) neural network was used to predict the strip rough rolling exit temperature. Through the experimental verification and comparative analysis of the data feature selection of hot continuous rolling process in actual steel mills, the results show that the average absolute error and root mean square error of strip temperature prediction before and after feature selection are reduced by 0.21 and 0.25℃, respectively, and the accuracy of prediction relative error within ± 3.0% reaches 99.07%.
  • Materials and Research
  • LI Baisong, LI Zhigang, SONG Enmeng
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 960-965. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200188
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    Abstract:X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were taken to analyze the Fe78Si9B13 amorphous ribbon, which is made by planar flow casting method. The results show that the Fe2O3 oxide layer with thickness of about 10 nm will be generated in the free-surface of Fe78B9B13 amorphous ribbon when the up-stream meniscus of liquid puddle is protected by CO. Meanwhile, Fe(Si) solid solution crystalline phase occurs at 2θ of 66.1° in the free-surface ascribing the existence of the above Fe2O3 oxide layer, leading to the deterioration of magnetic properties. By protecting the liquid puddle in both up-stream and downstream meniscus in the casting process, the free-surface oxidation can be effectively prevented, which will improve the magnetic properties.
  • ZHU Jian1, ZHOU Wenjian1, ZHANG Zhihao1,2, XIE Jianxin1,2
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 966-978. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200201
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    Abstract:Rare earth (RE) microalloying has been developed into an important method for high quality die steels. The RE H13 steel ingtos were prepared by electroslag remelting (ESR) process with RE slag. Besides, the composition, structure and inclusion of RE H13 ingots prepared by RE added alumina slag and alumina slag were investigated. Furthermore, the RE modification effect and mechanisms of RE added alumina slag for H13 ingots were revealed. The results indicate that H13 steel ingot with RE content of calculated 0.01 wt.% can be prepared by RE added alumina slag or RE added calcium oxide slag. And the S content of calculated 0.01 wt.% in electrode (raw material) can be notably reduced to 0.005 wt.% and 0.002 wt.%, respectively. The RE H13 ingots consist La enrichment in grain boundary, as well as La2O2S with size of 1.2μm. Compared with the alumina slag, the RE added alumina slag decreases the average size of secondary dendrite from 109.6μm to 84.9μm, as well as the average size of inclusions and liquation carbides from 5.1μm to 3.1μm, which notably improves the homogeneity of H13 ingots.
  • YANG Feifei1, ZHANG Zhonghua2, LIU Huasong1, LUO Ming2, LI Gen1, ZHANG Jiaquan1
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 979-986. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200220
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    Abstract: Banded segregation is one of major defects to affect the corrosion resistant performance of high strength steels. To reveal and understand the characteristics of a typical carbide banded structure in rolled steels, C110 grade oil casing steel was studied by aiming at the banded structure in its tube product, which is specially originated from the as-cast spot like segregation. The grain sizes and their distribution were studied experimentally at its various hot working stages by means of OM, SEM, EDS and EPMA. A kind of band-typed mixed grain structure was observed in the tube wall, in which coarse grains exist in the banded substrate area, while the much finer grains exist in the banded segregation area. It is shown that quench and tempering heat treatments can only improve the homogeneity of the grain sizes to a very limited extent. By EPMA analysis, the relationship between elemental segregation and grain size in the microstructurally banded region was revealed. And the mechanism of the unusual mixed grain structure behavior was explained through solute drag theory together with the pinning effects of the precipitated second phase particles.
  • LI Chenggang1, ZHOU Xiaoguang1, JIANG Xiaodong1, ZHANG Donghang1,LU Fenghui2, LIU Zhenyu1
    JOURNAL OF IRON AND STEEL RESEARCH . 2021, 33(9): 987-993. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200202
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    Abstract: Influence of cooling processes on microstructure and hardness of Ti micro-alloyed high strength steel was investigated through thermal simulation experiments. The results indicate that: when the final cooling temperature is 700℃, ferrite and pearlite microstructures are refined significantly, and the hardness of the experimental steel increases with the increase of cooling rate; with the decrease of the final cooling temperature, the grain size of polygonal ferrite decreases, ferrite and pearlite contents decrease gradually, pearlite interlaminar spacing decreases gradually, bainite content increases, and the hardness of experimental steel increases gradually resulting from fine grain strengthening and phase transformation strengthening; a small number of TiN and Ti4C2S2 particles are found in the experimental steel. When the cooling rate changes from 5℃/s to 30℃/s, the number of TiC precipitation particles increase gradually, and the average precipitation particle size decreases from 8.1nm to 6.7nm; when the final cooling temperature changes from 700℃ to 600℃, the number of TiC precipitation particles decrease gradually, and the average precipitation particle size decreases from 6.7nm to 5.9nm. The research results lay a theoretical foundation for the determination of the controlled cooling process of Ti micro-alloyed high strength steel.