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2024 Vol.  59 No.  2
Published: 2024-02-15

Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technical Reviews
1 SHEN Fengman, AN Haiwei, JIANG Xin, NI Jingfeng, ZHENG Haiyan, GAO Qiangjian
Research progress on sillico-ferrite of calcium and aluminum (SFCA) bonding phase in sintering process
The sintering process of iron ore is an essential part of the steelmaking process. Calcium ferrite, as the main bonding phase in sinter, significantly influences the sintering process and metallurgical properties of sinter. The research progress on the chemical composition, formation mechanism, reduction mechanism, and influence of gangue components of calcium ferrite and its complex system in the iron ore sintering process are reviewed. In summary, the chemical composition of calcium ferrite is determined by the concentrations of Fe, Ca, Si, Al, and other elements present in the sinter. The sillico-ferrite of calcium and aluminum (SFCA) can be expressed by the general formula xFe2O3·ySiO2·zAl2O3·5CaO, where x + y + z = 12; The formation mechanism of calcium ferrite is influenced by chemical reactions among gangue components and phase transformation processes under varying temperature and atmosphere conditions. Understanding the formation mechanism is crucial for effectively controlling the content of the bonding phase in the sinter; The reduction pathway of calcium ferrite is affected by the composition of the bonding phase, reduction temperature, and atmosphere. However, research on the reduction pathway of quaternary composite calcium ferrite is currently lacking. Studying the reduction mechanism is significant for improving the efficiency of iron ore smelting and reducing energy consumption; Gangue materials play a crucial role in the forming and reducing calcium ferrite. Elements such as SiO2, Al2O3, and MgO can alter the crystal structure of calcium ferrite and its formation and reduction mechanisms. Finally, based on the current research status of the calcium ferrite bonding phase, future research directions are proposed. These include exploring effective extraction and comprehensive utilization of valuable components during sintering, obtaining universal physicochemical data in calcium ferrite, and investigating related areas. These efforts will contribute to further advancing the theory of iron ore sintering.
2024 Vol. 59 (2): 1-12 [Abstract] ( 76 ) [HTML 1KB] [PDF 0KB] ( 120 )
13 LIU Qingmei, ZHANG Fuming
Research progress of carbon reduction and CO2 resource technology utilization in iron and steel industry
Under the background of the new development about "carbon peak and carbon neutrality", the low carbon development of steel industry is becoming particularly important.The research status of low-carbon cycle and carbon reduction fields in the iron and steel industry, as well as the developing states of the new types of CO2 resource utilization industry are analyzed.From the point of the iron and steel production process status, which is comparatively mature around the world, the carbon emission intensity of "BF-BOF""Total Scrap-EAF""Direct Reduction " and "Smelting Reduction" are introduced. Currently,the major global iron and steel manufacturing processes are the BF-BOF process and EAF poreces. The BF-BOF process carbon emission intensity of per ton is about 3 times of that of the EAF process. Combining with the evolution of global steel production, the values of CO2 emissions of the global steel industry from 2001 to 2022 is calculated, which expounds the urgency and necessity situation of carbon reduction and CO2 resource utilization.According to the present experience of carbon reduction in the steel industry,the low-carbon smelting projects of Japan, European and China are analyzed, including the experimental exploration and stage development targets during the period of carbon reduction. On the basis of carbon reduction of the iron and steel industry, promoting the resource utilization becomes an important task to achieve carbon neutrality in the steel industry. The research status and characteristics of carbon capture and sequestration technologies in iron and steel enterprises are expounded. Meanwhile, the current effective methods to facilitate the utilization of CO2 resources in the iron and steel industry systematically are summarized, which include the use of different modes of CO2 injection process in the steel-making converter and refining process, as well as the research of CO2 utilization of basic chemicals in the co-production of steel and chemical field.Considering from the perspective of the whole iron and steel industry chain, the key planning and development direction of carbon emission reduction and recycling industry in Japan, Europe and China are put forward.
2024 Vol. 59 (2): 13-24 [Abstract] ( 62 ) [HTML 1KB] [PDF 0KB] ( 100 )
Raw Material and Ironmaking
25 WU Ying, GAO Lihua
Effect of high-silicon iron ore on sintered on ore sintering process and metallurgical properties
At present, the global iron ore price index continues to rise, the issue of low-quality iron ore resources and rising steel production demand that iron and steel companies are currently dealing with had a significant influence to maintain their stable development. The Baoshan sintering base of Baosteel steadily increased the usage of high silicon iron ore powder to achieve the strategy of blast furnace ironmaking resources, extend the procurement channels of ore resources, and strengthen the right to speak of Baowu ore resources procurement. Nevertheless, the effect of increasing the proportion of high-silica iron ore powder on the sintering mechanism and the formation mechanism of compound calcium ferrate (SFCA) is not clear, so based on a high proportion of high-silica iron ore sintering test to research. The effect of high silica-type iron ore on the generation mechanism and solidification mechanism of SFCA as well as the metallurgical performance of sintered ore was researched using the micro sintering experiment, sintering cup test and the Baosteel sintering machine industrial test. The findings demonstrate that when the replacement ratio of high silica-type iron ore powder is raised to 12%, the assimilative temperature and liquid phase fluidity index increase gradually, but the decrease of the crystalline strength is more pronounced and decreases rapidly from 1 080.72 N to 745.79 N, which is primarily related to the formation of the silicate phase. The detrimental impact of silica on the formation of the binder phase was lessened with an increase in reaction time and temperature. The mass percent of ferrous iron increases from 8.7% to 9.1% as the proportion of high silica iron ore powder replacing Tubarang powder rises. This is due to an increase in calcium ferrate, which reduces the production of calcium silicate and iron olivine and improves the fluidity of the liquid phase binder phase. Consideration of the ideal high silica iron ore powder replacement ratio should be less than 12%. The results can provide theoretical guidance and a reference basis for the sintering of high silica iron ore and benefit the economical material strategy.
2024 Vol. 59 (2): 25-35 [Abstract] ( 44 ) [HTML 1KB] [PDF 0KB] ( 63 )
36 NI Jie, SHI Xuefeng, BAI Chenchen, ZHANG Yuzhu, LIU Lianji, XIAO Hong
Analysis of compressive strength and microstructure during mineralization process of flux based pellets
The compressive strength of the pellets is one of the main indicators to measure whether the pellets can enter the blast furnace smelting, and the compressive strength of the pellets is determined by the mineral composition and microstructure of the pellet. Zhongguan iron ore is used as the basic pelletizing raw material, and low-silica flux pellets are prepared by calcium and magnesium additives. By systematically studying the microstructure and mineral distribution morphology of pellets under different MgO content, alkalinity and SiO2 content, the change law of compressive strength of low silicon flux pellets was revealed. The results show that increasing the roasting temperature and alkalinity can effectively improve the compressive strength of pellets. When the SiO2 content was low, the pellets are mainly consolidated by hematite crystals, and the strength change is not obvious. When the mass percent of SiO2 increased to 3.5% and 4.0%, respectively, the hematite crystals were gradually interconnected into pieces, and the crystals gradually became coarse and compact, the structural strength was strong, and the compressive strength of the pellets increased. With the increase of alkalinity, hematite recrystallization is better, there are few granular alone and the crystals are interconnected into blocks, magnetite is reduced, the liquid phase of low silicon flux pellets increases during the roasting process, and the liquid phase of calcium ferrite system appears to increase the strength of the pellets. With the increase of MgO percentage, more Mg2+ entered the magnetite phase, which made up for the lattice defect, and the magnesium ferrite content increased and appeared needle-like or flake distribution in hematite, which inhibited the formation of liquid phase during the roasting process, and made the pores inside the pellet smaller during the cooling process, thereby improving the density of the pellet and enhancing the strength of the pellet. The content of MgO continued to increase, the content of magnetite and glass phase increased, and the content of hematite and calcium ferrite decreased relatively. And because the increase of Fe3O4 will reduce the conjunctive performance of Fe2O3, and eventually lead to the decrease of the compressive strength of the pellets. The above studies provide theoretical guidance and reference for the exploration of low silica magnesium flux pellets.
2024 Vol. 59 (2): 36-43 [Abstract] ( 35 ) [HTML 1KB] [PDF 0KB] ( 46 )
44 WANG Qi, SONG Yangsheng, LI Tingle, LI Zhexi, TIM Evans
A test and evaluation method of ore and coke coupling metallurgical properties
The reaction and characteristics of iron ore and coke in various areas of the blast furnace (BF) are important factors affecting the efficiency and yield of BF ironmaking, so that accurate evaluation of the quality of ore and coke has been arousing interests from ironmakers. The testing methods and indexes for evaluating the metallurgical properties of ore or coke have rapidly developed, and some methods have been standardized, including the method for determination of iron ore softening-melting performance under load and the determination of coke reactivity index and coke strength after reaction, etc. The methods have been widely adopted by iron and steel enterprises. However, it is still difficult to calculate the technical-economic indexes of BF from on the experimental results based on current testing methods and indexes. This may be due to insufficient simulation on the interaction between ore and coke through the entire process of reduction, solution loss, softening and melting in BF. Assigning values to the correlated behaviours and characteristics of ore and coke and constructing an indicator system to evaluate the interaction between them could not be achieved. Therefore, a test device and evaluation methodology (Qisunny method) have been invented, which deploy samples with coke-ores-coke layer structure in the crucible integrating the reduction under the load-thermogravimetric-gas analysis to simulate coupling ores and coke behaviours and properties, such as iron ore reduction, coke solution loss, burden softening, melting and dropping. The device and methodology can conduct coke and ore coupling behaviours and properties test and evaluate its coupling performance. The test results of changing burden structure and coke type showed that coupling coke and ore metallurgical performance evolved with different zones with distinct boundary in an order from indirect reduction zone to indirect and direction reduction co-existing and softening zone, to smelting direct reduction zone and to dripping direct reduction zone. The performance evaluation parameters included the temperature and the temperature interval of different zones, the indirect and direct reduction rate, the total reduction rate, the permeability parameters in melting zone, the solution loss rate and strength after dissolution of the top layer coke. The solution loss reaction of coke mainly taken place in the melting zone. The solution loss rate of the upper layer coke was close to the traditional coke reactivity index while its strength after dissolution was higher than the traditional coke strength index after reaction. The method can provide a totally new option for evaluating coupling coke-ore performances and optimising burden structure.
2024 Vol. 59 (2): 44-54 [Abstract] ( 42 ) [HTML 1KB] [PDF 0KB] ( 73 )
55 DAN Jiayun, YUAN Xiang, ZOU Fanqiu, LI Renguo, XU Kun, NING Xiaojun, WANG Guangwei
Analysis on characteristics of blast furnace mixed injection biochar and coal
Energy conservation and emission reduction have been elevated to the top priority for the green and sustainable growth of the iron and steel industry in light of the active promotion of the "Dual carbon" target. The application of biomass, a renewable carbon source, in blast furnace ironmaking can significantly lower the CO2 emissions associated with iron and steel production. To improve the metallurgical properties of biomass feedstock for blast furnace injection, this paper employs pyrolytic and hydrothermal carbonization to prepare biochar, and investigates the feasibility of mixing biochar with pulverized coal for blast furnace injection. The results showed that the volatile fraction of biomass hydrochar and pyrolysis char was higher than that of bituminous coal. The fixed carbon content and higher heating value of the mixed coal would gradually decrease when the biochar was mixed with pulverized coal at a ratio of 5% to 20%, though the reduction was only slight. The blended sample is non-explosive and has an ignition point greater than 350 ℃ when the proportion of biochar is less than 20%, which satisfies the safety performance requirements of the blast furnace comminution and injection system. Better grindability and combustibility of biochar can increase the pulverizing and combustion performance of blended sample. The ash melting point of pyrolysis char blends decreases significantly more than that of hydrochar blends due to the high alkali metal content of the ash component. The increase in alkali load of pyrolysis char was substantially more than that of hydrochar when the same proportion of biochar was injected, according to calculations of the alkali load variation of the biochar blending scheme. The alkali load rose by 0.394 3 kg/t for the pyrolysis char blending scheme and 0.006 4 kg/t for the hydrochar blending scheme when the biochar ratio was 20% and the blast furnace coal injection ratio was 140 kg/t. According to the analyses presented above, biomass hydrochar can successfully meet all metallurgical performance requirements for blast furnace injection, whereas biomass pyrolysis char cannot be used to blast furnace injection due to its high content of alkali metals. The development of biomass hydrothermal carbonization technology is therefore necessary to effectively use agricultural and forestry waste biomass resources in the blast furnace ironmaking process.
2024 Vol. 59 (2): 55-64 [Abstract] ( 36 ) [HTML 1KB] [PDF 0KB] ( 62 )
Steelmaking
65 QI Zhan, CHENG Rijin, WU Xianmin, HUO Liqiao, ZHU Juntao, LIU Chengsong, ZHANG Hua, NI Hongwei
Al2O3dissolution into molten CaO-SiO2-Al2O3-MgO-FeO slags
In order to control the Al2O3 inclusions in low-carbon Al-killed steel and improve the adsorption capacity of the slag system to Al2O3 inclusions, the isoviscosity diagram of CaO-SiO2-Al2O3-5%MgO-5%FeO slag system and the contour map of ΔC/ηC=CsAl2O3-CbAl2O3, η is the viscosity of slag) were simulated by FactSage 8.1. The dissolution rate of Al2O3 in CaO-SiO2-Al2O3-5%MgO-5%FeO slag system was studied. The effects of Al2O3 rod immersion depth, diameter, rotation speed, slag composition and temperature on the dissolution rate of Al2O3 were discussed. The activation energy of Al2O3 in the dissolution process was solved. Finally, the qualitative analysis of the micro-line elements at the interface between the alumina rod and the slag was carried out by field emission scanning electron microscopy (Apreo S HiVac). The results show that the dissolution rate of Al2O3 in slag is affected by many factors. The dissolution rate increases with the increase of rotation speed, rod diameter, immersion depth and temperature of alumina rod. The dissolution rate also increases with the increase of CaO content, and decreases with the increase of Al2O3 and SiO2 content. The dissolution rate is highly dependent on the viscosity of the slag. The viscosity of the slag is negatively correlated with the dissolution rate of Al2O3, and the dissolution rate of Al2O3 is positively correlated with the concentration driving force. Before the alumina rod is dissolved in the slag system, it will be transformed into intermediate phases CaO·2Al2O3 and CaO·6Al2O3, and the intermediate phase is dissolved in the slag. The apparent activation energy of dissolution in slag A is 410.9 kJ/mol. The dissolution rate of Al2O3 in slag was verified by comparing the dissolution rate diagram with the contour diagram of ΔC/η.
2024 Vol. 59 (2): 65-74 [Abstract] ( 47 ) [HTML 1KB] [PDF 0KB] ( 63 )
75 LIU Yong, CHENG Shusen, LIU Tong
Influence of a rising bubble on behavior of steel-slag interface
The interfacial contact area between molten steel and slag is one of the key factors influencing the efficiency of chemical reactions. The phenomenon of gas bubbles traversing the steel-slag interface by constructing a physical model of the water-oil system and employing image processing techniques isreconstructed. The study focuses on the effects of bubble size, slag layer density, viscosity, and interfacial tension on the entrainment volume of steel and the area of the steel-slag interface. The results show that as the bubble size increases, both the entrainment volume of steel and their growth rate also increase. When the initial diameter of the bubble increases from 5 mm to 15 mm and 25 mm, the entrainment volume increases by 733.33% and 3611.11%, respectively. As the viscosity of the slag increases and its density decreases, the entrainment volume of steel increases. However, the thickness of the slag layer has a low impact on this phenomenon. The variation in the area of the steel-slag interface caused by the process of bubble traversal is a key focus of attention. It is worth noting that the area of the steel-slag interface exhibits a trend of increasing and then decreasing as the bubble size increases. When the bubble diameter increases from 5 mm to 15 mm and 25 mm, the interface area increases by 312.97% and 113.44%, respectively. When the bubble size is 15 mm, an increase in the density of the oil phase from 0.76 kg/m3 to 0.84 kg/m3 results in a 67.44% increase in the growth rate of the interface area. However, when the viscosity increases from 8.9 mPa·s to 193.5 mPa·s, the growth rate of the interface area decreases by 31.39%. Furthermore, the maximum value of the liquid-liquid interface area grows by 2.96%, falls by 6.05%, and lowers by 9.14%, respectively, when the surface tension of the oil phase, water phase, or water-oil interface increases from 0.03 N/m to 0.06 N/m. Oil-air, water-air, and water-oil interface tension are the order of influence, going from high to low. Combined with secondary refining, the selection of flow rate and slag parameters plays a crucial role in enhancing refining efficiency. However, due to limitations in material properties in experimental studies, it is suggested to use numerical simulation in the future to analyze the effect of each parameter on the entrainment volume of metal and the interface area of steel slag.
2024 Vol. 59 (2): 75-84 [Abstract] ( 38 ) [HTML 1KB] [PDF 0KB] ( 59 )
85 ZHANG Fujun, YANG Shufeng, LIU Wei, SUN Ye, JIAO Aoteng, LI Jingshe
Mixing and interface mass transfer characteristics of electric arc furnace melt pool with composite stirring process
The lack of C-O reaction during the entire scrap steel arc furnace smelting process, coupled with the shallow dish shape of the melt pool, low stirring intensity of a single stirring method, and poor reaction kinetics conditions, are one of the main reasons that restrict the efficient smelting of the arc furnace. In order to improve the dynamic conditions in the molten pool during the arc furnace smelting process and improve smelting efficiency, physical simulation methods are used to study the flow field characteristics formed by a single stirring method. Based on this, further exploration was conducted on the mixing and interface mass transfer characteristics of the molten pool under different composite stirring combinations, and the optimal composite stirring method was explored. The research results indicate that the flow field formed by oxygen jet and side blowing is similar, mainly distributed in the upper and middle upper parts of the molten pool, and composite stirring cannot eliminate the weak stirring zone formed by single stirring. The entire molten pool is penetrated by the flow field from bottom blowing, but there are still weak stirring areas far from the center and bottom of the stream. Combined jet stirring the stirring effect can be greatly improved, with an average mixing time of 53-86 s.Adding a side blowing nozzle to the dead zone of jet and bottom blowing composite mixing, the stirring effect of the melt pool can be further strengthened, with an average mixing time of 31-68 s much lower than that of binary stirring. However, the effect of mixing inside the melt pool and the mass transfer at the steel slag interface is the different or even the opposite. Combining metallurgical effects under the “ternary” stirring conditions, the best comprehensive metallurgical effect is performed in groups 1 and 5.
2024 Vol. 59 (2): 85-98 [Abstract] ( 35 ) [HTML 1KB] [PDF 0KB] ( 65 )
99 XIA Shuaikang, WANG Pu, TANG Qunwei, LI Weitao, HU Kai, ZHANG Jiaquan
Solidified end characteristics and center quality control of bearing steel bloom
It is presently a dominant process to produce quality bearing steel by continuous casting and rolling instead of traditional ingot casting and forging. To improve the frequently observed severe center shrinkage and center segregation in the bloom continuous casting process of GCr15 bearing steel, the numerical simulation has been carried out to predict the solidification process of the continuous casting, and the industrial trials of adjusting the casting speed have been made to explore the influence mechanism and effect of external-field control technology such as F-EMS and soft reduction. The center shrinkage and cracks of the cross-sectional and longitudinal sections of the casting bloom under different processes were observed by the thermal acid etching tests. The distribution of C segregation on the cross-section of the casting bloom was detected by drilling cuttings sampling The results showed that the solidification endpoint at a casting speed of 0.95 m/min was only 13.0 m. Accordingly, although the center shrinkage could be improved by increasing the F-EMS strength and using soft reduction. But F-EMS also stirred more high-concentration molten steel into the center of the bloom. Due to the small width of the molten pool in the billet center, the dilution effect on the high-concentration solute was small, and the molten pool was difficult to dilute these molten steel, so that the segregation of the bloom center was worsened. However, under the process of F-EMS current intensity of 540 A and 7 mm under soft reduction, when the casting speed increased to 1.2 and 1.4 m/min, internal cracks were generated on the inner arc side of the strand, and due to the wide mushy zone of the GCr15 bearing steel, when the casting speed was 1.4 m/min, the crack sensitive interval of the casting blooms was closer to the surface of the casting bloom than the white bright band at the press-down roller where the crack was generated, and finally the white bright band is closer to the center of the billet than the depressed crack. At a casting speed of 1.1 m/min, although the central shrinkage was controlled, the negative segregation occurred in the central area, resulting in the homogeneity of the strand could not be controlled to a high level. Under the casting speed of 1.0 m/min, the central solid-phase rate at F-EMS was around 0.1, the central solid-phase rate of the strand at the No. 2 and No. 3 reduction rollers were within 0.30-0.75, the center shrinkage rating of the cross-section for strand was below 0.5, the center segregation degree was 1.003, and the carbon range was 0.125%, which was the best quality.
2024 Vol. 59 (2): 99-110 [Abstract] ( 39 ) [HTML 1KB] [PDF 0KB] ( 38 )
Metal Forming
111 LI Zizheng, LIU Luxuan, YIN Baoliang, KUANG Shuang, WANG Jianhui, BAI Zhenhua
Research on roll temperature field and hot roll crown of hot continuous rolling mills
Aiming at the problems of roll consumption and shape caused by the inability to accurately predict the roll temperature field of a hot continuous mill. In order to realize the accurate measurement of the temperature field of the roll and the shape of the hot roll, reduce the abnormal consumption of the roll and avoid the occurrence of major production accidents, a numerical finite difference method and roll heat conduction equation were used to establish a model suitable for the roll temperature field and hot roll profile of a hot rolling mill. Based on this model, the roll cooling water intelligent segmental cooling control system of the hot rolling mill is introduced above, fully considering the existence of the specific parameters of the cooling water in the complex state of the cooling water and the direct influence of the cooling water flow rate on the roll temperature field and the hot roll crown. Considering the equipment parameters and process characteristics in the rolling process of hot tandem rolling, and considering the cyclic superposition effect of the increasing number of rolled steel coils on the roll temperature field and hot roll profile, the program is written to combine the theoretical calculation formula, simulation control model and field practice. The combination of process equipment parameters is the research object of analysis. Firstly, the on-site roll temperature measurement equipment is used to measure the temperature of the work roll and the backup roll, and the measured actual temperature distribution value is compared with the calculated value of the model, and the similar roll temperature and roll crown change trend as well as the consistent temperature and crown are obtained. The degree value verifies the accuracy and validity of the model calculation. Subsequently, the influence of changes in the number of steel coils on the roll temperature and roll crown was obtained by means of research and analysis based on the results, found the superimposed effect of the increase in the number of steel coils on the temperature rise, and found that about 10 coils will complete the temperature rise of the roll temperature field, and at the same time analyzed the cooling water roll temperature distribution along the roll body direction at three different flow rates. Finally, the accurate prediction of the temperature field of the work roll and the backup roll and the shape of the hot roll is obtained, and it lays a model foundation for further regulating roll temperature distribution by using roll temperature field and hot roll model.
2024 Vol. 59 (2): 111-118 [Abstract] ( 34 ) [HTML 1KB] [PDF 0KB] ( 81 )
Materials
119 LIU Haining, CHEN Yangmin, CHEN Xiangru, LI Lijuan, ZHAI Qijie
Effect of PMO on dendritic structure and carbide of high-speed steel
In order to solve the problems of developed dendrite structure,uneven distribution of carbide network and eutectic carbides in high-speed tool steel on natural cooling conditions. The Center for Advanced Solidification Technology of Shanghai University used a unique dual-power vacuum induction melting device,applying Pulse Magneto-oscillation (PMO) for external field intervention during the natural solidification of high-speed steel. The results show that with PMO treatment,the developed dendrites in the as-cast microstructure of high-speed steel are transformed into equiaxed grains. PMO technology can effectively optimize the as-cast microstructure and morphology of high-speed steel,refine the size of carbide network and eutectic carbide,and improve the uniformity of carbide distribution. PMO has a significant refinement effect on the size of the eutectic carbide network intersection of high-speed steel. Taking the refinement of the eutectic carbide network intersection size of M2 high-speed steel as an example,the average size of the carbide intersection at 1/8D,1/4D,and 1/2D (where D is the radial diameter of the casting bille)is reduced by 48.5%,47.1%,and 43.4%,respectively,compared to the ingots without PMO treatment. Meanwhile,PMO can further refine the size of eutectic carbide particles. Taking M2Al high-speed steel as an example,the average size of eutectic carbide particles at 1/8D,1/4D,and 1/2D decreases by 49.1%,54.5%,and 40.2%,respectively. It provides a new idea and method to solve the cracking phenomenon in the process of high-speed steel pressure machining with large deformation and improve its yield. It also provides a new direction for improving the problems encountered during high-speed steel continuous casting,such as the aggregation of carbides in the center and coarse carbides.
2024 Vol. 59 (2): 119-128 [Abstract] ( 41 ) [HTML 1KB] [PDF 0KB] ( 64 )
129 ZHANG Qi, SHEN Yiping, CHEN Guanghui, XUE Zhengliang, XU Guang
Effect of solid solution temperature on microstructures and mechanical properties of Fe-30Mn-8Al-0.8C low density steel
To study the microstructure evolution and mechanical properties of Fe-30Mn-8Al-0.8C(wt.%) low density steel treated at different solid solution temperatures varying from 900 ℃ to 1 100 ℃,the growth behavior of austenite grains was analyzed using OM,EBSD and XRD. Sallars model was adopted to fit the austenite grain size after solution treatments with different temperatures and time. The growth model of austenite grains was established. Tensile tester and hardness tester were used to test the mechanical properties of the experimental steel. The relationship between the microstructure and mechanical properties of the experimental steel was analyzed based on the results of tensile tests and hardness measurements. The results show that the microstructure of experimental steel was austenite with undissolved κ-carbides after solid solution treatment at 900 ℃ for 90 min,which became fully austenitic after solid solution treatment at other temperatures. The austenite grain size increased with solid solution temperature. The austenite grain growth behavior was fitted and analyzed to give a model for the relationship among solid solution temperature,holding time and austenite grain size. The elongation,yield strength and tensile strength decreased gradually with increasing solid solution temperature. Due to the presence of incompletely solidified κ-carbides in the 900 ℃ specimens,which led to early fracture of the specimens,the elongation of the specimens solution-treated at 900 ℃ was slightly lower than that of the 950 ℃ specimens. The optimum strength and plasticity combination of the experimental steel was obtained after solution treatment at 950 ℃ for 90 min. The product of strength and elongation reached 44.3 GPa·%. As the solid solution temperature increased,the work-hardening rate decreased,resulting in a lower work-hardening term for the tensile strength. According to the Hall-Petch relationship,the equation for the relationship between yield strength and grain size of the experimental steel was given. The mechanical properties of as-solid-solution Fe-30Mn-8Al-0.8C austenitic low-density steels with high-Mn and high-Al concentration can be predicted by considering the growth model of austenite grain.
2024 Vol. 59 (2): 129-138 [Abstract] ( 51 ) [HTML 1KB] [PDF 0KB] ( 76 )
139 HU Zhiqiang, ZHANG Haoxuan, ZHAO Jiachen, CUI Lei, LI Xinxing, WANG Kaikun
Thermodynamic calculation,microstructure and property of Fe-Mn-Al lightweight high-strength steel containing rare earth Ce
In order to acquire the phase composition and microstructure and performance characteristics of the Fe-Mn-Al lightweight high-strength steel containing rare earth Ce,and then improve its comprehensive mechanical properties,the phase composition,microstructure and typical mechanical properties of it are studied by combining thermodynamic calculations and experiments and the effect of solution treatment temperature at 900-1 100 ℃ on its microstructure and properties are analyzed. The results show that the main phases of the tested steel includes ferrite,austenite,κ carbide,Ce2C3 and NbC in the temperature range of 600-1 200 ℃. When the temperature is higher than 865 ℃,the carbides are almost completely dissolved in the matrix and the single-phase austenite region exists between 865-915 ℃. When the temperature exceeds 915 ℃,ferrite begins to precipitate from the austenite. The ferrite content gradually increases with the increase of temperature,and the temperature range of 915-1 200 ℃ is the two-phase region of austenite and ferrite. The austenite content in the hot-forged test steel is about 86.4%,with an average austenite grain size of about 28 μm and a large amount of deformation twinning inside. After solution treatment,the ferrite content increases and the grains begin to coarsen. Most of the ferrite in the banded structure is broken and separated,distributed in small particles along the austenite grain boundaries,and a small amount of annealing twins begin to appear inside the austenite. Besides,the tensile strength of the test steel is significantly reduced,and the plasticity is improved. When the solution temperature is 1 000 ℃,the tensile strength of the tested steel is 889.6 MPa,the elongation at break is 47.1%,and the strength-ductility prod uct reaches a maximum of 42.08 GPa·%. It is for that,on the one hand,the plasticity of the test steel is significantly improved due to the increase of ferrite content,and on the other hand,the two-phase structure of austenite and ferrite is evenly distributed,and the grains are fine,which is conducive to the improvement of strong plasticity. Therefore,compared with that at the solution temperature 900 ℃,the tensile strength of the test steel at 1 000 ℃ did not decrease significantly,while the plasticity increased by nearly double.
2024 Vol. 59 (2): 139-146 [Abstract] ( 45 ) [HTML 1KB] [PDF 0KB] ( 53 )
147 ZHANG Jing, ZHAO Xuan, LI Shi, ZHANG Lifeng
Effect of casting speed on size and distribution of carbide in 30Cr13 continuous casting slab
30Cr13 is a high quality stainless steel for cutting tools. The development of continuous casting technology has greatly improved its production efficiency. Casting speed is an important process parameter and technical indicator in the continuous casting process. When the casting speed is not suitable,it is easy to form a large amount of unevenly distributed carbides,and the size and distribution of carbides are key factors affecting the quality of continuous casting slabs. Taking 30Cr13 continuous casting slab as the research object,the morphology,size,and type of carbides in different solidification structures in continuous casting slabs of 0.75 m/min,0.80 m/min,and 0.85 m/min were analyzed by Scanning electron microscope,Light microscopy,X-ray diffraction. The effect of casting speed on carbides in 30Cr13 continuous casting slab was studied based on the solidification microstructure morphology,and the effect law of casting speed on carbides in continuous casting slab was summarized. The results show that the main morphology of carbides is clusters,blocks,and strips,and the main components are Fe,Cr,and C. The main types of carbides have been determined to be (Fe,Cr)7C3 and (Fe,Cr)23C6. And it was found that there were no carbides present at the "white bright band",and a large amount of carbides appeared in the sample between the "white bright bands",with the most carbides appearing at the center of the slab. The casting speed has no effect on the shape,type,and location of carbides,but has a greater impact on the quantity and size of carbides. As the casting speed increases,the proportion of total carbide area and number density first decrease and then increase. When the casting speed is 0.80 m/min,the proportion of carbide area and number density in the continuous casting slab is the lowest. This change is consistent with the trend of the degree of deviation of the C segregation index from the normal value under different casting speeds. With the increase of casting speed,the proportion of small-sized carbides increases gradually,while that of large-sized carbides are almost zero. The speed of 0.80 m/min can effectively control the size distribution of carbides in continuous casting slab and improve the quality of the slab.
2024 Vol. 59 (2): 147-156 [Abstract] ( 38 ) [HTML 1KB] [PDF 0KB] ( 57 )
157 HUI Pengbo, ZOU Dening, LI Yunong, LI Miaomiao, HE Chan, CHEN Haodong
Effect of temperature on pitting corrosion behavior of 2507 steel in simulated flue gas desulfurization solution
Super duplex stainless steel(SDSS) has promising applications in flue gas desulfurization (FGD) due to its excellent corrosion resistance and superior mechanical properties as well as its cost-effectiveness. The pitting behavior of 2507 SDSS in flue gas desulphurization condensate at different temperatures (20,40,60,80 ℃) was studied in depth using metallographic microscope,scanning electron microscope and electrochemical workstation. The findings demonstrate that at a solution temperature of 40 ℃,the test steel has the best corrosion resistance with corrosion potential (Ecorr) of -0.078 V,corrosion current density (icorr) of 5.09 mA/cm2,pitting potential (Epit) of 0.956 V,the largest impedance spectrum radius and a charge transfer resistance (Rct) of 54 200 Ω/cm2. The impedance modulus at a frequency of 0.01 Hz |Z|f=0.01 Hz is 52 036 Ω. When the solution temperature was increased from 20 ℃ to 80 ℃,the Ecorr and Epit of the specimen increased first and decreased,the icorr decreased first and increased,the electrochemical impedance spectrum radius increased first and decreased,the Rct increased first and decreased,the number of pitting pits after corrosion decreased first and increased,the pitting corrosion resistance of the sample increased with an increase in temperature followed by a decrease. The analysis suggests that this is the result of the combined effect of the two opposite effects of temperature on the electrochemical process (blocking effect of reduced oxygen content and the promoting effect of increased ionic activity). When the temperature is below or at 40 ℃,the mass concentration of dissolved oxygen decreases,the activity and reaction ability of Cl- are weak,and the blocking effect of reduced oxygen content dominates. With the increase of temperature,the pitting corrosion resistance of 2507 SDSS is improved.when the temperature is above 40 ℃,high temperature will enhance the activity of corrosive halogen ions and their reactivity,Cl- activity to enhance the promotion of the effect of the dominant role. With the increase of temperature,the pitting corrosion resistance of 2507 SDSS decreases.
2024 Vol. 59 (2): 157-163 [Abstract] ( 55 ) [HTML 1KB] [PDF 0KB] ( 46 )
Environmental Protection and Energy
164 REN Xiaojian, ZHOU Rongbao, YANG Tao, MA Lei, LEI Jie, LONG Hongming
Development and application of composite binder for iron-bearing dust pellets molding
The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate, and becomes one of the development trends of iron-bearing dust sludge treatment technology. However, the poor balling performance of iron-bearing dust sludge leads to low strength and easy pulverization of the pellets, which seriously restricts the environmental and efficient production of the rotary hearth furnace process. An important means of improving the performance of raw materials and increasing the yield and quality of pelletized ore is the use of excellent binder. The composite binder was prepared by matching organic binder and bentonite, and the effect of composite binder on the cold performance and reduction performance of pellets was investigated. It was shown that the composite binder pellets exhibited excellent green pellets performance. The drop strength and compressive strength of green pellets in the CB2-3 group (3% bentonite+0.5% binder B) reached 8.5 times/0.5 m and 78 N/P, respectively. It is because the organic binder has rich oxygen-containing groups, such as —OH, —COO—, etc., which improves the hydrophilicity of the surface of the iron-bearing dust sludge and strengthens the connection between the bentonite and the iron-bearing dust sludge concentrate particles. The binder C forms a mesh structure during the drying process, which promotes the proximity of dust particles to each other, and was the main factor in the dry-ball strength enhancement of the CB3 group(3% bentonite+2% binder C). Meanwhile, the reduction of iron oxides and zinc oxides was more fully due to the increase in the content of organic components. The main reason is the pyrolysis of organic components at high temperature, which accelerates the pyrolysis of solid fuels and the diffusion of reduction products. However, excessive pore generation will lead to a decrease in the strength of the pellets. Industrial tests shown that compared with the composite binder YG-1 used in the field, the addition of CB2-3 and CB3 can significantly improve the production quality index of the iron-bearing dust pellets, while the cost of the binder decreased from 140 yuan/t to 115 yuan/t and 120 yuan/t, respectively, which achieves the effect of quality improvement and costs reduction.
2024 Vol. 59 (2): 164-172 [Abstract] ( 32 ) [HTML 1KB] [PDF 0KB] ( 59 )
173 CHEN Demin, LI Ning, LIU Xiao, ZHAO Yibo, LI Xiuping, CHEN Guang
Effect of oxygen-enriched combustion conditions on heat transfer characteristics of reheating furnace
Oxygen-enriched combustion has the advantages of increasing theoretical combustion temperature,reducing excess air coefficient and enhancing flue gas radiation capacity,so it has become a hot research topic in the field of industrial furnace. However,the influence of oxygen-enriched combustion position and the volume percent of oxygen on the flow and heat transfer process in steel rolling furnace is still unclear. In this paper,the flow models,oxygen-enriched combustion model and heat transfer model in the heating furnace are established and applied in the case reheating furnace. After the accuracy of the model is verified by the test data,the variation rules of temperature field,velocity field and billet heat transfer process in the furnace are analyzed when the oxygen-enriched combustion is located in the preheating stage,the first heating stage and the second heating stage respectively. Then the best position of oxygen-enriched combustion is obtained. Secondly,the variation law of flue gas heat loss,furnace thermal efficiency and energy saving rate is analyzed when the volume percent of oxygen changes from 21% to 49% in the fixed oxygen-enriched combustion position. Then the optimal range of the volume percent of oxygen is obtained. The results show that when the volume percent of oxygen is fixed,oxygen-enriched combustion is carried out in the preheating stage,the first heating stage and the second heating stage,the most obvious heat flux changes occur in the furnace positions of 17-25,17-34 and 29-44 m,respectively. The average heat flux increases at these locations were 4.95,7.42,and 7.95 kW/m2,respectively. When the oxygen rich combustion positions are fixed in the pre heating section,heating section 1,or heating section 2,and the volume percent of oxygen varies between 21% and 37%,for each 1% increase in the volume percent of oxygen,the flue gas loss decreases by 0.25%,0.55%,and 0.72%,the furnace thermal efficiency increases by 0.13%,0.3% and 0.39%,and the energy saving rate increases by 0.2%,0.99% and 1.09%,respectively. However,when the volume percent of oxygen is in the range of 37%-49%,the changes of flue gas loss,furnace thermal efficiency and energy saving rate are not obvious even if the oxygen-enriched combustion is implemented in the second heating stage. It can be seen that in the steel rolling reheating furnace,the high heat load stage implements oxygen rich combustion and the volume percent of oxygen is in the range of 21%-37% is the energy-saving effect most obvious.
2024 Vol. 59 (2): 173-184 [Abstract] ( 43 ) [HTML 1KB] [PDF 0KB] ( 43 )
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