20 June 2024, Volume 36 Issue 6
  
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    Reviews
  • YANG Zeyu1,WANG Min1,2,LI Yihong3
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    Abstract: Fine MnS inclusions in steel can significantly improve the cutting performance of steel, but MnS inclusions have good deformation properties and are easy to extend along the rolling direction into long strip inclusions with large aspect ratio, which will also deteriorate the mechanical properties of steel and large size MnS is also easy to become a crack source of corrosion. Controlling the formation of small, dispersed spherical or spindle MnS inclusions in steel is key to improving its machinability and guaranteeing its mechanical properties. The control of MnS inclusions in steel is a systematic project, involving the whole process of metallurgical process. The formation mechanism, influencing factors, and control measures of MnS inclusions in steel are systematically reviewed, which guides the control of MnS inclusions in highquality steel, and provides the basis for reasonable process path selection and process measure regulation in the actual production process.
  • TIAN Chunjian1,ZANG Ximin2,ZHANG Liwu3,ZHANG Yongjiao1,KONG Lingzhong1,WANG Zhiying1
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    Abstract: Steel scrap is a significant solid ferrite raw material, which can replace molten iron for smelting in the converter and effectively reduce coal consumption and waste gas emissions in the steelmaking process. In recent years, with the continuous growth of scrap steel production, there is an urgent need for “peak carbon dioxide emissions” and “carbon neutrality”. High steel scrap ratio steelmaking technology has become an important direction for the development of converter steelmaking technology. The current situation of steel scrap utilization at home and abroad was summarized, it was found that China′s comprehensive steel scrap ratio is lower than that of other countries, but the converter steel scrap consumption has increased significantly year by year. In the converter process, increasing the scrap ratio will affect the melting behavior of scrap, dephosphorization reaction, converter refractory erosion, and converter end point control. Increasing the scrap ratio will reduce the temperature in the converter, and the evolution of the melting behavior of scrap in the furnace can be studied by dynamic modeling of the steelmaking process. The dephosphorization reaction requires appropriate slag alkalinity. After increasing the scrap ratio, technical means such as slag-less smelting are required to maintain appropriate slag alkalinity. The addition of scrap steel not only has a physical impact on the furnace lining, but also indirectly affects the composition and amount of slag, thereby increasing the degree of corrosion of converter refractory materials. The difficulty of blowing and igniting the converter is affected by the scrap ratio, which in turn reduces the accuracy of the converter end point control. Domestic and foreign steel companies have developed technologies such as Jet Process, SMP, and secondary combustion oxygen lance to reduce the adverse effects of high scrap ratio, but these processes have the disadvantage of limited improvement. Therefore, exploring more economical and manageable converter technologies with high scrap steel ratios is necessary.
  • YANG Zhen1,ZHAO Shuo1,2,XUE Yuqiang1,WANG Jianfeng1,SUN Xiaolin1
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    Abstract: The strengthtoughness, corrosion resistance and service life of steel could be impacted by inclusions. In addition, the inclusions had the potential to cause wear and scratches on rolls during the rolling process. Therefore, it was crucial to examine the inclusions deformation behavior. In order to understand the new progress of inclusions deformation behavior more systematically, the characterization methods, control strategies and deformation affecting factors of the inclusions during the rolling process were briefly described. The analysis of the rolling process of different types of inclusions showed that the control method of MnS focused on reducing the hardness difference between MnS and the steel matrix, and selecting the appropriate rolling deformation process; the composition was mainly focused on being changed as the control method of silicate inclusions; the control of wellmodified calcium aluminate inclusions was not only to completely remove largesized particles, but also to control the size of highhardness inclusions. This discourse summarized the effects of inclusion hardness, position, deformation capacity and roll diameter on inclusion deformation behavior. Additionally, the key research directions for a comprehensive understanding of this behavior were proposed.
  • Smelting and Working
  • XI Jiahao,XING Xiangdong,ZHENG Zhaoying,WANG Yuxing,Lü Ming
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    Abstract: Sinter is one of the important raw materials in the blast furnace ironmaking process. The control of FeO content has an important impact on ironmaking process, iron quality and energy consumption. Due to the problems of feature selection deviating from reality and poor generalization ability of prediction model in the current research process, the prediction model of FeO content of sinter based on kernel principal component analysis (KPCA) and Logistics-SSA-BP was proposed. The feature parameters were screened and dimensionality reduced by Pearson and KPCA. Combined with Logistic-SSA-BP optimization algorithm, the collected data are trained, learned and verified. The experimental results show that the absolute error is stable within the range of [0,0.21], and the hit rate reaches 98.75% within ±0.2 between the predicted value and the actual value. The performance of the prediction model is better, and the evaluation indexes of MSE, MAE, and RMSE reach 0.013、0.101、0.115. The prediction model could accurately predict the FeO content of sinter, which could provide direction to blast furnace operators when establishing batching programs and executing process operations.
  • JIAO Yaxing1,ZHU Tanhua2,LI Yaoqiang2,GAO Xiaoyong2,ZHANG Lifeng3
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    Abstract:The effect of titanium on sulfide inclusions in 42CrMoS4 sulfur-containing steel was investigated. The sulfides were characterized by SEM, EDS and ASPEX. The three-dimensional morphology of the sulfides was characterized by electrolysis experiment. With the increase of Ti content, the number of pure MnS decreased and the number of MnS-TiN composite inclusions increased. When the mass fraction of Ti was 309×10-6, Ti4C2S2 sulfide precipitated. The trajectory for the evolution of sulfides in the steel was: MnS→MnS-TiN→Ti4C2S2. The size of Ti4C2S2 was obviously smaller than that of MnS and MnS-TiN, and the deformation resistance of Ti4C2S2 was obviously stronger than that of MnS and MnS-TiN. With the increase of Ti content, the number density of sulfides first increased and then decreased, and the size of sulfides first decreased and then increased. When the mass fraction of Ti was 400×10-6, the number density of sulfide was the largest and the average size was the smallest. For 42CrMoS4 sulfur-containing steel, the optimized mass fraction of Ti element was 400×10-6.
  • DONG Yannan1,BAI Yun2,SHEN Yu2,WANG Peng2,CHEN Bin2,WANG Pu1
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    Abstract:The tail strand casting of the slab is an unsteady-state working condition with a relatively higher surface crack occurrence, which significantly impacts molten steel yield during a sequence casting. The microstructure morphology near the surface cracks of the tail strand of a peritectic steel slab was analyzed, and the characteristics, formation mechanism and control methods of the corner transverse cracks were explored. The results show that the room temperature structure of the tail strand surface is ferrite and pearlite with obvious dendrite morphology. Under the tail strand casting process, the corners of the slab after exiting the mold have experienced a process of strong cooling → the corner temperature enters the ferrite temperature zone → temperature reheating → the corner structure is austenitized. Near the lowest temperature in this process, the corner of the tail strand is in the third brittle zone, causing fixed-side surface cracking under subsequent bending deformation. The key to the occurrence of such transverse cracks at the corners of the slab is that the corners of the slab are cooled too hard after exiting the mold. The control measures should consider reducing the cooling intensity of the corners of the slab after exiting the mold and shortening the casting time of the tail strand; Additionally, attention should be paid to the coverage of cooling water at the corners of the slab. After replacing the section, the position of the nozzle should be adjusted on time, and attention should be given to ensuring the alignment accuracy of the equipment to reduce the bending strain of the slab.
  • Materials Research
  • GAO Qing1,WANG Qi2,ZHANG Qingxue1,QIAN Yajun1,DENG Xiangtao2,WANG Zhaodong2
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    Abstract: Through the alloy reduction design on the basis of ordinary NM500 alloy, combined with high purity smelting and reasonable heat treatment, a low cost NM500 steel plate with easy welding, good comprehensive mechanical properties and wear resistance was successfully developed. The full thickness microstructure of low cost NM500 steel plate was lath martensite with the effective grain size of 1.94μm, and the proportion of high angle grain boundary was 71.6%. The HV hardness of low cost NM500 steel plate was between 500-520 with the yield strength, the tensile strength and the elongation of 1222MPa, 1583MPa and 9.6%, respectively. The impact energy of low cost NM500 steel plate at -40℃ was 58.8J. Its wear resistance was the same as that of ordinary NM500 steel plate, and the morphology was composed of grooves and a small amount of spalling pits. For the structure that can be completely quenched, the alloy reduction has little effect on the structure and properties.
  • FU Lei1,2,JIAN Ke1,LIN Li3,4,5,YAN Shisen1,ZHANG Yingqian6,LUO Yunrong1
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    Abstract: A variety of microbial species coexist in the soil where buried pipelines are in service, and the electron shuttles secreted by electricity-generating microorganisms may affect the corrosion behavior of microorganisms. Moreover, pipelines often experience low-frequency pressure fluctuations and long-term exposure to alternating loads, which can lead to low-cycle fatigue. Based on this, the influence of endogenous electron shuttles riboflavin on microbial corrosion fatigue was explored by studying the corrosion of X80 pipeline steel by sulfate-reducing bacteria. The results show that riboflavin promotes bacterial corrosion of metals by accelerating electron transfer, but does not change the corrosion products or process. Under the strain amplitude of 0.4% to 0.7%, the fatigue life of the two pre-corrosion systems relative to the noncorrosion system decreased by 17.5% to 27.8% and 33.5% to 58.1%, respectively. As the strain amplitude increases, the proportion of plastic strain amplitude in the total strain amplitude gradually increases. The cyclic response and Masing characteristics of the materials before and after corrosion remain unchanged. The prediction results of strain, strain energy density, and fatigue toughness life curves indicate that bacterial corrosion has a significant impact on the plastic strain life of steel, and fatigue fracture analysis verifies that bacterial corrosion accelerates the plastic failure of steel.
  • WANG Jingzhong1,YAO Huiqin1,ZHAO Peilin2,LI Chao2,LI Yuanzheng3,YANG Xirong1
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    Abstract: A deep study was conducted on the thermal deformation behavior of marine steel Q355NE under 870-1170℃ and 0.1-10s-1 conditions using a Gleeble-3800 thermal simulation testing machine. The microstructure evolution of experimental steel under different hot working conditions was observed using techniques such as metallographic microscopy, electron backscatter diffraction, and transmission electron microscopy, non-dimensional Z-parameters were introduced, and a critical strain model for dynamic recrystallization of Q355NE steel was successfully established based on work hardening rate and flow stress curve. The results show that during the hot compression process, the flow stress of Q355NE steel shows a significant decreasing trend with the increase of deformation temperature or the decrease of strain rate; meanwhile, higher deformation temperature and lower strain rate are more conducive to the appearance of dynamic recrystallization characteristics, and the calculated activation energy Q for hot deformation is about 368022kJ/mol. A critical strain model for Q355NE steel under low lnZ conditions has been established. The deformation temperature has a significant impact on the microstructure and mechanical properties of Q355NE steel. Under the condition of strain rate of 5s-1, as the temperature decreases within the experimental temperature range, the refinement degree of ferrite grains is significantly improved, the proportion of large angle grain boundaries increases, and the dislocation density inside the ferrite grains increases. This is conducive to the precipitation of small and dispersed Ti and Nb carbon nitride second phase particles, and effectively suppresses or avoids the formation of Weinstein structure, thereby improving the low-temperature impact toughness and strength of Q355NE steel.
  • SONG Weichen1,WANG Bing2,LI Ba2,JIA Shujun2,LIU Qingyou2
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    Abstract: By varying the volume of filling material in the environmental chamber, different hydrogen volume/sample notch surface area ratios (RV/S) were obtained. The fatigue life test and scanning electron microscopy (SEM) were used to study the effect of RV/S ratio on the fatigue life of pipeline steel under hydrogen environment. The hydrogen embrittlement theory of spontaneous dissociation of gaseous hydrogen molecules into hydrogen atoms in hydrogen pipelines was discussed. Compared with nitrogen, when RV/S increases from 2.6mL/mm2 to 24.4mL/mm2, the fatigue life loss rate of X52 pipeline steel girth weld in highpressure hydrogen environment increased from 21.2% to 57.2%, the fatigue life loss rate of X52 pipeline steel base material increased from 2.1% to 53.2%, the fracture surface toughness dimples in the fatigue life test rapid tearing zone of X52 pipeline steel girth weld and base environment reduced significantly; there was an increasing trend of defects such as cracks and voids in the ductile dimple area. During the fatigue life test, the crack stop propagating after the initiation of fatigue cracks in nitrogen. However, when the ratio of hydrogen volume to the surface area of the specimen notch was 244mL/mm2, the fatigue cracks continued to propagate once they initiated until the specimen fractured. The RV/S ratio has a significant impact on the fatigue life cycle number of X52 pipeline steel in highpressure hydrogen environment. The results provided experimental data support for the hydrogen embrittlement theory of spontaneous dissociation of gaseous hydrogen molecules into hydrogen atoms.
  • HUANG Zhenguang1,CHEN Zhongyi1,MA Yonglin1,DONG Lili1,2,LIU Baozhi3
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    Abstract: In order to further explore the effect of pulsed magnetic field annealing process on the microstructure and texture of oriented silicon steel, using a common grain oriented silicon steel containing 3.1 wt.% Si which after the first cold rolling, and a pulsed magnetic field experimental tube annealing furnace independently developed by the laboratory was applied for decarburizing annealing at 850℃ with a magnetic field intensity of 12mT, followed by a secondary cold rolling with a reduction rate of 57%. Microstructure and texture of decarburizing annealing and the secondary cold rolling were observed and analyzed by metallographic microscope and XRD. The results show that the decarburization efficiency of CGO steel when pulsed magnetic field is applied is much faster than that when no magnetic field is applied. After double cold rolling, the number of shear bands in the samples of CGO steel with pulsed magnetic field applied in the process of decarburizing annealing is significantly higher than that without magnetic field applied. The texture intensity of {111}<112> increases, the texture intensity of {111}<110> is dramatically weakened. This will facilitate the secondary recrystallization of the GOSS texture of the subsequent cold-rolled silicon steel during high temperature annealing, and improve the final magnetic properties. At the same time, the experimental basis for promoting the industrial application of pulsed magnetic field annealing process for oriented silicon steel is provided.
  • Energy and Environmental Protection
  • ZHANG Bokang1,2,LUO Guoping1,HAO Shuai1,LU Yuanyuan1,CHAI Yifan1
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    Abstract: To study the influence of process parameters on the carbonthermal reduction of steel slag and determine the optimal process conditions, Baotou Steel′s hot splashing slag and production coke particles as raw materials were used to study the influence of process parameters on carbon thermal reduction of steel slag through four factors and four levels of orthogonal experiments with different coke slag ratios, alkalinity, reduction temperature, and time. The optimal parameters for reducing slag iron recovery rate and pulverization rate were determined through range analysis and verified. The results show that the factors which affect the iron recovery rate after slag reduction are the coke slag ratio, reduction temperature, alkalinity, and insulation time. The optimal horizontal combination is a coke slag ratio of 10∶90, an experimental temperature of 1600℃, an alkalinity condition of 1.8, and an insulation time of 50min. The iron recovery rate after slag reduction can reach 59.67%; the factors that affect the 100-mesh screening rate of the powder after slag reduction are the coke slag ratio, alkalinity, reduction temperature, and insulation time. The optimal combination of levels is a coke slag ratio of 25∶75, an experimental temperature of 1450℃, an alkalinity condition of 2.2, and an insulation time of 30min. The 100-mesh screening rate of the powder after slag reduction is 78.08%, which is the highest level in all experiments; under the experimental conditions of a coke to slag ratio of 25∶75, reduction temperature of 1550℃, alkalinity of 2.0, and insulation for 60min, the iron recovery rate and 100-mesh screening rate of the slag sample after reduction are both good, reaching 47.18% and 43.83%, respectively.
  • Testing and Controlling
  • YANG Chunlong,Lü Donghao,ZHANG Yong,REN Yan,LI Shaobo
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    Abstract: To tackle the issue of reduced speed in deep learning-based network models due to limited computational resources in terminal detection equipment. An algorithm for detecting surface defects on strip steel was proposed, incorporating adaptive down-sampling. They first constructed the adaptive down-sampling module (ADWO) to enhance the network′s attention to different features by introducing weight coefficients and reducing module parameters through group convolution. Then, the CGC3 module was designed, combined with the context guided block, to improve the network′s ability to detect defective features by integrating local and surrounding context information. Additionally, the RFB attention mechanism was introduced to enhance the detection accuracy of small defects on the strip surface by integrating multiscale defect features. Experimental results showed that the improved algorithm achieved an average detection accuracy of 79.5% on the NEU-DET dataset, surpassing the original YOLOv5s network by 2%. Moreover, it increased FPS by 6 frames/s, reduced the number of parameters by 39.9%, and decreased floating-point operations by 39.8%. Ablation and comparison experiments confirmed the effectiveness of each improvement module and the superiority of the proposed algorithm.