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	2022 Vol. 57 No. 5
	Published: 2022-05-15



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

Technical Reviews

	1	LIU Ran, ZHANG Zhi-feng, LIU Xiao-jie, LI Xin, LI Hong-yang, LÜ Qing
		Development trend and prospect of low-carbon green ironmaking technology
		At present, in order to actively respond to a series of issues such as climate change, countries around the world have put forward green emission reduction plans. At the same time, China puts forward the corresponding "carbon peak, carbon neutral" energy conservation and emission reduction goals, and takes "1+N" and other policy systems as the core support to achieve sustainable development strategy, actively respond to climate change, fulfill the obligations of a big country. Steel industry, as the industry with the largest carbon emissions among 31 manufacturing sectors, naturally becomes the "vanguard" in the battle of energy conservation and emission reduction. At present, the complex blast furnace production process is still mainly taking coal, coke and other fossil resources as the main fuel, which makes it become a large carbon consumer, carbon emitter and pollution emitter in the iron and steel process, so the green and low-carbon transformation and upgrading of blast furnace ironmaking process is imminent. This paper discusses from three parts, that is background introduction, development trend of low-carbon green iron making technology and future development prospect. In particular, the development of green and low-carbon iron-making technology is elaborated in detail. Firstly, from two aspects of optimizing energy-saving and low-carbon operation and constructing circular economic environmental protection circle, it discusses how to realize low-carbon and green iron-making of blast furnace process from the perspectives of fine charge operation and improving production technology. Secondly, from the field of non-blast furnace, the development status of direct reduction process and melting reduction process at home and abroad is described, and the corresponding comparison and classification are summarized. Finally, the development trend for this kind of technology is discussed from the angle of innovative ironmaking process (hydrogen metallurgy, intelligent ironmaking). In the end, five aspects are prospected based on the latest developments of current green and low-carbon iron making technology, and the task direction of "green and low-carbon as the direction, energy saving and emission reduction as the target" is clearly defined.
		2022 Vol. 57 (5): 1-10 [Abstract] ( 575 ) [HTML 1KB] [PDF 2108KB] ( 831 )

Raw Material and Ironmaking

	11	YANG Cong-cong, ZHU De-qing, PAN Jian, GUO Zheng-qi
		Overseas research advances in evaluation methods of high-temperature fundamental sintering characteristics of iron ores
		Due to the increasing depletion of high-grade iron ore resources and the diminishing quality of iron ore sinter feeds, the steel mills at home and abroad are facing with problems that sintering raw material supply is unstable, iron ore property fluctuates greatly and raw material structure changes frequently, which has great adverse effect on sintering production, blast furnace smelting and product quality. Therefore, it's of great significance to conduct evaluations of fundamental sintering characteristics of iron ores. The basic properties of iron ores can be classified into two categories, i.e., cold and high-temperature characteristics. The former mainly includes the chemical composition, particle size distribution and mineralogical characteristics, etc., while the latter generally includes high-temperature mineralization behavior, such as assimilation, liquid phase formation characteristics of iron ores as well as the real sintering performance. This article mainly summarizes the overseas research advances in the evaluation of high-temperature fundamental sintering characteristics of iron ores. Meanwhile, the evaluation indexes and experimental methods proposed by various research institutions are summarized systematically. The previous studies show that, although the existing evaluation methods based on compact sintering provide deep insight into different sintering behavior of iron ores, it's still difficult to build accurate and reliable relationship with the real sintering performance. The main reason is that the key factors affecting the actual sintering performance of iron ore are not well understood, and the evaluation methods needs to be improved to simulate the real sintering conditions as much as possible. Therefore, to reveal the internal relations between fundamental sintering characteristics and its sintering performance of iron ore, the first premise is to develop deep understanding about the transfer law of the properties for materials derived from different operational stages, notably “iron ores-granules-sinter”. It is of great significance to find out the main factors influencing the iron ore sintering process, which can provide a proper breakthrough point for the evaluation of high-temperature fundamental sintering characteristics of iron ores.
		2022 Vol. 57 (5): 11-21 [Abstract] ( 319 ) [HTML 1KB] [PDF 5616KB] ( 373 )

	22	WANG Chen, ZHU Ren-liang, WANG Guang-wei
		Feasibility analysis of biomass hydrochar injection for blast furnace
		Iron and steel production consumes a lot of fossil fuels, emits CO₂ and discharges pollutants. Reducing CO₂ emissions in the process of iron and steel production has become the key to achieve the goal of "carbon peak" and "carbon neutrality" for the iron and steel industry. Biomass as a product of plant photosynthesis, which has the characteristics of large yield, renewable and carbon neutral, is the only renewable carbon source with good storage and easy transportation characteristics. The efficient application of abundant biomass resources in iron-making with blast furnace has become the key to achieve green and sustainable development of iron and steel industry. However, biomass generally has the disadvantages of high moisture content, low fixed carbon content and calorific value, more harmful elements of alkali metals (K, Na) and poor crushing performance. Without carbonization treatment, it is difficult to meet the requirements for the process performance of fuel injection for blast furnace iron-making. The differences of pyrolysis and hydrothermal carbonization (HTC) technology principle was analyzed, and two type preparation technologies of biomass carbon and the basis performance and processing property of blast furnace injection was investigated. Results showed that the pyrolysis carbonization can remove the volatile in biomass, improve fixed carbon content and calorific value, but the ash and alkali metal elements will be enriched into biomass during pyrolysis. The content of ash and alkali metals in pyrolysis biomass was increased significantly, and the alkali metal content in four pyrolysis biomass was more than 1%, far above the standard for alkali metal content in coal with high basicity, which cannot meet the requirements of blast furnace injection. Hydrothermal carbonization could effectively remove volatile and dissolved mineral elements of biomass. Biomass hydrochar prepared had low content of ash and alkali metal, high fixed carbon and calorific value, high grindability and excellent combustion performance, which was met the requirement of blast furnace injection. The biomass HTC technology solves the restrictive problems of low biomass energy density, high content of harmful elements, and difficulties in grinding and injecting. The implementation for new technology of high quality carbon-neutral fuel for blast furnace injecting through the biomass HTC technology is beneficial to Baowu Group to achieve green and low-carbon iron-making.
		2022 Vol. 57 (5): 22-30 [Abstract] ( 281 ) [HTML 1KB] [PDF 2604KB] ( 483 )

	31	LIANG Bin-jun, YU Ce-en, TANG Li-qun, HU Hai-xiang
		Growth characteristics of metallic iron particles during direct reductive of ludwigite ore
		Ludwigite ore will be the main source of boron-containing raw materials in China, and the key of its processing and utilization lies in the B-Fe separation. The growth characteristics of metallic iron particles in the direct reduction process of ludwigite ore under different conditions were investigated, which could provide theoretical support for B-Fe separation and achieve the purpose of resource utilization of ludwigite ore. The microscopic images of metallic iron particles in the reduced pellets were obtained by Leica DMI5000M optical microscope, the sizes of metallic iron particles were analyzed and counted by the software of Image-pro Plus 6.0, and then the metallization rate of iron in the reduces product was tested by chemical analysis. Meawhile, the promoting mechanism of Na₂CO₃ for iron oxide reduction and the growth behavior of metallic iron particles were studied by SEM. The results showed that the iron oxides of ludwigite ore pellets could be effectively reduced in the presence of Na₂CO₃. The metallization rate of iron and the size of metallic iron particles increased effectively with the extension of reduction time. When the pellets were roasted at 1 100 ℃ for 60 min in the absence of Na₂CO₃, the metallization rate of iron and the size of metallic iron particles in the reduced products were 84.36% and 8.55 μm. However, the metallization rate of iron and the size of metallic iron particles could reach to 91.72% and 14.07 μm with the same roasting conditions in the presence of 15% Na₂CO₃. The results of SEM-EDS analysis showed that Na₂CO₃ not only promoted the metallic iron to separate from other substances, but also affected the migration behavior of metallic iron particles during the reduction roasting process. The metallic iron particles first changed from "point" contact to "neck" contact, and then re-intersected to form new grain boundaries and became polygonal particles during the direct reducing process. Finally, the polygon particles were connected to each other to form a densified aggregate.
		2022 Vol. 57 (5): 31-39 [Abstract] ( 146 ) [HTML 1KB] [PDF 3389KB] ( 425 )

	40	QI Teng-fei, HUANG Jun, SUN Jun-jie, ZHANG Yong-jie
		DEM simulation for effect of sinter particle size composition on operation of vertical cooling furnace
		In order to improve the voidage distribution in the vertical cooling furnace and promote the heat transfer between hot sinter and cooling gas, three working conditions with gradually decreasing particle size distribution range were designed from the perspective of reducing the upper limit of sinter feeding particle size. Based on the quasi three-dimensional slot model of a single furnace cavity in the vertical cooling furnace of MeiSteel, the variation laws of sinter velocity distribution, voidage distribution and pressure drop distribution in the furnace were studied by discrete element method. The results showed that, with the feeding particle size composition of 10-150 mm, a rectangular low-speed zone was formed above the central hood, which reduced the uniformity of downward moving speed of sinter. The low voidage area gradually expanded and formed the distribution of low voidage in the middle area and high voidage in the edge and center area of the furnace cavity. The voidage segregation was the most serious and the distribution uniformity was the worst in the furnace. 40% of area in the furnace was the high pressure drop area, which was mainly distributed in the middle area. 20% of area was the low pressure drop area, which was mainly distributed in the central area, and resulting in the most serious gas flow segregation in the furnace. By reducing the upper limit of feeding particle size, the rectangular low-speed zone was eliminated and the integrity of sinter flow was improved. When the feeding particle size composition of 10-90 mm was adopted, the minimum voidage was increased, and the difference of voidage between the middle area and the side wall as well as the central area was reduced, so that the segregation degree of voidage was the minimum and the uniformity was the highest. At the same time, the composition reduced the maximum value and increased the minimum value of pressure drop, and expanded the range of medium pressure drop zone, so as to alleviate the gas flow segregation distribution in the furnace and improve its distribution uniformity. Reducing the upper limit of sinter feeding particle size by adding secondary crushing process can become a practical direction to improve the operation of sinter vertical cooling furnace. In the future, the most suitable sinter feeding particle size range and the mass percent of each particle size section should be studied.
		2022 Vol. 57 (5): 40-47 [Abstract] ( 194 ) [HTML 1KB] [PDF 3604KB] ( 365 )

Steelmaking

	48	MENG Yao-qing, LI Jian-li, ZHU Hang-yu, WANG Kun-peng
		Effect of LF soft bubbling time on oxide inclusions in Si-killed spring steel
		In order to ensure the cleanliness of molten steel, the long-time soft bubbling during LF refining process is often chosen for some Si-Mn deoxidized special steels, resulting in increased energy consumption in the process. Based on the industrial tests, the effects of LF soft bubbling time on the composition and number density of inclusions in Si-killed spring steel bloom were investigated through a scanning electron microscope (FEI Explorer 4), and the maximum size of inclusions in the crossing section of wire rods collected from the LF process with different soft-bubbling times was compared and evaluated by the extreme-value statistical method. The results showed that for the LF processes with two soft-bubbling time, 10 min and 40 min, the compositions of oxide inclusions larger than 5 μm in the blooms were close, and both in the low-melting point region at the eutectic zone of pseudo-wollastonite, anorthite, and gehlenite of CaO-SiO₂-Al₂O₃ phase diagram. The proportion of oxide inclusions falling into the low-melting point region in the 10 min soft-blowing process was higher than that in the 40 min soft-blowing process. The number densities of oxide inclusions with size larger than 5 μm were 11.70 /100 mm² and 14.59 /100 mm² respectively in the blooms adopted 10 min and 40 min soft-bubbling processes. Meanwhile, the number densities of oxide inclusions with size above 15 μm were 0.53 /100 mm² and 1.65 /100 mm², respectively. The number density of large oxide inclusions in the bloom of 10 min soft-bubbling process was slightly lower than that of 40 min soft-bubbling process. When the predicted area was 30 000 mm², the maximum sizes of oxide inclusion in the cross sections of wire rods were 27.1 μm and 28.1 μm respectively, and there was no significant difference of them. The low-melting point CaO-SiO₂-Al₂O₃ inclusions with large size in Si-Mn killed steel mainly come from the emulsification of ladle slag, which had a small interface-contact angle with molten steel and argon bubble and was difficult to be removed by argon floating. It is suggested that the soft-bubbling time during LF refining should be controlled in a short time for Si-Mn deoxidized steel.
		2022 Vol. 57 (5): 48-54 [Abstract] ( 205 ) [HTML 1KB] [PDF 2491KB] ( 451 )

	55	WANG Jie, ZENG Jia-qing, YANG Li-bin, WANG Cheng-yi
		Fine control technology and its co-optimization of converter steelmaking
		Converter steelmaking is a complex open system, which is affected by interaction of many factors simultaneously or alternately, such as multiple chemical reactions of different impurity elements or substances, continuous rising and control of temperature, inhomogeneous spontaneous stirring of molten pool, inhibiting liquid steel peroxidation during removal of impurity elements, fine operation and timing control in converter etc., its operation law within its space-time boundary is dynamic and nonlinear. The isolated system knowledge is not appropriate to reveal the transformation law from traditional single production output index to multi-objective coordination for production output, quality and environmental protection etc. The functional orientation of modern converter steelmaking should be focus on efficient and stable primary smelting of clean molten steel, and then combined with subsequent molten steel refining technique to meet the furnace-machine matching requirements of multi-heats continuous casting with high / constant drawing speed in the whole process. From vision of function positioning and related operations timing matching of converter steelmaking, the "point technique" containing furnace protection by slag splashing, efficient oxygen supply, molten pool uniform mixing, composition of molten steel matched with temperature, post stirring, rapid steel extraction and separation of slags and steel, efficient recovery of converter gas were discussed. It points out that the aim of above-mentioned "point technique" application should be focused on fine control effect, at the same time, it is necessary to meet the requirements of timing planning of converter steelmaking and collaborative operation of upstream and downstream processes, so as to ensure high quality, stable and smooth operation of the whole process, and constantly tap the ultimate potential of converter steelmaking.
		2022 Vol. 57 (5): 55-63 [Abstract] ( 321 ) [HTML 1KB] [PDF 2231KB] ( 530 )

	64	WANG Xu-feng, WANG Qiang-qiang, ZHANG Xu-bin, WANG Qian, HE Sheng-ping
		Effect of AlN on properties of CaO-SiO₂ based mold fluxes for high-Al steel
		Al added to steel as alloying elements can not only refine grain size, inhibit aging phenomenon of low carbon steel, achieve a good combination of corrosion resistance, heat resistance and other properties of steel, but also to meet the new generation of automotive steel for automotive safety and lightweight requirements. However, when w([Al]) in molten steel is too high, the AlN generated before the solidification of molten steel rises to the interface of steel and reacts with the mold fluxes in the mold, which leads to changes in the composition and deterioration in properties of the mold fluxes, thus affecting the alignment of continuous casting and the surface quality of billet. FactSage7.2 thermodynamic software was used to calculate the formation thermodynamics of AlN in high-Al molten steel, the change of viscosity, melting temperature and break temperature of traditional CaO-SiO₂ based mold fluxes after adding mass fraction of 2%, 4%, 6% and 8%AlN was analyzed by hemisphere point melting temperature tester and rotary viscometer, and the slag samples after adding AlN were tested by XRD. The results show that with the increase of w([Al]) and w([N]) in steel, the formation temperature of AlN increases and the total formation amount of AlN increases. When the amount of AlN increases from 0 to 8%, both the viscosity and melting temperature of mold fluxes increase. The viscosity increased about 0.032 Pa·s and the melting temperature increased about 13.5 ℃ with each added mass fraction of 1% AlN. When the mass fraction of AlN was 2%, the break temperature decreased from 1 002 ℃ to 980 ℃. When the mass fraction of AlN was more than 2%, the break temperature gradually increased to 1 117 ℃ at 8%AlN. With the increase of AlN content, the amount of cuspidine precipitation in the traditional CaO-SiO₂mold fluxes decreases gradually in the process of condensation. When the AlN content is 8%, the main phase in the slag sample is CaF₂.
		2022 Vol. 57 (5): 64-71 [Abstract] ( 181 ) [HTML 1KB] [PDF 3015KB] ( 493 )

	72	YAN Xiao-peng, LIU Lei, HAN Xiu-li, WANG Yin-hui, ZHANG Di
		Effect of boron on microstructure of fluorine-free mold fluxes
		Nowdays, under the background of steel overcapacity and energy conservation in the steel industry, actively looking for substitutes to fluorine in mold fluxes and developing new fluorine-free mold fluxes have become an important way to achieve green and efficient continuous casting production. As an ideal substitute for fluorine, boron has become a new research focus of fluorine-free mold fluxes technology due to its economic cost and fluxing effect, and it is considered to have the broadest application prospects. In order to explore the melting and crystallization mechanism of boron-containing and fluorine-free mold fluxes, and to clarify the internal cause for the change of viscosity properties of boron-containing and fluorine-free mold fluxes from the perspective of the change of melt microstructure, blast furnace slag, limestone, quartz sand, soda ash and borax was used as the main raw material to prepare boron-containing and fluorine-free mold fluxes, in order to realize its industrial application. Combined with Raman spectroscopy and Scigress molecular dynamics simulation, the microstructure such as bond length, coordination number and structural unit of fluorine-free mold fluxes were analyze. The results show that as the borax content increases from 4% to 16%, the structure of boron-oxygen backbone in the slag has undergone major changes, the average coordination number of B—O increases from 3.028 to 3.096, and the average coordination number of Si—B increases from 0.229 to 0.898, moreover, the [BO₃] trihedron transforms into [BO₄] tetrahedron, and the average bond length of B—O remains unchanged at 1.375 nm. The number of bridging oxygen in the slag increases, and the structural unit changes from a simple island-like structure and a ring-like structure to a complex one. The layered structure and the framework structure are transformed, forming a complex borosilicate structure, which increases the DOP of slag, as a result, atomic groups and the migration resistance of ions is strengthened. This is not conducive to the nucleation and growth of crystals, and inhibits the crystallization of mold fluxes, thereby reducing the viscosity of mold fluxes further. On the whole, when the borax content in the boron-containing fluorine-free slag system is 7%-16%, the slag polymerization degree is higher, the network structure is more complex, and the viscosity stability is better.
		2022 Vol. 57 (5): 72-80 [Abstract] ( 115 ) [HTML 1KB] [PDF 2981KB] ( 373 )

Metal Forming

	81	YANG Ting-song, BAI Yu-hang, LEI Zhen-yao, XU Zhi-qiang, DU Feng-shan
		Influence of magnetic gathering structures on roll profile electromagnetic control ability
		Roll profile electromagnetic control technology (RPECT) is a dynamic control technology of roll profile. The technology relies on the thermal expansion of electromagnetic stick and internal restraint mechanism of electromagnetic control roll, forming thermal-force expansion to achieve dynamic adjustment of roll profile. In this technology, improving the thermal-force driving ability is the key to optimizing the control process of RPECT, and also the main method to improve the timeliness and control effectiveness of the technology. According to the principle of electromagnetic induction and the structural characteristics of electromagnetic control roll, the reasonable magnetic structure has the ability to improve the spatial distribution of magnetic force lines, which can be used to improve the thermal-force driving ability of RPECT. Based on the characteristics of RPECT and the electromagnetic induction principle, this paper proposes three forms of magnetic gathering structures, including complete magnetic gathering structure, local magnetic gathering structure and non-magnetic gathering structure. Through the simulation model of RPECT, the influence of magnetic gathering structures on roll profile electromagnetic regulation characteristics is analyzed, and the difference of regulation effects is identified. The results show that the magnetic gathering device can improve the temperature level of induction heating zone and contact zone, and significantly improve the regulation energy efficiency of electromagnetic stick. The temperature rise in the contact area further enhances the heat exchange between the roll and the electromagnetic stick, and finally improves the internal temperature level of the roll. Under the influence of different magnetic gathering structures, the temperature rise of roll and stick can improve the proportion of force contribution roll crown and the controllability of electromagnetic control roll. Among the three magnetic gathering structures, the complete magnetic gathering structure has the most significant influence on the thermal-force driving ability of the electromagnetic control roll, followed by the local magnetic gathering structure, and the non-magnetic gathering structure is the weakest. This paper provide a method to improve the energy efficiency of RPECT. The research results of this paper have certain guiding significance for the structural design and process setting of electromagnetic control roll and electromagnetic stick.
		2022 Vol. 57 (5): 81-89 [Abstract] ( 112 ) [HTML 1KB] [PDF 5699KB] ( 368 )

Materials

	90	CHENG Zhao-yang, ZHONG Bo-lin, JING Wen-qiang, YU Yao, SONG Xin-li, LIU Jing
		Effect of Cr on microstructure, texture and properties of Nb-containing high strength non-oriented silicon steel
		High strength non-oriented silicon steel is mainly used in high-speed motors, which requires good mechanical and magnetic properties. However, it is difficult for non-oriented silicon steel to obtain high strength and good magnetic properties at the same time. In this paper, the Cr-microalloyed Nb-containing high strength non-oriented silicon steel was designed and prepared. The effect of Cr on the microstructure, texture, mechanical properties and magnetic properties of Nb-containing high strength non-oriented silicon steel was studied by optical microscopy, EBSD, universal tensile testing machine, four-probe tester and magnetic properties test. The results show that the mass fraction addition of 0.5% Cr impedes the recovery of hot-rolled microstructure, and inhibits the recrystallization of normalized and final annealed microstructure. At the same time, the area fraction of favorable texture increases after normalization and annealing with the mass fraction addition of 0.5% Cr, while the area fraction of unfavorable texture decreases. Moreover, the mass fraction addition of 0.5% Cr increases the yield strength significantly and magnetic induction slightly of Nb-containing non-oriented silicon steel, but almost has no effect on the iron loss of the steel. The increase of yield strength of Nb-containing high strength non-oriented silicon steel after adding Cr is due to the solid solution strengthening effect of Cr, and the promotion of Nb precipitation by adding Cr and hence enhances the precipitation strengthening effect of Nb. The improvement of magnetic induction after adding Cr is owing to the promotion of favorable textures formation and the inhibition of unfavorable texture formation, which increases the texture factor. The resistivity of non-oriented silicon steel is increased after adding Cr, and hence decreases the iron loss. However, on the other hand, the promotion of Nb precipitation after adding Cr will increase iron loss by impeding the growth of crystal grains, and inhibiting the movement of magnetic domain. Thus, the mass fraction addition of 0.5% Cr will almost has no effect on iron loss of Nb-containing high strength non-oriented silicon steel as the co-effect of these two factors. Therefore, adding a small amount of Cr to the Nb-containing high strength non-oriented silicon steel will increase the strength and improve the comprehensive magnetic properties of steel due to the solid solution effect of Cr and its promotion of Nb precipitation.
		2022 Vol. 57 (5): 90-98 [Abstract] ( 213 ) [HTML 1KB] [PDF 8027KB] ( 380 )

	99	YU Wen-chao, ZHANG Xiao-lu, JIN Guo-zhong, HU Fang-zhong, HE Xiao-fei
		Influence of sulfide modification on inclusions and cutting properties of 20MnCr5 gear steel
		Gear steel is widely used in automobile, machinery and other drive systems. Free cutting is one of the main ways to improve gear processing efficiency and reduce manufacturing cost. Increasing sulfur content in steel is an effective way to improve the cutting performance of gear steel. However, excessive sulfur will form strip MnS during rolling, which will increase the anisotropy of steel. Therefore, it is necessary to modify the sulfide. 20MnCr5 gear steel was employed and modified with sulfide by Ca treatment and Mg treatment respectively. Through the characterization of mechanical properties, microstructure, inclusion distribution and cutting performance, the influence of different modification methods on the material was compared and analyzed. The results show that the strength and plasticity of steels treated by Ca and Mg are consistent, while the grain size of the sample treated by Mg is smaller, leading to a higher toughness. The amount of MnS inclusions in Ca-treated steel is larger, and the proportion of long strip inclusions is relatively higher by comparing with Mg-treated one. However, Mg treatment can effectively reduce the number of inclusions in steel, increase the average size of inclusions and the number of small aspect ratio inclusions at the same time, however, the number of composite oxide inclusions also increases. The dry cutting tests were carried out at speed range of 240-280 m/min. The results show that both steels appear the front tool surface wear, the flank wear and the boundary wear. The tool wear of the Ca-treated sample is more serious, and the built-up edge and edge breakage phenomenon occur at the higher cutting speed. On the contrary, the sample treated with Mg has a longer tool life and a lower sensitivity to cutting speed. Based on the results obtained, there are more large-size spherical sulfide inclusions in Mg-treated steel, which improves the stress concentration effect and is more conducive to improving the free cutting performance, so the sulfide modification effect is better.
		2022 Vol. 57 (5): 99-106 [Abstract] ( 151 ) [HTML 1KB] [PDF 3900KB] ( 605 )

	107	HU Yong, ZHANG Hui-ying, LIN Hong-ze, OUYANG Ming-hui, CHU Cheng, WANG Li-hua
		Effect of elements and cooling rate on solidification mode of high-silicon stainless steel
		High-silicon austenitic stainless steel as a special steel is commonly used in the acid industry due to its excellent corrosion resistance for high silicon content. However, the addition of high silicon content will cause problems such as aggravation of casting defects, component segregation and an increase of precipitation phases in the steel, resulting in hot cracking during hot working. The content, morphology and distribution of δ ferrite in the solidification process of high-silicon austenitic stainless steel are closely related to the chemical composition and hot processing history of the alloy, while the solidification structure depends on the precipitation order of the precipitates and subsequent solid phase transformation. As a result, the solidification mode of stainless steel will inevitably affect the thermoplasticity of alloy. This work adopted metallographic microscope (OM), X-ray diffractometer (XRD), scanning electron microscope/energy spectrum analysis (SEM/EDS), electron probe (EPMA), JMatPro calculation and other methods to study the influence of alloy composition and cooling rate on the solidification mode of high-silicon austenitic stainless steel by adjusting the contents of Si and Cr elements, and the classic chromium-nickel equivalent algorithm was evaluated. The results show that the Schneider chromium-nickel equivalent algorithm is more accurate in predicting the solidification mode of most alloys than the Rajasekhar chromium-nickel equivalent algorithm. The solidification mode of alloy changes from the AF mode to the FA mode with the contents of Si and Cr in the alloy increasing, the alloy undergoes more “δ→γ” solid phase transition during solidification, and the increase of δ ferrite with a mass fraction of 6%Si alloy slows down. The solidification mode of alloy changes from the AF mode to the A mode with the cooling rate increasing of 5%Si ingot. The Hammar and Svensson solidification route criterion can accurately predict the initial precipitation phase of high-silicon austenitic stainless steel. This study provides a theoretical basis for rationally formulating the alloy composition and forming process of high-silicon austenitic stainless steel.
		2022 Vol. 57 (5): 107-117 [Abstract] ( 170 ) [HTML 1KB] [PDF 8593KB] ( 268 )

	118	LU Jin-long, QIU Wen-sheng, CHENG Guo-guang, LONG Hu, LI Yao
		Control mechanism of compound sulfides in steel for automotive control arms containing Ca
		There is a large cutting workload during automotive control arm manufacturing processes because of its complex shape. In order to increase the cutting performance of parts, a small amount of Ca element is further added into steel with 0.03% sulfur, so that common slender strip MnS would be transformed into spindle (Ca, Mn)S. However, when the sulfur mass fraction is 0.03%, the solubility of Ca element in molten steel is very low, and the generation of pure (Ca, Mn)S during cooling and solidification processes is quite small. Therefore, controlling mechanism of sulfide morphology is proposed to induce (Ca, Mn)S to nucleate and grow on oxides containing CaO formed in molten steel, promoting generation of a large number of duplex compound sulfides. In order to obtain the formation mechanism of optimal duplex compound sulfides, 3 commercial steels with different smelting processes were selected. Morphologies and component characteristics of typical compound sulfide were investigated with scanning electron microscope and energy spectrum analysis (SEM-EDS), size characteristics were manually measured, and evolution behaviors of inclusions during cooling and solidification were calculated by thermodynamic software FactSage. The results show that inside oxides of compound sulfides are mainly Al₂O₃ or magnesium aluminum spinel with low MgO ratio, wrapped sulfides are pure MnS with long strip shape after rolling in the steel without Ca treatment. After Ca treatment, there are two different compound sulfides.One is typical D or Ds type inclusions, with high CaO ratio inside oxides and high CaS ratio wrapped (Ca, Mn)S, basically no deformation. The other is spindle-shaped, with low CaO ratio inside oxides and low CaS ratio wrapped (Ca, Mn)S. Controlling the proper proportion of CaO in liquid oxides of Ca-treated steel is the key to obtain a large amount of spindle-shaped sulfides in steel, owing to high sulfide nucleation ability of core oxides and proper CaS proportion in peripheral (Ca, Mn)S. When the Ca/S ratio in steel is about 0.07, the optimal Ca content in peripheral sulfide is about 2%-5%.
		2022 Vol. 57 (5): 118-128 [Abstract] ( 198 ) [HTML 1KB] [PDF 4382KB] ( 511 )

	129	LIU Shuai, LÜ Zhi-qing, ZHAO Ji-qing, YANG Gang, XIN Rui-shan, YU Zhan-yang
		Thermodynamic calculation and experimental analysis on equilibrium precipitation phase in 2Cr12Ni4Mo3VNbN steel
		In order to analyze the influence of the main equilibrium precipitated phase and alloying element content in the 2Cr12Ni4Mo3VNbN steel on the precipitation behavior of the precipitated phase, the equilibrium phase diagram of 2Cr12Ni4Mo3VNbN steel was calculated by Thermo-Calc thermodynamic software when all elements in the composition range were median, and the equilibrium phase diagram of steel when the content of C, Cr, Mo, Nb, and N changed was calculated. To verify the reliability of thermodynamic calculations, XRD, SEM and TEM analysis methods were used to identify the types of precipitates in the heat-treated 2Cr12Ni4Mo3VNbN steel. The results show that the equilibrium precipitated phases in steel are MX phase, M₂₃C_6, M₆C, Z phase and Laves phase. Under thermodynamic equilibrium conditions, MX phase transforms into Z phase at 850 ℃, and M₆C transforms to Laves phase at 787 ℃. However, in the heat treatment process, due to the short holding time and the faster cooling rate, the above conversion process will not occur, so the main precipitated phases in the steel are MX phase, M₂₃C₆and M₆C. The types of equilibrium precipitates are basically consistent with the experimental results of microstructure observation and phase analysis. There are large-scale primary MX phases and nano-level MX phases in the MX phase. MX phase is mainly affected by Nb and N. The precipitation amount increases with the increase of N content, and the precipitation temperature increases with the increase of Nb content. The precipitation temperature of M₂₃C₆ phase increases with the increase of C content, and the precipitation amount increases with the increase of C content. The precipitation temperature of M₆C decreases with the increase of Cr content, and increases with the increase of Mo content. Within the composition range, the element control principle is to increase the C content to increase the precipitation strengthening effect of M₂₃C₆, reduce the Cr content to avoid entering the δ-Fe phase area during hot working, reduce the Mo content to reduce the precipitation tendency of the Laves phase, reduce the Nb content to Lower the precipitation temperature of the primary MX phase, the N content needs to take an intermediate amount to reduce the precipitation of the primary MX phase, and increase the precipitation of the dispersed fine MX phase in the low temperature stage.
		2022 Vol. 57 (5): 129-136 [Abstract] ( 185 ) [HTML 1KB] [PDF 2826KB] ( 450 )

Environmental Protection and Energy

	137	XU Xiang-shuai, ZHAO Zheng, ZHANG Yan-ling
		Sulfur distribution in slag-iron bath process of treating carbon-containing pellets of pickling sludge
		The sulfuric acid pickling process of stainless steel produces a large amount of pickling sludge, which contains high content of CaSO₄, and valuable metals such as Fe,Cr. Activated carbon will lose its activity after several adsorption, but it still maintains reducing performance. The pellet containing carbon is made by mixing acid sludge and activated carbon and roasting. When the slag and iron are mixed out of the blast furnace, the pellet is thrown into the slag-iron bath for reduction. The Fe, Cr in the acid sludge are reduced and enter the molten iron, and other substances enter the blast furnace slag to achieve the goal of detoxification, absorption and resource utilization of the pickling sludge. In view of the fact that the pickling sludge contains a large amount of S, the paper focuses on discussing the effect of the roasting temperature of pellets, the amount of C, and the amount of pellets added in the smelting process on the distribution behavior of S in each phase, mainly by thermodynamic theoretical calculation, laboratory test and other research methods. The results show that when the pellet C/S is 2 and the roasting temperature is 400 ℃, adding 1% pellets to the slag-iron bath, the w([S_f]) of molten iron at the end of the molten iron bath can be controlled at about 0.01%, and the slag fixation rate can reach 50%. When the pellet C/S is 0.5 and the roasting temperature is 400 ℃ or 800 ℃, adding 3% pellets into the slag-iron bath can also reduce the w([S_f]) to about 0.010%,and the recovery of Fe/Cr in sludge reaches 88.27%, but the sulfur fixation rate of the slag is lower. The study demonstrates that slag-iron bath process of treating pickling sludge can effectively control the w([S_f]) to lower level through reasonable adjustment of the test parameters, and achieve deep desulfurization effects. Meanwhile, Fe/Cr has a high recovery efficiency, before and after the reaction, the slag composition changes is extremely small, which will not affect the safety and subsequent utilization of the blast furnace slag, and has high environmental and economic benefits.
		2022 Vol. 57 (5): 137-145 [Abstract] ( 134 ) [HTML 1KB] [PDF 2749KB] ( 493 )

	146	ZHENG Wei-cheng, ZHAO Ling, ZHANG Hao, LIU Zi-min, PEI Yuan-dong, LONG Hong-ming
		Activation mechanisms of silica fume and blast furnace slag on steel slag hydrated gelling systems
		It is of great significance to strengthen the hydration process of steel slag and stimulate the cementitious activity of steel slag for improving the utilization rate of steel slag resources. In order to study the influence of the addition of blast furnace slag and silica fume, also the particle size of steel slag on improving the hydration process, the orthogonal experimental method was adopted, and the hydration products of 3 d and 28 d were characterized to reveal the activation mechanisms of silica fume and blast furnace slag on steel slag hydrated gelling systems. The orthogonal test results show that the effect of silica fume on the early 3 d hydration of steel slag is more significant, while the impact of blast furnace slag on the 28 d later hydration is more significant. when the addition of silica fume is 2%, the addition of blast furnace slag is 15%, the compression strength of steel slag at 3 d, 28 d can increase by 18.34%, 28.26%, respectively. The results of XRD, TG-DTA and SEM showed that the seeding effect, volcanic effect and the micro-assembly effect of silica fume and the relatively high activity aluminum oxyphae in the blast furnace slag can synergistically strengthen the hydration reaction in the high alkaline liquid phase system of steel slag, generating more C-S-H gel and AFt crystals. C-S-H gel is tightly wrapped in AFt crystals, and both interlaced growth form complex and compact network structures, thus improving the mechanical properties of steel slag materials and achieving the purpose of stimulating the cementitious activity of steel slag. Apply steel slag, slag, silica fume composite blend into the concrete, and the results show that when the cement is replaced by 20%, the concrete mechanical properties and anti-carbonation properties are maximized, of which 3 d, 28 d mechanical properties compared with the pure cement concrete increased by 31.53%, 25.88%, and the anti-carbonation properties compared to pure cement concrete increased by 18.75%, 24.11%, respectively.
		2022 Vol. 57 (5): 146-155 [Abstract] ( 218 ) [HTML 1KB] [PDF 3679KB] ( 560 )

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