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15 April 2024, Volume 59 Issue 4
    

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    Technical Reviews
  • Review of decarbonization pathways and progress for main iron ore mining companies
    ZHU Deqing, LI Xiaobo, PAN Jian, GUO Zhengqi, YANG Congcong
    Iron and Steel. 2024, 59(4): 1-8. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230445
    Abstract ( ) Download PDF ( ) XML Related Articles File   Knowledge map   Save
    In 2022, China imported 866 Mt of iron ore from Rio Tinto, Vale, BHP and FMG, accounting for 78% of its total iron ore imports. As the most important raw material supplier, the big four mining companies actively participating in the decarbonization process in steel industry. The big four iron ore mining companies had issued their decarbonization targets, pathways and the corresponding finance budget. It's a kind of actions to extend responsibility as a raw material supplier to respond the climate change and policy for the global market. Mining companies are focusing on developing high-quality iron ores and purifying low-grade iron ores through beneficiation to provide high-grade materials for steel mills to reduce carbon emissions in ironmaking process. In addition, Vale plans to produce "green briquette" through cold pressing+drying process to partially replace traditional sinter or pellets as blast furnace burden, so as to reduce carbon emissions in agglomeration process. On the other hand, with the development of China steel industry towards EAF process, mining companies actively layout the transformation by using hydrogen or biomass energy in combination with direct reduction technology to provide green pig iron for steel mills. Representative technologies including HYFOR green ironmaking process, Tenored process, direct reduction+electric smelting furnace process, etc. Besides, some companies also seek for the change from a pure mining company to green energy supplier with the breakthrough in green electricity, green H2 and green ammonia projects. The decarbonization strategies and results of big four mining companies will have a profound impact on China steel industry.
  • Research progress on solidification behavior and segregation control of continuous casting billet along casting direction
    HOU Zibing, GUO Dongwei, PENG Zhiqiang, WEN Guanghua
    Iron and Steel. 2024, 59(4): 9-16. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230518
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    Continuous casting billet is the main base material of rod and wire steel products. The defects such as macro/semi-macro segregation reflect the uneven microstructure and composition distribution of the billet to a certain extent, which is an important factor affecting the quality improvement of high-end steel. At present, it is the main means to control the segregation defects in the billet by characterizing, analyzing and optimizing the macrostructure in the billet from the two-dimensional cross section. However, both the solidified dendrites and the center segregation inside the billet have three-dimensional spatial morphology and distribution characteristics, so there may be some errors in the study only by two-dimensional cross section. At the same time, the fluctuation characteristics of solidified dendrites and segregation in the direction of continuous casting billet （perpendicular to cross section） can more directly reflect the fluctuation of internal microstructure and quality along the length direction of continuous casting billet, which is also one of the keys to affect the quality stability of continuous casting billet of high-quality steel and subsequent products. The research progress on the casting direction of continuous casting billets in recent years is summarized from three aspects： solidification behavior, structure fluctuation and center segregation control. CET transition is the key point of solidification structure control of casting billet, and its determination basis and its correlation with segregation show that the CET position along casting direction fluctuates and is related to the morphology of center segregation. The fluctuating characteristics of solidification dendrites and the periodic fluctuation of solidification end point are caused by the asymmetric flow field and temperature change in the liquid phase. Meanwhile, the actual casting billet and related qualitative and quantitative models also show that the distribution of segregation elements along casting direction is characteristic of fluctuation feature, and can be analyzed by using time series technology. The development of center segregation control technology has obviously improved the internal quality uniformity of continuous casting billet, and segregation can be reduced from the casting direction based on segregation characterization method and heredity behavior model. Finally, as to the three-dimensional solidification mechanism, fluctuation characteristics of various kinds of blanks, surface quality, structure characterization, high casting speed, intelligent analysis and prediction, fine control, more and more analysis may be carried out along the casting direction of continuous casting in the future.
    • Raw Material and Ironmaking
  • Effect of gas-based reduction of high-phosphorus oolitic hematite and dephosphorization agent on phosphorus removal effect
    YANG Shuangping, LIU Yachen, WANG Miao, LIU Qihang
    Iron and Steel. 2024, 59(4): 25-33. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230517
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    Aiming at the current situation that high-phosphorus oolitic hematite can not be effectively utilized due to its complex and diversified mineral composition, fine embedded particle size, impurity components such as SiO2 and Al2O3, and high phosphorus content, the gas-based direct reduction and dephosphorization agent-magnetic separation process was used to study the influence of each process parameter on the reduction product and the magnetic separation of the iron ore concentrates with grade and phosphorus content indexes. Using hydrogen as the reducing agent and dephosphorizing agent, experimental research on high-phosphorus oolitic hematite ore with iron grade of 46.75% and mass percent of phosphorus of 0.92% in a foreign region were conducted. In the test, the dephosphorizing agent not only destroys the oolitic structure and inhibits the reduction of phosphorus-containing minerals, but also promotes the growth of iron particles in the reduction process. Under the conditions of reduction temperature of 1 050 ℃, holding time of 90 min, alkalinity of 1.2 and H2 flow rate of 200 mL/min, the effects of the type and dosage of dephosphorizing agent and different process parameters, such as the particle size of the reduction products and the intensity of the magnetic field, on the effect of iron and phosphorus removal in this ore were investigated by means of chemical composition analysis, particle size analysis and microstructural analysis, including polarized light microscopy and scanning electron microscopy analysis. The results show that the iron grade and iron recovery rate of iron concentrate are improved and the phosphorus content is also greatly reduced after adding dephosphorization agent. Among the four commonly used dephosphorization agents CaCO3, Na2CO3, Na2SO4 and SiC, the dephosphorization agent Na2SO4 has a better effect on improving iron grade and phosphorus removal, and the dephosphorization agent Na2CO3 has a better effect on improving iron recovery. When the particle size of the reduced ore powder is less than 0.074 mm, the magnetic field strength is 1 000 Gs, the mass ratio of Na2SO4 to Na2CO3 is 9∶7, and the total mass percent is 16%, the phosphorus content is reduced to 0.23%, and the iron recovery rate is 82.35%. Some theoretical guidance for phosphorus removal from high phosphorus oolitic hematite are provided.
  • Migration of sulfur in raw materials of blast furnace ironmaking
    HUA Jianming, ZHENG Zhuang, YOU Yang, LÜ Xuewei
    Iron and Steel. 2024, 59(4): 34-41. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230487
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    The emissions of SO2 in the steel industry account for 13.9% of the total industrial emissions in the country, and the blast furnace ironmaking process is a crucial stage in sulfur emissions during steel production. With increasing environmental regulations, reducing the content of sulfides in blast furnace gas has become particularly important. In order to elucidate the evolution mechanism of sulfides in blast furnace raw materials during the smelting process, chemical analysis and X-ray Photoelectron Spectroscopy （XPS） to characterize the forms and content of sulfur in the actual raw materials used in Baosteel's blast furnace were employed. Subsequently, the blast furnace sulfur load was calculated. Furthermore, a thermodynamic calculation method was used to study the distribution mechanism of sulfur in the slag-iron-gas three-phase system in different zones of the blast furnace. The results indicate that the primary source of sulfur in blast furnace raw materials is coke, accounting for 72.3% of the total sulfur input, followed by pulverized coal at 19.7%, while the combined sulfur content in iron-bearing materials （sinter, pellets, and lump ore） is less than 10%. Sulfur in coke and pulverized coal primarily exists in the forms of organic sulfur such as sulfoxides, sulfones, thiophenes, and inorganic sulfur such as sulfides and sulfate sulfur. Additionally, the sulfur content in coke is higher than that in pulverized coal. The sulfur in the lump zone blast furnace gas mainly originates from the pyrolysis of inorganic sulfur in the raw materials, gaseous H2S and COS generated from the reaction between the burden and the reducing atmosphere, and the remaining COS after the absorption of gaseous sulfides produced in the lower region of the cohesive zone. Additionally, the COS content in blast furnace gas is typically higher than that of H2S. In the cohesive zone of the blast furnace, the raw materials are conducive to sulfur absorption, and sulfur primarily exists in the newly formed primary slag. In the hearth region, sulfur mainly exist in the slag, followed by molten iron, and lastly in the gas phase. With increasing temperature, the desulfurization capacity of slag improves, leading to more sulfur transferring from molten iron to slag.
  • Research status of intelligent control of sintering process and prediction of metallurgical properties of sinter
    DING Chengyi, CHANG Rende, GUO Shenlan, XUE Sheng, LONG Hongming, YU Zhengwei
    Iron and Steel. 2024, 59(4): 42-56. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230566
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    With the development of artificial intelligence, Internet of Things and other technologies, the use of big data, automatic control and other means to achieve intelligent control and performance prediction of the sintering process has become the development trend of smart ironmaking. The purpose is to review the research status of intelligent control and performance prediction of sintering process, including intelligent ignition, layer condition monitoring, endpoint control and sinter performance detection, and comprehensively analyze the advantages and disadvantages of different technologies from multiple perspectives such as production cost, quality, efficiency, control and prediction accuracy. In terms of intelligent ignition, the importance of the control of key parameters of the ignition process is analyzed in detail, and the application status of mechanism analysis, data-driven, PIDNN control algorithm and modified EID technology in intelligent ignition is pointed out. In terms of layer temperature control, the accuracy of temperature simulation system, Matcom, VC++ and multi-threaded technology application is analyzed, and the influence of oxygen balance analysis, fluid mechanics and infrared thermal imaging technology on the air leakage monitoring of sintering machine is introduced. At the endpoint control level, the technical characteristics and optimization suggestions such as grey theory, backpropagation neural network, AdaBoost.RS algorithm, subtractive clustering and particle swarm optimization method are systematically discussed. In the field of sinter performance detection, it covers the research of online detection of sinter components and sinter performance prediction and control, intelligent analysis of sinter composition through PGNAA, LIBS and online monitoring based on DNN and LSTM, and introduces the application status of machine Xi algorithms and neural networks in sinter performance prediction and control. It comprehensively introduces the development and application effect of the sintering process under the background of informatization, intelligence and carbon peaking and carbon neutrality, systematically analyzes the development status and characteristics of sintering process control, predicts and summarizes the development context of the future sintering process under the new situation, and provides a theoretical and application basis for iron and steel enterprises in the field of intelligent sintering research.
    • Steelmaking
  • Matching of slag composition, performance and furnace temperature based on double slag process
    ZHANG Zhenkai, ZHAO Junxue, WANG Ze, KANG Yi, CAO Geng, WANG He, CHEN Yuanping
    Iron and Steel. 2024, 59(4): 57-65. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230449
    Abstract ( ) Download PDF ( ) XML Related Articles File   Knowledge map   Save
    In the process of converter smelting, the temperature of molten pool, the composition of metal and the composition of slag are constantly changing, which leads to the change of slag performance and has an important influence on the smelting process and the quality of molten steel. The double-slag process is a new converter steelmaking process that has received extensive attention in recent years. However, there is a lack of systematic research on the coupling and matching of slag composition and performance changes with temperature and their effects during the slag formation process of double-slag process. Based on the conditions of a steel plant, the material balance was established, and the effects of slag retention and slag dumping on slag composition and dephosphorization ability were calculated. In addition, based on the production data of double-slag process of slag formation, the related research of double-slag process and the reasonable selection and calculation of slag performance model, the changes of bath temperature, slag composition, slag melting point and viscosity, phosphorus capacity, phosphorus distribution ratio and sulfur capacity in the process of converter double-slag smelting are sorted out. The matching status of various parameters in the converter steelmaking process is analyzed, and its influence on dephosphorization and desulfurization effect is discussed, which can provide reference for the implementation and optimization of the double-slag process in the plant. The results show that compared with conventional smelting, the consumption of slag and iron loss are significantly reduced by double slag and slag retention method. The consumption of lime in the enterprise is reduced from 34.07 kg/t to 17.04 kg/t, and the consumption of light burnt dolomite is reduced from 14.07 kg/t to 8.89 kg/t. The dephosphorization distribution ratio is higher and the dephosphorization effect is better. At the same time, the stable control of slag retention and slag dumping has an important influence on the performance of slag. In the early stage of smelting, the late stage of dephosphorization stage and the early stage of decarburization stage, the phenomenon that the melting temperature of slag is still higher than the furnace temperature is still easy to occur, and attention should be paid to the slag melting. In addition, the temperature of molten pool in the early stage of converter double slag smelting is relatively low, and the good matching of slag fluidity and dephosphorization ability is the key to the efficient dephosphorization of this process.
  • Thermodynamic calculation and experimental analysis on effects of rare earth Ce on TiN phase precipitation in 20CrMnTi steel
    WANG Jian, PENG Jun, ZHANG Fang, PENG Jihua, LIU Shuang, AN Shengli
    Iron and Steel. 2024, 59(4): 66-73. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230496
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    The size and morphology of TiN inclusions have an effect on the quality and service performance of gear steel 20CrMnTi. Controlling the size and morphology of TiN precipitation is the key to improving the service stability of 20CrMnTi. The nucleation behaviors of TiN inclusions in 20CrMnTi before and after the addition of rare earth Ce element was studied by the calculations and experiments. The morphologies, types and sizes of the inclusions were characterized and analyzed statistically. The behavior mechanisms of rare earth Ce on the modifications of TiN inclusions in 20CrMnTi were studied. The results show that TiN precipitation temperature calculated by thermodynamics is 1 744 K.TiN inclusions cannot precipitate in the molten steel at 1 873 K. TiN can only precipitate and grow during the solidification of the steel. After the additions of rare earth Ce, a composite phase enriched with Ti, O, Ce, Al and N elements will be formed in the steel. The composite phase is angular contracted, and the shape is spherical or ellipsoid, smaller than TiN and Al2O3-TiN inclusions. Through phase identification analysis, it can be seen that the composite phase is CeAlO3 produced by the reaction of rare earth Ce and Al2O3 in steel, which can be used as the nucleation cores of TiN inclusions to form the ellipsoidal CeAlO3-TiN, and then achieve the purpose of modifying titanium-containing inclusions. After the addition of Ce element, the total areas of TiN-containing inclusions in steel does not decrease, but a smaller CeAlO3-TiN is formed. Due to the formations of the smaller composite inclusions of CeAlO3-TiN, the number of inclusions with a size larger than 5 μm reduces by 17.2%, and refines TiN containing inclusions in steel. The addition of Ce effectively reduces the size of TiN inclusions in steel, and achieves the effect of modifying TiN in terms of morphology and size.
  • Mechanism analysis and application practice of influencing carbon-oxygen product in combined blown converter
    CAI Wei, WU Wei, YANG Libin, WANG Jie
    Iron and Steel. 2024, 59(4): 74-84. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230646
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    Clean steel production is an important direction for the development of contemporary steelmaking technology. The control of carbon and oxygen accumulation in molten steel has always been a particularly important indicator for converter steelmaking, and it is also a focus of attention for metallurgical researchers. In recent years, the carbon and oxygen deposition w（[C]）×w（[O]） in converter steel has repeatedly hit new lows, and there are considerable objections in the industry regarding the actual control level of carbon and oxygen deposition and the data of steel liquid inspection and testing. Based on the classic carbon oxygen balance formula, analyzing the influence of steel composition on the activity coefficient of carbon oxygen reaction, the thermodynamic influence of gas phase composition at the "steel gas phase" reaction interface in the emulsification zone, the influence of steel temperature on carbon oxygen reaction balance, the influence of efficient bottom blowing smelting technology and post stirring technology on carbon and oxygen accumulation, and exploring the mechanism and application practice of the influence of all factors on carbon and oxygen accumulation in converter steel. The research results indicate that thermodynamic analysis of the carbon oxygen equilibrium limit in converter steel requires analysis of the carbon oxygen activity coefficient, Gibbs free energy of carbon oxygen reaction,$P_{\mathrm{CO}} /\left(P_{\mathrm{CO}}+P_{\mathrm{CO}_{2}}\right) $ and $P_{\mathrm{CO}} /\left(P_{\mathrm{CO}}+P_{\mathrm{Ar} / \mathrm{N}_{2}}\right) $. When the decarbonization rate is low, the theoretical situation $P_{\mathrm{CO}} /\left(P_{\mathrm{CO}}+P_{\mathrm{Ar} / \mathrm{N}_{2}}\right) $ can be reduced to 0.80 even more; The bottom blowing effect of the converter is the main factor affecting the carbon and oxygen accumulation in the steel liquid. The steel liquid in the top blowing converter and open-hearth furnace is not fully mixed and stirred, resulting in the carbon and oxygen reaction far from reaching equilibrium. The carbon and oxygen accumulation can reach 0.004 0, and the bottom blowing has good kinetic conditions to make the carbon and oxygen accumulation in the steel liquid closer to the equilibrium value. The high flow rate and high intensity post stirring process can further reduce the carbon and oxygen accumulation in the steel liquid; Temperature is a secondary factor affecting the equilibrium value of carbon oxygen reaction in molten steel. Low temperature is beneficial for reducing the Gibbs free energy of carbon oxygen reaction. $\left(a_{[\mathrm{C}]} \times a_{[\mathrm{O}]}\right) / P_{\mathrm{CO}}$ increases by 0.000 1 for every 50 ℃ increase in temperature, and low temperature is beneficial for reducing $P_{\mathrm{CO}} /\left(P_{\mathrm{CO}}+P_{\mathrm{CO}_{2}}\right) $. The keys to controlling the carbon and oxygen accumulation in molten steel are the endpoint control of converter smelting and the stirring process after gun lifting and waiting.
  • 1∶1 mold water simulation of optimization of submerged entry nozzle of super large round bloom
    CHEN Xiqing, BAI Yun, WANG Pu, WANG Peng, XIAO Hong, SHEN Yu, ZHANG Jiaquan
    Iron and Steel. 2024, 59(4): 85-95. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230597
    Abstract ( ) Download PDF ( ) XML Related Articles File   Knowledge map   Save
    In order to optimize the metallurgical effect of the super large round bloom continuous casting mold, a full-scale large round bloom（≥ϕ800 mm） mold water modeling platform was established. Under a fixed immersion depth, the flow field and liquid level behavior in the mold due to different submerged entry nozzle （SEN） structures were quantitatively and qualitatively evaluated by observing the liquid level fluctuation, monitoring the average surface velocity, and conducting ink display flow field and water-oil simulated slag entrapment experiments. The results show that the free liquid surface velocity decreases gradually with the SEN port angle continuously downward, and the simulated slag entrapment situation also decreases gradually, but the free liquid surface is too calm when the SEN angle is downward 15°. When the SEN angle is upward 15°, the liquid level in the area from the middle of the mold to the mold wall is more active, accompanied by more serious liquid surface exposure and slag entrapment situation. The SEN with runway, round, inverted trapezoidal and rectangular flared side port shapes were analysed. It can be seen that the SEN with round port shape will make the jet concentrated, resulting in the surface velocities and level fluctuations are much larger than the other SEN port shapes, but also lead to a very serious slag entrapment and liquid surface exposure phenomenon, the slag entrapment of the length of the time proportion can be as high as 98%. However, the rectangular flared shape makes the jet more dispersed so that the surface velocities are small, and the level fluctuations in the middle region of the mold are high. The free liquid surface can be active in a large area without liquid surface exposure, and the slag entrapment occurs only 27% of the time. At the same time, the liquid surface flow rate of the rectangular flared nozzle does not change significantly as the casting speed increases. The five-port rectangular flared shape with a 15° upwards are much better for controlling the flow of molten steel in a super large round bloom mold than the five-port runway shape with a 15° upwards currently in use. It is more conducive to the surface quality and internal quality control of the bloom.
  • Elastoplastic deformation behavior of grains during tension of Q355B slab at high temperature
    ZHUO Shuo, WANG Weiling, ZHAO Yang, ZHU Miaoyong
    Iron and Steel. 2024, 59(4): 96-105. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230526
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    Taking the continuously cast Q355B slab in a domestic steel plant as the research object, the tensile tests were carried out at the temperatures of 1 300, 1 340 and 1 380 ℃ and the strain rate of 0.001 1/s on a Gleeble-3800 thermo-mechanical simulation tester. Based on the obtained grain morphology, representative volumetric elements of grains near the fracture were selected, and a finite element model （RVE-FEM） was established with the Ramberg-Osgood constitutive equation. Then, the deformation mechanism of the grain structure and the distribution patterns of the stress and strain during tension processes at high temperature were revealed. The results show that the closer to the fracture, the larger the average grain size is, and the smaller the stress it can bear. Because of the uneven distribution of grains and grain boundaries, the irregular distribution of stress appears in grains and at the grain boundary, and the high stress is mainly concentrated at the grain boundary. At the temperature of 1 380 ℃, the average stresses are 7.01 and 9.91 MPa in grains and at the grain boundary as the sample is at 70 mm below the slab surface. With the increase of the tensile temperature, the average size of grains enhances, the area of the grain boundaries reduces. It causes that the hindrance to deformation is weakened, and the yield and tensile strengths decline. At 60 mm below the slab surface, the yield strength and maximum tensile strength decrease from 9.87 to 4.36 MPa and from 12.51 to 4.49 MPa, respectively, as the temperature increases from 1 300 to 1 380 ℃. At the temperature of 1 380 ℃, the yield strength and maximum tensile strength decrease from 9.44 to 7.42 MPa and from 10.75 to 9.10 MPa, respectively, as the sample moves from 10 to 40 mm below the slab surface. The stress-strain curves calculated by RVE-FEM agree with the measured results at different temperatures and sampling locations. The grain size is a decisive factor for the tensile property, and it depends on the size of the initial solidification structure and the tensile temperature. From the slab surface to the center, the secondary dendrite arm spacing increases. It causes that the grain size increases at the same tensile temperature. Particularly, from 10 to 40 mm below the surface, the length of the grain's long axis is the key factor. For the same sampling position, the lengths of the grain's long and short axes increase significantly with the increase of tensile temperature.
    • Metal Forming
  • Optimal design of key structural parameters of VC roll sleeve and mandrel
    ZHANG Ji, WANG Jiachen, WANG Shuai, SU Delong, SAHAL Ahmed Elmi, BAI Zhenhua
    Iron and Steel. 2024, 59(4): 106-115. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230684
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    As one of the models that efficiently control the quality of strip steel, VC roll has a lot of production and application experience but lacks key independent design methods. For this purpose, starting from the basic structure of VC roll interference assembly. The variation in thickness of the sleeve over the service life is taken into account and analyzed in terms of roll strength, sealing, relative sliding and effective convexity. The key structural parameters of the optimal design of VC rolls were determined to be sleeve thickness, original interference amount, and oil cavity width. Further, based on the structural parameters and actual production process parameters of a domestic imported VC rolling mill. The effects of each key structural parameter on the sleeve crown, the actual interference force distribution, the original interference force of the filling pressure and the original interference of the filling pressure were analyzed. On the basis of the influence of key structural parameters on each process parameter, the design focus and ideas of each key structural parameter were determined. Finally, the strength of the VC rolls, sealing, avoidance of relative sliding, and safety from contact fatigue were considered. Based on the premise of the optimal design of the extreme production process and the ultimate working state, the evaluation index, objective function and constraints of the optimal design of the key structural parameters of the VC roll are given. And the overall process approach to optimize the design was determined. After applying the optimization design method to a domestic imported VC rolling mill. The strength safety factor, the relative sliding safety factor and the objective function under the existing parameters and the design parameters of the rolling mill structure were compared. The analysis showed that, under the premise of ensuring the crown and sealing of the sleeve, the design parameters achieved an overall improvement in strength safety, relative sliding avoidance and uniformity of interference force distribution compared with the existing parameters. The establishment of the optimal design method provides a theoretical reference for the design and verification technology of VC rolls, and has certain practical application value.
    • Materials
  • Induction heating and extrusion forming process of high frequency straight seam welded pipe
    LI Dalong, JIAO Yiwei, LU Yanlu, XIAO Yao, DI Xin, HAN Yi, HUANG Huagui
    Iron and Steel. 2024, 59(4): 116-126. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230714
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    At present, most welding pipe factories in China in the production and processing process, long-term rely on operators to observe the state of EDM and weld burr morphology and other macro physical characteristics to adjust the welding production related process parameters, but rely on human eye observation method error is large, lack of quantitative, scientific theoretical guidance, prone to cold welding or over burning and other quality defects. The induction heating model and extrusion forming model of the straight seam welded pipe were established, and the distribution of temperature field and stress field in the induction welding process of the welded pipe was obtained by numerical simulation, as well as the evolution of the burr morphology of the welded pipe, and the relationship between the change of the macroscopic morphology characteristics of the welded burr forming and the electrical and geometric parameters was revealed. The metal streamline Angle is used as the evaluation standard of welding quality, and the aspect ratio of welding burr is introduced as the characteristic value to describe the internal relationship between the height and width of burr. The influence of different welding parameters on the macroscopic morphology of welding burr forming was analyzed one by one by using the control variable method. It was found that the characteristic values of metal streamline Angle and aspect ratio increased with the increase of extrusion amount, welding speed and coil distance, and decreased with the increase of current frequency and current size. Finally, relevant experiments on metal flow line distribution during welding were carried out, and the numerical simulation results were compared with the experimental results. The results showed that the error between the metal flow line Angle obtained by numerical simulation and the experimental value was less than 4°, and the metal flow line Angle between the two tended to be consistent with the change of the extrusion amount in the welding process, which verified the rationality of the simulation results. The research results in this paper provide a theoretical reference for further optimization of welding parameters of high-frequency steel pipe.
  • On structure-property relationship in hot-rolled low-carbon carbide-free bainitic steel
    LIANG Jiawei, YANG Dapeng, ZHOU Junlong, YI Hongliang, WANG Guodong
    Iron and Steel. 2024, 59(4): 127-135. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230463
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    Carbide-free bainitic steel（CFB steel） exhibits a good balance of strength and ductility due to the presence of a fine bainite microstructure combined with residual austenite. However,these superior mechanical properties are usually achieved by adding a high carbon content in combination with additional bainitic isothermal treatment,which not only deteriorates the weldability,but also discourages economic costs and productivity. To overcome this drawback, instead of the conventional bainitic isothermal treatment,two hot rolled low carbon CFB steels with ferrite + bainite microstructures （refer as F-B steels） and complete bainite （refer as B steels） were designed by the curling process after hot rolling. The relationship between the microstructure and mechanical properties of these two steels was investigated. The yield strength,ultimate tensile strength,total elongation,and fracture strain of F-B steel are （575±8） MPa,（853±12） MPa,19.0%±0.1% and 0.63±0.03,respectively. Compared to F-B steel,B steel exhibits a lower total elongation of 14.7%±0.2%,while its yield strength,ultimate tensile strength,and fracture strain are significantly improved to （772±11） MPa,（1 160±10） MPa,and 0.78±0.02,respectively. The higher yield strength and ultimate tensile strength exhibited by B steel are mainly attributed to the complete bainite structure,which can achieve effects similar to dislocation strengthening,fine grain strengthening and second-phase strengthening. Moreover,their deformation and damage behavior were further revealed and the related results showed that the presence of ferrite and more stable residual austenite in F-B steel contributes to the more durable work-hardening ability of F-B,which is the key to its higher total elongation. For B steel,a more homogeneous microstructure and lower carbon content result in better-coordinated deformation,which significantly inhibits the deformation damage formation and thus contributes to higher fracture strain.
  • Effect of Mn on hot deformation behavior of medium grade non-oriented silicon steel without normalizing process
    WANG Yongqiang, LU Qinyang, LI Na, ZUO Rui, PEI Yinghao, ZHENG Chengsi
    Iron and Steel. 2024, 59(4): 136-147. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230465
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    The energy saving,low carbon emission and low-cost production will be come true when there is no normalization in the process of non-oriented electrical steel. This need to be optimal alloying design,Mn element could be a potential option. However,at present,the role of Mn element in the hot deformation of non-oriented electrical steel still needs comprehensive understanding. The effect of Mn on the hot deformation behavior of 1.5%Si-0.3%Al medium grade non-oriented electrical steel was investigated by the methods of thermodynamic phase diagram calculation,thermal simulation and microstructural characterization experiments. Rheological peak stress constitutive equations of specimens with different Mn content have been established and the critical strains of dynamic recrystallization in specimens have been calculated on the basis of constitutive equations. The grain size and volume fraction of recrystallization in specimens with different Mn content was also analysed. The results show that the more the Mn content,the higher the activation energy,in addition,the flow stress of specimens increased with the increase of Mn content on the same deformation condition,while,the ratio of critical strain to peak strain for dynamic recrystallization decreased. Moreover,the volume fraction of dynamic recrystallization in specimens improved with the increase of Mn content. It means that Mn element can promote the occurrence of dynamic recrystallization,which is beneficial for the production of non-oriented silicon steel without normalizing process. At the range of hot deformation temperatures,austenite phases in specimens increased with the increase of Mn content and the solid solution atoms in specimens increased too. This brings,on one hand,more harder austenite phases which offer more resistance to hot deformation,so the higher activation energy and flow stress are obtained. On the other hand,dislocations are less mobile and relative difficulty to climb or cross slip at high temperatures owing to the low stacking-fault energy in austenite and dynamic recovery is limited. Thus,deformation storage energy can be effectively accumulated. Besides,higher lattice distortion energy due to more solid solution Mn atoms can also hinder dislocations movement effectively which is also beneficial for the accumulation of deformation storage energy. Consequently,the occurrence of dynamic recrystallization took place more fully in specimens with more Mn content.
  • Effect of Mo content on microstructure and wear resistance of hardfacing layer of high chromium cast iron
    ZHANG Kai, GUO Zhi, SUN Dongyun, LI Yanguo, ZHANG Ming
    Iron and Steel. 2024, 59(4): 148-158. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230484
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    The high chromium cast iron surfacing layer is widely used in the internal lining of various large industrial equipment due to its high wear resistance. It is found that the carbide formed by the Mo element can provide core points for the primary carbides to refine the structure. However,whether the Mo element plays other roles besides providing core points remains to be studied. To investigate the influence of Mo content on the organization and performance of the high chromium cast iron surfacing layer, Mo ultra-carbon high chromium surfacing wear-resistant plate was designed. The effect of the Mo element on the structure and phase composition of the surfacing layer,as well as the surface and longitudinal section of the wear surfacing layer,is analyzed using XRD. The distribution in each phase,and further using the hardness and dry sand abrasive wear test,the influence of Mo alloying on the hardness and wear resistance of high chromium and high carbon surfacing layer was studied. The results indicate that the structure of the Fe-Cr-Mo-C alloy surfacing layer mainly consists of the gamma phase and M7C3 （M=Fe,Cr）. With the increase of Mo content,the primary carbide content in the surfacing layer decreases,the austenite content increases,and the size of a single primary carbide decreases first and then increases. The hardness of the primary carbide increases,and the macroscopic hardness of the surfacing layer increases and then decreases;after wear,the truncated pattern of the primary carbide decreases,and the sample showed the peeling of eutectic carbide. After adding 0.13% Mo,the grinding loss weight was reduced by 13.6%,and after adding 0.30% Mo,the grinding loss weight increased by 20.0%. This is because the inclusion of Mo atoms increases the hardness of the primary carbide,but with the content of primary carbides decreasing,it results in an initial increase and then a decrease in the hardness of the surfacing layer and a corresponding variation in grinding loss weight. The research results provide guidance for selecting the appropriate Mo addition in the preparation of high chromium cast iron surfacing layers. The composition of this test is designed with three samples with a Mo content ranging from 0.04% to 0.30%. The results indicate that the primary carbide shows a trend of first refinement and then coarseness,which necessitates further study.
  • Effect of cold rolling reduction on microstructure and mechanical properties of Fe-10Mn-6Al-0.4C steel
    LI Boyu, LIU Kun, FENG Yunli, LI Tao, WANG Shuhuan, SU Hongdong
    Iron and Steel. 2024, 59(4): 159-167. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230495
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    Fe-Mn-Al-C medium manganese steel has broad application prospects due to its low density,high strength and high plasticity. In the experiment,Fe-10Mn-6Al-0.4C was used as the research object. After hot rolling,it was annealed at 700 °C for 60 min and air-cooled to room temperature. Subsequently,they were cold rolled at 40%,60% and 70% reduction ratio,respectively. After cold rolling,they were annealed at 750 °C for 30 min and air-cooled to room temperature. The microstructure evolution after cold rolling and annealing was detected by SEM and EBSD,and the mechanical properties were measured by universal tensile testing machine. The results show that the microstructure of cold rolled plate is composed of banded δ ferrite,martensite （M）,austenite （A） and α ferrite. The microstructure of the annealed plate is composed of α ferrite,austenite and banded δ ferrite. With the increase of cold rolling reduction rate,the microstructure of the annealed sheet is layered structure,and the average grain size,the proportion of fine grain and the proportion of austenite phase composition decrease first and then increase,while the degree of recrystallization increases from 69% to 83.5%,and the GND density of the annealed sheet decreases. When the reduction rate is 60%,the GND density in austenite decreases sharply. The annealed plate is composed of fine equiaxed austenite,α ferrite and banded δ ferrite. The ferrite grain size is bimodal distribution. The yield strength is 818.7 MPa,the tensile strength is 962.3 MPa,the elongation is 34.3%,and the product of strength and plasticity is 33.01 GPa·%. The combination of strength and plasticity is excellent. The tensile fracture shows that the tensile fracture with a reduction rate of 60% has dense and fine dimples,which promotes the elongation of the annealed plate,while the reduction ratio of 40% and 70% have different degrees of cleavage steps,which deteriorates the elongation. Controlling the reduction rate combined with short-time annealing can form a layered structure under the premise of reducing the process cost,thereby improving the mechanical properties of the material.
  • High-temperature flow behavior and critical conditions of dynamic recrystallization of B55SiCr steel
    WANG Qingjuan, ZHANG Zhao, DU Zhongze, QI Zejiang, YANG Tongyao
    Iron and Steel. 2024, 59(4): 168-178. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230503
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    B55SiCr steel is mainly used to make automobile suspension springs,valve spring steel wires,etc. It plays a pivotal role in the stability and safety of automobiles,and has high requirements for organizational performance. Taking B55SiCr steel as the research object,thermal compression experiments were carried out in the range of deformation temperature and strain rate of 800-1 050 ℃ and 0.1-20 s-1,and based on the Zener-Hollomon parameters,a linear fitting method was used to construct a double Curved sine Arrhenius constitutive model. It is found that the flow stress of B55SiCr steel decreases with the increase of deformation temperature and increases with the increase of strain rate,and its thermal deformation activation energy（Q）is about 317 kJ/mol. The linear correlation coefficient（R）and the average absolute relative error（$|\bar{\delta}|$） of the flow stress prediction results and the test results obtained through the constitutive model are 0.992 15 and 3.70%,respectively. The work hardening rate curve was plotted. According to the stress-strain curve and the work hardening rate curve,the critical stress and strain for dynamic recrystallization（DRX）of B55SiCr steel were determined,and the critical condition and Z parameters are all in an exponential relationship. The microstructure of B55SiCr steel was analyzed,and it was found that under the condition of low temperature thermal deformation,mixed crystal structure appeared,and the microstructure was in a non-uniform state,and under the condition of high temperature thermal deformation,the microstructure was uniform equiaxed crystal;the KAM diagrams and local orientation difference distribution diagrams under different deformation conditions were drawn respectively. It was found that with the decrease of strain rate and the increase of deformation temperature,the dislocation density significantly decreased,the DRX became more complete and the grains gradually coarsened. The deformation conditions The HAGBs content at 1 050 ℃/0.1 s-1 increased by 13.51% compared with 850 ℃/10 s-1. At 1 050 ℃/0.1 s-1,the material is completely recrystallized and the grains are coarsened. Under this deformation condition,B55SiCr steel has good hot workability; as the strain rate increases,the grains become refined.
  • Effect of grain orientation in raw materials on texture of ultra-thin grain-oriented silicon steel
    ZHANG Bo, ZHANG Ning, HE Chengxu, MA Guang, HAN Yu, MENG Li
    Iron and Steel. 2024, 59(4): 179-187. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230540
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    Considering the different microstructure and texture evolution laws for different oriented grains in raw material during cold rolling and annealing processes in the preparation of ultra-thin grain-oriented silicon steel, the deformation and recrystallization behaviors of three types of grains with different deviation from exact Goss orientation was analyzed. It was found that,for Ⅰ-type （exact Goss） grains,sharp {111}<112> texture and abundant shear bands and deformation bands were formed during cold rolling,and a small amount of Goss oriented areas were observed in shear bands and deformation bands. During annealing,Goss oriented grains in shear bands and deformation bands nucleated preferentially,with the majority existing in shear bands,then η-fiber texture peaked at Goss component and uniform structure with relative lower average grain size were obtained. For Ⅱ-type （{0kl}<100>,k,l≠1） oriented grains,{111}<112> and {113}<361> textures were formed during cold rolling. There existed a small amount of η fiber areas in shear bands and deformation bands,while no shear bands were obtained in {113}<361> oriented regions. During annealing,η-fiber nucleation in shear bands and deformation bands occurred preferentially,and a large number of non-η fiber oriented nuclei presented an uneven distribution,then showed obvious growth advantage in following stage and thus obtained an uneven annealing structure with a lower proportion of η-fiber grains. The deformation and recrystallization behaviors of Ⅲ-type （{011}<uvw>） grains were similar to that of Ⅰ-type grains,while a lower intensity of {111}<112> texture was obtained during cold rolling,and the recrystallization texture showed a diffuse distribution characteristic along η-fiber; During annealing,η-fiber orientated grains also nucleated preferentially mainly in shear bands and deformation bands. The nucleated non-η-fiber grains presented a uniform distribution,and not marked uneven annealed microstructure with a higher proportion of η-fiber grains and relative larger average grain size were achieved. By overall considering microstructure and texture,the raw material with lower proportion of Ⅱ-type grains and moderate proportion of Ⅲ-type grains can be used to prepare ultra-thin oriented-grain silicon steel.
    • Metallurgical Process Engineering
  • Intelligent optimization of locomotive scheduling for multi-mode transportation on ironmaking and steelmaking interface
    HE Shujing, ZHENG Zhong, ZHU Daofei, ZHANG Kai, WANG Fei, SHA Yuanyang
    Iron and Steel. 2024, 59(4): 188-199. https://doi.org/10.13228/j.boyuan.issn0449-749x.20230588
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    In the current research of locomotive scheduling on the one-ladle technology on ironmaking and steelmaking interface, the multi-ladle transportation task has insufficient overall optimization ability, such as supply and demand matching, transportation path selection, and the transportation mode of the ladles, which limits the optimization of locomotive scheduling. In order to reduce the number of locomotives used, the empty-loaded rate of locomotives and the cost of locomotive transportation, on the premise of ensuring the demand of empty ladles for blast furnace tapping and the demand of heavy ladles in various steelmaking plants, a locomotive scheduling's mathematical model which takes the minimized multi-mode locomotive transportation cost as an optimization object is established by taking the transportation path characteristics, the types of ladles, the locomotive transportation capacity, the transportation mode of the ladles, the combined transportation time of the ladles and the safe time window of the locomotive into consideration, and a hybrid genetic algorithm combining genetic algorithm and Dijkstra algorithm is designed to solve the model, which realizes the rapid optimization of locomotive scheduling and transportation route under multi-ladle mode. The simulation experiment results based on the actual production data of an enterprise within 12 h show that the mathematical model and solution algorithm of locomotive dispatching plan can work out a reasonable locomotive scheduling plan within 7 min. Compared with the traditional ant colony optimization algorithm, the hybrid genetic algorithm has faster convergence speed, the number of locomotives is reduced from 17 to 16, the number of locomotive transportation tasks is reduced by 2.94%, and the empty-loaded rate is reduced by 4.59%. Compared with the actual production, the number of locomotives used is reduced from 18 to 16, the number of locomotive transportation tasks is reduced by 10.81%, and the empty-loaded rate is reduced by 35.43%. This method can effectively reduce the cost of locomotive transportation, reduce the influence of different locomotive dispatchers' personal experience on the rationality of locomotive scheduling scheme preparation, and reduce the difficulty and workload of dispatchers in optimizing locomotive scheduling.
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