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	2022 Vol. 57 No. 6
	Published: 2022-06-15



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

Technical Reviews

	1	LI Bao-kuan, HUANG Xue-chi, LIU Zhong-qiu, QI Feng-sheng
		Characteristics and evolution of advanced modern electroslag remelting technologies
		Electroslag remelting (ESR) is a key technology for the preparation of high-quality steel and alloys. It has obvious advantages in ingot quality and material formation rate. With the rapid development of China′s equipment manufacturing industry, the requirements for the quality and performance of the steels and alloys used are constantly improving. However, the traditional electroslag remelting technology has faced problems such as high electricity consumption and poor stability of product quality. The core of the development of modern electroslag metallurgy technology lies in the stable control of the shallow flat metal pool and the efficient removal of impurity elements. The goal is reaching a higher cleanliness, a higher solidification quality and a higher production efficiency. In order to let national metallurgists understand the latest development of current electroslag remelting technology, so as to facilitate its development and application in China. The advanced technologies and theories that have emerged in recent years at home and abroad are reviewed. The application characteristics and evolution direction of related technologies at home and abroad are analyzed. China is basically synchronized with the international advanced level in the electroslag furnace equipment manufacturing, gas-protected electroslag remelting technology, coaxial power supply technology and crystallizer conductive technology. Compared with foreign countries, perfect and reliable slag system configuration theory and thermodynamic and kinetic theory of the refining process have not been formed in China, which seriously limits the improvement of quality of electroslag products. Low frequency power technology, vacuum electroslag remelting technology and electroslag remelting technology with a rotating electrode have high prospects for industrial application, impact of which on the process and product quality needs to be further clarified. Swing control has become the major control technology of international advanced electroslag enterprises, but the shortcomings of China′s electroslag furnace manufacturing. The constant pool shape control technology with the help of online detection and simulation technology will be the development direction of control technology of electroslag metallurgy in China.
		2022 Vol. 57 (6): 1-11 [Abstract] ( 742 ) [HTML 1KB] [PDF 5580KB] ( 847 )

Raw Material and Ironmaking

	12	HU Meng-jie, CHEN Tie-jun, PAN Liao-ting, ZHOU Xian-lin, HUANG Xue-zhong, LIU Jia-wen
		Experiment on strengthening sintering performance of laterite nickel ore by separated granulating and separate fuel adding
		In the sintering production of laterite nickel ore, in order to realize the comprehensive utilization of resources, sintering dust, blast furnace gravity ash, fine particle return mine and other materials are often added in the batching process. However, these materials are easy to have adverse effects on the permeability and sintering performance of the layer due to poor granulating. In order to improve the permeability of the layer and sintering performance, the sintering dust, gravity ash of blast furnace and fine particle return mine were separated granulated. In addition, in order to prevent the pellets from underburning, the fuel was added separately to the separated granulating materials. The effects of separated granulating and separate fuel adding on the permeability of layer and sintering performance were studied by sinter pot experiment. The process mineralogy of sinter was analyzed by X-ray diffraction and metallographic microscope, and the related mechanism for strengthening sintering of laterite nickel ore was revealed. The results show that, compared with the reference, when 30% of anthracite is added into separated granulating, the average particle size of mixture increases from 4.18 mm to 5.99 mm, and the layer permeability index increases from 0.233 to 0.482. At the same time, the sintering performance is greatly improved, the sintering yield increases from 68.69% to 79.37%, the tumbler index increases from 51.73% to 60.82%, the vertical sintering speed increases from 24.44 mm/min to 33.48 mm/min, the productivity increases from 0.77 t/(m²·h) to 0.99 t/(m²·h), and the solid fuel consumption decreases from 147.10 kg/t to 130.29 kg/t. The process mineralogy shows that compared with the reference, the pores and cracks of the separated granulating sinter are greatly reduced and the microstructure is more dense. Meanwhile, the wetting degree between the main solid phase iron spinel and the liquid phase is improved, and the acicular and interleaved SFCA are increased, therefore the consolidation conditions of sinter are greatly improved.
		2022 Vol. 57 (6): 12-21 [Abstract] ( 181 ) [HTML 1KB] [PDF 5495KB] ( 389 )

	22	LI Tao, SU Bu-xin, WANG Guang-wei, LIANG Wang, ZHANG Cui-liu, REN Kun
		Optimization of pulverized coal injection into blast furnace
		Pulverized coal injection is one of the most effective measures to reduce coke ratio in blast furnace production. To obtain a higher coal/coke replacement ratio and reduce the cost of blast furnace production, it is necessary to select and match the coal injection types reasonably from a varieties range of coal. 12 types of coal provided by foreign steel plant were selected as experimental materials, and their basic property and process property which played a key role of pulverized coal injection in blast furnace were investigated systematically. Furthermore, comprehensive performance of different pulverized coal was studied based on the basic property result of test, and provided a guidance for optimal selection of pulverized coal injection into blast furnace. The results are shown that among the 12 kinds of coal powders, No.4 is high metamorphic anthracite, No.6, No.7 and No.12 are high metamorphic meager-lean coal, No.5, No.10 and No.11 are low metamorphic meager-lean coal, and No.1, No.2, No.3, No.8 and No.9 are low metamorphic bituminous coal. Compared with the pulverized coal injected into blast furnace in China, the 12 kinds of pulverized coal provided by foreign steel plant have lower ash and sulfur content, it is beneficial to reduce the amount of slag and sulfur load. Meanwhile, the pulverized coal has good jet performance, high fluidity and higher ash fusion temperature. Low metamorphic bituminous coal is explosive and cannot be used as blast furnace coal injection alone. The grindability and combustion performance of different coal powders vary greatly, which is the key to limit their application in blast furnace injection production. According to the calculation results of comprehensive performance evaluation indexes of different pulverized coal in blast furnace, the No.8, No.10, No.11 and No.12 pulverized coal were selected as pulverized coal into blast furnaces. Considering the different cost of pulverized coal, the No.12 pulverized coal was selected to inject into blast furnace can reduce the production cost most significantly.
		2022 Vol. 57 (6): 22-31 [Abstract] ( 246 ) [HTML 1KB] [PDF 3483KB] ( 366 )

	32	ZHU Rui-zong, ZHANG Fang, PENG Jun, WANG Yong-bin, CHANG Hong-tao
		Effect of Barun concentrate ratio on strength of finished pellets
		In order to give full play to the characteristics of Barun iron concentrate with high iron grade, concentrated particle size distribution and excellent pellet-forming performance, while suppress the weakness of high content of K₂O, Na₂O and F, how to improve the utilization rate of Barun ore on the basis of ensuring the strength of finished oxidized pellets by reasonably matching it with the ore in the region with low content of harmful elements was studied. In the research process, the influencing factors on strength of finished ball under different ratios of Barun iron concentrate were analyzed by FactSage7.3 thermodynamic software calculation, oxidation roasting, compressive strength detection, chemical composition detection, mineral phase analysis, SEM-EDS analysis and other experimental research methods. The results show that the iron concentrate in the area has a wider particle size range than the Barun iron concentrate, with the average particle size of 53.21 μm and 32.01 μm, respectively. The mineral powder particles smaller than 0.043 mm(<300 mesh) of iron concentrate in the area is accounting for 78.65%, while the mineral powder particles of Barun iron concentrate is accounting for 84.70%. The strength of finished ball with 40% ratio of Barun iron concentrate is the highest, which is 4 602.2 N /P. Thermodynamic calculation shows that with the increase of Barun iron concentrate ratio, the slag phase in the finished ball increases. In the process of oxidizing roasting and cooling, pyroxene and quartz are the main precipitates of finished ball slag phase for 40% Barun iron concentrate, while calcium iron olivine is the main precipitates of 100% Barun iron concentrate. In terms of mineral phase structure, with the increase of Barun iron concentrate ratio, the hematite intercrystal effect decreases, but the slag phase distribution is uniform at 40% ratio, which plays a good role of bonding phase. One of the reasons for low compressive strength of magnesium-bearing magnetite particles formed by MgO content of 1.05% in 100% Barun finished ball is its poor intercrystal.
		2022 Vol. 57 (6): 32-41 [Abstract] ( 191 ) [HTML 1KB] [PDF 7341KB] ( 464 )

Steelmaking

	42	WANG Kun-peng, WANG Ying, XU Jian-fei, CHEN Ting-jun, XIE Wei, JIANG Min
		Investigation on evolution of inclusions in bearing steel during secondary refining
		Composition, type and quantity of inclusions in bearing steel during LF refining and RH vacuum treatment were studied. The experimental results were analyzed and discussed in combination with thermodynamic calculation and interface parameters between inclusions and liquid steel. The inclusion analysis results showed that the deoxidization product Al₂O₃ disappeared after 25 min refining, and the inclusions in steel were mainly pure spinel, spinel containing small amount of CaO, CaO·2Al₂O₃ and CaO·Al₂O₃. Pure spinel, spinel containing small amount of CaO, CaO·2Al₂O₃ and CaO·Al₂O₃ were still the main inclusions in steel after 65 min refining to the end of LF refining. After RH vacuum treatment for 25 min, the total number of inclusions in steel was reduced by 75% compared with that after LF refining. The removal efficiency of pure spinel and spinel containing small amount of CaO inclusions was 99.5% and 93.2%, respectively, and that of CaO·2Al₂O₃ inclusion was 67%. The inclusions after RH treatment were mainly liquid calcium aluminate CaO·Al₂O₃ and 12CaO·7Al₂O₃. The size of spinel inclusions in the refining process was concentrated below 10 μm, and the inclusions above 20 μm were mainly calcium aluminates in the liquid phase, which had appeared in the early stage of LF refining. Solid inclusions pure spinel, spinel containing small amount of CaO and CaO·2Al₂O₃ whose contact angle with molten steel was greater than 90° were easy to remove in RH vacuum treatment, while liquid inclusions CaO·Al₂O₃ and 12CaO·7Al₂O₃ whose contact angle with molten steel was less than 90° were not easy to remove. Therefore, controlling the inclusions into solid inclusions after LF refining was beneficial to the high efficient removal of inclusions in RH vacuum treatment. The thermodynamic calculation results show that when the w(T[O])is 0.001 0% and w([Mg]) in steel exceeds 0.000 18%, the deoxidization product Al₂O₃ cannot be stable in thermodynamics. It is difficult to obtain solid Al₂O₃ inclusions under the condition of Al deoxidation and high basicity slag refining. To obtain fully solid spinel or high melting point calcium aluminate inclusions, w([Ca]) in steel should be controlled below 0.000 1%。When w([Ca]) in steel exceeds 0.000 2%, it will achieve the thermodynamic conditions for formation of liquid inclusions.
		2022 Vol. 57 (6): 42-49 [Abstract] ( 396 ) [HTML 1KB] [PDF 2832KB] ( 524 )

	50	LÜ Nai-bing, GAO Hang, LIU Ke, LIU Bin, XU Shi-xin, ZHOU Jie
		Effects of cooling intensity on MnS growth during solidification in ultra-high sulfur medium carbon steel billet
		Medium-carbon ultra-high sulfur free-cutting steel SAE144 is a structural steel with both mechanical properties and machinability,thus used as automotive engine sealing valves, etc. The production process is mostly converter/electric furnace→LF refining→continuous casting→wire rod hot rolling→cold drawing and machining,the market popularity has steadily increased in recent years. If the MnS inclusions in the steel are not properly controlled, problems such as failure in flaw detection, poor machinability, severe band structure, significant dissimilarity in mechanical properties, and even drawing fractures are likely to occur. MnS inclusions are mostly formed in the late stage of billet solidification and are deformed synchronously with the steel matrix during rolling. Controlling the original size of MnS in the billet has become the most critical step to control the morphology and size of MnS inclusions in hot-rolled products.In order to control MnS inclusions in hot-rolled ultra-high sulfur medium-carbon steel wire rod, the segregation of S element and generation, growth and ripening of MnS was analyzed by the billet solidification numerical simulation calculation, second phase precipitation theory and Ostwald ripening theory in 160 mm² billet. The calculation results show that MnS is generated at the end of the solidification in cast billet when solid phase fraction f_s=0.446 with the segregation ratio of S reaches 2.19. The growth process of MnS during solidification determines the diameter of MnS particles in the billet. The theoretical calculation shows that when the secondary cooling water volume is fixed to 0.6 L/kg, the MnS in the 160 mm² billet center grows up to 30.6, 32.2 and 34.6 μm at the casting speed of 1.6, 2.1 and 2.6 m/min respectively, which is consistent with the actual test results. The key to controll the size of MnS in wire rod is to increase the cooling intensity of the secondary cooling zone and reduce the casting speed of the billet. Based on the calculation method in this paper, control range of continuous casting process parameters matching the MnS diameter in 160 mm² billet is presented.
		2022 Vol. 57 (6): 50-56 [Abstract] ( 230 ) [HTML 1KB] [PDF 2544KB] ( 390 )

	57	MA Yu, TANG Hai-yan, LIU Yan-bin, LIU Jin-wen, JIANG Ye, ZHANG Jia-quan
		Modification of non-metallic inclusions in 55SiCr high stress spring steel by rare earth Ce
		55SiCr high stress spring steel is the main raw material used in the manufactures of vehicle valve, suspension and braking springs. The fatigue failure caused by large-sized compounded inclusions and the anisotropy and the sensitivity of hydrogen-induced crack caused by strip MnS in the steel are the important aspects to reduce the service life and performance of the springs. The modification process of inclusions in this steel by rare earth Ce and its mechanism, along with the influence of Ce content on inclusions were studied through high-temperature tube furnace smelting experiments combined with SEM-EDS detections and thermodynamic calculations. The research results show that after adding Ce, a large number of small-sized rare earth inclusions are generated in the steel first. As the reaction progresses, the number of inclusions gradually decreases and most of them are removed. A proper amount of rare earth can purify the molten steel. Moreover, the Ce content has a great influence on the characteristics of inclusions. When it is added 0.02%, the inclusions in steel are mainly of modified MnS, Ce-O-S and Ce-S inclusions with sizes 1-3 μm, spherical or ellipsoid in geometry. When the Ce addition is increased to 0.26%, the MnS inclusions disappear, generating a large number of angular and irregular Ce-O and Ce-O-S inclusions, which will adversely affect the fatigue properties of the steel. It is pointed out that MnS is modified by Ce through three ways, outside inwards, side inwards and inside outwards. To make the inclusions harmless in steel, an appropriate addition amount of rare earth is suggested to be 0.01%-0.02%, at which the mass percent of Ce in steel will reach to 0.009%-0.014%.
		2022 Vol. 57 (6): 57-71 [Abstract] ( 293 ) [HTML 1KB] [PDF 9741KB] ( 411 )

	72	WANG Pan-feng, FU Jian-xun, SHEN Ping
		Effect of magnesium treatment on inclusions in 1215 free-cutting steel
		Sulfide inclusions in 1215 free-cutting steel not only affect the machinability of steel, but also have a big influence on the anisotropy and the quality of steel. The control of sulfide inclusions is the key to improvement of steel quality. In the current study, Mg treatment was employed to control the morphology, size and distribution of inclusions to explore the effect of Mg on the inclusion modification. Through the high-temperature smelting experiment, a series of steel ingots with different Mg contents were prepared. Using the optical microscope, scanning electron microscope and non-aqueous solution electrolytic etching method, the distribution of inclusions and the two-dimensional as well as the three-dimensional morphology of inclusions in the steel were analyzed. Besides, thermodynamic calculation was conducted to figure out the modification mechanism of inclusions. The results show that, Mg has a strong deoxidation ability, which has a significant influence on the morphology and distribution of sulfide inclusions. When the Mg mass fraction increases from 0 to 0.000 6% and 0.001 7%, the morphology of inclusion changes from spherical, ellipsoidal (type I sulfide) to cluster, chain-like, coralloid (type II sulfide), and then to polyhedron, irregular block (type III sulfide). When the Mg mass fraction further increases to 0.002 7%, the effect of Mg is no more significant. MnS can not be generated in the molten steel. MnS mainly precipitates in the solid-liquid two-phase region during the solidification process, the corresponding precipitation temperature and solidification fraction of steel is 1 502.0 ℃ and 0.409, respectively. During the solidification process, part of MnS takes oxide inclusions as heterogeneous nucleation points, and forms complex inclusion with internal oxide and external sulfide. Once the Mg is added, Al₂O₃ inclusions are modified to dispersive distributed tiny MgO·Al₂O₃ inclusions, which has little possibility of aggregation and growing, providing more heterogeneous nucleation points for the precipitation of MnS. Therefore, the number density of inclusions is increased, while the average equivalent diameter is decreased.
		2022 Vol. 57 (6): 72-81 [Abstract] ( 186 ) [HTML 1KB] [PDF 2641KB] ( 429 )

Metal Forming

	82	WANG Xiao-jian, QIAN Sheng, CUI Meng-yu, BAI Zhen-hua
		Prediction and influencing factors of scraper force for sink roll system of hot dip galvanizing unit
		The sink roll in hot galvanizing units blown not clean on the surface of zinc slag leads to the strip surface defects, which seriously affect strip product quality grades. The characteristics of equipment and process of hot galvanizing unit were combined in this paper. Firstly, the force of sink rollers scraper mechanism was analyzed and the model of scraper force was established on the basis of steady state condition. Considering the influence of gap fluctuation between axle sleeve and bearing bush, the residual zinc residue deposited on the roll surface and the blade wear on the blade force in the actual working conditions of sink roll system, the scraper force model was modified to calculate the scraper force under unsteady conditions. Then the influence mechanism of scraper angle, journal eccentricity, blade wear and residual zinc residue on scraper force was analyzed. The calculation process of scraper force was developed according to the scraper force modification model, and the model was applied to actual production. Three typical specifications of strip steel were selected to predict the scraper force. The relative error between the predicted value and the measured value was less than 15%, and met the precision requirement of the unit. Finally, the influence of strip production parameters (strip tension, strip speed, surface galvanization) on the predicted value of scraper force was analyzed by taking strip A as an example. The results show that the scraper force increases with the increase of scraper angle in a small range (9°-12°), and the scraper force increases nonlinearly with the journal eccentricity increasing. The increase of blade wear will reduce the slag removal ability of scraper. The increase of residual zinc residue on the roller surface leads to the increase of scraper force, which is easy to cause the phenomenon of roller system sticking or slipping. The scraper force increases linearly with strip tension and decreases linearly with strip speed, but the influence of surface galvanization on scraper force is relatively small.
		2022 Vol. 57 (6): 82-90 [Abstract] ( 201 ) [HTML 1KB] [PDF 4266KB] ( 456 )

	91	ZHANG Wei-feng, SHI Ru-xing, ZHANG Yan-ling, WANG Guan-bo, CHENG Guo-guang, WANG Peng-fei
		Formation mechanism and improvement of detected defects in large forged Cr5 back-up roll
		Based on ultrasonic flaw detection on the large forged Cr5 back-up roll during manufacturing process, the flaw detection was analyzed by anatomical sampling, IF→LF→VD→VC smelting process of forged roll was traced and sampled, defects type on the forged roll and source of the whole smelting process was determined by scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). Combined with FactSgae 8.1 software, the formation mechanism and control of flaws leading to the ultrasonic flaw detection were calculated theoretically. The research results show that the defects leading to the incompatibility of flaw detection are linearly aggregated SiO₂-MnO-Al₂O₃ large-size inclusions, the size of single particle can reach 200 μm, the compositions of inclusion of flaws are consistent with the inclusions before pouring of vacuum casting(VC). A large amount of SiO₂-MnO-Al₂O₃ inclusions are found before the tapping of IF and still a few remained at the end of LF process, while large SiO₂-MnO-Al₂O₃ inclusions are entrapped to the roll melt during VD process under large stirring conditions. SiO₂-MnO-Al₂O₃ inclusions with a low contact angle can be well wetted by the liquid steel, it is difficult to float and remove from the liquid steel during the LF refining process. The inclusions are aggregated and remained during the solidification process to form the area of large inclusions and lead to ultrasonic flaw detection after forging eventually. Thermodynamic calculations show that SiO₂-MnO-Al₂O₃ liquid inclusions will be stable with the steel composition containing mass fraction of Al below 0.003% and O above 0.015%, and SiO₂-MnO-Al₂O₃ liquid inclusions are stable with a higher O content with increasing of Al content in liquid steel.SiO₂-MnO-Al₂O₃ phase stable field will disappear with Al increasing to 0.023% in the liquid steel. Before the tapping of IF and in the subsequent processes, controlling the Al mass fraction in the liquid steel above 0.023% can effectively modify the SiO₂-MnO-Al₂O₃ liquid inclusions into Al₂O₃ or Al₂O₃-rich inclusions with a good removability. Practical results show that the unqualified rate of ultrasonic flaw detection of Cr5 back-up roll forgings is reduced.
		2022 Vol. 57 (6): 91-99 [Abstract] ( 189 ) [HTML 1KB] [PDF 6095KB] ( 336 )

	100	JIN Hao-yue, SUN Jie, WEI Zhen, WANG Long-jun, HOU Fan, ZHANG Dian-hua
		Flatness control analysis of tension levelling process based on finite element method
		Flatness is an important index to judge the quality of strip steel. The common flatness defects are edge wave,middle wave,quarter wave and so on,which is essentially the uneven distribution of residual stress in the bandwidth. Wave defects can be effectively eliminated by the joint action of tension roller, bending roller and straightening roller. In the straightening process,plastic elongation occurs on strip under the effect of tension which is below yield strength. The flatness and quality of strip can be significantly improved. However,in the design and application of the tension leveler,the adjustment of tension leveler parameters is mostly based on experience and lacks theoretical guidance. To quantitatively analyze the improvement effect of tension leveler with different process parameters on the straightening of wave defects and increase the straightening effect of tension leveler in actual production,the tension levelling process of strip steel in a 1 450 mm cold pickling-rolling line was analyzed by the finite element software ANSYS/LS-DYNA which based on the three-dimensional elastic-plastic finite element method. The influence of tension and roll-intermesh on the flatness of straightened strip with initial flatness defect was analyzed. The influences of intermesh and tension on the flatness of strip with initial edge wave or middle wave shape defects are consistent. The results shown that wave defects of strip steel can be significantly improved by tension levelling. The intermesh of straightening roll is the main influencing factor,with the increase of intermesh the type of strip defect changes from edge wave to straight,and with the further increase of intermesh for straightening roller,the edge wave defect appeared again. With the increase of inlet tension,the type of strip defect changes from edge wave to medium wave after tension levelling.
		2022 Vol. 57 (6): 100-109 [Abstract] ( 210 ) [HTML 1KB] [PDF 7643KB] ( 337 )

Materials

	110	LIU Ji-meng, HUANG Shuo, ZHANG Xiao-min, DUAN Ran, LIU Kang-kang, QIN He-yong
		Microstructure analysis of GH2132 alloy band-typed mixed grain structure and its effect on mechanical properties
		Band-typed mixed grain structure defect was an important reason affecting the stability of microstructure and properties of GH2132 alloy, so the band-typed mixed grain structure with cold drawn bars were experimentally studied in this article. By means of metallography, EPMA, EBSD and TEM, combined with thermodynamic equilibrium phase diagram and hardness test, the main causes of band-typed mixed grain structure were revealed, as well as the analysis of its internal microstructure and the effect on microhardness. The results show that the grain size of fine grain zone in band-typed mixed grain structure is generally less than 10 μm, while the maximum grain size in coarse grain zone is over 60 μm. It is analyzed that element segregation and cold drawing deformation are the causes for the difference of grain size, and the forming of band-typed mixed grain structure. Ti, Mo, C and B elements in the as-cast structure of the alloy show positive segregation, among which the segregation of C and Ti element is greater, leading to the precipitation of MC and M₃B₂ phases between dendrites, which will finally appear between the grain boundaries in austenite. The solute enrichment between grain boundaries not only plays a pinning role to prevent the grain growth during recrystallization, but also reduces the migration rate of grain boundary through solute drag, which hinders the grain boundary deformation. Finally, the solute enrichment area forms a fine grain zone, with the depleted region forming a coarse grain region. Both display band-typed mixed grain structure along the cold drawing direction. In addition, due to the different crystal orientation, the actual strains of grain deformation under the same drawing force are not consistent during cold drawing deforming, which will also aggravate the mixed grain phenomenon. The microscopic observation shows that after cold deformation, the deformation of fine grain region is more uniform compared with the coarse grain region, and the average dislocation density in the microstructure is higher. Annealing twins and deformation twins are observed in the mixed grain region, while the twin density in the fine crystal region is higher. To sum up, the different numbers of grain boundaries, with the change of dislocation density and the gradient structure of twin distribution finally lead to the microhardness gradient in the mixed grain region, where the hardness of fine grain region is significantly higher.
		2022 Vol. 57 (6): 110-119 [Abstract] ( 198 ) [HTML 1KB] [PDF 8056KB] ( 341 )

	120	SI Zhi-wang, FU Han-guang
		Research progress of quenching and partitioning process for alloy steel
		With the continuous development of metallurgy, machinery and other fields in China, the requirements for the properties of iron and steel materials are becoming more and more strict. Automotive steel is required not only to lose weight but also to have high enough impact resistance to ensure safety. Wear-resistant materials should have not only strong hardness but also good toughness. The Quenching and Partitioning (Q&P) process of alloy steel was proposed by Professor Speer J G of the United States in 2003 inspired by Trip steel. The ultimate goal is to obtain a certain amount of soft phase retained austenite on the hard phase matrix, so as to improve the plasticity and toughness of the steel. Martensite and bainite ensure strength and retained austenite can improve toughness, and the combination of the two phases has good comprehensive mechanical properties. Different from the traditional process of quenching tempering (QT) inhibiting carbide precipitation, the carbon in the steel is not decomposed into carbide, but is rediffused to austenite in the process of heat preservation, which improves the stability of austenite. Q&P steel has the characteristics of low cost, good performance and relatively simple process, when initially applied to automobile high strength steel, it can greatly reduce the weight of automobile, improve anti-collision ability and reduce the degree of deformation. In succession, some researchers have applied Q&P process to wear-resistant materials, and found that the toughness can be greatly improved with little or no loss of wear resistance. In order to further improve the properties, many researchers at home and abroad have done a lot of research. In the optimization of heat treatment process, it is found that the parameters such as austenitizing temperature, quenching process and partitioning process have great influence on the microstructure and properties of Q&P steel. In terms of alloying element control, not only conventional alloy elements such as C, Mn and Si have important influence on the properties of Q&P steel, micro alloying elements such as Nb and Mo also have great influence on the microstructure and properties of Q&P steel. The proposal and development of Q&P process were described mainly, the research status at home and abroad, and the application of Q&P process were discribed mainly. Finally, the future development of Q&P process is prospected and summarized.
		2022 Vol. 57 (6): 120-131 [Abstract] ( 251 ) [HTML 1KB] [PDF 4825KB] ( 359 )

	132	CAO Fang, YANG Mao-sheng, YANG Shu-feng, LI Jing-she, LUO Zhi-qiang, LIU Wei
		Carbide distribution and high-temperature fracture mechanism of high nitrogen stainless bearing steel
		The high temperature fracture behavior of high nitrogen stainless bearing steel was studied by high temperature tensile test. The distribution characteristics of carbide in 170 ℃ and 470 ℃ tempered steel were investigated. The tensile fracture, microstructure evolution and carbide distribution law were analyzed. The results show that with the tempering temperature increasing from 170 ℃ to 470 ℃, the carbide larger than 0.8 μm in high nitrogen steel increases significantly, M₂₃C₆ strengthening increment increases by 2.59 MPa, and solution strengthening increment decreases by 118.82 MPa. The tensile strength of 470 ℃ tempering steel decreases at room temperature, and the tensile fracture behavior of the steel at room temperature is quasi-cleavage and a small amount of tear dimms. When the tensile temperature is increased to 300 ℃, the fracture surface of sample is equiaxed dimple, and the size of fracture source carbide of the 170 ℃ and 470 ℃ tempering samples is 2.8-3.6 μm and 5.5-6.7 μm, respectively. The tensile fracture at 450 ℃ is characterized by plastic-pore dimples, and the size of fracture source carbide at 170 ℃ and 470 ℃ is 2.7-3.4 μm and 5.8-6.4 μm, respectively. When the tensile temperature increases from 300 ℃ to 450 ℃, the effect of solution strengthening and dislocation strengthening is weakened, the interatomic bonding energy of metal decreases, the discontinuous stress distribution between carbide and matrix increases the deformation incompatibility, and the carbides bear higher stress then fracture occurs. Under the action of pure heat, the percentage of carbides of 0.5-0.8 μm increased. Under the action of thermodynamic coupling, dislocation proliferation caused by stress in steel provides channels for carbon diffusion, and 0.2-0.8 μm carbides are nucleated at grain boundaries and dislocation lines. The crack propagates rapidly along the maximum shear direction at angle of 45° with the tensile direction and then fractures. Finally, serrated fracture is formed. The increase of small carbides hinders dislocation slip and results in reduced plasticity. The large size carbides in steel distribute unevenly among the carbides to form large deformation plastic holes and increase the plasticity of steel.
		2022 Vol. 57 (6): 132-142 [Abstract] ( 170 ) [HTML 1KB] [PDF 6220KB] ( 474 )

	143	CAI Feng, LIU Man, XU Guang
		New processing routes of fabricating high-strength bainitic steels with high hardness and better corrosion resistance
		The wear resistance and corrosion resistance of bainitic steels are highly required in railway transportation and construction machinery,and boronization and chromizing are common effective methods to improve surface hardness and corrosion resistance. In the existing research work,the austempering for obtaining bainite matrix and surface modification technologies for strengthening surface are carried out separately. The processing route is complicated and increases the production cost. New processing routes for fabricating medium-carbon high-strength bainite steels with high surface hardness and high corrosion resistance were proposed,which integrated the surface modification technologies and austempering. The new processes routes can not only simplify the processing treatment,but also reduce the production cost and environmental pollution. The integrated process of boriding/chromizing and austempering (boro-austempering/chro-austempering) were utilized to fabricate medium-carbon high-strength bainitic steel with high surface hardness and corrosion resistance. The effects of boro-austempering and chro-austempering processes on the microstructure and properties of a bainitic steel were compared and analyzed by means of microstructural observation,hardness test and corrosion experiment. The results show that,compared with only austempering process,extremely hard chromizing layer and boronization layer with Vickers hardness of over 1 500HV(about 3.3 times that of bainite matrix) were synthesized on the bainitic steel surface,and the corrosion performance in 0.5% NaCl solution was obviously improved by chro-austempering and boro-austempering treatments. After being exposed to 0.5% NaCl solution for 3 h,the boro-austempered steel yielded better corrosion resistance. A new type of high strength bainitic steel with bainite as substrate and produced layers on the surface can be fabricated by two integrated processes. Under the same treating time,compared with the chro-austempering process,the boro-austempered steel showed a faster growth rate of the boronization layer and the higher adhesion strength between the boronization layer and the bainite steel matrix.
		2022 Vol. 57 (6): 143-149 [Abstract] ( 255 ) [HTML 1KB] [PDF 5082KB] ( 358 )

	150	WANG Xian-hui, LIU Zhao-yue, LI Rui-feng, GAO Qian, TENG Ren-hao
		Formation process of forsterite film in grain-oriented silicon steel manufactured by acquired inhibitor method
		The forsterite film of oriented silicon steel is an important part of product structure. The control of forsterite film is not only a process difficulty, but also a bottleneck of improvement of product performance. However,there are few previous studies on the formation of forsterite film, and there is a lack of theoretical support for the development and quality improvement of thin standardized high-performance products of high magnetic induction oriented silicon steel. Therefore, the formation process of forsterite film in grain-oriented silicon steel manufactured by the acquired inhibitor method was simulated by a high temperature annealing interruption experiment, and the microstructure and composition evolution of forsterite film during annealing were analyzed. The reaction formation process of forsterite film during high temperature annealing was clarified. The Mg₂SiO₄ particles nucleate on the surface of the steel at about 900 ℃ and grow up as the increase of annealing temperature. Up to 1 050 ℃, the Mg₂SiO₄ particles begin to become compact, and the densification process finishes at about 1 100 ℃. The key temperature for the formation of forsterite film is 900-1 100 ℃. In addition, the Al₂O₃·MgO spinel is formed under the forsterite film that can make a "pinning effect" on the forsterites film. During the formation of forsterite film, the Mg²⁺ of MgO diffuses from the surface to the oxide film and reacts with SiO₂. At the same time, SiO₂ in the oxide film matures. The content of Al released by AlN decomposition in the substrate above 1 000 ℃ reacts with Mg₂SiO₄ to form spinel. The excellent forsterite film structure is formed by the original decarburization annealing oxide film surface layer 1 μm to form dense Mg₂SiO₄ and the rest 2-3 μm thickness into a certain amount of ellipsoidal Al₂O₃· MgO spinel for "pinning" bonding layer. Its main control directions are, improving the activity of oxide film, selecting high activity MgO, adding low melting point reaction additives, etc.
		2022 Vol. 57 (6): 150-158 [Abstract] ( 361 ) [HTML 1KB] [PDF 9142KB] ( 471 )

Environmental Protection and Energy

	159	QIAO Li-zhu, ZHANG Wei-li, PENG Han-zhong, WU Sheng-li
		Influence of desorption parameters on regeneration process and regeneration effect of activated coke
		The thermal desorption parameters of activated coke are crucial to the desulfurization and denitrification performance and mechanical strength of regenerated activated coke. In order to clarify the influence of desorption parameters on the regeneration process and regeneration effect of activated coke, the effects of desorption temperature and desorption time on the residual ratio of desulfurization product in activated coke, the amount of CO₂ and CO generated, and the desulfurization and denitrification performance of regenerated activated coke were investigated through thermal desorption experiments to determine the appropriate thermal desorption parameters of activated coke. The results show that the desulfurization products are rapidly decomposed at around 317 ℃ in the process of activated coke thermal desorption, and then the decomposition rate drops rapidly. After entering the constant temperature desorption stage, the decomposition rate of desulfurization products first decreases rapidly and then enters a slow desorption state, and the residual sulfur ratio decreases with the increase of constant temperature desorption temperature. The residual sulfur ratio decreases with the increase of constant temperature desorption temperature, and desulfurization products can be completely resolved at 530 ℃ for 3 h. When the desorption temperature is higher than 430 ℃, the decomposition amount of oxygen-containing functional groups, such as phenolic, quinone, lactone, on the surface of activated coke increases significantly, and continues to increase with the increase of constant desorption temperature. And the amount of CO₂ and CO generation will also increase significantly, which will further develop the pore structure of the activated coke, which is not conducive to the maintenance of mechanical strength of the activated coke. When the desorption temperature is lower than 530 ℃, the residual sulfur ratio continues to decrease with the increase of desorption temperature, so that the desulfurization and denitrification performance of the regenerated activated coke continues to be improved. After the desorption temperature is higher than 530 ℃, the decomposition amount of oxygen-containing functional groups continues to increase with the increase of desorption temperature, which will help to improve the SO₂ oxidation reaction rate on the surface of activated coke, and then the desulfurization performance of regenerated activated coke will continue to increase. The decomposition of acidic oxygen-containing functional groups such as phenolic and lactone groups reduces the adsorption performance of regenerated activated coke for NH₃, thereby reducing its denitration performance. When considering various factors such as desulfurization and denitrification performance, mechanical strength and production efficiency of regenerated activated coke, constant temperature analysis at 430 ℃ for 3 h is a relatively optimal desorption parameter. Under these conditions, the residual sulfur ratio is only 1.8%, the oxygen-containing functional groups have not been decomposed in large quantities, and the desulfurization and denitrification performance of regenerated activated coke is relatively good.
		2022 Vol. 57 (6): 159-166 [Abstract] ( 224 ) [HTML 1KB] [PDF 3303KB] ( 516 )

	167	HE Sai, LIN Lu, LIU Ya-qin, LÜ Yan, HU Yan-bin, LIANG Qiang
		Recovery of valuable elements from molten modified phosphorous steel slag by carbothermic reduction
		For the recovery of valuable elements(Fe,P,Mn) in phosphorus-containing converter slag and the utilization of disposed slag,the thermodynamic conditions and influence laws of carbothermal reduction and recovery of valuable elements from the phosphorous-containing steel slag after melting and reforming were systematically analyzed through the theoretical calculation,experiments in resistance furnace,induction furnace test and other research methods. The research results showed that,the reduction temperature was 1 723 K,the basicity was 1.0-2.0,and the low basicity was beneficial to the reduction of Fe₂O₃ and P₂O₅ and the recovery of Fe and P resources in the slag. When the basicity of slag was 1.0,the reduction rates of Fe₂O₃,P₂O₅ and MnO could reach 99.50%,84.47% and 3.26% respectively,and the recovery rates of Fe and P in slag were 99.50% and 68.69% respectively. When the basicity was 1.5,the reduction rates of Fe₂O₃ and P₂O₅ were 90.45% and 63.73% respectively,which were lower than that of when the basicity was 1.0. When the basicity was 2.0,the reduction rate of Fe₂O₃ in slag was 71.43%,slag and iron was not separated completely. At the condition of that basicity was 1.0,the temperature was 1 723 K,the recovery rate of Fe was over 99% and that of P in the slag was 47.18%,in induction furnace experiments on carbonthermal reduction of molten modified industrial slag. Through thermodynamic analysis,it was found that FeO and P₂O₅ were easier to be reduced by carbon than MnO. At the same time, FeO and P₂O₅ were reduced firstly,and MnO began to be reduced after 20 min in slag,the MnO content in slag decreased slightly during the whole reduction process. at the end of the reduction process. The content of FeO,P₂O₅ and MnO after carbonthermal reduction in slag were 0.07%,0.93% and 2.83% respectively. Using FactSage to compare the phase composition of modified slag before and after reduction,it could be seen that the iron-containing phase(Ca₃Fe₂Si₃O₁₂) in steel slag was effectively controlled,calcium phosphate content decreased obviously,and olivine content increased greatly,which improved the application range of steel slag. A reference for recycling and resource utilization of valuable elements in steel slag containing phosphorus is provided.
		2022 Vol. 57 (6): 167-174 [Abstract] ( 191 ) [HTML 1KB] [PDF 4638KB] ( 356 )

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