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2021 Vol. 56 No. 10
Published: 2021-10-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Expert Forum
Expert Forum
1
KANG Yong-lin
China steel rolling technology progress in the 13th five-year plan and prospection
Under the promotion of the 13th five-year plan,the steel rolling technology of China has made rapid progress and remarkable achievements,presenting a large number of high-level achievements in science and technology. Modern technologies,such as big data,Internet,digitization and intellectualization,provide advanced and efficient means for research and development,production,scientific and technological innovation of high quality and performance steel. The steel output has increased from 1.048 billion tons in 2016 to 13.25 billion tons in 2020,with the self-sufficiency rate of high performance steel exceeding 98.5%,which provides the key basic material support for the national economic development and construction. The development and progress of China's steel rolling technology and the representative scientific and technological achievements during the 13th five-year plan period were briefly introduced and analyzed,focusing on the overall production situation of China's steel rolling products and the representative scientific and technological achievements of steel rolling technology. The key technologies and application of representative scientific and technological achievements are briefly introduced from the aspects of rolling process basis and microstructure controlling,greening rolling,digital and intelligent rolling,development of high strength and performance hot rolling products and advanced hot rolling technology,high performance,high strength,high precision cold rolling products and advanced cold rolling technology. Finally,the future development of steel rolling technology is prospected.
2021 Vol. 56 (10): 1-15 [
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Technical Reviews
16
ZHAN Dong-ping, YANG Yong-kun, JIANG Zhou-hua, LEI Hong
A review of research on inclusions evolution in steel during heating process
Inclusions control is an important topic in the research field of clean steel, which is vital to the quality of steel and product performance. In recent years, the research on inclusion expands from the traditional control of refining and continuous casting processes to the evolution study of re-heating, hot rolling and other hot working processes. In order to fully understand the evolution of inclusions during heating process and obtain the control strategy of inclusions, the evolution researches of MnS, TiN, and oxide in steel during the heating process at home and abroad was reviewed, the changes of morphology, composition, and size of inclusions, as well as the inclusions evolution mechanisms during the heating process was summarized, the application of inclusions evolution in oxide metallurgy technology was prospected, in order to provide a reference for the inclusions control research in the hot working process and the reasonable adjustment of the hot working technology.
2021 Vol. 56 (10): 16-27 [
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28
LIU Zheng-jian, NIU Le-le, ZHANG Jian-liang, WANG Yao-zu, LI Si-da, SHAN Chang-dong
Status quo and trend of technology and equipment optimization for sintering granulation in iron and steel enterprises
In order to clarify the current development progress of the sintering granulation process and future development trends, the sintering granulation process and equipment of steel enterprises have been fully summarized and analyzed. Sintering granulation performance directly affects the air permeability of the materials layer and the distribution of quasi-particle structure and it is an important link in the sintering process of iron and steel enterprises. For a long time, the thermal performance of the iron ore sintering process has received more attention, while the granulation performance has not been paid much attention. In recent years, with the development of theory and technology, sintering granulation has received more and more attention from iron and steel enterprises and then many optimization measures of technology and equipment have been adopted for granulation. First, the significance of sintering granulation optimization was explained and then the optimization technologies made by domestic and foreign steel enterprises in the four aspects of raw material pretreatment, mixer equipment, quicklime digestion, and mixture moisture monitoring in recent years were summarized. The understanding of sintering granulation and the knowledge of emerging artificial intelligence technologies help to look forward to the trend of sintering granulation optimization in steel enterprises in the foreseeable future at the end.
2021 Vol. 56 (10): 28-35 [
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36
LI Xiao-ming, XI Hao-dong, MIAO De-jun, LIU Jun-bao, LÜ Ming
Nitrogen dissolution and control of molten steel in steelmaking process
As a typical coexistence element in steel, the content of nitrogen has an important influence on the properties of steel products. In the process of steelmaking, the nitrogen content in molten steel fluctuates obviously, which leads to unstable properties of finished steel, because the exposed molten steel easily leads to nitrogen increase, or the yield of nitrogen in nitrogen-containing alloy is unstable due to different compositions of molten steel and improper operation. Therefore, the precise control of nitrogen has become a key issue in the production of nitrogen-controlled steel or nitrogen-containing steel. The sources of nitrogen, the thermodynamics and kinetics of nitrogen dissolution in molten steel were analyzed, the changes of nitrogen in molten steel production process, the research status and technical measures of nitrogen control were summarized, and the development direction of precise control of nitrogen in steelmaking process puts forward.
2021 Vol. 56 (10): 36-44 [
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Raw Material and Ironmaking
45
LÜ Qing-qing, ZHOU Jun-lan, WANG Guang-hui, DU Ping, TIAN Yong-sheng
Morphology and metallurgical behavior of coke at tuyere of blast furnace
To study the coke deterioration process in the tuyere area, two coke samples were obtained from the edge of the tuyere and the tuyere area. The morphology and products of the reaction interface between coke matrix and oxidizing gas, slag and iron were detected by microspectrophotometer and scanning electronic microscope. The metallurgical behavior of coke in the tuyere zone was analyzed. The results show that oxidizing gas erodes the coke structure by consuming carbon matrix. Slag disintegrates coke by reaction, eroding and extruding gas coke pore walls. The hot metal at the edge of the tuyere area erodes coke mainly through carburization. The residual ash covers the surfaces of the pore wall, which may hinder the chemical reaction with slag and liquid iron. The disintegrated coke was highly graphitized, showing a flake graphite structure. The change of microstructure leads to the reduction of coke strength and finally disintegrated and powdered. After the coke disintegrates, the internal ash and slag powder mixes with the slag and finally forms the final slag.
2021 Vol. 56 (10): 45-53 [
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54
LIU Song, ZHAO Ya-di, GAN Li, FENG Wei, LI Fu-min, LÜ Qing
Discussion on intelligent manufacturing of sintering system and application of big data technology
In order to improve the intelligent manufacturing level of the sintering process, the research progress about the sintering system model in recent decades was systematically summarized. For the current problems in the models of sintering endpoint prediction, composition and quality prediction of sinter ore, and batching optimization, the prediction and optimization of the parameter in the sintering system were investigated by using big data, integrated learning and deep learning. Accordingly, the remarkable results in terms of the improvement in the prediction accuracy and the generalization ability were also emphatically introduced. Moreover, based on the parameter prediction model mentioned above, the hardware and software structure design methods of the parameter prediction and optimization system for on-site application were put forward. Finally, starting from the needs of the iron and steel industry, the point of view, the further integration of advanced information technology and industrial automation equipment was an important way to improve the level of intelligent manufacturing of sintering systems was analyzed, and the research direction and application prospects of big data and artificial intelligence technology in the sintering were also discussed.
2021 Vol. 56 (10): 54-64 [
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65
YANG Shuang-ping, LIU Hai-jin, WANG Miao, LIU Qi-hang, ZHANG Pan-hui
Existing forms of phosphorus in high phosphorus oolitic hematite and its dephosphorization mechanism
Based on difficulty in dephosphorization caused by the complex mineral structure of high phosphorus oolitic hematite, the morphology and micro dephosphorization process of phosphorus in the mineral reduction process were studied to achieve the purpose of deep dephosphorization. The high phosphorus oolitic hematite with the iron grade of 44.78% and the phosphorus mass percent of 0.92% was used in the experiment. From the surface scanning electron microscope and mineral phase structure diagram, it is known that the minerals were inlaid and formed oolitic structure layer by layer, with quartz, oolitic mud and hematite wrapping together, and phosphorus was concentrated and distributed in the fluorapatite inside the oolitic. The dephosphorization mechanism of high phosphorus oolitic hematite was studied based on the scanning electron microscope (SEM) and energy spectrum analysis (EDS). The results show that the oolitic structure is destroyed during the reduction process when the content of YM-1 dephosphorization agent is 16%, resulting in the gradually precipitated and aggregated from the oolitic of iron, separating of gangue from iron particles, and phosphorus removed in different forms. After magnetic separation, the tailings and iron are completely separated, and almost all phosphorus elements were found in the tailings. After adding composite dephosphorization agent YM-1 for calcined magnetic separation, the iron grade of the iron concentrate is 90.16%, the iron recovery is 91.25%, the mass percent of phosphorus is 0.056%, and the dephosphorization rate is 93.91%. The indexes of iron concentrate powder meet the requirements of industrial smelting.
2021 Vol. 56 (10): 65-73 [
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Steelmaking
74
ZHANG Yue-xin, ZHANG Li-feng, WANG Ju-jin, NIU Kai-jun, WANG Ya-dong
Prediction of composition distribution of non-metallic inclusions in a billet
In order to study the spatial distribution of non-metallic inclusions in continuous casting billet, the variation of the average composition of inclusions in a cord steel billet from the loose side to the fixed side was analyzed. With the increase of the distance from the surface layer of the billet, the SiO
2
content ascended significantly from 53% to about 75% firstly, and then declined to 60%. While the change of MnO content in inclusions declined to 12.59% firstly, and then ascended to 27.87%. The contents of CaO and Al
2
O
3
inclusions changed little. An integrated model coupled with heat transfer, solidification, thermodynamic transformation of inclusion composition, and diffusion of dissolved elements in steel was established to predict the composition distribution of inclusions in the continuous casting billet. The calculated variation trend of oxide inclusion composition was consistent with the experimental one, which verified the accuracy of the model. Meanwhile, the evolution of inclusions in continuous casting billets of different total aluminum, total calcium, and total oxygen content was studied by using the model. The content of total aluminum had the greatest influence on the composition distribution of inclusions. When mass pertent of total aluminum increased from 0.000 1% to 0.001 0%, mass percent of SiO
2
decreased from 57%-64% to 34%-39%; mass percent of Al
2
O
3
increased from 8%-10% to 37%-41%; the content of MnO changed little; and mass percent of CaO decreased from 13%-17% to 8%-10%.
2021 Vol. 56 (10): 74-82 [
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WANG Lan-qing, ZHU Hang-yu, ZHAO Ji-xuan, LI Jian-li, SONG Ming-ming, XUE Zheng-liang
Interaction between MgO and low-density molten steel and its effect on non-metallic inclusions
The interface reaction between Fe-20Mn-10Al-C (20%Mn, 10%Al) low-density molten steel and MgO refractory rod at 1 600 ℃ was investigated to understand the interaction between high Mn and high Al steel and refractory. The microstructure of MgO refractory and the characteristics of non-metallic inclusions in the steel were observed for the interface reaction with 30 and 60 min. The results show that the MgO refractory transforms into a three-layer structure after the interface reaction, including the dense MgO·Al
2
O
3
spinel interface layer, the transition layer composed of MgO·Al
2
O
3
spinel particles, the calcium aluminate phase and MgO particles, and the original layer filled with MgO particles. As the reaction time increases, the thickness of the spinel interface layer increases. Under the interaction between the high Mn high Al low-density steel and the MgO refractory, the main non-metallic inclusions in the steel are single MgO·Al
2
O
3
inclusion, AlN inclusion, MgS inclusion and composite inclusions such as MgO·Al
2
O
3
-AlN and MgO·Al
2
O
3
-MgS.
2021 Vol. 56 (10): 83-90 [
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91
YANG Bi-wen, WANG Hai-bei, ZHENG Chao-zhen, CHEN Liang, HU Yi-hang
Effect of B
2
O
3
-Na
2
O slag modifier on desulfurization slag performance of hot metal containing vanadium and titanium
In order to solve the problems of thick of slag, large of iron loss, and much of resulfurization in the slagging-off process after pre-desulfurization of hot metal containing vanadium and titanium, the effect of B
2
O
3
-Na
2
O slag modifier on resulfurization, melting point, and viscosity of the desulfurization slag was investigated by using FactSage thermodynamic software and combing with high-temperature experiments. The results showed that the melting point and viscosity of the desulfurization slag decreased significantly with the addition of B
2
O
3
and Na
2
O. And the addition of CaO to the slag modifier helped to reduce resulfurization. The formula of slag modifier (45%-55% of CaO, 10%-12% of SiO
2
, 5%-8% of Al
2
O
3
, 15%-20% of B
2
O
3
, and 5%-10% of Na
2
O) to improve the performance of desulfurization slag was presented. It effectively reduced the melting point and viscosity of desulfurization slag and decreased the resulfurization, when the added amount of the slag modifier was 5%-10% of the desulfurization slag.
2021 Vol. 56 (10): 91-98 [
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Metal Forming
99
TANG Wei, TAO Gui-lin, WANG Xing-dong, KONG Jian-yi, WANG Zi-yang, LI Zhen
Internal stress of coreless thin silicon steel coil and collapsing mechanism of coreless heart-shaped coil
In a grain-oriented silicon steel rewinding line,due to adopting the constant tension winding method and the coreless winding scheme,about 5% coreless wound rollers collapse after stripping,causing heavy economy loss. In order to investigate the mechanism and influencing factors of the heart-shaped roll,and to reduce the probability of collapse,an inner stress model for winding and stripping was proposed based on the elastic superposition theory and the axisymmetric model. Base on the proposed model and the buried pressure tubes model,a critical criterion for heart-shape buckling of winding coils was obtained. Buckling parameters of 12 groups heart-shape roll with thickness of 0.23 and 0.283 mm were measured,which conform to that predicted by the proposed model,validating the accuracy of the model. Finally,the influences on parameters such as the thickness and roughness of the steel strip,and the equivalent radial stiffness of the rubber layer,were studied. It is found that as the thickness and roughness of the steel strip,and the equivalent radial stiffness of the rubber layer increasing,the probability of the heart-shape buckling and the buckling layers increase,which conforms to actual condition. By decreasing the thickness and increasing the elastic module of the rubber layer,the equivalent radial stiffness increase,leading to significant decrements of the coil pressure,the probability of buckling and the thickness of buckling layers.
2021 Vol. 56 (10): 99-107 [
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108
LIU Ya-xing, GU Qing, ZHANG Wen-jun, BAI Zhen-hua
Improved model for calculating rolling load of ultra-high strength steel in cold rolling process
In order to solve the problem of large error in calculation of roll flattening curve in rolling deformation zone of ultra-high strength steel during cold rolling,fully considering the rolling characteristics of ultra-high strength steel,a new function model of roll flattening curve was constructed by analyzing the variation of roll flattening curve under different flattening radius,and the solution method of characteristic parameters of contact arc length and roll flattening curve in the function was given. Based on this,according to the relationship between deformation and stress in elastic-plastic theory,the calculation process of unit rolling pressure distribution in entrance elastic deformation zone,plastic reduction deformation zone and exit elastic deformation zone was deduced,and the calculation model of total rolling force in cold rolling process of ultra-high strength steel was established. And,the model has been applied to 2030 tandem cold rolling mill of a steel plant to verify the calculation accuracy of the model. The results showed that the roll flattening curve in the cold rolling process of ultra-high strength steel is expressed by quadratic function,which can more accurately reflect the roll flattening state,and the calculated results are in good agreement with the actual values. Meanwhile,it provides a theoretical basis for the evaluation of ultimate rolling capacity and the formulation of rolling schedule of ultra-high strength steel products produced by tandem cold rolling mill.
2021 Vol. 56 (10): 108-116 [
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Materials
117
WANG Zhan-hua, HUI Wei-jun, ZHANG Yong-jian, ZHAO Xiao-li, HAO Yan-ying, DAI Guan-wen
High-cycle fatigue properties of microalloyed medium-carbon forging steel 45MnVS with modified sulfide
The elongated sulfide inclusion is primarily responsible for the mechanical properties anisotropy of hot-rolled and forged sulfur-containing structural steels. In order to explore the fatigue anisotropy of microalloyed ferritic-pearlitic forging steel with modified sulfide,high-cycle fatigue properties of a commercial microalloyed forging steel 45MnVS with as-forged and quenched and tempered (QT) microstructures was studied by using axial-force-controlled fatigue testing with a stress ratio of -1. The results show that the sulfides are primarily short rod-like or slightly elongated with an average length to width ratio of 3.4±1.7 and relatively uniformly distributed in the steel. Although there are still ductility and toughness anisotropy in the tested steel,this anisotropy is significantly lowered than that of other microalloyed medium-carbon forging steels which did not subjected to sulfide modification. The fatigue properties of the as-forged and QT samples in the transversal direction are slightly lower than those in the longitudinal direction,and the fatigue limit ratio of the QT samples (0.52-0.54) is notably higher than those of the as-forged samples (0.46). The transversal sample exhibits a slightly higher fatigue crack growth rate than the longitudinal sample only when the stress intensity factor range is higher than about 35 MPa·m
1/2
. Further fatigue fracture surface investigation revealed that the fatigue fractures are primarily initiated at short rod-like sulfides for both the as-forged and QT samples,and this influence is more notably for the QT sample. It is thus concluded that the fatigue anisotropy of the tested steel with modified sulfide is rather small and the anisotropy degree of the as-forged sample is slightly lower than of the QT sample,although the latter exhibits more superior fatigue properties than the former.
2021 Vol. 56 (10): 117-126 [
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127
CHEN Xin, CUI Qing, CHENG Zi-jian, XU Chang, WEN Bin, LIN Xiao-ping
High-pressure heat treatment induced martensitic transformation of industrial pure iron
In order to study the microstructure and transformation mechanism of martensite under high pressure quenching,the effect of high-pressure quenching on martensite structures and mechanical properties of industrial pure iron was analyzed by means of SEM and EBSD. The high-pressure heat treatment of industrial pure iron was carried out by a CS-1 V hexahedron pressure facility under 3,4 and 5 GPa. The results show that the martensite can be obtained by quenching the industrial pure iron at 6 ℃/s after austenitizing under GPa-level pressure. At 3 GPa,the quenched martensite structure of industrial pure iron presents typical low carbon martensite morphology. Its formation process is similar to that of plate martensites at 4 GPa,the preformed lath bundles penetrate the whole austenite grain which is divided,and then the subsequent lath bundles formed are limited. At 5 GPa,the "cooperative matrix" of martensite which transforms from parent phase to new phase in a cooperative way is large in number,small in size and neat,and most of them grow in trapezoid shape. The mechanical properties of industrial pure iron quenched at 5 GPa are close to that of 0.2% C steel quenched at atmospheric pressure,with hardness of 415HV and yield strength of 700 MPa.
2021 Vol. 56 (10): 127-135 [
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136
YU Run-zhen, YU Sheng-fu, QI Bin, DAI Yi-li
Microstructural evolution behavior and mechanical property of HSLA steel by wire arc additive manufacturing
Wire arc additive manufacturing (WAAM) is a novel and important method for forming high-performance HSLA steel components. In order to reveal the microstructural evolution behavior of HSLA steel during WAAM,the temperature field,thermal cycle,heat affected zone partition and its microstructure transformation of component during deposition were investigated. The results showed that in WAAM process,the deposited metal of HSLA steel consisted of solidification zone (SZ) and heat affected zone,and the latter could be divided into coarse austenitic-grain zone (CAZ),normalizing zone (NZ) and tempering zone (TZ). Under the action of thermal cycle,SZ successively turned into CAZ,NZ,and finally became TZ. Meanwhile,Residual ferrite nuclei,high-density dislocations near inclusions,ferrite sympathetic nucleation,grain boundaries pinning by second-phase particles,and continuous dynamic recrystallization all facilitated the microstructure refinement,making coarse columnar grains,grain boundary ferrites,ferrite slide plates,a small amount of acicular ferrites and pearlites evolved into fine equiaxed ferrites and pearlites,beneficial for improving strength,toughness and inhibiting mechanical anisotropy. The vertical,horizontal tensile strength of WAAMed component were 519.6,520.8 MPa respectively,and impact energy at -20 ℃ was 124.7,122.1 J respectively.
2021 Vol. 56 (10): 136-145 [
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146
PU Chun-lei, LIN Yin-he, YIN Guo-liang, TIAN Ye, CHENG Xiang-kui, FANG Shi-nian
Influence of Nb and V on recrystallization of high-strength steel bars and design of rolling process
In order to study and design the quantitative control of the recrystallization behavior of the austenite region during the rolling process of high-strength steel bars after adding niobium and vanadium,the Gleeble-3500 thermal simulator was adopted to conduct uniaxial hot compression tests on niobium and vanadium microalloyed high-strength rebars. Based on the thermodynamic principle of the critical condition of recrystallization,the Avrami equation was used to obtain the recrystallization kinetic curve under different deformation conditions through the analysis of the stress-strain curve under different deformation conditions. And the niobium is quantitatively compared and analyzed according to the recrystallization kinetic curve. The effect of vanadium microalloying on the beginning,transformation,and end process of recrystallization of high-strength rebar was studied carefully. The results showed that the hot compression process of niobium and vanadium microalloyed rebars showed obvious characteristics of dynamic recrystallization. The addition of microalloying elements Nb/Nb+V hindered the dynamic recrystallization of 20MnSi steel and increased the deformation temperature. Or an increase in strain rate can promote recrystallization. Rolling Process design was carried out for the use of dynamic recrystallization and organization control in production. The calculations indicated cooling and recovery could be carried out before the finished stand in the finishing mill to ensure the recrystallization fraction(95%),where the temperature was around 830 ℃.
2021 Vol. 56 (10): 146-151 [
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Environmental Protection and Energy
152
ZHANG Qi, SHEN Jia-lin, XU Li-song
Carbon peak and low-carbon transition path of China's iron and steel industry
In 2020,China announced that it will increase its nationally determined contributions and strive to reach the peak of CO
2
emissions by 2030. As a typical resource- and energy-intensive industry,the iron and steel industry is an important industry that takes the lead in achieving carbon peaks. Here, the influences of steel production,production structure,energy conservation and emission reduction technologies,and carbon tax on the carbon emissions of China's iron and steel industry were analyzed. That different steel production peak times will have different effects on the iron and steel industry's carbon peak,and technologies and production structure factors will have an important impact on China's iron and steel industry. The region is the main body responsible for implementing the national carbon peak task. The carbon emissions of four key areas(Beijing-Tianjin-Hebei and surrounding areas,the Yangtze River Delta region,the Fenwei Plain and the Guangdong and Guangxi regions) with different steel production characteristics were analyzed,which is necessary to speed up the formulation of the regional peaking plan. To formulate a low-carbon transformation path for the iron and steel industry(in terms of adjusting the industrial structure,promoting low-carbon technologies,changing the energy structure,promoting inter-industry coupling,and strengthening carbon asset management) is of great significance to achieving the early peak of carbon emissions and carbon neutrality in China's iron and steel industry.
2021 Vol. 56 (10): 152-163 [
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