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2021 Vol. 56 No. 5
Published: 2021-05-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Technology Exchange
Technical Reviews
1
SHANGGUAN Fang-qin, ZHOU Ji-cheng, WANG Hai-feng, LI Xiu-ping
Climate change and decarbonization development of steel industry
The Chinese government has paid great attention to the issue of climate change,and has actively made emission reduction commitments. As an important field of industry,the steel industry is not only a big energy consumer but also a major CO
2
emission source. The current situation of CO
2
emission from the Chinese steel industry was analyzed,and it is shown that the specific CO
2
emission per ton steel has decreased significantly. And the total amount of CO
2
emission has reached a peak in 2014,and then has shown a downward trend. However,due to the huge output of crude steel,the CO
2
emission of the steel industry still accounts for a high proportion of the total CO
2
emission in China. Therefore,it is necessary to take the road of decarbonization for the steel industry. Through the analysis of the development strategies and technologies of decarbonization in the steel industry,it is shown that the most practical pathway for decarbonization development of the steel industry is to promote and increase the ratio of EAF process with 100% scrap strategically.
2021 Vol. 56 (5): 1-6 [
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415
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Raw Material and Ironmaking
7
WANG Xin-dong, JIN Yong-long
Strategy analysis and testing study of high ratio of pellet utilized in blast furnace
The advantages and problems of using high-proportion pellets in blast furnaces from the perspective of strategic development were analyzed, and the strategic opportunities for using high-proportion pellets in blast furnaces was clarified. According to the characteristics of domestic high-silicon iron concentration, basic researches on green pellet-making, drying and roasting of magnesia pellets with high silicon acidity and flux properties have been carried out. Furthermore, the compressive strength of pellets, high-temperature metallurgical properties, and ring formation in the production process of rotary kiln have been analyzed. The basic characteristics such as formation mechanism and the design characteristics of the basic operating parameters for pellet production were put forward, and the stable continuous production of high silica magnesia acid and flux pellets produced by the grate rotary kiln was realized. Two high-proportion pellet blast furnace production trials have been completed. Practice has proved that the production of high-proportion pellet smelting blast furnaces was stable and smooth, and all indicators were better than those of high-proportion sinter smelting blast furnaces. The operating ideas can be replicated, the smelting results can be reproduced, the operating experience can be promoted, and the environmental benefits are huge. The emissions of SO
2
, NO
x
, PM and CO
2
are far superior to blast furnaces produced with a high proportion of sintered ore. It is foreseeable that the preparation of high-quality metallurgical pellets and the smelting of high-proportion blast furnace pellets will be the best measure to break the long-term steel process in China to reduce total pollutant emissions and achieve low-carbon smelting and sustainable development.
2021 Vol. 56 (5): 7-10 [
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17
ZHANG Cheng-bo, SHAO Lei, XIAO Qi-lin, ZOU Zong-shu
Diagnosis model for profiles of skull and remaining lining in blast furnace hearth
The erosion of the lining and the formation of the skull in a blast furnace hearth determines the lifespan of the hearth. Combined with numerical heat transfer, equivalent thermal resistance method, and three optimization algorithms of Levenberg-Marquardt method, Quasi-Newton method, and gradient method, a mathematical model for diagnosing the profiles of the skull and remaining lining in the blast furnace hearth and providing a basis for blast furnace maintenance was established. Emphasis was put on the construction process of the model, and the validity and accuracy of the model were verified by providing an elephant-foot-shaped erosion sample. The practical application was further demonstrated through a calculation example using an actual composite hearth structure. The results indicated that among the three optimization algorithms the Levenberg-Marquardt method has the best performance. Also, it was shown by the application example based on an industrial blast furnace hearth that, 150 weeks after blow-on, the melting and buildup of the skull in the hearth is in a dynamic equilibrium state, and the erosion of the remaining lining is slow.
2021 Vol. 56 (5): 17-22 [
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207
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23
WU Di, JIN Feng, LIU Yong, BI Chuan-guang
Flow and heat transfer characteristics and erosion monitoring model in hearth
To analyze the flow and heat transfer characteristics in the hearth of the blast furnace under actual working conditions and predict the erosion line in the carbon bricks, computational fluid dynamics(CFD) and two-dimensional fast backstepping calculation methods are used to simulate the furnace bottom. The research results show that the full-scale furnace bottom CFD simulation better shows the temperature field and flow field characteristics of the furnace bottom fluid-solid zone, and the measured point temperature and the historical thermocouple temperature value are less than 5.2%; when there is an air gap in the furnace body, the air gap The extreme hot zone and the extreme cold zone are formed on the left and right, which is consistent with the phenomenon of the sudden temperature change of the thermocouple in the historical data. When the thickness of the air gap is 10, 20 and 30 mm, the temperature difference between the left and right of the air gap is 14.7, 18.9, 21.4 times respectively compared with no air gap; the two-dimensional fast reverse calculation deduced the shape of "elephant-foot" erosion, the maximum erosion position is within 1-3 m below the taphole, and the minimum residual thickness has an error of 13.5% from the actual measured value, it is also consistent with the actual erosion of the blast furnace.
2021 Vol. 56 (5): 23-30 [
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Steelmaking
31
ZHANG Yan-chao, ZHANG Cai-jun, ZENG Kai, XUE Rui, ZHU Li-guang, BAI Feng-qiang
Optimization and simulation of bottom blowing system for 300 t combined blown converter
The top and bottom composite blowing converter steelmaking method is the mainstream steelmaking method at present. The type, number, arrangement mode and bottom blowing gas supply intensity of the bottom gas supply element directly affect the mixing effect of the converter molten pool. The reasonable flow field can not only reduce the production cost, but also shorten the smelting cycle and increase the enterprise benefit. Based on the research characteristics of cold water simulation and CFD numerical simulation, a 300 t converter in a steel plant was taken as the prototype, and the mixing time, dead zone and weak flow zone volume of the molten pool under different bottom blowing conditions were evaluated. The bottom lance arrangement, bottom blowing gas supply mode (non-uniform gas supply and uniform gas supply), and bottom blowing gas supply intensity of 300 t converter are systematically studied. The results show that when the position of the bottom lance is from 0.3
D
(
D
is the diameter of furnace bottom) to 0.5
D
, the stirring capacity of the bottom blowing system on molten steel at the furnace wall is obviously enhanced, but the volume of the dead zone and weak flow zone in the molten pool increases obviously, which makes the mixing time of the whole bath increase. It is found that when the critical value of bottom blowing strength is 0.28 m
3
/ (t·min), the stirring effect is the best. The stirring effect of the bottom blowing system on the molten pool will change with the different gas supply modes. When the bottom blowing flow distribution is 2:1, the bottom blowing system has the best stirring effect, followed by the uniform gas supply mode (1:1). When the distribution ratio is 3:1 and 4:1, the stirring effect of the bottom blowing system on the molten pool will be greatly affected due to the relatively large gas supply intensity on the large flow side of the bath.
2021 Vol. 56 (5): 31-40 [
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41
LIU Zeng-xun, ZHANG Zhao-yang, XIAO Peng-cheng, ZHU Li-guang, ZHOU Jing-yi, ZHANG Jun-guo
Influence of cooling process on heat transfer of high-speed continuous casting mold
In order to analyse the influence of the cooling water supply process on the temperature field of mold copper wall and cooling water gap,based on the mold temperature data measured by thermocouples in the copper wall,a mathematical model for the inverse heat transfer question of the slab/copper wall and the forward question of the copper wall/cooling water were constructed. The numerical analysis model of the slab/copper wall/cooling water of thin slab casting mold was established by ANSYS. Coupled heat transfer analysis of the temperature field of the reactor is carried out to analyze the influence of different cooling processes on the heat transfer behavior in the high-speed thin slab continuous casting mold. The result shows that the direction of water flow in the water gap has a significant impact on the temperature field of the copper wall. The top-down "reverse water supply" is adopted,which reduces the peak temperature of the hot surface of the copper wall by 117 ℃ compared with the conventional cooling process,and the maximum temperature of the cooling water on the copper wall side Lowering 24 ℃ can effectively improve the working condition of the copper plate and suppress the local boiling tendency of cooling water. Increasing the cooling water speed can further reduce the temperature of the copper wall and the cooling water,and the cooling water temperature has less influence on the temperature field of the copper wall.
2021 Vol. 56 (5): 41-48 [
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49
ZHOU Mei-jie, AI Li-qun, HONG Lu-kuo, LI Ya-qiang, SUN Cai-jiao, HOU Yao-bin
Comparison of decarburization of Fe-C alloy strips in CO
2
and H
2
O atmosphere
In order to investigate the decarburization behaviour of Fe-C alloy in CO
2
and H
2
O, the Fe-C alloy strips with a carbon content of about 4.2% were decarburized in Ar-CO-CO
2
and Ar-H
2
-H
2
O atmospheres respectively. The atmospheric conditions that ensure the strips can be decarburized but iron not be oxidized were made by combining thermodynamic analysis and tests. The atmospheric conditions of the Ar-CO-CO
2
atmosphere were gas flow rate of 850 mL/min, mass percent of CO of 25%, $P_{CO_2}$/(
P
CO
+$P_{CO_2}$) = 0.26. The atmospheric conditions of the Ar-H
2
-H
2
O were gas flow rate of 500 mL/min, mass percent of H
2
of 15%, water bath temperature of 313 K. The average mass percent of carbon was 0.6% after 50 min at 1 413 K in Ar-H
2
-H
2
O. The average mass percent of carbon was 0.92% after 70 min at 1 413 K in Ar-CO-CO
2
. The decarburization effect of Ar-H
2
-H
2
O was better than that of Ar-CO-CO
2
at the same decarburization time and temperature. The reason is that the carbon activity of the strips in Ar-H
2
-H
2
O is lower than that of the Ar-CO-CO
2
atmosphere when the decarburization reaction is in equilibrium. As a result, the carbon concentration gradient of Fe-C alloy strips in Ar-H
2
-H
2
O is higher than Ar-CO-CO
2
. And the diffusion flux in Ar-H
2
-H
2
O is higher than Ar-CO-CO
2
.
2021 Vol. 56 (5): 49-55 [
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56
AN Rui-dong, LIU Fu-bin, CHEN Kui, GAO Jun-zhe, KANG Cong-peng, JIANG Zhou-hua
CAFE simulation of electroslag remelting GH984G directional solidification structure
The control of electroslag remelting solidification structure is directly related to the quality of superalloys and actual production applications. Aiming at the directional solidification process of electroslag remelting GH984G, considering heat transfer and solute diffusion, based on the combination of CAFE method and C language, a three-dimensional microstructure evolution model of the electroslag remelting solidification process is established, and the temperature field and solidification structure evolution are simulated and predicted. The results show that, the ingot temperature field and bath depth are shallow and flat at first, then deepen until finally stable. At the beginning of electrode melting, the molten pool is shallow and the growth direction of the dendrite is vertical upward, and then the molten pool deepens continuously, and the vertical upward columnar crystal direction at the bottom becomes about 26 ° oblique upward. At the same time, equiaxed crystals appear on the centerline of the ingot, and the equiaxed crystals grow with columnar crystals after nucleation and growth. Besides, with the increase of the electrode melting rate, the rising speed of the slag metal interface increases, and the depth bath becomes wider and deeper. The simulation results are consistent with the experimental results, which verifies the applicability of the model and nucleation parameters.
2021 Vol. 56 (5): 56-64 [
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Metal Forming
65
XIE Hong-biao, REN Jian-kai, YU Chao, XIAO Hong
Simulation and experiment on periodic interfacial fluctuation in clad plate rolling
In order to explore the mechanism and influencing factors of the periodic thickness fluctuation at the composite interface after rolling,a finite element model of aluminum/steel/aluminum three-layer symmetrical composite plate rolling was established based on commercial FEM software ABAQUS. Through the analysis of the stress variation law of each layer in the rolling process of the clad plate,it is found that the deformation of steel layer and aluminum layer is obviously inconsistent,and the deformation trend of the aluminum layer is obviously greater than that of the steel layer,which leads to the tensile stress in the rolling direction of steel layer and the thickness thinning of steel layer. At the same time,the occurrence of thickness thinning changes the stress distribution in the surrounding area and makes the thickness fluctuation presents periodic characteristics. The correctness of the simulation and analysis results is verified by the rolling experiment in the laboratory.
2021 Vol. 56 (5): 65-71 [
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72
SHEN Li-tao, XU Peng, ZHANG Ya-zhen, GU Qing, KONG Peng-hui, BAI Zhen-hua
Strip shape change and its tension compensation technology in process of speed increase and decrease of cold continuous rolling mill
Aiming at the problems of unstable rolling and poor shape quality caused by the fluctuation of rolling pressure in the speed increase and decrease stage of the tandem cold rolling process. In order to reduce the rolling force fluctuation and obtain high-quality strip shape,based on the equipment and process characteristics of cold continuous rolling mill,the influence of rolling speed fluctuation on the rolling pressure change under sufficient and insufficient emulsion flow was fully considered,and the shape evolution mechanism in the process of increasing and decreasing the speed of cold continuous rolling was analyzed. On this basis,a set of corresponding tension compensation models was developed and applied to the production of an 1 800 five-stand tandem cold rolling mill with the minimum overall rolling pressure fluctuation during the speed increase and decrease process of the tandem cold rolling mill as the objective function. In practice,good results have been achieved,and the rolling stability and the strip shape quality have been effectively improved,which has the value of further popularization and application.
2021 Vol. 56 (5): 72-79 [
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80
ZHENG Yi, YANG Ting-song, QU Chun-tao, DU Feng-shan, XU Zhi-qiang
Electromagnetic compensation and initial roll gap under new type of electromagnetic control rolling mill bending roll
In order to solve various flatness problems in the process of thin strip rolling,a new type of electromagnetic control rolling mill was used as the research object, and a three-dimensional thermal-mechanical coupling finite element model was established by Marc, and the bending force under the combined action of the bending roll and the electromagnetic control roll was analyzed. And the rolling force affected the roll shape state, plate shape distribution, slab edge stress, roller contact stress, and bearing roll gap shape.The results show that the application of the roll bending mechanism will directly promote the stable bulging of the electromagnetically controlled rolls,and the bulging crown of the electromagnetically controlled rolls will be compensated integrally. Based on the good shape of the plate,a reasonable bending roll for the new electromagnetically controlled rolling mill is given. Comparing the changes of roll gap functions with different bending forces and rolling forces,different secondary and fourth crowns are formed,which provides a basis for shape control and initial roll gap settings.
2021 Vol. 56 (5): 80-90 [
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Materials
91
YIN Hui-fang, YANG Gang, ZHAO Ji-qing
Tempering temperature effect on precipitation and properties of COST-FB2 rotor steel
The effects of tempering temperature on the microstructure and properties of COST-FB2 rotor steel was investigated by OM,SEM and TEM to adjust the strength and toughness of COST-FB2 steel. The results show that with the increase of tempering temperature,the strength and hardness of the tested steel decreases continuously,while the plasticity and impact energy increase;the total displacement of oscillograph at room temperature increases with the increase of tempering temperature. The high strength and low toughness of the tested steel after tempering at 350 ℃ and 570 ℃ can be improved by tempering at 700 ℃ again. The residual austenite in COST-FB2 rotor steel after quenching can be eliminated by tempering at 570 ℃. There are no M
3
C in martensitic lath after quenching with oil cooling. There are a large number of needle-like M
3
C within martensitic lath of the tested steel after tempering at 350 ℃ and 570 ℃. M
3
C phase disappeared and M
23
C
6
precipitates at prior austenite grain boundary and martensite lath boundary after tempering at 700 ℃. There is aggregation and coarsening of M
23
C
6
at prior austenite grain boundary,and some martensite lath recovered.
2021 Vol. 56 (5): 91-97 [
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98
ZHANG Zhi-hui, GU Yang, YUAN Rui, WU Hui-bin
Corrosion behavior of low carbon medium chromium steel under simulated CO
2
-EOR environment
In order to study the corrosion mechanism of Cr5 and Cr7(wt.%) steel under CO
2
-EOR high temperature and high pressure service condition,the corrosion behavior was simulated by using high temperature and high pressure reactor,and the corrosion rate was measured by weight loss method to compare the corrosion resistance of two test steels. Corrosion products were observed and analyzed by SEM,EDS,XRD and XPS. The corrosion mechanism of test steels under CO
2
corrosion conditions was discussed,and an intuitive corrosion mechanism model during the entire corrosion process was constructed. The research results show that the corrosion rate of Cr5 steel is 0.734 75 mm/a,and that of Cr7 steel is 0.217 32 mm/a. Corrosion products are composed of FeCO
3
crystals in the outer layer and amorphous FeCO
3
and Cr(OH)
3
in the inner layer. In the initial stage of corrosion,the product film is formed by in-situ generation and gradually deposited after anodic dissolution. After the product completely covers the substrate,the diffusion and deposition of ions at the interface becomes the main way for product film growth.
2021 Vol. 56 (5): 98-104 [
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105
YI Ya-li, KONG Yao-jie, WANG Yu-han, JIN He-rong, ZHAO Ding-xuan
Effect of coating slab preparation on stainless steel/low alloy steel composite interface
To investigate the effect of coating Fe-Co-Ni interlayer method on the interfacial surface cleanliness of stainless steel/low carbon steel composite slabs,the orthogonal test method was used to establish the preferred process parameters for interlayer coating by Procast simulation software. Based on the simulation results,the composite slabs with coating interlayer were prepared and compared with the composite slabs made by solid interlayer embedding method to analyze the effect of different forming methods on the microsructure and mechanical properties after rolling and forming. It appears that the carbon and chromium diffusion preforms of the composite plate interlayers of both types are blocked,and the tensile and shear strength of the samples meets the requirements of the relevant standards. Compared with the embedding method,the ability to block the diffusion of chromium is significantly improved and a flatter bonding interface is obtained through the coating method. The content of inclusions and oxides were also reduced. The mass percent of oxygen of the coating method (4.1%) is significantly lower than that of the embedding method (11.1%),and the tensile strength of the coating method (531 MPa) is higher than that of the embedding method (503 MPa).
2021 Vol. 56 (5): 105-112 [
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518
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Technology Exchange
113
XIAO Yao, NIU Shen-shen, HAN Yi, LIU Feng, GAO Xin-liang, YU En-lin
Analysis of intermediate frequency heat treatment parameterson high frequency straight welded pipe
In order to reduce the residual stress concentration in the heat-affected area and improve the weld quality performance,the high-frequency straight seam welded pipe must undergo intermediate frequency heat treatment. However,after intermediate frequency induction heating,there is a certain temperature difference between the upper and lower surfaces of the welding seam. Affected by the heat transfer sequence,the lower surface of the thick-walled pipe is not easy to reach the heat treatment temperature,which will seriously affect the quality of the finished steel pipe. According to the characteristics of intermediate frequency electromagnetic heating of welded pipe,the effects of the axial distance of two sets of coils,the turning angle of coils,and the distance between main and secondary coils on the induction heating effect are analyzed. The temperature difference between the upper and lower surfaces of the weld and the temperature at point H after heating presented a decreasing trend with the increase of the axial distance between the two coils. When the coil angle is positive,the temperature and temperature difference at point H increase with the increase of the angle,and the minimum value occurs when the angle is 50°. When the angle is negative,the temperature difference and the temperature at point H fluctuate within a certain range. In this case,the temperature at point H is higher and the temperature difference is smaller. When the distance between the primary and secondary coils of a single set is 30 mm,the temperature difference is the smallest. Professional welding software SYSWELD was used to conduct tissue field simulation,and the tissue distribution on the upper surface of the weld after heat treatment was compared and analyzed. It was found that after intermediate frequency heat treatment,the volume percent of ferrite increased to about 25% and the volume percent of pearlite decreased to 75%. Finally,the Gleeble thermal simulation experiment and metallographic experiment were conducted to indirectly verify the correctness of the temperature model. It provides a theoretical reference for further optimizing heat treatment process parameters of straight seam welded pipe and has certain guiding significance for the production improvement of enterprises.
2021 Vol. 56 (5): 113-121 [
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122
HAN Wei-gang, HU Chang-qing
An entropy-based evaluation model of operation order of steel manufacturing process
The quantitative evaluation of the operation order of the steel manufacturing process is an important issue in the management and control of steel enterprises. In order to quantitatively study the order of process from the aspect of connection and matching state of devices,referring to information entropy, the average uncertainty of input and output of unit
i
in the steel manufacturing process as its operation state entropy
E
(
i
)was defined,the ratio of operation state entropy and maximum operating state entropy
E
(
i
)/
E
max
(
i
) as its operation disorder degree was taken,and
R
(
i
)=1-
E
(
i
)/
E
max
(
i
) as its operation order degree was taken. On this basis,the weighted average value of the operation order degree of all units is defined as the operation order degree of the steel manufacturing process,which is used as the evaluation index of operation order of steel manufacturing process. Finally,the BOF-CC section of a steel enterprise is taken as an example,the operation order degree in a certain month is calculated to be 0.396 1.
2021 Vol. 56 (5): 122-128 [
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