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	2023 Vol. 58 No. 1
	Published: 2023-01-15



	Technical Reviews Raw Material and Ironmaking Steelmaking Metal Forming Materials

Technical Reviews

	1	ZHANG Li-feng
		Development history and future prospects of steelmaking (Ⅱ)—Future prospects
		Firstly, the development of the hot metal pretreatment, BOF steelmaking, steel secondary refining and continuous casting motivated by the science and technology progress was summarized and exampled. The conventional KR hot metal pretreatment process was improved by injecting the desulfurization flux powders through a lance with carrying gas so that powder particles penetrated the hot metal deeper and the coagulation of particles less occurred and the desulfurization efficiency was improved. During the production of the stainless steel through BOF process, a second lance was used to low Cr-ore powders with carrying burning gas and oxygen gas, through which the oxidation of the Cr was lowered and the required temperature was reached as well. The progress of the steel secondary refining was fully supported by technologies of argon blowing, vacuum techniques and electromagnetic techniques. The defect-free continuous casting semis was achieved with the support of electromagnetic stirring, mechanical reduction and digital technology. Secondly, the future of steelmaking was forecasted, including the limit of the steel cleanliness, future steelmaking technologies and continuous steelmaking process. Currently, the control level of oxygen, carbon, nitrogen, phosphorus, sulfur and hydrogen in the steel was as low as 0.006 0% while techniques for the removal of zinc, tin, lead, antimony, bismuth and arsenic from the steel need to develop. With the development of information and automatic technologies, the intelligent BOF steelmaking without splashing and unmanned situation can be achieved in the future. The big data technology, software technology and the cyber physical system have been tentatively employed in advanced steel plants. In Europe, the reduction of mineral iron ores by pure hydrogen has been tried in pilot scale. With development of the scientific and technology progress, the continuous steelmaking will become reality within future 50 years. At last, the future fundamental studies on steelmaking were briefly predicted. The multiscale, multiphase and multicomponent physical phenomena of steelmaking will be focused through first-principles calculations, the steel grade design based on the material gene calculation, the thermodynamics and kinetics of physical and chemical reactions coupling fluid flow, heat transfer and solidification of the steel.
		2023 Vol. 58 (1): 1-12 [Abstract] ( 270 ) [HTML 1KB] [PDF 7494KB] ( 755 )

Raw Material and Ironmaking

	13	CHAI Yi-fan, FAN Ying-jie, GAO Xing, LUO Guo-ping, WANG Yi-ci, AN Sheng-li
		Influence of basicity on reduction swelling properties of pellets prepared from Bayan Obo iron ore
		High-proportion pellet smelting is the development trend of blast furnace ironmaking. Due to the differences in chemical composition, mineral composition and structure, the reasons for the reduction and swelling of pellets produced or used by different enterprises are different and relatively complex. Facing the major national strategic needs of ensuring the safe supply of mineral resources. Pellets prepared from Bayan Obo iron ore concentrate were selected as the research object. According to the iron oxide reduction theory of pellets, the influence mechanism of basicity on the reduction swelling performance of pellets was studied from the perspective of thermodynamics. The XRD results were combined to investigate the change law of calcium-binding phase in pellet production and the influence on the reduction swelling of pellet. A reasonable basicity that meets the requirement of reducing swelling rate of flux pellets in blast furnace ironmaking was found. Increase the proportion of Bayan Obo iron concentrate pellets in iron and steel smelting production. Improve the reduction and swelling theory of special ore pellets to provide theoretical support for the efficient smelting of complex intergrowth ores. The results show that with the increase of basicity, the swelling rate of pellets first increased and then decreased. When the basicity was 0.8, the swelling rate was the largest, reaching 75.743%. Its shape was like an open petal, and it could not maintain its original spherical shape. The optimum basicity of the pellets prepared is 1.4 by synthesizing the iron grades of pellets with different basicity and the reduction swelling rate. With the increase of basicity, the amount of liquid phase generated of pellets first decreasing and then increasing. The amount of liquid phase generated at an basicity of 0.8 was the least. The reason for the increase in the swelling rate of the pellets is that the crystallinity of the pellets increases, the grains are coarse, and the crystal structure gradually tends to be ordered, which lays the foundation for the growth of iron whiskers; The reason for the decrease in swelling rate is because of the generation of calcium ferrite. Calcium ferrite has excellent binder phase properties and good reducibility,which improves the strength of the pellets,enhances the ability to resist swelling stress, and promotes the uniform swelling of the pellets. The volume swelling caused by the crystal transformation of Fe₂O₃→Fe₃O₄ is reduced.
		2023 Vol. 58 (1): 13-21 [Abstract] ( 151 ) [HTML 1KB] [PDF 4478KB] ( 458 )

	22	SHAN Chang-dong, ZHANG Jian-liang, WANG Yao-zu, TANG Yong-hong, NIU Le-le, LIU Zheng-jian
		Effect of high magnetite concentrates ratio on sintering index and metallurgical properties under oxygen-enriched conditions
		In order to investigate the effect of magnetite proportioning on the sintering index and metallurgical properties of sintered ore under oxygen-rich conditions in depth, the sintering index, reducibility, low-temperature reduction pulverization and soft fusion characteristics under different magnetite proportioning were studied using sinter pot experiments, reduction and soft fusion equipment. The experimental results showed that as the magnetite powder ratio increased from 0 to 56.4%, the percentage of less than 10 mm particle size sintered ore decreased, the percentage of more than 40 mm particle size sintered ore had large fluctuations, and the percentage of finished sintered ore increased after oxygen enrichment of the sintered material surface; the vertical sintering speed decreased from 22.35 mm/min to 15.87 mm/min, the yield increased from 73.88% to 79.08%, and then decreased to 77.49%, the utilization coefficient reached the highest at powder A ratio of 32.4%, the drum index increased from 59.26% to 76.09%, shrinkage and burn loss decreased significantly as powder A increased; Oxygen enrichment and increased magnetite powder ratio together led to longer sintering time and increased drum index, and as powder A ratio increased from 0 to 56.4%, the reduction of sintered ore decreased from 88.51% to 82.13%, the low temperature reduction pulverization index of sintered ore increased from 74.70% to 80.75%, the soft melting temperature increased, the soft melting interval had a downward trend and the soft melting interval became narrower, the drip rate showed an overall decreasing trend and the melt drop drip volume decreased, the changes of melt drop characteristics were due to the increase of the chemical composition of sintered ore mainly w(MgO)/w(Al₂O₃) caused. The structure of ore distribution is the main factor affecting the change of metallurgical properties, which is greater than the effect of oxygen enrichment on the smelting performance of sintered ore for gold. In summary, when the sintering process material surface is oxygen-rich and the oxygen-rich rate is 25%, the magnetite proportion should not exceed 32.4%.
		2023 Vol. 58 (1): 22-30 [Abstract] ( 201 ) [HTML 1KB] [PDF 3138KB] ( 604 )

	31	BAO Guo-ying, LIU Lei, HAN Xiu-li, DUAN Bo-wen, QIN Li-wen
		*Optimization of sintering raw material blending scheme based on RDI_{＞3.15 mm} response surface methodology*
		The sinter is prone to fragmentation and pulverization under the low temperature reduction atmosphere of blast furnace, which will seriously affect the permeability of blast furnace and destroy the smooth operation of blast furnace. Low temperature reduction degradation index(RDI_{＞3.15 mm}) is an important index to reflect the occurrence degree of low temperature reduction pulverization of sinter, but its size is affected by the main factors such as MgO, Al₂O₃ and alkalinity R in sintering raw materials. In order to explore the influence and interaction of sintering raw material composition factors on the low-temperature reduction and pulverization performance of sintered ore, an optimization method of sintering raw material blending based on RDI_{＞3.15 mm} response surface was proposed. Firstly, with w(MgO), w(Al₂O₃), and the basicity R as independent variables, and with the sinter RDI_{＞3.15 mm} index as the response value, the sinter RDI_{＞3.15 mm} index was established. Secondly, the sinter RDI_{＞3.15 mm} index obtained from the experiment was fitted to obtain the prediction formula of the sinter RDI_{＞3.15 mm} index. Finally, the sinter was made by the optimal raw material ratio and its RDI_{＞3.15 mm} index was measured. The RDI_{＞3.15 mm} index verifies the accuracy of the proposed method. The results show that the fitting degree R² of the new model to the sinter RDI_{＞3.15 mm} index is 0.990 4, and the correction coefficient R²_adj is 0.978 0, indicating that the predicted value fits the actual value well, and the sinter RDI_>3.15 _mm response surface model is proved. It is statistically significant; the significant degree of influence of each factor on the sinter RDI_{＞3.15 mm} index is w(MgO) > basicity R > w(Al₂O₃), and w(MgO) and w(Al₂O₃), w(MgO) and alkalinity R, w(Al₂O₃) and alkalinity R have significant interaction between two factors; The determined optimal raw material ratio is w(MgO) of 2.66%, w(Al₂O₃) of 2.02%, and alkalinity R of 2.2. Based on the prediction formula and experiment of RDI_{＞3.15 mm} index, the optimal raw material ratio conditions are obtained. The measured value (74.51%) of the lower sinter RDI_{＞3.15 mm} is basically consistent with the predicted value (74.21%). The new method of sintering and ore blending optimization introduced provides a theoretical basis for improving the performance of sintered ore reduction and pulverization at low temperature.
		2023 Vol. 58 (1): 31-38 [Abstract] ( 171 ) [HTML 1KB] [PDF 2927KB] ( 486 )

Steelmaking

	39	ZHOU Yun, WEI Guang-sheng, ZHU Rong, DONG Kai
		Effect of bottom blowing CO₂ on dynamic conditions of molten pool in stainless steel smelting
		In recent years,the resource utilization technology of CO₂ in the iron and steel industry has been widely developed. The research showed that the application of CO₂ in stainless steel smelting has great potential. The effect of bottom blowing CO₂ on the dynamic conditions of molten pool under the condition of stainless steel smelting was quantitatively studied by establishing the dynamic model of bottom blowing CO₂ bubble reaction and combined with hydraulic simulation experiment. Since it is not clear that the increase of gas volume caused by CO₂ decarburization will cause bubble expansion or splitting, two extreme conditions is assumed,namely,condition a. CO₂ bubble only expands without splitting after the increase of gas volume;condition b. CO₂ only splits without expanding;taking the medium-term process parameters of 70 t stainless steel furnace in a plant,the CO₂ bubble reaction kinetics under the two conditions was calculated. The results showed that under the conditions of this study,the gas increase after the bottom blowing CO₂ reaction during stainless steel smelting,whether it leads to bubble expansion or splitting,the final bubble volume at the reaction equilibrium was about 1.3 times of the initial volume,and the bubble volume changes linearly with the reaction time. The hydraulic simulation study found that compared with the control group experiment,the mixing time of the molten pool under condition a and condition b was shortened by 16.5 s and 8.4 s respectively. Therefore,it was concluded that the actual bottom blowing CO₂ would shorten the mixing time of the molten pool by 8.4-16.5 s after the reaction,and significantly improve the dynamic conditions of the molten pool. In addition,the effect of bottom blowing CO₂ on the flow field of molten pool was observed by ink tracer. It was found that the bubble expansion caused by the reaction of bottom blowing CO₂ would promote the lateral diffusion of solute in molten pool and relatively inhibit the longitudinal diffusion speed of solute. On the contrary,the bubble splitting caused by CO₂ reaction would promote the longitudinal diffusion of solute in the molten pool and relatively inhibit the transverse diffusion rate of solute.
		2023 Vol. 58 (1): 39-46 [Abstract] ( 167 ) [HTML 1KB] [PDF 3142KB] ( 336 )

	47	ZHAO Yi-jiang, LI Guang-qiang, MENG Ze, WANG Xi-jie, ZHAO-Rui, LIU Yu
		Effect of deoxidizer with different Al content on cleanliness of molten steel
		Al possesses strong deoxidation ability, thus is widely used in the deoxidation of molten steel during steelmaking. However, the high melting point and large size Al₂O₃ inclusions produced by Al deoxidation will not only seriously reduce the cleanliness of molten steel, and deteriorate the toughness and fatigue life of steel, but also easily cause nozzle nodules, which will affect the continuous casting process. Considering that local supersaturation has an important effect on the nucleation and growth of inclusions, pure Al and Fe-30%Al alloy (mass percent) were used to deoxidize the molten steel, and the actual amount of Al addition was consistent, and the effect of Al contents on the cleanliness of the molten steel was studied by analyzing the molten steel composition and inclusion characteristics of different deoxidation times (30, 60 s). The results show that compared with pure Al deoxidation, Fe-30%Al alloy has better deoxidation effect, and the dissolution rate of Al element in the alloy is slower. In addition, the maximum size of inclusions in the steel samples deoxidized with pure Al can reach 9 μm, while that in the test of Fe-30%Al alloy is only 4 μm. The average size of inclusions in the steel after pure Al deoxidation for 60 s is 1.35 times that of Fe-30%Al alloy deoxidation, and the number of inclusions per unit area is increased by 23%. The inclusions remained in the molten steel during the deoxidation process of the two deoxidizers are mainly polyhedral inclusions, and there are some loose cluster-like inclusions formed by collision and aggregation. Deoxidation of molten steel with Fe-30% Al alloy is more effective than that with pure Al, which depends on different local supersaturation in the initial deoxidation process.
		2023 Vol. 58 (1): 47-54 [Abstract] ( 167 ) [HTML 1KB] [PDF 3526KB] ( 623 )

	55	DENG Ya-cen, ZHAO Li, WANG Qiang-qiang, ZHANG Xu-bin, HE Sheng-ping
		Interface wettability between steel with various contents of titanium and Al₂O₃ and MgAl₂O₄
		Non-metallic inclusions will be formed in molten steel at high temperature, which will adversely affect the casting process of steel and the properties of steel products. In order to to provide some theoretical and experimental basis for the design, preparation and application of high titanium steel by studying the interfacial wetting behavior between high titanium steel and inclusions. Three kinds of steel samples with different titanium content and typical inclusions (Al₂O₃ and MgAl₂O₄) were taken as research objects, and the high-temperature wetting experiments were carried out by a modified sessile drop method, and the apparent contact angles between solidified steel samples and inclusion substrates were obtained. After the experiments, the interface morphology and elements of the samples were characterized by electron probe microanalyzer, and the interface wetting behavior between steels and inclusions was explained by thermodynamic calculation. The main results are as follows. When the mass percent of titanium in steel was 0.01%, 0.31% and 0.68% respectively, for the Al₂O₃/steel wetting system, the apparent contact angles were 96°, 90° and 112°, respectively, and the interface between solidified steels and substrates was uniform with no new reaction phase and obvious element enrichment were found. For MgAl₂O₄/steel wetting system, the apparent contact angles were 113°, 106° and 130°, respectively, and no reaction phase was found at the interface between steel with low titanium content(w(Ti)=0.01%), but a discontinuous chemical reaction layer existed at the interface between steels with high titanium content and substrates, which may be a mixture of MgS, MgO, Ti₄S₂C₂ and MgAl₂O₄. Research showed that the decrease of the apparent contact angle was due to the decrease of the surface tension of molten steel caused by the addition of titanium content. However, when the titanium content in steel reached 0.68%, many TiN particles entrained in the steel leaded to the increase the viscosity of molten steel and then hindered its spreading. The effect of viscosity on the apparent contact angle was much greater than that of surface tension. Therefore, the apparent contact angles of both systems decreased and then increased obviously with the increase of titanium content. Molten steel at high temperature is a very complex mixture system. At present, the wettability between steel and inclusions is mainly evaluated by contact angle, interface morphology and chemical reaction. Therefore, the evaluation method of interface wetting system between high-Ti steel and inclusions needs to be further explored and improved in the future research.
		2023 Vol. 58 (1): 55-66 [Abstract] ( 168 ) [HTML 1KB] [PDF 7308KB] ( 413 )

	67	CHENG Biao, CAI Zhao-zhen, AN Jia-zhi, ZHU Miao-yong
		Effect of cyclic phase transformation cooling process at returning temperature on microstructure and plasticity of steels
		Continuous casting of Nb-bearing steels is easy to produce transverse cracks on slab corners. Applying a cyclic phase transformation cooling process(γ→α→γ),which can greatly improve the structure ductility of steel at high temperature,to the slab corners during continuous casting,the cracks could be greatly reduced. As one of most important parameters,the returning temperature at the stage of α→γ phase transformation is an important factor affecting the applying effect of the process. In the present work,the detection methods,such as Gleeble thermal simulation,OM,TEM,as well as the fracture scanning are used to analyze the micro-structure evolution and plasticity of a Q345D-Nb steel under the different returning temperatures of the cyclic phase transformation cooling process. The results showed that the austenite grains would not be refined at the returning temperature of 850 ℃. The average size of the grains was about 502.2 μm,which was similar to that of the conventional cooling process. When the returning temperature rose to 900 ℃,the austenite showed mixed growth. When the returning temperature rose to 950 ℃,the grain size was refined to 61.2 μm. When the returning temperature rose to 1 000 ℃,the austenite grain coarsely grew. The average size of austenite grains increased 38.07 % compared with that of the returning temperature to 950 ℃. Under the conventional cooling process and the cyclic phase transformation cooling process at the returning temperature of 850,900,950 and 1 000 ℃,respectively,the minimum reduction of area (RA) at the temperature range of 700-900 ℃ were 29.6%,45.0%,56.3%,68.2%,and 63.2%. Under the conventional cooling process,the thickness of ferrite film at grain boundary of the steel at 750 ℃ was 20-25 μm,and the carbonitride precipitated with large size and chain structure distribution,and the fracture mode was intergranular brittle fracture. At the same tensile fracture temperature,the thickness of ferrite film of austenite grain boundary under the cyclic phase transformation cooling process decreased to 5-10 μm,and the carbonitride precipitates dispersedly and finely. The fracture mode transforms to the plastic fracture gradually. The plasticity was significantly improved. Applying the cyclic phase transformation cooling process to the practice,the average grain sizes of austenite at the depths of 5 mm and 10 mm below the corner of slab were refined to 186 μm and 362 μm,which increased the ability of slab to resist cracks.
		2023 Vol. 58 (1): 67-77 [Abstract] ( 157 ) [HTML 1KB] [PDF 5784KB] ( 440 )

	78	GUO Dong-wei, HOU Zi-bing, GUO Kun-hui, ZHANG Fu-li, ZENG Zi-hang, WEN Guang-hua
		Fluctuation phenomenon and variation regulation of solidification behavior in centerline of continuous casting billets
		Nowadays,the development of the steel industry needs to improve the quality uniformity and stability of the continuous casting billets. The centerline segregation formed in the continuous casting process represents the nonuniformity of solute elements and quality of the billets,which is closely related to the solidification process of solute-enriched liquid in the centerline of the billets. At the same time,the final electromagnetic stirring (F-EMS) and mechanical soft reduction (MSR) are widely used in the actual continuous casting process to improve the inner quality uniformity of the billets. However,the fluctuation of the solidification end point will affect the effect uniformity of the F-EMS and MSR. Thus,it′s essential to investigate the solidification behavior and fluctuation characteristics in the centerline and explore the fluctuation of the solidification end point for improving the quality uniformity of the billets. It′s found that the fluctuation of solid fraction in the centerline will cause the fluctuation of the local cooling rate, and ultimately affect the quality uniformity of the billets. Subsequently, this work has analyzed the fluctuation periods of solid fraction and local cooling rate in the centerline of the billets and proposed the periodic fluctuation mechanism of the solidification end point in the continuous casting process. At the same time,the judgment equation of fluctuation distance of solidification end point under different casting speeds was obtained. On this basis,the effect of casting speed on the fluctuation of solid fraction in the centerline was discussed,and the influence of fluctuation distance of solidification end point on the effect uniformity of the F-EMS and MSR was also analyzed. The results show that the increase in casting speed can reduce the fluctuation degree of solid fraction and improve the inner quality uniformity of the billets. On the other hand,although the fluctuation distance of the solidification end point increases with the increase of the casting speed,its influence degree on the effect uniformity of the F-EMS and MSR is gradually reduced due to the increase of the liquid core length.
		2023 Vol. 58 (1): 78-90 [Abstract] ( 190 ) [HTML 1KB] [PDF 4758KB] ( 650 )

	91	SUN Tao-an, CAO Rui-hong, XIA Yun-jin, WANG Hai-chuan, FAN Ding-dong, DENG Ai-jun
		Melting and reduction behavior of core-shell microsphere in steel slag
		The ultimate goal of this study is the application of steel slag fibrosis. The application technology of core-shell structure in polymer materials science is introduced into the field of iron and steel metallurgy for efficient reduction and refactoring of molten steel slag. The melting and reduction behavior of core-shell microsphere in slag was studied by using ultra-high temperature laser confocal microscope. The effects of temperature and acidity coefficient on the melting rate of microsphere reduction base were analyzed. The results show that when the core-shell microsphere is suspended in the middle part of the slag,the melting reduction reaction reaches the equilibrium state 6 min earlier than that of the conventional powder reduction. The reduction and recovery timeliness of metal oxides in slag is obviously improved. The comparison of core-shell microsphere with different reduction substrates show that the aluminum-based microsphere exhibits an excellent reduction timeliness,and the reduction rate reaches 95.17% within 3 min. The slag with high temperature and high acidity coefficient can promote the rapid melting of core-shell microsphere and effectively improve the thermodynamic conditions of reduction reaction. It can improve the timeliness of metal oxides in reduction slag,and achieve the effect of rapid separation of slag and metal. Based on the melting kinetics model of the substrate and slag interface of microsphere,the effective binary diffusion coefficients of microsphere reduction substrate range from 3.86×10^-11 to 4.92×10^-11 m²/s under different conditions. For the industrial application of steel slag refactoring and modification by reducing substrate,carbon can be used as the main reducing substrate and an appropriate amount of aluminum or silicon can be added to prepare the core-shell microsphere for the reduction and refactoring of steel slag,which can significantly improve the timeliness of the reduction and refactoring of steel slag and achieve high economic benefits. It provides a new idea for the efficient reduction of steel slag.
		2023 Vol. 58 (1): 91-99 [Abstract] ( 152 ) [HTML 1KB] [PDF 3600KB] ( 492 )

	100	CHENG Ri-jin, QI Zhan, ZHANG Hua, LIU Cheng-song, NI Hong-wei
		Optimization of refining slag of 20SiMn alloy structural steel
		In order to control the [O] content and inclusions in 20SiMn structural steel for forgings, firstly, the iso-oxygen line of CaO-SiO₂-Al₂O₃-5%MgO refining slag in equilibrium with 20SiMn liquid steel at 1 600 ℃ were calculated by using thermodynamic software FactSage 8.1, and the composition of refining slag was optimized. At the same time, the dominant area diagram of Fe-Mg-Al-O system in steel with different oxygen content was calculated. Secondly, four groups of refining slag components were designed in the laboratory, and the slag-steel equilibrium experiments were carried out in a high-temperature resistance furnace at 1 600 ℃. After the test, the slag components were determined by X-ray fluorescence spectrometry, and the composition of the steel samples were analyzed by inductively coupled plasma optical emission spectrometer, infrared carbon sulfur analyzer and oxygen nitrogen combined analyzer. The composition and morphology of inclusions in the sample were analyzed by field emission scanning electron microscope, and the number and composition of inclusions in steel were counted. The effects of different refining slags on the oxygen content, composition, number and size of inclusions in steel were experimentally studied. Finally, a dynamic model was established to describe the inclusion removal behavior on the "steel-slag" interface. The experimental and thermodynamic model results reveal the relationship between typical Al₂O₃ and MgO·Al₂O₃ inclusions in steel and the contents of oxygen, magnesium and aluminum in steel. The kinetic model describes the corresponding relationship between inclusion separation rate, total oxygen content and overall wettability. When the contents of CaO, SiO₂, Al₂O₃ and MgO in the optimized slag system are 0-24.7%, 44.3%-55.1%, 20.5%-48.2% and 5%-8% respectively, the dissolved oxygen in steel can be controlled within 0.000 5%. The slag system with typical composition of 50.4%CaO-40.3%Al₂O₃-4.3%SiO₂-5%MgO can control the amount of T[O] and impurities in steel at 0.001 42% and 9.9 pieces/mm² respectively. The experimental results are basically consistent with the model prediction.
		2023 Vol. 58 (1): 100-107 [Abstract] ( 193 ) [HTML 1KB] [PDF 4291KB] ( 601 )

	108	WANG Kun-peng, WANG Ying, XIE Wei, XU Jian-fei, CHEN Ting-jun, JIANG Min
		Influence of RH vacuum treatment on spinel inclusions of high carbon chromium bearing steel
		Spinel inclusions in steel not only deteriorate the castability of steel, but also may lead to macroscopic inclusions in finished products, and RH vacuum treatment is an important step to remove the inclusions in steel. The number, composition and types of inclusions of high carbon chromium bearing steel in RH vacuum treatment were studied, and the influence of vacuum pressure on the stability of spinel inclusions in high carbon chromium bearing steel was discussed through thermodynamic calculation. The experimental results show that when the vacuum pressure is 30 Pa, the total amount of liquid steel circulation reaches 200-400 t after 10 min of vacuum treatment, and all the spinel inclusions disappear. After 15 min of vacuum treatment, the total number of inclusions decreased from 480/(200 mm²) to 97/(200 mm²), and the total number of inclusions decreased by 80%. After vacuum treatment, the number of liquid inclusions in steel increases and inclusions become highly liquid. Compared with that before vacuum treatment, the number of liquid inclusions increases from 44/(200 mm²) to 71/(200 mm²), an increase of 61%, and the proportion of liquid inclusions increases from 9% to 73%. The spinel inclusions were single granular throughout the whole process, and no collision or aggregation was found. Thermodynamic calculation shows that the spinel inclusions in high carbon chromium bearing steel can be reduced and decomposed by C in the steel under vacuum condition. At 1 600 ℃, the critical decomposition pressure is 16 000-22 000 Pa. The higher the vacuum degree, the more conducive to the reduction and decomposition of spinel inclusions. When the vacuum pressure is 4 900 Pa, the total amount of liquid steel circulation reaches 511-1 022 t after 7-14 min of vacuum treatment, and the spinel inclusion disappears completely. When the vacuum degree is 20 400 Pa, spinel inclusions still exist even when the treatment time is extended to 40 min and the total circulating volume of liquid steel is increased to 2 360 t. Compared with the view that inclusions are physically removed, the reduction and decomposition of spinel inclusions by Cin steel under vacuum can better explain the spinel inclusions change characteristics during vacuum process.
		2023 Vol. 58 (1): 108-115 [Abstract] ( 164 ) [HTML 1KB] [PDF 3396KB] ( 487 )

Metal Forming

	116	PENG Wen, WEN Hong-bo, LI Xu-dong, FAN Xing-guo, SUN Jie, ZHANG Dian-hua
		Head bending law during rough rolling processbased on thermo-mechanical coupling
		Head bending is a common defect in the process of hot rough rolling process. It affects the quality and rolling stability of strip products during the production process seriously. In actual production,due to the asymmetry of the temperature drop on the upper and lower surfaces of the rolled piece and the rolling process parameters,the rolled piece is prone to head bending after rough rolling. In order to realize the modeling description of the head bending law,based on the heat transfer theory and the rigid-plastic variational principle,the thermo-mechanical coupling finite element model is established by ABAQUS. In the case of misalignment of the rolling line,the effect of the temperature distribution of the rolled piece on the head bending,and the effect of roll speed ratio,reduction rate and entry thickness on the head bending under the condition of misalignment of rolling line and temperature difference between upper and lower surfaces of rolled piece were systematically analyzed. Finally,the effect of various process factors on the head bending was obtained by fitting,and the prediction of the head bending was realized. The simulation results show that with the increase of the temperature difference between the upper and lower surfaces,the downward bending of the rolled piece gradually increases;the roll speed ratio,the reduction rate and the entry thickness all have an effect on the head bending,and are coupled with each other;with the increase of the roll speed ratio,the bending angle gradually becomes larger,and the head the rolled piece changes from the downward bending to upward bending;with the increase of the thickness,the head of the rolled piece gradually tends to be straight;with the increase of the reduction rate,the bending angle fluctuates within a certain range. The field measurement data shows that based on the established prediction model,the proportion of the predicted angle deviation within ±5° is 90.10%,which verifies the validity of the established model and achieves accurate prediction of head bending. It can provide a reference for the process optimization of the rough rolling process.
		2023 Vol. 58 (1): 116-124 [Abstract] ( 182 ) [HTML 1KB] [PDF 5445KB] ( 366 )

	125	ZHANG Jie, KONG Ning, WANG Yi-bo, SONG Yu-wei
		Quantitative evaluation and analysis on spalling of powdered iron oxide scale for automobile beam steel
		After hot rolling,the automobile beam steel plate is directly used for stamping and forming of automobile parts. The control of its surface iron oxide scale is responsible to the stability of the stamping process and the workshop environment. Therefore,it is of great theoretical and practical significance to carry out quantitative evaluation and analysis on the spalling of powdered iron oxide scale for automobile beam steel. In order to improve the serious powdered iron oxide flaking of beam steel,the spalling amount and composition analysis of iron oxide powder have been carried out under different hot rolling finishing temperatures and coiling temperatures through industrial tests. The layered structure and density of iron oxide scale have been investigated by scanning electron microscope. The relationship between iron oxide in Fe₃O₄ and FeO contents and iron oxide flaking problem has been studied on the hot rolled 610L steel through industrial tests. When the mass percent of Fe₃O₄ is 80% and the mass percent of FeO is of about 3%,iron oxide of 610L steel is the least likely to fall off. The oxide scale is able to form the "black steel" characteristics with high plasticity and non-falling powder. The relationship between FeO content and flaking characteristics of iron oxide scale has been investigated through a three-point bending experiment for simulating the subsequent cold forming processing with oxide scale spalling. The iron oxide scale with high FeO content flakes more than those with low FeO content under small deformation condition in plastic bending process. In the case of large deformation,the iron oxide scale peels less than the sample with less FeO content. The characteristics of flaking weight shows a "first negative and then positive" trend. With the increase of bending displacement,the oxide scale spalling increases gradually. The scale spalling on the compression surface is more than that on the tension surface. Under the action of tensile stress,the iron oxide scale on the tensile surface produces a strip crack perpendicular to the length of the specimen,while the iron oxide scale on the compressive surface peels off in the form of a large fragment. The low strength and excellent plasticity of FeO is responsible to the flaking rule of iron oxide scale with different FeO contents.
		2023 Vol. 58 (1): 125-132 [Abstract] ( 184 ) [HTML 1KB] [PDF 3737KB] ( 440 )

Materials

	133	WANG Jun-cai, CAO Jian-chun, ZENG Min, LUO Han-yu, WANG Chuang-wei, YE Xiao-yu
		Effect of Zr content on austenite microstructure of high-strength and high-toughness Ti-Zr microalloyed steel
		In order to meet the requirements of various industries for steel materials with higher strength and better toughness, adding the right amount of micro-alloying elements in the steel and combining with a reasonable control of tying and cooling process is conducive to obtaining fine and uniform austenite recrystallization grains in the high temperature rolling stage, which is one of the effective ways to improve the strength and toughness of steel. This paper simulates the actual rolling of two Ti-Zr microalloyed low carbon steels with different Zr contents by multiple passes of compression deformation on a Gleeble-3800 thermal simulation experimental machine, the thermal deformation behavior of the test steels under different Zr contents and different deformation methods (isothermal deformation and variable temperature deformation) was studied, as well as the effects of Zr contents and deformation conditions on the austenite organization hyperfine behavior and precipitation behavior of the test steels. The results show that the increase of deformation temperature can reduce the rheological stress of high Zr steel in all passes. Under variable temperature deformation conditions, the increase in Zr content raises the rheological stress in each pass of the test steel; austenite grains will be refined with the increase of Zr content and the decrease of deformation temperature, the use of variable temperature deformation method is more favorable than isothermal deformation method to obtain fine austenite grains, high Zr steel at 1 050 ℃→1 25 ℃→1 000 ℃ variable temperature deformation obtained the smallest average austenite grain size (for 8.2 μm); the increase in Zr content increases the number of precipitation in the test steel. the deformation method has little effect on the number of precipitations, and the increase in deformation temperature causes the precipitation to grow. The increase of deformation-induced precipitation caused by the increase of Zr content and the decrease of temperature in the process of deformation of variable temperature play the role of inhibiting the growth of austenite grains, refine the austenite recrystallization grains, and playing a favorable role in improving the strength and toughness of steel.
		2023 Vol. 58 (1): 133-140 [Abstract] ( 156 ) [HTML 1KB] [PDF 4659KB] ( 469 )

	141	CHEN Teng-sheng, ZHANG Li-qin, HU Feng, TONG Ming-wei, JI Mei-feng, HU Lei
		Effect of Mg-treated on impact toughness and crack propagation of CGHAZ
		Mg-bearing composite inclusions were introduced into Q345GJ steel by Mg-treated,and the effects of Mg-bearing composite inclusions on the microstructure and fracture toughness of coarse-grained heat affected zone (CGHAZ) with high heat input welding (energy input 100 kJ/cm) were studied. The results show that the CGHAZ toughness of test steel after Mg-treated is significantly improved (impact energy increases from 56 J to 108 J). Because of in the process of weld thermal cycle cooling,Mg-bearing composite inclusions are preferentially formed in the CGHAZ,the presence of Mn depletion zone and high-energy strain field around the mg-bearing inclusions with high surface energy promotes the nucleation of acicular ferrite (AF),with the AF ratio of (82.9±2.0)%(volume percent) and the width of (0.96±0.1) μm((32.4±1.5)% and (3.13±0.2) μm for the Mg-free steel). The formation of micropores and crack propagation in CGHAZ impact specimens after high heat input welding were investigated. There are a large number of dislocations near the inclusions in test steel. During the deformation process,stress concentration is caused by the accumulation of dislocation loops. When the dislocation source of stress concentration to adjacent grains cannot is activated. Micropores are formed on the orientation which is not conducive to slip and then connected to form cracks under external force. Micropores of Mg-free steel are denser,which provides favorable conditions for crack initiation. The proportion of high angle grain boundaries(HAGBS) in Mg-treated steel is 80.2%,the geometric necessary dislocation density (GND) is 0.806,and Kernel Average Misorientation (KAM) is 0.912. (with 71.9%,0.896 and 0.956 for the Mg-free steel). The small and self-locking AF in CGHAZ improves the impact toughness of Mg-treated steel due to hinders the expansion of micropores and inhibits the propagation of cracks. The crack propagates along the HAGBS,the crack propagation path is prolonged and the energy consumption increases when the crack encounters AF.
		2023 Vol. 58 (1): 141-152 [Abstract] ( 169 ) [HTML 1KB] [PDF 10260KB] ( 410 )

	153	CUI Gui-bin, JU Xin-hua, YAN Chun-lian, MA Ze-jun
		Microstructure characterization of hot-dip Zn-Al-Mg coating of low alloy high strength steel
		Hot-dip Zn-Al-Mg coating is widely used in automobiles and home appliances because of its better notch protection performance and corrosion resistance,and the corrosion resistance of Zn-Al-Mg coated steel sheet is closely related to its phase composition. Therefore,in order to better study the microstructure and phase structure composition of the surface and cross-section of the Zn-Al-Mg coating on the hot-dip low alloy high strength steel. Micro-machining and fine polishing of the coating section by focused ion beam (FIB),a flat,bright and stress-free surface to be observed is prepared. Firstly,the microstructure,morphology and composition of the surface and cross-section of the Zn-Al-Mg coating were preliminarily analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS),secondly,the phase structure and composition of the Zn-Al-Mg coating were accurately determined by means of electron backscatter diffraction (EBSD) Kikuchi pattern calibration. The research shows that the phase composition of the surface of the Zn-Al-Mg coating is the same as that of the cross-section,which is composed of a coarse dendritic primary Zn-rich phase,a relatively fine fishbone-like or dendritic Zn-Mg binary eutectic phase,and more fine grained or striped Zn-Mg-Al ternary eutectic phase. In addition,a large number of nano-precipitated Al-rich phases are uniformly dispersed in the bulk primary Zn-rich phase. The phase structure of the hot-dip Zn-Al-Mg coating was accurately determined by the EBSD Kikuchi pattern calibration. The Zn-Mg binary eutectic phase is Zn-MgZn₂ with the same close-packed hexagonal structure,and the finer granular or strip-shaped Zn-Mg-Al ternary eutectic phase is Zn-MgZn₂-Al. In addition,the nano-scale Al-rich phase particles precipitated in the primary Zn phase can effectively improve the surface hardness of the coating. At the same time,the edges of the primary Zn phase and the eutectic phase are covered with a layer of MgZn₂ phase,which can effectively delay the corrosion process and improve the corrosion resistance of the coating.
		2023 Vol. 58 (1): 153-160 [Abstract] ( 194 ) [HTML 1KB] [PDF 5224KB] ( 367 )

	161	ZENG Bin, WANG Jing, LIANG Liang, LI Zhao-dong, YONG Qi-long
		Study on production process of steel for frame saw blade developed by continuous heat treatment line
		Frame saw has been widely used in the stone processing industry. Steel for frame saw blade is an essential material for preparing frame saw and also a high value-added product in steel materials. The continuous quenching-tempering heat treatment equipment designed independently in China was used. It is planned to develop 75Cr1 high-strength and high-toughness heat-treated steel strip for 2.0 mm thin gauge frame saw blade,which is not used in the domestic and foreign markets at present,so as to improve the utilization rate of stone material. The austenitizing temperature of heating furnace,the melt temperature of Pb-Bi alloy and the tempering temperature were set in sequence on the continuous heat treatment line,and the effects of the three parameters on the microstructure and mechanical property of heat-treated steel strip were studied by using the material testing machine,Rockwell hardness tester,metallographic microscope and scanning electron microscope,to explore the optimal heat treatment process for producing high-performance frame saw blade material. The results show that the high-performance 75Cr1 heat-treated steel strip can be prepared with a thin gauge of 2 mm by martempering,when the austenitizing temperature is 930 ℃,the melt temperature of Pb-Bi alloy is 250-315 ℃,and the tempering temperature is 500-520 ℃. While,the yield strength is 1 157-1 241 MPa,the tensile strength is 1 275-1 368 MPa,the elongation is 8.8%-13.8%,the surface hardness is 39.5HRC-42.5HRC,the microstructure is tempered troostite+a small amount of bainite,and the grain size is extremely fine and uniform. By comparing the microstructure and mechanical property with the now available 3.0 mm thick gauge high-quality imported material from abroad, the developed 2.0 mm new thin gauge material can attain eqaul in quality of 3.0 mm imported material,and the 2.0 mm thin guage frame saw blade steel has been successfully developed,with superior comprehensive mechanical properties. The principle and parameter range of this continuous heat treatment are different from the traditional oil quenching and salt bath quenching. It is a new report and systematic study for heat treatment of 75Crl steel,which can provide process guidance for the development of this material.
		2023 Vol. 58 (1): 161-169 [Abstract] ( 183 ) [HTML 1KB] [PDF 9451KB] ( 324 )

	170	YANG Shuang-ping, ZHANG Tian-tian, GAO Wen-bin, LIU Shou-man, SUN Hai-xing
		Experiment on process optimization of one-step preparation of vanadium carbonitride
		Focusing on the development of continuous,efficient and low-cost technology for the synthesis of vanadium carbonitride by one-step method,on the basis of summarizing the research on the production process of vanadium nitride,this paper takes vanadium pentoxide as the raw material,coke as reducing agent,after crushing,mixing and pressing into blocks,drying to reduce the nitride process. The optimum technological conditions for the preparation of vanadium carbonitride by one step carbothermal reduction at high temperature were investigated under high purity nitrogen atmosphere. The reduction process of vanadium pentoxide was thermodynamically analyzed and calculated,and the theoretical analysis was carried out by FactSage thermodynamic software. The single factor test analysis of reaction temperature,reaction time,nitrogen flow rate,pressure and other influencing factors was analyzed by XRD and SEM test methods. The results show that the nitriding reaction of vanadium carbide was carried out step by step,and the reaction process of vanadium carbonitride was V₂O₅→V₂O₄→V₂O₃→VC→VCN. The CO produced in the experiment will change the gas partial pressure in the furnace,which will affect the carbonization temperature and nitriding temperature. Therefore,the CO and N₂ partial pressure of the system should be strictly controlled in the reaction process. The reaction time and nitrogen flow rate had different effects on the contents of vanadium,nitrogen and carbon in the reaction products. The vanadium content and nitrogen content increased with the increase of reaction time and nitrogen flow rate,while the carbon content decreased with the increase of reaction time.The pressure determines the porosity of the reactants. On the basis of ensuring the quality of the block product,increasing the sample preparation pressure can increase the contact area between the particles and the specific surface area of the reaction,and the reduction effect is good. Considering comprehensively,setting the carbon distribution coefficient of 35%,sample preparation pressure of 20 MPa,carbothermal reduction at 900 ℃ and nitridation reaction at 1 480 ℃ for 180 min,the test can obtain (mass percent) 75.55%V,13.91%N,4.96%C of vanadium carbonitride products finally,in line with national standards.
		2023 Vol. 58 (1): 170-178 [Abstract] ( 192 ) [HTML 1KB] [PDF 2649KB] ( 550 )

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