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2020 Vol. 55 No. 5
Published: 2020-05-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Equipment Technology
Technical Reviews
1
ZHOU Ming-shun, WANG Yi-dong, ZHAO Dong-ming, HAN Hong-liang,LI Xian-chun, LU Li-ming
Development on sintering technologies with high proportion of magnetite concentrates
Due to the depletion of reserves of traditional high-grade iron ore,the ore resources have changed drastically from hematite to complicated and comprehensive ore types. However,the level of impurities and the loss on ignition in some kinds of iron ores are relatively higher,and more iron ore fines in the ores,which have significant impacts on the sinter quality and sintering performance,including Fe-grade,sinter strength,and solid fuel consumption. Magnetite concentrate is typically high in Fe grade and releases extra heat when oxidized to hematite. This will not only improve the sinter quality but also have a beneficial impact on the fuel consumption of the sintering process. But,most of the concentrates available are very fine,which will negatively impact the green bed permeability and consequently the productivity of the sintering process. The sintering characteristics of magnetite concentrates was discussed firstly,and then reviews and comments on the recent technological advances in sintering with high proportions of magnetite concentrate,including additive technology,pre-treatment technology,multi-sintering technology,gas fuel injection technology,double layers of pre-sintering technology,etc. In order to obtain the full advantage of magnetite,the permeability and chemical reactions in the sintering bed were reviewed,which can give theoretical guidance and technology support for the application of 100% and high proportion magnetite in the sintering process.
2020 Vol. 55 (5): 1-9 [
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Raw Material and Ironmaking
10
RONG Tao, TANG Hui-qing, FAN Kai, SUN Yan-jun
Applying high-carbon metallic briquette in blast furnace for coke saving
The blast furnace (BF) ironmaking is the dominant process for hot-metal production and the low-coke operation in BF ironmaking has been long focused. Applying high carbon metallic briquette (HCMB) in BF for coke saving has been studied.The HCMB was prepared using ultrafine iron oxide and non-coking coal fines, and the mass percent of the HCMB sample was 15.6%. Under the simulated BF conditions, the behavior of the HCMB, including mass change, crushing strength change, and microstructure evolution was examined. The gasification kinetics of the HCMB carbon was investigated using the custom-built experimental setup. The coke saving effect of applying HCMB in the BF was analyzed by simulations. Experimental results show that an iron crust was formed in the outer periphery of the briquette under the BF simulation conditions and the briquette has a good anti-pulverization capability; the main reaction of the briquette is carbon-solution loss reaction, and the briquette has a high CO
2
reactivity in the BF. Simulation results on a BF of 2 500 m
3
indicate that by mixing 5% HCMB in the ore burden, the BF can realize coke reduction of 11.9 kg for producing 1 t hot metal from the ore, and a productivity increase of 419 t/d; moreover, change of the BF operation condition is not required.
2020 Vol. 55 (5): 10-19 [
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407
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20
HE Zhan-wei, XUE Xiang-xin
Basic sintering characteristics of several typical vanadium titanium magnetite
In recent years, the prices of important metals such as vanadium, titanium, and chromium have skyrocketed. The efficient development and utilization of vanadium titanium magnetite resources can not only alleviate the shortage of iron ore resources, but also solve the contradiction between supply and demand of important metals. It is conducive to the sustainable development of China′s steel industry. The sintering basic characteristics of five typical vanadium titanium magnetite concentrates with large domestic usage were systematically studied by micro-sintering equipment. The phase composition of vanadium titanium magnetite concentrate was analyzed by XRD and SEM-EDS. The results show that the sintering basic characteristics of vanadium titanium magnetite are closely related to its chemical composition and phase composition. The main phase of low-titanium vanadium titanium magnetite is magnetite, and the comprehensive evaluation index of sintering basic characteristics is relatively better, of which CJ is the best. However, the main phase of high-titanium vanadium titanium magnetite is magnetite and ilmenite, their basic characteristics are very poor,which is mainly affected by titanium. On the whole, the vanadium titanium magnetite has a poor sintering basic characteristic and should be matched with iron concentrate with better basic characteristics as much as possible.
2020 Vol. 55 (5): 20-25 [
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420
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Steelmaking
26
LIANG Qiang, CAI Jun
Water modeling experimenton bottom lime injection base fluxes with oxygen into combined blown converter
In order to research the bath mixing characteristics of the combined blowing converter during the bottom lime injection base fluxes with oxygen, a water model of the combined blown converter with bottom powder injection was established to investigate the powder distribution and the melt bath mixing. Water and hollow glass microspheres were used to simulate liquid iron and lime powder, respectively. The powder distribution and the melt bath mixing were studied using the image processing method. The mixing time of powder injection and the mixing time without powder injection were researched using electrical conductivity detection technology in the melt bath under the same carrier gas flow. The results showed that the bottom lame injection could promote the melt bath mixing, and powder diffusion velocity increased with carrier gas flow increasing. The mixing time without bottom powder injection decreased withcarrier gas flow increasing. Under the same bottom blowing carrier gas flow, the mixing time of bottom powder injection in melt bath was shorter than that without powder injection in the combined blown converter, in the experiment range, blending time of bottom powder injection in melt bath appeared minimum at 2 m
3
/h of carrier gas flow.
2020 Vol. 55 (5): 26-30 [
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31
QIN Zheng-feng, XUE Zheng-liang, LI Jin-bo, LI Bo-si
Origin of large spherical or bar-shaped inclusions in calcium treated steel
Large inclusions have a very harmful effect on the processing properties, mechanical properties and corrosion resistance of steel. The properties of large spherical or bar-shaped inclusions, which were obtained by electrolytic extraction method in calcium treated steel, were investigated. The results of both the scanning electron microscopy (SEM) and elemental composition analysis indicated that the large spherical or bar-shaped inclusions were originated from the clustered aluminum de-oxidation product, such as Al
2
O
3
. A large number of small Al
2
O
3
particles had the tendency to form large-sized inclusion clusters, which further form a spherical or bar-shaped by the complex flow field in the ladle. During the calcium treatment process, the modified inclusions can form a low melting calcium aluminate, which can form dense spherical shaped inclusions during the solidification process of molten steel; the shape of the inclusions with insufficient modified was still kept the same morphology as Al
2
O
3
inclusion. The
w
([Ca])/
w
([Al]) ratio required for calcium treatment to modify Al
2
O
3
inclusions is primarily affected by the content of S. The calcium aluminate has a strong absorption and dissolution ability to S in molten steel. During the casting process, as the temperature of molten steel decreasing, the S element absorbed by the calcium aluminate was precipitated from the matrix in the form of CaS inclusions.
2020 Vol. 55 (5): 31-38 [
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39
WANG Yi, ZHANG Li-feng, REN Ying, REN Qiang
Mechanism of inclusion evolution during refining process of 37Mn5 steel production
The chemical compositions of non-metallic inclusions evolve during refining process and affect the performance of steel product.During the refining process of 37Mn5 steel production, the compositions of inclusions changed from Al
2
O
3
to Al
2
O
3
-CaO-SiO
2
-MgO-CaS, without calcium treatment. Samples were taken from 37Mn5 steel plant for inclusion analysis to study the mechanism of inclusion evolution.The results showed there was a significant difference between the compositions of larger inclusions and smaller ones. The changing tendencies during the refining process varied in inclusions with different size groups. The inclusions with diameters larger than 10 μm had similar compositions to the refining slag. Thus these inclusions were caused by slag entrapment or peeling off of slag building-up. 1.17% calcium was detected in Fe-Si alloy, which resulted in a similar effect to calcium treatment, as a big amount of small size CaS inclusions were formed in a short time.The analysis of compositions, amounts, and morphologies of inclusions, slag compositions, and thermodynamic calculation indicated that inclusions evoluted due to deoxidation, refractory corrosion, slag entrapment, reactions between calcium and liquid steel, reacted between inclusions and liquid steel, the mechanism of inclusion evolution during the refining process of 37Mn5 steel production was revealed.
2020 Vol. 55 (5): 39-44 [
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45
ZENG Ze-yun, LI Chang-rong, LI Zhi-ying, LIU Zhan-lin,LI Zheng-song, ZHAI Yong-qiang
Thermodynamic analysis of titanium precipitation in HRB500E seismic steel
The study of the existence of titanium compounds in liquid phase and solid phase during the solidification of molten steel has an important influence on the properties of solid phase structure, and the second phase precipitation played the role of grain refinement. In order to analyze the precipitation law of TiN, TiC and Ti(C,N) precipitate in HRB500E aseismic steel bar, the thermodynamics of TiN, TiC and Ti(C, N) precipitates were calculated. The results show that TiN and TiC cannot precipitate in the homogeneous state of molten steel, TiC
0.19
N
0.81
precipitates at the temperature of 1 843 K; TiN has thermodynamic conditions for precipitation during solidification because of the enrichment of Ti and N at the solidification front with a temperature of 1 745 K; TiN and TiC particles have thermodynamic properties for precipitation in solid austenite; while TiC precipitates at a lower temperature than TiN,TiC particles precipitation in ferrite.
2020 Vol. 55 (5): 45-51 [
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52
LIU Ke, HAN Yi-hua, YANG Fan, ZHU Li-guang
Effect of MgO on microstructure of CaO-Al
2
O
3
based quaternary system mold fluxes
In order to study the influence of MgO on the microstructure of CaO-Al
2
O
3
-B
2
O
3
-MgO quaternary slag system,the slag network structure model of CaO-Al
2
O
3
-B
2
O
3
-MgO-based quaternary slag system was constructed by Scigress molecular dynamics software. The results demonstrated that high-coordinated Al and tri-coordinate oxygen appear in the molten slag to compensate for [AlO
4
]
5-
tetrahedral negative charge excess;Boron as the network forming body has the strongest binding ability with O,and its coordination structure exists as Tri-coordinated trigonal and tetra-coordinated tetrahedrons;MgO acts as a network modifiers to compensate for charge and depolymerization networks. With the increasing of MgO content,the stability of the Al—O network structure enhanced,while the degree of polymerization of the melt and the complexity of the network structure decreased.
2020 Vol. 55 (5): 52-58 [
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59
WANG Xing-yu, HAN Yan-shen, LIU Qing, XIAO Dong,CHEN Jun, GUAN Min
Effect of F-EMS on inner quality of spring steel continuous casting billet
The 55SiCrA spring steel is prone to be affected by inner quality problems in continuous cast billets. Appropriate final electromagnetic stirring (F-EMS) can effectively improve the inner quality of the billets,however,the unreasonable stirring parameters fail to improve the inner quality of the continuous casting billets,or even deteriorate the inner quality. In order to improve the inner quality of the continuous casting billets and to obtain the optimal F-EMS scheme,the influence of F-EMS parameters was studied on the inner quality of 55SiCrA billet with a section size of 150 mm×150 mm. The solidification condition of the casting blank under the current process was analyzed by establishing a solidification and heat transfer model,and the position of F-EMS was determined to be 8.45-8.73 m away from the meniscus. On the basis of measuring the center magnetic induction intensity of the billets under F-EMS,the matching of current and frequency is studied,and the corresponding industrial tests are conducted. The results indicate that the comprehensive quality of the continuous casting billet is best when the F-EMS parameter is 300 A/8 Hz. For billets,the average center carbon segregation index reaches 1.007,the center pipe of the continuous casting blank is improved,and the central equiaxed crystal ratio is increased.
2020 Vol. 55 (5): 59-67 [
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Metal Forming
68
QIN Da-wei, LIU Hong-min, ZHANG Dong, WANG Jun-sheng
Prediction models of coating mass per unit area for hot-dip galvanized strip based on artificial neural network
In order to solve the problems of large mass per unit area deviation,long adjustment time,and waste of zinc raw materials for continuous hot-dip galvanizing of steel strip,an air knife pressure preset model and a coating mass per unit area prediction model were established using historical data of the production process. Based on the production practice of the hot-dip galvanizing of steel strip,the influence factors and the control strategy of the coating mass per unit area were analyzed. The static sample data was collected,and the multi-variable partial correlation analysis was carried out,which showed that the coating mass per unit area was related to the air knife pressure,the air knife distance and the steel strip speed. According to the sample data,taking the coating mass per unit area,the distance of air knife and the speed of strip steel as input variables,BP neural network was used to establish the preset model of air knife pressure,and the preset precision reached 3 000 Pa. The sample data of time series during the hot-dip galvanizing process was collected and a prediction model of coating mass per unit area was established using NARX dynamic neural network. The prediction accuracy reached 6 g/m
2
. The foundation for closed-loop control of the coating mass per unit area for hot-dip galvanized strip was provided.
2020 Vol. 55 (5): 68-72 [
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Materials
73
ZHAO Yun-peng, YU Chao, XIAO Hong, WU Zong-he, XU Peng-peng, XIE Hong-biao
Effect of pure iron interlayer on mechanical properties of hot rolled stainless steel clad plate
In order to reduce the formation of brittle compounds at the bonding interface of stainless steel and carbon steel during hot rolling, and improve the mechanical properties of the composite plates,the vacuum hot rolling composite experiment with different thickness of pure iron interlayer was carried out under the conditions of rolling temperature of 1 000,1 100,1 200 ℃ and reduction of about 70%. The effect of pure iron interlayer on the interfacial microstructure and tensile properties of composite plate was studied by optical microscopy,SEM observation and tensile test. The results show that the tensile properties of stainless steel/carbon steel composite plates are improved to varying degrees at the same temperature when different thickness of pure iron interlayer was added. And under less than 70% reduction,2 mm thick pure iron interlayer can completely prevent the carbon element in carbon steel from diffusing to stainless steel side,avoid the formation of carbochromium compounds,so as to improve the microstructure of the bonding interface and mechanical properties.
2020 Vol. 55 (5): 73-79 [
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80
LI Zhao-zhen, SONG Xin-li, LIU Jing, CHENG Zhao-yang, BI Yun-jie, JIA Juan
Effect of Cr,Mn and annealing temperature on properties of non-oriented silicon steel
In order to study the effect of Cr,Mn and annealing temperature on the properties of high-strength non-oriented silicon steel,the microstructure and properties of three groups of non-oriented silicon steel with different Cr,Mn content under different manufacturing processes were analyzed by means of OM,SEM,EBSD and universal tensile tester. The results show that the structure of experimental steel is not uniform after hot rolling,and the core is distributed in fibrous structure along the rolling direction,and there are a small amount of receystallization grains at the edge. Normalized treatment can significantly improve the structure uniformity of hot rolled plate,promote recrystallization and eliminate the fibrous structure at the center of hot rolled plate. Polygonal Ferrite grains were obtained by cold rolling and annealing at 930 and 960 ℃. The grain size of the three groups of experimental steel annealed at 960 ℃ was larger,but the favorable {100} texture volume percent decreased and the unfavorable {111} texture volume percent increased. The steel with composition of 0.2Mn-1Cr and annealing at 960℃ has the largest iron loss and less magnetic inductance. After annealing at 930 ℃,the magnetic properties and strength of the steel of 0.5Mn-1Cr are the best:
P
1.5/50 is 2.41 W/kg,
P
1
.0/ 400 is 17.36 W/kg,
B
5 000is 1.638 T,tensile strength is 685 MPa.
2020 Vol. 55 (5): 80-86 [
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87
SHAO Cheng-wei, WANG Jun-tao, ZHAO Xiao-li, HUI Wei-jun
Microstructure and mechanical properties of intercritically annealed Al-contain medium Mn steel
In order to investigate the effect of intercritical annealing temperature on the microstructure and mechanical properties of a newly designed cold-rolled aluminum-containing medium Mn steel (0.2C-0.6Si-5Mn-1.2Al)(mass percent,%),the microstructure was characterized by scanning electron microscopy (SEM) and X-ray diffraction(XRD). The mechanical properties were tested by uniaxial tensile test. The results show that an excellent combination of ultimate tensile strength (UTS) of 1 276 MPa,total elongation (TEL) of 51.8% and UTS×TEL of 66.1 GPa·% could be obtained after annealing at 670 ℃ for 10 min. The inverted austenite of the cold-rolled steel gradually coarsenes and transforms into martensite,and the mechanical stability gradually decreased with increasing intercritical annealing temperature. The mechanical stability of inverted austenite is mainly affected by the content of C in retained austenite and the grain size,while the content of Mn in the retained austenite has little effect on it.
2020 Vol. 55 (5): 87-93 [
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94
SUN Li-gen, LEI Ming, ZHANG Xin, LIU Yun-song, ZHU Li-guang
In-situ research on microstructure refining effect of Mg treatment for shipbuilding steel at high temperature
With Mg treatment process,the welded heat affected zone performance of shipbuilding steel is significantly improved. To further clarify the mechanism of action of Mg,the microstructure evolution of the traditional shipbuilding steel and Mg treated shipbuilding steel during the temperature rise and fall process was observed by high temperature laser confocal microscopy,and the phase transformation of the steel structure during continuous cooling with different holding time was also studied. By comparison,it is found that the austenite grain size was not coarsened due to the pinning action of the fine inclusion particles for Mg treatment during heating process,and a large amount of IAF(intragranular acicular ferrite) were induced by inclusions inside the austenite grains during the cooling process also. The both effects caused the steel structure to be further refined,and the inclusions,which induced the IAF,exhibit a law of increasing gradually with the prolongation of the holding time. At the same time,statistics on the number and distribution of inclusions also provide strong evidence for the above results.
2020 Vol. 55 (5): 94-102 [
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343
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103
CAO Yun-fei, YU Wei, LIU Min, JIANG Rui, WANG Chun
Austenite grain growth model of 38MnSiVS bearing microalloyed forging steel
Refinement of austenite grain is an important method to control the microstructure and mechanical properties of steel. In order to control the grain size of 38MnSiVS non-quenched and tempered steel during the waiting time of rolling, the recrystallized austenite grain growth law of 38MnSiVS non-quenched and tempered steel after deformation at different holding temperature and time by means of thermal deformation and quantitative metallography were studied. The results show that the recrystallization austenite grain growth process of 38MnSiVS non-quenched and tempered steel met the power exponential relationship. Sellars model,Anelli model,and Sellars-modified model are established accordingly by numerical calculation analytic method and nonlinear regression method on the basis of experimental data. Among them,the Sellars-modified model is proved to have the best accuracy of 0.73%,which could more accurately express the grain growth law of 38MnSiVS non-quenched and tempered steel. Due to the influence of deformation energy storage and other factors,the activation energy of recrystallized austenite grain growth after deformation is 161 737.65 J/mol,far lower than that of austenite grain growth during reheating.
2020 Vol. 55 (5): 103-108 [
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Environmental Protection and Energy
109
ZHANG Wei-li, WU Sheng-li, HU Zhong-jie
Analysis of affecting factors of activated coke denitrationefficiency for sintering flue gas
In order to clarify the denitration performance changes of activated coke during the recycling process in the sintering flue gas purification system and the main operating parameters affecting the denitration rate of sintering flue gas,to improve the purification efficiency of sintering flue gas by activated coke method,FTIR and simulation experiments were carried out to study the changes of activated coke property and its effect on denitration efficiency during recycling. The main process parameters affecting the activated coke denitration efficiency for sintering flue gas and its influence law were clarified through statistical analysis of production data. The results show the quantity of phenol and quinine on activated coke increase after recycling,hence the NO adsorption capacity decreases,which leads to the decrease of initial denitration efficiency of active coke. While the pre-adsorption of ammonia can greatly increase the initial denitration efficiency,it can be deduced that the denitration efficiency from top to bottom of cross-flow denitration tower experienced 100%,rapid decreasing,slow rising until equilibrium. Secondly,denitration efficiency is positively correlated with the NH
3
-NO
x
ratio,O
2
volume percent,NO
x
mass concentration,and desorption temperature,and negatively correlated with the H
2
O volume percent,SO
2
mass concentration,flue gas flow,and activated carbon bed temperature. Besides,NH
3
-NO
x
ratio,O
2
volume percent,and NO
x
mass concentration have great influence on the denitration efficiency,which should be focused on in the parameter optimization process.
2020 Vol. 55 (5): 109-115 [
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Equipment Technology
116
CHEN Zuo-bing, CHENG Yin, TAN Hong, XIE Qiang
Spray cooling performance of a spray drum cooler
The spray drum cooler is one of the key equipment in the rotary hearth furnace process. In order to improve the cooling performance of the cooler,a CFD numerical simulation technology was used to establish a coupling model of the heat transfer process based on the heat transfer characteristics of the external spray cooling system of the drum. The effects of layout parameters such as the number of nozzles,pitch and offset on heat transfer were studied. Effects of nozzle distribution parameters including nozzle number,nozzle distance and nozzle offset on the spray cooling were studied. Too many nozzles with too small distance or too few nozzles with too large distance are not conducive to the cooling performance. An appropriate number and distance have an important impact on the cooling performance of the equipment. Compared to rectangular array nozzles,the parallelogram array has better cooling performance. Finally,the correctness of the research results was verified by specific engineering applications.
2020 Vol. 55 (5): 116-123 [
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