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	2024 Vol. 59 No. 1
	Published: 2024-01-15



	Technical Reviews Raw Material and Ironmaking Steelmaking Metal Forming Materials Environmental Protection and Energy

Technical Reviews

	1	ZHANG Shuhui, WU Xiaozhang, LIU Ran, LAN Chenchen, YAO Hongyong, JI Heng
		Discussion on smelting characteristics and problems of blast furnace with hydrogen-rich gas injection
		The smelting process of blast furnace has high energy consumption and high CO₂ emission, which is the key point of energy saving and emission reduction in iron and steel industry. In the face of increasingly serious energy crisis and environmental problems, it has become a common understanding to achieve carbon emission reduction in blast furnace smelting process. Under the above background, the blast furnace injection hydrogen-rich gas smelting technology has been widely concerned by metallurgical workers. The main purpose of this technology is to replace carbon with hydrogen, reduce the consumption of carbon reducing agent and achieve the emission reduction of CO₂ in the blast furnace. Based on the thermodynamic analysis of the combustion reaction of hydrogen rich gas in front of tuyere, the smelting characteristics, existing problems and solving measures of blast furnace with hydrogen-rich gas injection are discussed systematically, and the future research work is prospected. The results show that compared with the traditional blast furnace smelting, the smelting characteristics of the blast furnace with hydrogen-rich gas injection have changed significantly: hydrogen rich gas can promote the reduction of iron ore, reduce the FeO content in the initial slag, reduce the slag content, and the melting point, reduce the pressure difference of the soft melt zone, as well as improve the air permeability. Hydrogen-rich gas injection is easy to reduce the temperature of the lower part of the blast furnace, and develop the air flow towards the center. It can promote the gasification reaction of coke in massive zone and affect the contact characteristics of coke and slag iron in high temperature zone. When the blast furnace of hydrogen-rich gas injection plays the advantage of hydrogen reduction, there are still some problems, such as insufficient heat in the lower part, reduced pulverized coal combustion rate and serious pulverized iron ore. For the smelting process of blast furnace with hydrogen-rich gas injection, it is suggested to strengthen on the mechanism research of interaction among hydrogen abundance of gas, metal iron carburizing and coke properties, and to explore the reasonable operating profile of blast furnace type. The raw fuel conditions suitable for blast furnace smelting with hydrogen-rich gas injection should be developed, and the development of hydrogen gas transportation, storage and injection equipment should be accelerated in order to promote the industrial implementation of smelting of blast furnace with hydrogen-rich gas injection.
		2024 Vol. 59 (1): 1-11 [Abstract] ( 78 ) [HTML 1KB] [PDF 0KB] ( 279 )

	12	SHANGGUAN Fangqin, CUI Zhifeng, ZHOU Jicheng, NI Bing, LI Tao
		Research on development strategy of electric arc furnace process in China under background of double carbon
		In order to actively respond to the "dual carbon goals" proposed by China, a series of policy documents for the steel industry have been successively issued by various ministries and commissions. It has been clearly pointed out that the development of the full-scrap electric arc furnace process should be guided in an orderly and reasonable manner, and the green and low-carbon transformation of the steel industry should be further promoted. In this context, a study was conducted to calculate direct carbon emissions, indirect carbon emissions, and product carbon sequestration credits resulting from China's iron and steel industry between 1991 and 2021. The calculations were based on the final energy consumption data of the iron and steel industry from the "China Energy Statistical Yearbook." The current state of CO₂ emissions in China's steel industry was analyzed as well. Furthermore, CO₂ emissions caused by typical long and short-process iron and steel production enterprises were calculated to explore variations in carbon emissions between these two process types. This quantification allowed for the assessment of the potential carbon reduction of the electric arc furnace process. It was determined that the rational and orderly promotion of the electric arc furnace process development stands as the primary direction for the steel industry's future transformation and advancement. Challenges and obstacles in China's electric arc furnace process development were also examined within the context of the current state of the iron and steel industry. Addressing the aforementioned issues, the study delved into resource-energy security, development modes, and the necessary technical structure for the electric arc furnace process. Preventative solutions were formulated based on these aspects. Building upon this research, a dual-carbon analysis model was constructed for China's electric arc furnace process. This model laid the groundwork for outlining a low-carbon development roadmap for the electric arc furnace process in China, considering both process-based and time-based levels. The findings revealed that the electric arc furnace procedure and rolling procedure exhibit the most substantial potential for carbon reduction, accounting for 40.7% and 36.7% of the entire process's carbon reduction potential, respectively. Through the integration of low-carbon technologies across various stages, it is projected that the carbon emission intensity per ton of steel in the electric arc furnace process will decrease by 35.1% in 2030 compared to 2020, by 74.7% in 2040, and by 2050, achieving a state of "near-zero carbon" smelting.
		2024 Vol. 59 (1): 12-21 [Abstract] ( 115 ) [HTML 1KB] [PDF 0KB] ( 233 )

Raw Material and Ironmaking

	22	ZHAO Tianle, ZHANG Fang, PENG Jun, WANG Yongbin, CHANG Hongtao, GAO Weimin
		Effect of B₂O₃ on degree of hematite crystallization during oxidation roasting
		Adding B₂O₃ to the raw materials in the ball preparation process is beneficial for obtaining low melting point compounds, improving the ball strength, and reducing reduction swelling, thus enhancing the metallurgical performance. However, there is still a lack of in-depth research on the mechanism of how B₂O₃ affects the crystallization and crystal continuity of hematite. Therefore, in order to understand the influence of B₂O₃ on the crystal continuity and occurrence pattern of hematite, different proportions of B₂O₃ pure reagents were added to Fe₃O₄ pure reagents. The mixture was then pressed, oxidized, and transformed into hematite, simulating the process of hematite formation in the roasting of magnetite pellets. SEM-EDS, XRD, XPS, and other methods were used to study the influence of different B₂O₃ contents on the crystal continuity, crystal growth, and microstructure of hematite in the roasting pellets. Raman spectroscopy was used to analyze the effect of B₂O₃ on the crystal structure of hematite. Furthermore, the microstructure, crystallinity, and grain size were determined. Finally, the impact of different B₂O₃ contents on the crystal continuity of hematite was discussed and summarized. The research results show that B₂O₃ has a promoting effect on the crystal continuity of hematite during the oxidation roasting process, followed by inhibitory effects. The proper addition of B₂O₃ can promote crystal growth and enhance the crystal continuity of hematite. When the mass percent of B₂O₃ is 6% and the roasting time is 40 minutes, the crystallinity of hematite is the best, reaching 83.68%. XPS analysis demonstrates that as the B₂O₃ content increases, the proportion of Fe³⁺ in hematite gradually increases, with Fe³⁺ accounting for up to 92.53%. As the B₂O₃ content further increases, the influence of B₂O₃ on slag fluidity and slag phase content increases. The slag phase infiltrates the hematite grains, inhibiting grain growth and crystal continuity. Raman spectroscopy analysis of the hematite crystal structure reveals that with the increase in B₂O₃ content, the peak intensities of the LO mode and E_u mode of hematite increase, indicating an increase in symmetry disruption caused by lattice defects, higher crystal disorder, and corresponding higher defect content.
		2024 Vol. 59 (1): 22-33 [Abstract] ( 54 ) [HTML 1KB] [PDF 0KB] ( 109 )

	34	TIAN Xu, ZHOU Heng, HUANG Jian, CAI Haoyu, KOU Mingyin, WU Shengli
		Numerical study of effect of φ(CO)∶φ(H₂) on reaction process in a direct reduction shaft furnace
		With the development of hydrogen production technology, it is feasible to use green hydrogen as a reducing agent in gas-based direct reduction shaft furnace. Among many non-blast furnace ironmaking technologies, the hydrogen-rich direct reduction shaft furnace process is expected to solve the problem of high CO₂ emission in traditional blast furnace long process. However, the common problem faced by the hydrogen-rich direct reduction shaft furnace is that when the volume percent of H₂ is too high, the reduction heat absorption leads to insufficient heat in the furnace, which affects the gas utilization rate and metallization rate. How to adjust the φ(CO)∶φ(H₂) of reduction gas, make the CO reduction process release heat to make up for the heat absorbed by H₂ reduction, and cooperate with other operating parameters and the optimization of furnace structure to fully utilize the physical energy and chemical energy, so as to improve the utilization rate of gas and metallization rate, has become an urgent problem to be solved for the hydrogen-rich direct reduction shaft furnace. In order to solve this problem, this paper established a two-dimensional CFD mathematical model of hydrogen-rich direct reduction shaft furnace, and investigated the influence of φ(CO)∶φ(H₂) in reduction gas on the multiphase and multi-field distribution of shaft furnace. The CFD model was validated by means of comparing simulation results with industrial test data. The results show that when the volume percent of H₂ in the reduction gas increases, the temperature in the shaft furnace continues to decrease. With the increase of the volume percent of H₂, the utilization coefficient of H₂ decreases while the utilization coefficient of CO increased slowly. The comprehensive utilization coefficient of reducing gas shows a trend of first increasing and then decreasing. When the volume percent of H₂ is 60%, the comprehensive utilization coefficient reaches the highest of 0.28. The mole percent of Fe concentration at the outlet of the furnace shows a trend of first increasing and then decreasing with the increase of the volume percent of H₂. When the volume percent of H₂ is 40%-50%, the highest mole percent of Fe can reach 95.67%. In the actual practice, maintaining the φ(CO)∶φ(H₂) in the reduced gas at around 40%∶60% can achieve high gas utilization rate and product metallization rate.
		2024 Vol. 59 (1): 34-40 [Abstract] ( 40 ) [HTML 1KB] [PDF 0KB] ( 171 )

	41	BAI Chenchen, SHI Xuefeng, WANG Mingyang, YU Hao, HU Changqing, HAN Tao
		Numerical simulation analysis of direct reduction of gas-based shaft furnace
		Aiming at the difficulty that the operation degree of the reduction reaction cannot be directly observed during the direct reduction process of the gas-based shaft furnace, based on the three-interface unreacted nuclear model, a direct reduction model of the gas-based shaft furnace is established under the condition of ignoring the internal temperature of the model pellet and assuming that the thermal effect of the pellet reduction reaction completely occurs in the solid phase, and the valence state transformation of iron oxide is numerically simulated and verified. The results show that since the established gas-solid model contains three interfaces, the reaction radius of each interface eventually tends to zero with the stepwise reduction of iron oxides, and the reduction reaction rate increases first and then decreases with the increase of shaft furnace depth. When the pellets descend to a depth of 3 m in the shaft furnace, a FeO reaction interface with a radius of 15 mm appears, where the pellet reduction rate is about 28%. As the pellets continue to descend about 2 m in the shaft furnace to a depth of 5 m, the radius of the interface of Fe₃O₄ decreases to 0, at which point the iron oxide completely transforms into the floatite form, and the pellet reduction rate is about 34%. By changing different process parameters for simulation, it can be found that the metallization rate and reduction rate of the reducing pellet increase with the increase of gas temperature. When the gas temperature increases at 50 ℃ and the reducing gas flow rate increases at a gradient of 5 040 m³/h, the corresponding pellet metallization rate increases by about 8% and 4%, respectively. In contrast, the metallization rate of the pellets is much more affected by the cutting speed than the gas temperature and reducing gas flow, which is manifested as follows: when the cutting speed increases by 0.02 t/h, the metallization rate decreases by about 0.07%. When the pellet size decreases, the metallization rate will show an increasing trend, and the pellet size decreases by 1 mm, and the pellet metallization rate increases by 2.23%.
		2024 Vol. 59 (1): 41-48 [Abstract] ( 56 ) [HTML 1KB] [PDF 0KB] ( 241 )

Steelmaking

	49	LU Hongbin, ZHU Hongchun, JIANG Zhouhua, LI Huabing, YANG Ce
		Prediction of end-point temperature in electric arc furnace based on e-FCNN
		The development of the EAF steelmaking short process is an important strategic way to realize the green development of the iron and steel industry. The end-point control of EAF steelmaking determines the quality of tapping and smelting efficiency, especially the end-point temperature control. The establishment of the prediction model to achieve the EAF end-point temperature prediction in advance helps to adjust the smelting process in time and realize the fast and efficient tapping operation. The EAF end-point temperature prediction model is mainly divided into the mechanism model and the data-driven model. Data-driven modeling is the main research direction at present, but the modeling process usually relies on a large amount of historical data, and it is difficult to achieve accurate end-point temperature prediction under small sample data conditions. Therefore, tightly combined with the metallurgical mechanism, with artificial intelligence algorithms as the core, established a highly adaptive EAF end-point temperature prediction model. The input parameters of the model were obtained by metallurgical mechanism and Pearson data correlation analysis. Based on the FCNN algorithm, the early stopping strategy was introduced, the e-FCNN algorithm was proposed to prevent the overfitting phenomenon of the FCNN algorithm, and the end-point temperature prediction model of the EAF was established based on the e-FCNN algorithm. Simulation results show that the e-FCNN model end-point temperature prediction error is within ±5 ℃ with a hit rate of 93.33%. In addition, CART, RF, ε-SVR, and v-SVR models were developed using hyperparametric random grid search under the condition of small-sample historical data, and the results show that the accuracy of the e-FCNN model is significantly better than others. Using the e-FCNN model to continuously track the actual production of 30 heats, the hit rate reaches 96.7% when the prediction error is within ±6 ℃, which can effectively guide the production. In the future, further improvement of the combination of mechanism and data-driven is the development direction of EAF end-point temperature prediction models.
		2024 Vol. 59 (1): 49-57 [Abstract] ( 67 ) [HTML 1KB] [PDF 0KB] ( 190 )

	58	WANG Shisong, WANG Yunbo, TANG Qing, ZHANG Xubin, HE Shengping
		Control of temperature of high-Ti steel on top surface and "floater" formation
		During the production of the high-Ti steel, TiN inclusions formed under the reaction of the tatinium and nitrogen in the liquid steel, and aggregated near the steel-slag interface, which easily resulted in the formation of the "floater" on the steel-slag interface at the low-temperature zone and then the troubled continuous casting. The numerical simulation was established and used to solve the problem of the "floater" formation in the continuous casting mold during the casting of high-Ti steel. In order to reduce the formation of "floater" in the mold by increasing the temperature of the steel on the surface, the influence of the current by the electromagnetic stirring, casting speed and casting superheat on temperature of the steel on the surface was discussed, and the adjustment of the basicity of the mold slag was conducted. Through mathematical simulation, it is found that the temperature of the steel on the surface can be raised by the application of the electromagnetic stirring equipment in the mold with the casting speed of 0.85 m/s and 1.05 m/s, and the temperature is the highest with the stirring current of 200 A. With the current of the electromagnetic stirring constant, the increase of the casting speed and casting superheat can result in the increase of the steel temperature on the surface and the decrease of the size of the low temperature zone at the corner of the mold. Through the trial in the steel plant, it is found that with the casting superheat increasing from 25 K to 60 K, the formation of "floater" did not occur in the mold, and the slag-entrapment defects on the surface of continuous casting billet were significantly reduced when the continuous casting parameters except the casting speed were constant. With the basicity of continuous casting mold slag increasing from 0.60 to 0.88, the ability of crystallization and the heat-transfer control increased, and during the trial in the steel plant the thickness of liquid slag increased from 6 mm to 8 mm, which indicates that the temperature of liquid steel on the surface increased. Besides, the "floater" also did not occur with the application of the optimized slag during the low-superheat casting (40 K). Hence, the formation of "floater" in the continuous casting process of high-titanium steel was affected by the temperature of the liquid steel at the surface, and the formation of "floater" in the mold could be reduced by increasing the casting superheat and improving the control ability of the heat transfer of the continuous casting slag. The optimized slag could be used for the casting of high-titanium steel with low superheat, and would provide theoretical guidance for improving the casting ability of high-itanium steel.
		2024 Vol. 59 (1): 58-66 [Abstract] ( 53 ) [HTML 1KB] [PDF 0KB] ( 239 )

	67	BAO Xiangjun, CHEN Kai, LI Xiuping, YANG Xiaojing, LIU Xiao, CHEN Guang
		Prediction model of converter gas production based on deep-learning
		The prediction of the occurrence of converter gas provides important support for the micro differential pressure control at the converter inlet, the improvement of converter gas recovery quality, and the overall gas balance scheduling of the plant. Based on the actual occurrence data of converter gas during the blowing process of a certain steel plant, a deep learning method was used to establish three prediction models for converter gas occurrence: BP neural network, LSTM long short memory neural network, and RBFNN radial basis function neural network. The effects of three parameters, namely prediction steps, input sample size, and hidden unit number, on the accuracy and computational efficiency of the prediction model were compared and analyzed. The research results indicate that the prediction accuracy of the model decreases with the increase of prediction steps, and choosing 30 step prediction is more in line with the actual needs of steel mills. As the sample input increases, there is no significant change in the accuracy of LSTM, while the accuracy of BP shows a decreasing trend. The accuracy of RBF first increases significantly and then slowly decreases. The prediction efficiency of LSTM showed no significant change, BP significantly decreased, and RBF remained unchanged. When the three models are under the optimal sample input and 30 step prediction conditions, the accuracy of LSTM remains basically unchanged as the number of hidden units increases. BP first slightly increases and then slowly decreases, while RBF first increases significantly and then remains stable, and then decreases significantly. The prediction efficiency of LSTM has slightly decreased, BP has significantly decreased, and RBF remains unchanged. Finally, under the condition of 30 step prediction, the optimal parameter conditions for LSTM, BP, and RBF models are as follows: LSTM sample input quantity is 125, hidden unit number is 135, E_RMS minimum is 13.38, and training duration is 4.7 min; The input amount of BP samples is 50, the number of hidden units is 60, and the minimum E_RMS is 31.46, with a training duration of 16.8 min; The input amount of RBF samples is 210, and the number of hidden units is 210. At this time, the minimum E_RMS is 2.07, and the training duration is 1.2 min. Compared with actual data, RBF has the best prediction effect. By using the prediction results of converter gas generation to regulate the speed of the fan, the micro differential pressure at the furnace mouth can be maintained in a more stable state, reducing the suction air volume, and improving the heat value of the recovered gas.
		2024 Vol. 59 (1): 67-74 [Abstract] ( 66 ) [HTML 1KB] [PDF 0KB] ( 85 )

	75	LI Xiaoming, WANG Yang, ZHU Jiayu, YANG Yongkun, WANG Jianli, WANG Weian
		Effect of nozzle position on flow field and solidification in billet mold
		Owing to the loss of symmetry in the flow field of the inner and outer arcs when the curved continuous casting nozzle is centered, as well as the uneven temperature of the inner and outer arcs during the production, the solidification quality of the continuous casting billet is seriously affected. Studying the effect of nozzle positioning on improving flow field distribution is particularly crucial. In this study, the mathematical model of electromagnetic, flow, heat transfer and solidification coupling of steel in arc mold is established. The influence of SEN offset direction and offset distance on the flow behavior is studied, and the symmetry index I_s is introduced to evaluate the uniformity of solidified shell. It is found that the SEN offset to inner arc increases the flow field difference and produces the bias flow phenomenon, and the application of electromagnetic stirring exacerbates this phenomenon. When the SEN is offset to the outer arc, regardless of whether electromagnetic stirring is applied or not, the index of I_s increases and then decreases of each plane, improving the flow field distribution in the mold and make it tend to be symmetrical, which is beneficial to improve the quality of the casting billet. When M-EMS is applied, the vortex core gradually moves to the center of the electromagnetic stirring center surface with the distance of SEN offset to the outer arc increase. Although the steel flow is not symmetrical in the form of inner and outer arcs, there is a certain deflection angle, which increases the temperature difference between the inner and outer arcs in all case models. However, for M-case 6, the temperature difference increases is only 1.666 ℃. When the SEN is offset to the outer arc by 6.5 mm, the index of I_s and the uniformity of the solidified shell are the highest, the velocities of the inner and outer arc almost coincide, the temperature difference between the inner and outer arcs is the smallest, the distribution of the steel flow field is the best. By adjusting the position of the SEN, the symmetry of the flow field in the mold can be improved, the uniformity of the solidified shell can be enhanced, and the bias flow phenomenon caused by the mold curvature and the electromagnetic stirring intensification can be eliminated.
		2024 Vol. 59 (1): 75-90 [Abstract] ( 51 ) [HTML 1KB] [PDF 0KB] ( 82 )

Metal Forming

	91	WANG Jin, PENG Yan, ZHAO Xiangyang, WANG Menghan, LI Aimin, MA Bin
		Normal inter-roll contact stiffness model considering friction factor
		With the growing demand for high-quality strip products, the precision requirements for strip mill equipment have become increasingly stringent, and the precision of the mill equipment plays a pivotal role in ensuring product quality. The contact stiffness between rolls in the strip mill is a fundamental parameter that not only ensures product quality but also significantly impacts the stability of the rolling process. Presently, the rolling mill roll contact stiffness model takes into account the elastic deformation of the roll system and the force relationship. However, during the service cycle of the rolls, the surface condition continually deteriorates, leading to changes in the roll contact friction state. The conventional roll contact stiffness model does not consider these contact friction factors, resulting in an inability to accurately reflect the rolling process and the influence of the roll surface state on the inter-roll contact stiffness. To address this limitation, a comprehensive investigation into the inter-roll contact stiffness of rolling mills requires the establishment of a model that considers friction. This study leverages fractal theory to model the rough surface of rolls and analyzes the deformation state of micro-convex body contacts on the roll's rough surface, along with the curved surface contact characteristics of the roll system. As a result, a normal contact stiffness model is developed, which incorporates frictional effects between rolls. The 2 250 mm hot rolling mill is used as a case study to explore the impact of fractal parameters, contact parameters between rolls, and the size of the roll system on the inter-roll contact stiffness. The findings indicate that fractal dimension and fractal roughness are positively and negatively correlated with inter-roll contact stiffness, respectively, suggesting that a rougher roll surface results in lower inter-roll contact stiffness. Additionally, an increase in the inter-roll contact friction coefficient leads to a gradual decrease in inter-roll contact stiffness, while larger inter-roll contact loads and roll diameters result in higher inter-roll contact stiffness. The model established in this paper can provide a parametric basis and theoretical basis for evaluating the accuracy of rolling mill equipment.
		2024 Vol. 59 (1): 91-98 [Abstract] ( 45 ) [HTML 1KB] [PDF 0KB] ( 212 )

	99	WANG Youlong, LI Weigang, WANG Yongqiang
		Crown prediction of hot strip steel based on integrated feature selection and SVR
		As a key index to evaluate the shape quality of hot strip steel plate,the crown of hot strip steel plate has the characteristics of multi-variable,nonlinear and hereditary. The traditional crown model of hot continuous rolling plate has some problems, such as complicated mechanism, difference between theory and practice and limited accuracy of the model. In order to solve these problems, a prediction model for crown of hot continuous rolling plate based on integrated feature selection and support vector regression is proposed in this paper. Firstly, an ensemble learning model based on Random Forest (RF), eXtreme Gradient Boosting (XGBoost) and Gradient Boosting Decision Tree (GBDT) is established, and the comprehensive application of these base learners can fully mine the feature information in the data. Secondly, the feature importance obtained by the base learner is weighted by the ensemble learning model, and the most informative input features are selected according to the feature importance ranking after fusion, which can effectively reduce the feature dimension. Then, Grey Wolf Optimization (GWO) is used to optimize the parameters in the Support Vector Regression (SVR) prediction model, which can not only eliminate the subjectivity and blindness of traditional manual parameter selection. It can also better adapt to the characteristics of the data. Finally, the selected features are input into the SVR prediction model with optimized parameters, which is used to predict the crown of hot continuous rolling plate. The experimental results show that the absolute error of the model is more than 99% within 15 μm. The prediction model not only improves the prediction accuracy, but also provides powerful guidance and support for the precise control of crown and the improvement of shape quality of hot continuous rolling plate. It provides useful methods and ideas for solving the key problems in complex hot continuous rolling production and improving the sustainability and efficiency of the production process.
		2024 Vol. 59 (1): 99-107 [Abstract] ( 43 ) [HTML 1KB] [PDF 0KB] ( 248 )

	108	ZHANG Xiaoyan, ZHANG Ji, WANG Zhuo, BAI Shuo, BAI Zhenhua
		Calculation model of asynchronous rolling pressure during flattening process
		The phenomenon of asynchronous rolling, where the friction coefficients between the upper and lower surfaces of the strip differ due to the uneven distribution of leveling fluid droplets on the lower surface of the strip during the temper rolling process, leads to limited accuracy when predicting the rolling pressure using conventional engineering-level leveling models. To address the issue of significant errors in calculating the rolling pressure for asynchronous rolling using these models, a calculation method suitable for asynchronous rolling is proposed. This study takes into account the process characteristics of asynchronous rolling and the actual operating conditions of the equipment. Firstly, the differences in lubrication conditions and force deformation between the upper and lower surfaces of the strip are analyzed, and equilibrium equations for the deformation zone and the equation for calculating the unit rolling pressure are established. Secondly, the differences in flattening between asynchronous and synchronous rolling are investigated. Based on the geometric relationships of deformation and the theory of elastoplastic mechanics during the rolling process between the upper and lower rolls, the calculation methods for various parameters in the deformation zone are determined. An iterative method is then employed to improve the accuracy of the calculation model. A rolling pressure calculation model suitable for the asynchronous rolling process in leveling units is established, along with a method for back-calculating the friction coefficient between the upper and lower surfaces of the strip. Finally, to validate the accuracy of the model, equipment parameters from a domestic leveling unit and typical process parameters for strip production are used. The theoretical values obtained from the rolling pressure model under different lubrication conditions are compared with calculating the rolling pressure for rolling using engineering model and the on-site measured data. The results demonstrate that the proposed asynchronous rolling pressure model can applicable to asynchronous rolling, it reduces the error by 5% compared to the engineering model during the temper rolling process and provides valuable insights.
		2024 Vol. 59 (1): 108-116 [Abstract] ( 47 ) [HTML 1KB] [PDF 0KB] ( 167 )

Materials

	117	HUANG Riqing, REN Ying, ZHANG Lifeng
		Characteristics of inclusion in low carbon martensitic stainless steel during solidification and cooling process
		Low carbon martensitic stainless steels were widely used in various industries of economy and social development due to their excellent comprehensive properties. Non-metallic inclusions in steel have an obvious influence on the performance of low carbon martensitic stainless steel. Previous studies mainly focused on the formation,removal,modification,and other control methods of inclusions in the liquid steel. The characters of inclusions in low carbon martensitic stainless steel during the solidification and cooling process of the liquid steel was rarely studied. Therefore,it is necessary to study the inclusion characteristics in the solidification and cooling process of low carbon martensitic stainless steel to lay a foundation for the control of inclusions in the final low carbon martensitic stainless steel products. Inclusions in S400 low carbon martensitic stainless steel were investigated in the current study. Steel samples were cooled at different cooling rates of 1,10,20 and 50 ℃/s by high temperature confocal microscopy. The effect of cooling rate on the composition transformation of inclusions in low carbon martensitic stainless steel. During the solidification and cooling process of steel,the Al₂O₃ content in inclusions increased obviously,the CaO content of increased slightly,and MgO and SiO₂ content increased first and then decreased. The change of thermodynamic equilibrium between inclusions and the steel matrix caused by the change of temperature was the main driving force for the composition transformation of inclusions during in the solidification and cooling process. At a cooling rate of 50 ℃/s,the main composition of inclusions was 21%Al₂O₃-12%MgO-35%CaO-29%SiO₂. With the decrease of the cooling rate,the content of SiO₂ decreased and the content of Al₂O₃ increased gradually. With a higher cooling rate,the low carbon martensitic stainless steel was quickly cooled from the high temperature to the low temperature,the inclusion in the effective reaction time was shorter,which retarded the rapid diffusion of elements in the steel. Then,the composition of the inclusion changed little.
		2024 Vol. 59 (1): 117-123 [Abstract] ( 57 ) [HTML 1KB] [PDF 0KB] ( 256 )

	124	FENG Zan, GAO Hailiang, TUO Chende, WANG Zhen
		Effect of nitride on strength and impact property of rack steel
		When smelting rack steel with steel ingots,due to the absorption of N during the casting process,the N content in the steel is relatively high,which affects the solid solution B content in the steel,reduces the hardenability of the steel plate,and affects the performance of the center the steel plate. In order to improve the strength and toughness matching of the steel ingot rolling gear steel,the addition of Al or Ti elements to reaction with N in the steel ensures sufficient solid solution B in the steel plate,improves the hardenability of the steel plate,and increases the proportion of tempered sorbite in the center of the steel plate. By comparing the properties and microstructure of steel plates,it was found that both adding Al and Ti can improve the hardenability and strength of the steel plate. The steel plate with Ti has better hardenability and higher strength,but its low-temperature impact absorption energy decreases. Analyzing the impact fracture surface of the steel plate,it was found that there are large particles of TiN inclusions in the steel plate. Cracks exist between the inclusions and the matrix or between the inclusions themselves,which become the source of cracks in the impact test and reduce the toughness of the steel plate. Comparison of steel plates with Al and Ti added Statistical analysis of inclusions above 2 μm shows that there are a large number of large particle TiN inclusions in Ti steel,with a maximum inclusion size exceeding 15 μm. There are still a small amount of TiN inclusions in the Al added steel plate,but the number and size of TiN inclusions have decreased,and AlN has not significantly increased. In situ analysis and comparison were conducted between the Al element in the Al steel plate and the Ti element in the Ti steel plate. It was found that the Al element is negatively segregated at the center and has a lower degree of segregation. The Ti element is positively segregated at the center and has poorer uniformity,with local segregation. Thermodynamic calculations indicate that when titanium is used for nitrogen fixation,TiN will precipitate at the solidification front,resulting in a higher precipitation temperature;when using aluminum nitrogen fixation,if the mass fraction of aluminum is not less than 0.08%,AlN precipitates in the solid state at a temperature higher than BN,which can ensure the solid solution boron content in the steel plate,ensure the hardenability of the steel plate,and control the size of TiN precipitates in the steel.
		2024 Vol. 59 (1): 124-131 [Abstract] ( 50 ) [HTML 1KB] [PDF 0KB] ( 139 )

	132	QI Xiangyu, YAN Ling, DU Linxiu
		Welding properties of high strength steel for coal mine hydraulic support
		In order to realize the high quality welding of Q550D high-strength mid-thick plate,and promote its popularization and application in the field of coal mine hydraulic support. The welding test of 550 MPa high-strength mid-thick plate for coal mine hydraulic support was carried out by CO₂ semi-automatic gas-shielded arc welding. The microstructure of welded joint was observed by optical microscope. The crystallographic characteristics and fine morphology of coarse-grained heat-affected zone in welded joint were observed by electron backscattered diffraction and transmission electron microscope. The comprehensive mechanical properties of the welded joint were measured by tensile and impact testing machines. The results showed that the yield strength and tensile strength of the welded joint are 655 MPa and 747 MPa,respectively. The elongation is 18.5%,and the fracture occurs at base metal. The impact energy of weld metal,fusion line,fusion line outward 1 mm,fusion line outward 3 mm and fusion line outward 5 mm at -20 ℃ are 82,113,106,124 and 159 J,respectively. The average hardness of weld metal,coarse-grained heat-affected zone,fine-grained heat-affected zone,intercritical heat-affected zone and base metal are 294.07HV,293.18HV,264.67HV,275.02HV and 278.49HV,respectively. Compared with the base metal,the weld metal and coarse-grained heat-affected zone are local hardening zone with hardening rates of 5.59% and 5.27%,respectively. And the fine-grained heat-affected zone and intercritical heat-affected zone are local softening zone with softening rates of 4.96% and 1.25%,respectively. The acicular ferrites with high dislocation density crisscross and bite each other,which can effectively prevent crack propagation and improve the mechanical properties of the coarse-grained heat-affected zone. The large angle boundary ratio of granular bainite,strip bainite and acicular ferrite generated within the parent austenite grain in the coarse-grained heat-affected zone is 72.12%,and the average equivalent sub-grain size is 1.28 μm. High proportion of large-angle grain boundaries and equivalent sub-grains with small size can effectively resist crack propagation,which is the main reason for the excellent low-temperature impact toughness of the welded joint.
		2024 Vol. 59 (1): 132-138 [Abstract] ( 59 ) [HTML 1KB] [PDF 0KB] ( 248 )

	139	YANG Honglüe, XIAO Zhixia, FENG Jianhang, CHEN Jiaqi, CHEN Xingfu, LIU Jiebing, SHI Liyong
		Effect of inoculation treatment and holding time on microstructure and mechanism of high nickel-chromium cast iron
		High nickel-chromium centrifugal composite rolls have excellent strength and hardness as well as great resistance to thermal shock and thermal cracking,which is attribute to the good match of graphite and eutectic carbides in the structure of high nickel-chromium cast iron. However,the unsuitable inoculation would not effectively improve the structure and even form inclusions to deteriorate the material properties. Meanwhile,in the process of roll manufacturing,holding time of high-temperature iron liquid in the intermediate ladle is uncertain,due to the instability of iron smelting process and casting process. Eutectic carbide and graphite in the as-cast structure of high nickel-chromium cast iron was studied after holding for 3 h,5 h and 7 h,and followed by adding 0.4%,0.8% and 1.2% inoculant before pouring. The influence of holding time and inoculant treatment on hardness was also compared. The results show that with the increase of holding time,the average size and volume fraction of graphite increases,but the number density decreases,and the content of eutectic carbides decreases obviously. After inoculation treatment with holding time of 3 h,the nucleation of graphite could be effectively promoted,but the average size and number density of graphite did not improve significantly even if the amount of inoculant was increased after increasing holding time. When the holding time is less than 5 h,the content of eutectic carbide can be reduced by inoculation treatment,but the content of eutectic carbide can be increased by inoculation treatment after increasing the holding time. The hardness of high nickel-chromium cast iron decreases gradually with the increasement of holding time. When the holding time is more than 5 h,the hardness of incubated samples can increase 16HRC. In the smelting process of high nickel-chromium cast iron,the holding time should be controlled within 3 h,too long holding time will lead to excessive growth of graphite and reduce the amount of graphite. At this time,the amount of graphite can be increased by adding 0.4%-1.2% inoculant,but after holding for more than 5 h,even adding inoculant can not effectively improve the amount of graphite.
		2024 Vol. 59 (1): 139-147 [Abstract] ( 38 ) [HTML 1KB] [PDF 0KB] ( 203 )

	148	JIN Herong, SHEN Xiaolong, FENG Kangkang, ZHANG Biao, YI Yali, ZHAO Dingxuan
		Effect of interlayer residual stress on microstructure and properties of sandwich composite plate
		Adding a filling interlayer between stainless steel composite plates by interlayer vacuum coating technology will produce interlayer residual stress. In the subsequent hot rolling process,the microstructure and mechanical properties of the composite plates may be changed due to the influence of interlayer residual stress. The residual stress between the layers of the stainless steel clad plate is generated by the combined action of the thermal stress and the phase transition stress during the solidification process of the filling interlayer. The residual stress between the layers is eliminated by heat treatment before rolling. The heat treatment process before rolling is formulated by combining numerical simulation and experimental verification. Two kinds of stainless steel clad plates with and without eliminating residual stress between the layers are prepared by interlayer vacuum differential pressure coating,heat treatment before rolling and hot rolling experiments. The effects of residual stress on the microstructure and properties of the clad plate are analyzed by metallographic observation,hardness test,interface energy spectrum scanning,tensile shear and other characterization and performance test experiments. The results show that the rolling pretreatment process to eliminate the residual stress between layers is heating to 400 ℃,holding for 3.5 h and slow cooling under the condition of ensuring the same structure of base layer,interlayer and composite layer. After pre-rolling treatment,the residual stress between layers is reduced by 96.3%. Compared with the composite plate without eliminating interlayer residual stress,the interlayer stress of the composite plate with eliminating interlayer residual stress is significantly enhanced after rolling,and the grain is refined by 81.7%. At the same time,eliminating interlayer residual stress can increase the shear strength of the composite plate by 13.3%,the tensile strength by 3.9%,the elongation after fracture by 4% and the microhardness of the interlayer interface by 3.5%. The research content of this paper improves the overall performance of the sandwich composite plate with filling by eliminating the residual stress between the layers,which can provide theoretical guidance for the improvement of the performance of the related casting forming components,and expand the new idea for the further popularization and application of the process.
		2024 Vol. 59 (1): 148-156 [Abstract] ( 37 ) [HTML 1KB] [PDF 0KB] ( 69 )

Environmental Protection and Energy

	157	LÜ Weijian, WANG Long, ZHANG Hao, LI Zongxu, WANG Ling, LI Fuping
		Research on progress of zinc extraction process from iron and steel metallurgical sludge
		Iron and steel metallurgical dust sludge is a by-product of iron and steel smelting processes,which contains a certain amount of metalic zinc resources. Adopting reasonable technology to extract zinc from iron and steel dust sludge can not only reduce environmental pollution,reduce the adverse effects of zinc on smelting processes,promote green production in iron and steel enterprises,but also increase zinc resources. On the basis of summarizing of the source,chemical composition and phase composition of iron and steel metallurgical sludge,the utilization status and treatment technology of zinc resources in iron and steel metallurgical dust were summarized. The principles,advantages and disadvantages of zinc extraction processes such as physical method,fire method,wet method,deep eutectic solvent leaching method,ultrasonic method,microwave method and biological method were described in detail. The physical treatment process has the advantages of simple operation,low investment and operation cost,but the treatment efficiency is generally not high,and it is generally only used as a pretreatment process for fire and wet processes. Although pyrometallurgical methods can handle large amounts of metallurgical sludge,the purity of the products obtained is not high. Meanwhile,there are problems such as high pollution and high energy consumption. Compared with pyrometallurgical methods,wet process requires less capital,has higher environmental benefits and higher selectivity,lower energy consumption and less harmful gas emission. However,it also has some disadvantages such as high concentration of leaching agent,slow reaction speed and serious corrosion to equipment. The emerging processes such as deep eutectic solvent leaching,ultrasonic method and biological method have certain advantages over traditional processes in zinc extraction. However,in practical applications,there are also some problems that need to be improved and further promoted. The effective combination of emerging zinc extraction technologies with traditional processing methods and the development of cleaner and more environmentally friendly and efficient zinc extraction processes are important directions for the future resource utilization of steel and iron metallurgical sludge.
		2024 Vol. 59 (1): 157-167 [Abstract] ( 84 ) [HTML 1KB] [PDF 0KB] ( 196 )

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