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2020 Vol. 55 No. 9
Published: 2020-09-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technical Reviews
1
HAN Yi, ZHANG Long, XIAO Yao, YU En-lin, WANG Qing-liang, ZHAO Yu-qian
Research status and prospect of fatigue life of hollow drill steel
Hollow drill steel is a special steel material for manufacturing rock drill rod and also a representative product of rock drill steel industry. All the hollow drill steel used in the high quality rock drill tools around the world has high fatigue life and stable quality,which is fine steel with high technology and high value-added. Compared with imported high-end hollow drill steel,the fatigue life of domestic hollow steel of the same type still has a large room for improvement. China is a major producer and user in the rock drill steel and tools industry,in order to achieve high-quality development,the new technology and process of steel industry will be used for reference,and the new method to improve the fatigue life of hollow drill steel will be explored to produce high-quality hollow drill steel with high fatigue life and stable quality. In view of the failure form of hollow drill steel and the main factors that affect its fatigue life,the present research results of improving and estimating its fatigue life are reviewed. In the future,the advanced technology such as electromagnetic stirring,electropulsing treatment will be used to further improve the quality of hollow drill steel,the application conditions of the combination of the intelligent prediction and management system of fatigue life and the technology of crack repairing will be developed.
2020 Vol. 55 (9): 1-10 [
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295
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Raw Material and Ironmaking
11
CHEN Wen, WANG Xin, LEI Ying, LI Yu, HE Si-qi, LIAO Zhen-hong
Isothermal reduction kinetics of high-phosphorus iron ore carbon-containing pellets
To study the isothermal reduction kinetics of high-phosphorus iron ore carbon-containing pellets, at the temperature of 1 173, 1 273, 1 323, 1 373, 1 423 and 1 473 K. Several solid-state reaction mechanism functions, i.e. interfacial chemical reaction model, Jander equation, Ginstling-Broushtein equation, and G Valensi-R E Carter equation were used to fitting the reduction reaction process. The phase, microstructure and elementary composition were characterized by using X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive X-Ray Microanalysis (EDX) techniques. With the increase of the reduction degree, the reaction rate increased from zero to the maximum rapidly, and then gradually decreased and became flat. The reaction rates increase with increased temperature. At the temperature form 1 173 to 1 373 K, the reduction reactions are well fit to the interface chemical reaction model, the apparent activation energy and correlation coefficients are 70.02 kJ/mol and 0.948 1 respectively; At the temperature form 1 373 to 1 473 K, the reduction reactions are well fit to the Jander model, the restrictive step is iron ion solid-state diffusion, the apparent activation energy, and correlation coefficients are 215.36 kJ/mol and 0.991 2 respectively.
2020 Vol. 55 (9): 11-15 [
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16
LI Shen-zi, LONG Yue, PAN Xiang-yang, DU Pei-pei, XING Lei
Effect of
w
(MgO)/
w
(Al
2
O
3
) on droplet performance of composite burden
The appropriate
w
(MgO)/
w
(Al
2
O
3
) in the blast furnace charge can improve the metallurgical properties of the slag, which is beneficial to the smelting of the blast furnace, so as to achieve the smelting purpose of increasing production, energy-saving and reducing consumption. In order to explore the influence of
w
(MgO) on the performance of composite charge, Change the
w
(MgO)/
w
(Al
2
O
3
)of the sintered ore and pellets in the composite charge, use a high-temperature melt drop furnace to test its droplet performance, and perform XRD and SEM-EDS detection on undripped droplet to explore the composition and distribution of slag. Finally, a reasonable
w
(MgO) partition structure was obtained. The test results show that during the increase of
w
(MgO)/
w
(Al
2
O
3
) from 0.8 to 1.2 in the sintered ore, the dropping temperature first decreases and then increases, the position of the reflow zone is continuously lowered and shows a trend of first narrowing and then widening. The content of feldspar and forsterite increased continuously, while the content of spinel and periclase gradually increased after
w
(MgO)/
w
(Al
2
O
3
) exceeded 1.0; during the increase of
w
(MgO)/
w
(Al
2
O
3
) in pellets from 1.39 to 2.09, the melting interval decreased first and then increase, the reflow zone first moves up and then decreases. When the
w
(MgO)/
w
(Al
2
O
3
) in the sintered ore is 1.0 and the
w
(MgO/
w
(Al
2
O
3
) in the pellets is 1.74, the characteristic value of the droplet is 95.55 kPa·℃, and the composite droplet has the best droplet performance, which is beneficial for the blast furnace to go forward.
2020 Vol. 55 (9): 16-22 [
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23
MA Hong-you, WANG Zhen-yang, DAI Jian-hua, YUAN Jun, LI Xiu-liang, WANG Yong-long
Segregation of material flow under different chute shapes
The bell-free furnace top equipment mainly adjusts the distribution matrix by changing the inclination of the chute, and finally changes the distribution of the charge in the blast furnace. In addition, the charge distribution is also affected by the shape of the chute, and the chute of different shapes cause different material surface segregation. The segregation phenomenon of cloth under different chute is explored, and three types of chutes with different square proportions, storage chute, and broken chute are used, and the coke model is established using the discrete element method. The discrete element method is used to study the surface and burden distribution characteristics of the chute, and to investigate the segregation phenomenon and the stress of the chute of the charge under different chutes. The simulation results show that, compared with the circular exit chute, the square exit chute has a small width and uniform distribution, which is more conducive to accurate distribution. The storage chute can reduce the erosion of the chute in charging material progress and extend the chute life; the flow width of the broken chute is large, the burden distribution is uneven, and the segregation of the material surface is increased.
2020 Vol. 55 (9): 23-28 [
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Steelmaking
29
WANG Yu-mo, TAO Lin, GUO Hao-yu, ZUO Da-wen, WEI Jie, YANG Shi-shan
Dephosphorization influence factors in converter hot metal pretreatment
Dephosphorization of hot metal pretreatment in the converter is nowadays playing an important role in the production of low or super low phosphorus steel grades. Based on the pretreatment dephosphorization converter practice in “duplex converter steelmaking” process in domestic iron and steel enterprises, experimental studies on dephosphorization influence factors in converter hot metal pretreatment were imitatively carried out by top addition of dephosphorization agent and immersed blowing of gaseous oxygen in SiC electric resistance furnace of molten pig iron. The effects of different hot metal temperature, initial silicon content in hot metal
w
(Si)
i
, slag basicity, oxygen supply (the ratio of gaseous oxygen and total oxygen), stirring strength, and fluorspar addition on dephosphorization efficiency are compared. The results showed that the ranking order of different factors affecting dephosphorization ratio is hot metal temperature＞
w
(Si)
i
＞oxygen supply＞slag basicity, stirring strength＞fluorspar addition,the appropriate process parameters are the hot metal temperature of 1 300 ℃,
w
(Si)
i
of 0.10%-0.26% or less than 0.30%, slag basicity of 2.9 to 3.0, oxygen supply of 50% solid oxygen or a few more, and with stronger stirring,and the dephosphorization agent is probable without fluorspar during hot metal dephosphorization pretreatment in the converter.
2020 Vol. 55 (9): 29-37 [
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38
LI Chao, LI Jian-xin, LIU Zhan-li, ZHANG Fei, JIANG Jing-yu, LI Jie
Production process of low-cost clean steel for wide and heavy plate
In order to further improve the cleanliness of steel plate and reduce production cost,the production process of low-cost clean steel with LF-VD refining for the wide and heavy plate was studied by theoretical calculation and industrial tests. In the VD refining process, SiO
2
in the refining slag reacted with Al in the steel, reducing the mass percent of SiO
2
and increasing the mass percent of Al
2
O
3
in the slag. By optimizing the converter and refining deoxidization and alloying system, the mass percent of SiO
2
in the refined slag and the mass percent of Al in the steel before VD were reduced, and the reaction of slag-steel in VD process was weakened. Aluminum loss in the VD process was reduced by 29%. Not only did the aluminum consumption of per ton steel decrease by 0.68 kg, but also the cleanliness of the steel plate increased significantly. The mass percent of total oxygen and nitrogen were decreased by 0.000 6%, and the number density of inclusions which more than 2 μm and more than 5 μm in the steel plate were decreased by 74% and 81% respectively.
2020 Vol. 55 (9): 38-42 [
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267
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43
JIANG Xue-feng, PENG Fei, ZHANG Yan-long, XUE Wen-hui
Application of carbon deoxidation in ladle top slag modification
In order to further reduce inclusion defects and improve product quality, the modification of ladle top slag based on carbon deoxidation was studied.The production process of cold-rolled products is,hot-metal pre-treatment→BOF converter →RH refining →continuous casting. In order to reduce the content of inclusions in steel, the ladle slag should be modified to reduce its mass percent of TFe. Top slag modification process based on carbon deoxygenation was applied, in which carbon particle was used modify the steel bag top slag, partially replace the aluminum slag ball. Good results were got, the mass percent of TFe in the ladle slag and the mass percent of [O] in the tundish steel were reduced,meanwhile the Al
2
O
3
inclusions in the billet was also optimized. Cost savings about 5.16 yuan/t(steel),in the "30 kg carbon particle + aluminum slag ball" modification process, was got.
2020 Vol. 55 (9): 43-48 [
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49
NIU Liang, ZHAO Jun-xue, QIU Sheng-tao, TANG Wen-dan, YANG Ling-zhi
Numerical simulation of flow and heat transfer in a continuous casting round bloom with eccentric M-EMS
In order to explore the effect of eccentric mold electromagnetic stirring (M-EMS) on the flow and heat transfer of molten steel in continuous casting round bloom and reduce the adverse effect of eccentric M-EMS on round bloom, a coupled three-dimensional mathematic model is established to study the flow and heat transfer characteristics of molten steel in
Φ
380 mm round bloom with eccentric M-EMS and the effects of M-EMS parameters. The results show that under the action of eccentric M-EMS(300 A/2 Hz): the molten steel entering the mold from the nozzle flows to the external arc side, and a large recirculation zone will be formed after molten steel hitting the arc side; the temperature of molten steel near the external arc side is higher than that near the inner arc side; as the distance from the meniscus increases, the temperature of the molten steel on the external arc side increases first and then decreases, the temperature at the center of the M-EMS is the highest at 1 779 K; the temperature of the molten steel on the inner arc side has been decreasing. As the current intensity increases from 100 A to 500 A, the recirculation zone under the round bloom changes from one to two; the temperature difference of the molten steel on the inner and external arc sides first decreases and then increases, which is the smallest at 300 A, and the temperature difference is 8.4 K. As the current frequency increases from 1 Hz to 5 Hz: the recirculation zone near the external arc side becomes smaller until it disappears. When the current frequency is less than 3 Hz, the temperature difference of the molten steel on the inner and external arc sides is less than 10 K, and when the frequency is greater than 3 Hz, the temperature difference is greater than 16 K. The recommended M-EMS parameter for
Φ
380 mm round bloom is 300 A/2 Hz.
2020 Vol. 55 (9): 49-56 [
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Metal Forming
57
WANG Si-hai, ZHAI De-jia, LIU Li-hui, HE Hai-nan, LI Lei, XU Dong
Wear control strategy of work roll in 1 250 mm hot continuous rolling
Concave work rolls with negative crown are commonly used in a large number of 1 250 mm hot continuous rolling production lines in China. Due to the configuration of the roll and the characteristics of the rolling process,the work rolls will suffer serious "cat ear" wear,resulting in local high points in the section of the hot-rolled strip. In order to improve the wear of 1 250 mm hot rolling work roll and improve the strip profile quality,a control strategy for 1 250 mm hot rolling work roll wear was proposed. While ensuring the plate and strip rolling stably,the wear of the work roll was controlled by optimizing the roll shape curve and the work roll shifting strategy. This strategy has been applied to Delong iron and steel company,the industrial test showed that this strategy can reduce the amount of work roll wear,make the roll wear more even and increase the control ability of roll bending. The work roll rolling mileage per unit cycle is extended by 40%,which has research value and promotion prospect for 1 250 mm hot continuous rolling production line work roll wear control.
2020 Vol. 55 (9): 57-63 [
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64
WANG Dong-cheng, ZHANG Ya-lin, XU Yang-huan
Research on problem of "pseudo-bad flatness" at tail of hot rolling strip
The head and tail of hot rolling strip are in the non-stationary rolling zone, which is prone to various size, shape and quality defects. In the process of rolling soft and thin strip, a kind of "pseudo-bad flatness" which have similar characteristics with middle wave often appears at the tail of strip, but its mechanism is completely different from that of bad flatness, so the conventional flatness control method cannot solve this problem. For this reason, the mechanism of the problem is analyzed firstly, and it is found that the reason of this phenomenon is the sudden shrinkage caused by the disappearance of tension in the moment of steel throwing. According to the above mechanism, the velocity matching relationship between F8 stand and coiler before steel throwing is optimized, which greatly improves the problem of "pseudo-bad flatness" at the tail of strip and avoids the scratch between strip surface and roller table.
2020 Vol. 55 (9): 64-68 [
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69
YI Ya-li, HAN Xiao-kai, JIN He-rong
Research on mathematical model of asymmetric rolling force of sandwich clad plate
In order to realize the prediction of the asymmetric rolling force of the sandwich clad plate, a force analysis was performed on a stainless steel clad plate in which a thin plate was directly added as an intermediate layer. The rolling deformation zone was divided into five zones according to the deformation characteristics of each metal layer and the change of the rolling frictional direction. The linear distribution of the normal stress and shear stress at the vertical sides of each slab between the layers of the metal was considered. The effects of shear yield stress ratio, roll diameter ratio and friction coefficient ratio on the stress distribution of each layer element and the positional changes of neutral point and connection point under different reduction ratios are studied. Five-pass asymmetric rolling simulation of 316L/Ni/EH40 clad plate is carried out using MSC.Marc finite element simulation software. The stress state of the rolling deformation zone was consistent with the theoretical model. The error between the rolling force and the theoretical calculation value of each pass was within 10%.The results show that the model can improve the accurate prediction of the asymmetric rolling force of sandwich clad plate.
2020 Vol. 55 (9): 69-80 [
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Materials
81
HE Fang, WANG Rui-zhen, YANG Cai-fu, JIA Ya-fei, WU Yan-xin, LI Mian
Ferrite transformation law of Q&P steel during cooling process
In order to study the ferrite transformation of Q&P (quenching and partition steel) during cooling,the ferrite phase transformation thermal expansion data of different cooling rates of Q&P steel with chemical composition 0.2%C,1.25%Si,2.0%Mn was measured on the thermal dilatometer. The soaking hot treatment process was 846 ℃ soaking for 200 s. The thermal expansion data were treated as the relationship between the phase volume fraction and temperature by lever law. The ferrite phase volume fraction and ferrite grain size were measured by optical microscope. Based on the mixed model,the phase boundary migration rate of ferrite was obtained. Combined with the starting temperature of transformation,the end temperature of transformation was calculated by the mixed model. The evolution process of ferrite grain size in the process of transformation was discussed. The calculated value of ferrite grain size was in good agreement with the measured value. The error between the calculated value and the measured value of the end temperature of transformation was within ±15 ℃. The obtained ferrite transformation law can be used to control the ferrite volume fraction in the cooling process of Q&P steel.
2020 Vol. 55 (9): 81-85 [
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86
ZHAN Fang, LIN Tian-zi, YIN Shu-biao, CAO Jian-chun, GAO Peng, LU Chun-xiang
Effect of rolling process on microstructure and properties of high strength anti-seismic fire resistant steel plates
In order to improve the yield strength of construction steel,optimize the rolling process and reduce production costs. Laboratory steel rolling experiments are combined with room temperature and high temperature tensile tests,as well as scanning and transmission electron microscopy observations. The microstructure and mechanical properties of high-strength anti-seismic refractory steel plates under four different rolling processes were studied. The results show that the microstructure of the steel plates are mainly composed of ferrite and granular bainite. When the rough rolling temperature is higher,the yield strength of room temperature and high temperature of the steel plates are higher,and the volume fraction of granular bainite is also large. When the rolling and cooling temperatures are high,the yield strength of the high temperature can meet the mechanical performance requirements of the construction fire-resistant steel plate. With the increase of the opening temperature,the yield strength of the test steel plate is further improved,but the ferrite in the structure is large and the toughness is poor. According to the results of the impact test,it can be found that as the impact temperature decreases,the fracture absorption work of the test steel plate decreases more. The analysis results of the precipitated phase show that the precipitated phases are mainly (Nb,Ti)C and (Ti,Nb,Mo)C,and the size of the precipitated phase is larger.
2020 Vol. 55 (9): 86-96 [
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97
LIU Si-han, WANG Cun-yu, XU Hai-feng, CAO Wen-quan
Superplasticity and microstructure evaluation of cold rolled medium manganese steels
In order to study the superplastic properties of aluminum-containing cold-rolled medium-manganese steel and the evolution of its microstructure under superplastic deformation,cold-rolled aluminum-containing medium-manganese steel was subjected to a high-temperature tensile test at 800 ℃ and the microstructure under different deformation. The results show that the elongations of 0.05C5Mn2Al,0.10C5Mn2Al and 0.15C5Mn3Al steels have reached 740%,850% and 350%,respectively,and they have obtained superplasticity. The EBSD characterization results show that the two cold-rolled microstructures of 0.05C5Mn2Al and 0.10C5Mn2Al are uniform and fine. It has high stability during high-temperature tensile process. During the tensile process,ferrite and original austenite grow uniformly,and the maximum grain size is less than 10 μm. However,0.15C5Mn3Al cold rolled microstructure has band-shaped ferrite. This microstructure is easy to grow abnormally by annexing fine ferrite and original austenite grains,and the size reaches 20 μm after high temperature tensile. By analyzing the relationship between the superplastic behavior and microstructure evolution of three cold-rolled medium-manganese steels containing Al,it is considered that the initially uniform cold-rolled microstructure has high stability which is conducive to superplasticity. Band-shaped ferrite is prone to abnormal growth and not conducive to superplasticity.
2020 Vol. 55 (9): 97-103 [
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104
KANG Di-na, PANG Yu-hua, LUO Yuan, SUN Qi, LIN Peng-cheng, LIU Dong
Constitutive equation for hot deformation of F45MnVS steel
In order to establish the constitutive model of F45MnVS steel which can meet the calculation accuracy,the isothermal compression experiment of the steel was completed by Gleeble-3500 testing machine,and the rheological behavior of the metal was obtained when the deformation temperature was from 800 to 1 000 ℃,the strain rate was from 0.01-10 s
-1
,and the deformation was from 0 to 70%. The results show that the change of stress with strain has the characteristics of dynamic recrystallization,and the stress increases with the decrease of deformation temperature and the increase of strain rate. Based on the analysis of parameters between Arrhenius and Zener-Hollomon equation,the activation energy
Q
of thermal deformation was obtained,and the peak stress constitutive model was established. Based on the stress dislocation relationship and dynamic recrystallization dynamics,the mechanism constitutive model of two stages of work hardening dynamic recovery and dynamic recrystallization was established,which was used to describe the relationship between stress and strain at different deformation temperature and strain rate. The model was used to predict the stress and strain under different deformation conditions. Compared with the experimental results,the correlation coefficient was 0.997 and the agreement was high.
2020 Vol. 55 (9): 104-110 [
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111
SUN Deng-yue, WANG Peng-he, XU Shi-min, RU Wen-di, SUN Chen-guang
Properties of WC-20Cr-7Ni coating by plasma spraying on straightening roller of continuous casting machine
Straightening roller as the important component of continuous casting machine,whose working condition is poor and the wear is serious. In order to reduce the wear of roller,the WC-20Cr-7Ni coating with thickness of 0.2 mm was prepared on the surfaces of straightening roller and H13 steel plate by plasma spraying technology. The thermal shock resistance and abrasion resistance of the WC-20Cr-7Ni coating were investigated respectively through water quenching thermal shock and rolling experiments. Metallographic analysis and hardness testing were performed on the samples before and after thermal shock. The results show that the porosity of WC-20Cr-7Ni coating is low,the resistance of wear and thermal shock are both excellent,which can effectively improve the service life of the straightening roller.
2020 Vol. 55 (9): 111-117 [
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254
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275
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Environmental Protection and Energy
118
GUO Rui-hua, WANG Shu-huan, LI Chen-xiao, ZHOU Chao-gang, ZHAO Ding-guo, CHEN Hu
Experimental on coke reduction dephosphorization converter slag gasification dephosphorization
In order to solve the problem that the phosphorus mass percent in the dephosphorization converter slag is too high to directly realize the recycling in the converter,the hot state experiment of coke reduction dephosphorization converter slag was carried out in the laboratory,and the effects of different carbon equivalent,temperature,alkalinity,FeO mass percent,and nitrogen flow rate on the gasification dephosphorization rate were systematically studied. The results show that the gasification dephosphorization effect using the twice carbon equivalent is better,and the gasification dephosphorization rate gradually increases with the increase of temperature,reaching 68.6% at 1 733 K;The gasification dephosphorization rate gradually increases with the decrease of alkalinity. When the alkalinity is controlled to 1.4,the gasification dephosphorization rate can reach 45.6%. When the FeO mass percent varies from 10% to 30%,the gasification dephosphorization rate increases first and then decreases with the increase of FeO mass percent. When the FeO mass percent is 25%,the gasification dephosphorization rate can reach 43.5%. The gasification dephosphorization rate first increases and then decreases with the increase of nitrogen flow rate. When the nitrogen flow rate is 80 L/h,the gasification dephosphorization rate is 45.37%. From SEM analysis results,it can be seen that phosphorus in dephosphorization slag is mainly enriched in silicon and calcium enrichment areas,and there is no special rule of phosphorus distribution in micro-areas after gasification dephosphorization reaction.
2020 Vol. 55 (9): 118-124 [
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125
WANG Xin-dong, CHANG Jin-bao, LI Jie
Development and application of "Interface" technology of billet continuous casting-rolling
In this paper, the development and application of hot delivery and charging, direct rolling and endless rolling technology of casting-rolling of billet are introduced with the view of metallurgical process engineering. Taking the process of billet continuous casting and rolling as an example, the key elements which influence the energy dissipation of the process were studied and the key technologies to realize "laminar flow" operation of material flow, energy flow and information flow in the typical dissipative system of the metallurgical process were discussed. Through theoretical analysis and factory examples, it is proved that by optimizing the "interface" connection of continuous casting and rolling, establishing the optimized operation network of material flow, energy flow, and information flow and realizing efficient operation, the energy dissipation of the whole process can be significantly reduced, a large number of energy sources can be saved, to realize cost reduction, efficiency increase, energy conservation, and emission reduction, and green production.
2020 Vol. 55 (9): 125-131 [
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