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2019 Vol. 54 No. 5
Published: 2019-05-15
1
ZHANG Jian-jun1，2， MAO Xin-ping 2， WANG Chun-feng3， ZHU Wan-jun2
Development and expection on high-efficiency producing technology of steelmaking in TSCR line
he thin slab continuous casting and rolling technology has developed for nearly 30 years. It has developed from the original single slab rolling mode to the present endless rolling. The continuous application of new steelmaking-continuous casting technologies runs through its entire development process，especially the continuous progress of the high-efficiency production and the slab defect-free technology，which has promoted the development of the thin slab technology. The development of the thin slab continuous casting and rolling production line was briefly reviewed，the development of key technologies of the steelmaking and continuous casting for the thin slab continuous casting and rolling production line was introduced，the characteristics and difficulties of each key technology and the progress made in the development of some key equipments were analyzed，and on this basis the development direction of the steelmaking and continuous casting technology of the thin slab continuous casting and continuous rolling production line was put forward.
2019 Vol. 54 (5): 1-8 [
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WANG Xiao-ai1， JIANG Xin2， GAO Yuan3， HUO Hong-yan3， SHEN Feng-man2
Investigation on fluidity of SFCA and sintering strength based on phase diagram
The fluidity of the bonding phase SFCA （sillico-ferrite of calcium and aluminum） is important for the sintering strength. The fluidity of SFCA with different w（SiO2） was investigated based on the phase diagram analysis in the present work considering that the SFCA has not a certain chemical composition. The experimental results show that ，for different iron ore （different SiO2）， the chemical composition （or basicity） aimed for best fluidity is different； the fluidity of the SFCA is proportional to the amount of liquid， and is inversely proportional to the liquidus temperature. Then， the effects and mechanism of the fluidity and the w（SiO2） in iron ore on the sintering strength were investigated by sinter pot tests. The sintering experiments show that， in case of iron ore with w（SiO2）＝4.30%， the sintering strength is higher in the range of 1.8-2.2 of basicity， while in case of iron ore with w（SiO2）＝12.42%， the sintering strength obviously decreases when the basicity is higher or lower than 2.0 （peak value of basicity）. The fundamental mechanism is due to thermodynamics. The liquid zone is wider for low-SiO2 iron ores （w（SiO2）＝4.30%）. However， the liquid zone is narrower for high-SiO2 iron ores （w（SiO2）＝12.42%）. Therefore， the iron ore with higher w（SiO2） is not proposed being used in the sintering production. The research content and results are important for the application of iron ores and their matching.
2019 Vol. 54 (5): 9-13 [
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ZHANG Lin-lin， FU Gang-hua， GUO Yu-feng， CHEN Feng， ZHENG Fu-qiang
Effect of basicity on quality of green fluxed pellets
Fluxed iron ore pellets， which have a fine metallurgical performance， are the high quality burden for blast furnace ironmaking. In order to investigate the effect of basicity on the properties of green pellets， the hematite concentrated combined limestone powder to adjust the basicity of pellets， then the pelletizing and the drying characteristics of green pellets were carried out. The results show that the drop strength of green pellets is increasing with the increase of basicity， and the crushing strength and drying rate of green pellets have no obvious changes. Meanwhile， the optimum proportioning of bentonite decreased slightly and the decrepitation temperature increased obviously with increasing the basicity of pellets. Compared with the basic experiment， when the basicity was more than 0.6， the optimum proportioning of bentonite decreased to 1.1% from 1.2% and the decrepitation temperature increased by over 50 ℃.
2019 Vol. 54 (5): 14-18 [
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MA Xiao-gang， CHEN Liang-yu， LI Yang
Calculation of convective heat transfer coefficient of hearth cooling stave and furnace heating transfer characteristics
The cooling performance of the hearth cooling stave is mainly reflected by the convective heat transfer between the cooling water and the pipe. For the empirical formula of the convective heat transfer coefficient commonly used in engineering calculations cannot satisfy different flow conditions， which will result in a large analysis error of the thermal stress of the hearth. Therefore， a blast furnace （BF） hearth structure is taken as an example in this article， and the expressions of comprehensive convective heat transfer coefficients of the cooling water in different flow states are deduced firstly utilizing the heat transfer criterion number equation. At the same time， the applicable range of the empirical formula for the convective heat transfer coefficient is discussed. Then， the expression of the comprehensive convective heat transfer coefficient of the cooling water in a laminar flow state while considering the attenuation of the thermal resistance is deduced by the iterative calculation method. Based on these conditions， the thermomechanical basis of the micro-water furnace heating and even the closed-water furnace heating is obtained through the transient heat transfer and cooling analysis of the hearth side stave heat transfer model under furnace heating conditions， which can be used to assess and perfect the initial formulation of the BF furnace heating system.
2019 Vol. 54 (5): 19-26 [
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27
KANG Wei1， JIN You-lin2
Inclusions control in anti-fatigue stress steel
n order to effectively control the inclusion damage in steel with anti-fatigue stress，through the theoretical analysis of the typical harmful inclusions in the fatigue stress steel， some optimizations and improvements have been carried out from the aspects of deoxidation process， refining slag system， calcium treatment process， soft blowing process and casting protection in continuous casting etc， and the corresponding effects have been achieved. The effective control of inclusions in the steel is realized，the shape of inclusions is mainly small spherical and block-shaped，the inclusions are mainly composed of calcium aluminate and MnS composite inclusions，the inclusion size is controlled within 20 μm， of which more than 90% of the inclusions are controlled within 7 μm.
2019 Vol. 54 (5): 27-31 [
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ZHANG Yan-chao1，2， ZHANG Cai-jun1，2， ZHU Li-guang1，2， ZHOU Quan-lin1，2
Numerical simulation of high Mach number oxygen lance under high oxygen pressure
Based on the 100 t converter in a steel plant in the north， a three-dimensional mathematical model of the flow field in the top-blown converter was established using Fluent software to study the dependence of oxygen jets with different high Mach numbers and the velocity distribution of the molten steel in the molten pool. The study found that the high Mach number oxygen lance has a stable curve at Ma＝2.0～2.3， at which the pressure of the supplied oxygen is most optimal. With the rising of the oxygen supply pressure， the maximum velocity of the oxygen jet， the impact diameter and the impact depth of the molten steel surface also increase. The simulation results show that the oxygen jet has the weakest mutual interference between jets under the designed operating oxygen pressure of 1.0 MPa. The oxygen jet has a smaller increase in the impact diameter and the impact depth after the design oxygen pressure is greater than 1.0 MPa. Based on the above research， after the application of the high Mach number oxygen lance in the actual production， combined with the variable gun position and the variable pressure， the molten steel flow at the bottom of the molten pool can be improved， and the converter blowing process can be stabilized， and the slag splash can be controlled.
2019 Vol. 54 (5): 32-38 [
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CUI Jin-xing1， HAN Shi-chao2， SUN Jian-liang1， PENG Yan1
Evolution characteristics of residual stresses in medium-thick plate during thinning process
The redistribution law of the transverse residual stress due to the thinning of the medium and heavy plate was studied to understand the deformation mechanism of the medium-thick plate in service. Based on the theory of the peeling method，the residual stress distribution model and the deflection deformation model in the thinning process of the medium-thick plate were established，and the plate thinning process was simulated by the finite element method. The results of the residual stress distribution and the deflection degree of the plate were compared with those of the finite element simulation，which verified the feasibility of the two methods. Furthermore，the effect of the stress distribution and the thickness reduction on the thinning process was further analyzed. The results showed that both analysis results could reflect the deformation characteristics of the plate thinning process，but the results of the finite element simulation method were more accurate，which changed the restraint state of plate with thinning process. The research results provide a theoretical basis for the rational production design and use of medium-thick plate.
2019 Vol. 54 (5): 39-46 [
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PAN Hong-jiang1，2， QIU Sheng-tao2
Formation of secondary recrystalliztion in columnar-grained high silicon electrical steel
Secondary recrystallization would remarkably change the microstructure and texture of electrical steel，which further influenced its magnetic properties. The microstructure and texture of cold-rolled columnar-grained high silicon electrical steel were investigated by multiple annealing methods. The occurrence conditions，formation reason and control methods of secondary recrystallization were clarified. The results showed that the temperature of secondary recrystallization was ranged between 850～1 000 ℃. The maximum grain size was obtained in the sample annealed at 900 ℃. The reason for secondary recrystallization was determined to be texture inhibition of initial recrystallization. The normal grain growth was inhibited by low-angle grain boundaries，while the grains with high-angle grain boundaries occurred secondary recrystallization by oriented growth due to high energy （HE） and high grain boundary mobility. When the annealing temperature was higher than 1 000 ℃， the secondary recrystallization could be restrained by increasing heating and cooling rates higher than 5 ℃/min.
2019 Vol. 54 (5): 47-53 [
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54
WANG Xiao-hui， KANG Jian， LI Zhen-lei， LI Yun-jie， YUAN Guo， WANG Guo-dong
Effect of isothermal time on microstructures and mechanical properties in hot rolled TRIP steels with low Si and more Al
In order to achieve the industrial application of hot rolled TRIP steels with low Si and more Al，hot rolled TRIP steels with low Si and more Al were set as studied object using scanning electron microscopy，transmission electron microscopy，tensile test and X-ray diffraction to study the effect of different isothermal time on microstructures and mechanical properties of experimental steels. The results show that the microstructures of experimental steels consist of polygonal ferrite，bainite ferrite and retained austenite. With isothermal time increasing，the volume percent of laminar bainite increases，while the volume percent of granular bainite decreases. When isothermal time is 20 min，the comprehensive mechanical properties of experimental steels reach the best，and the tensile strength，the total elongation and the strength ductility balance is 732.25 MPa，36% and 26.36 GPa·%，respectively. The volume percent and carbon concentration of retained austenite initially increases and then decreases，and the experimental steels exhibit excellent work hardening behaviour with isothermal time 20 min.
2019 Vol. 54 (5): 54-59 [
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CHEN Hao1，2， ZHOU Tian-peng1，2， CHEN Ze-jun1，
Tempering temperature effect on microstructure and mechanical properties of 30Cr15Mo1N
In order to explore the evolution of microstructure and properties of high nitrogen martensitic steel during tempering， the tempering treatment of 30Cr15Mo1N high nitrogen steel at different temperatures was carried out. The changes of microstructure and mechanical properties of high nitrogen steel during tempering were studied by OM， XRD， tensile， impact， SEM and TEM. The results show that after 30Cr15Mo1N steel is quenched after 1 h austenitizing at 1 030 ℃ and tempered twice at 150-700 ℃， with the increase of tempering temperature，the phase a matrix gradually recovers and recrystallizes in the microstructure，the body morphology gradually disappeared，and the carbonitrides first precipitated in the form of flakes or rods at the martensite slab boundary，and gradually evolved into a granular dispersion distribution. At 700 ℃，the carbonitride aggregates grow and spheroidize. As the tempering temperature increases，the matrix of 30Cr15Mo1N steel continues to soften，and the precipitation strengthening is continuously enhanced，resulting in less change in strength when tempered below 500 ℃. Based on the mechanical test，it is found that after tempering at 500 ℃，the strength is linear with increasing tempering temperature decline. With the increase of tempering temperature，the U-notch impact absorption of 30Cr15Mo1N steel is basically maintained at the level and then continues to rise. At last，it is concluded that the change of impact performance under different tempering temperatures is closely related to the change of strength and plasticity. The impact toughness is mainly determined by the plasticity.
2019 Vol. 54 (5): 60-67 [
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ZHANG Guo-qiang， HE Xiao-fei， YU Wen-chao， SHI Jie， WANG Mao-qiu
Grain coarsening behavior of high temperature carburizing gear steels
In order to develop gear steel for carburizing at high temperature of 980 ℃，austenite grain coarsening of case hardening steel 18Cr2Ni2Mo with the addition of niobium in contents of 0，0.036%，0.060% and 0.100% was investigated by means of pseudo-carburizing at 930 and 980 ℃. Results show that the grain size of tested steel austenitizing at 930 and 980 ℃ can be significantly refined by niobium addition due to the pinning effect of NbC precipitates，and with the increase of niobium mass percent in steel，grain coarsening at high temperature of 980 ℃ can be evidently hindered. After austenitizing at 980 ℃ for 20 h，the average grain size of the 18Cr2Ni2Mo gear steel with 0.100% Nb addition is still about 26 μm，so the steel can be used for carburizing at high temperature of 980 ℃.
2019 Vol. 54 (5): 68-72，77 [
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LIN Guo-biao， ZHAO Pan， AO Wei
Effect of tempering temperature on microstructure and properties of medium carbon alloy steel 4Cr5MoSiV1Nb
The effect of tempering temperature on microstructure and properties of medium carbon alloy steel 4Cr5MoSiV1Nb was studied in order to optimize properties of the alloy. The results show that the secondary hardening temperature of 4Cr5MoSiV1Nb alloy steel ranges from 300-550 ℃ and the peak value appears at 550 ℃. The hardness of 4Cr5MoSiV1Nb steel reaches 56.3HRC and meanwhile，its impact toughness decreases markedly. The reason for the decrease of impact toughness is that the fine and short bar cementite containing Cr precipitates at grain boundary during tempering. It can be speculated that reducing the segregation of Cr in its parental quenched alloy steel will reduce the precipitation at grain boundaries of the tempered alloy and improve its impact toughness. The addition of trace Nb forms strengthening particles of （V，Nb）C phase. The alloy tempered at 250-350 ℃ can reach the best comprehensive properties higher than 15 J/cm2 impact toughness and 55HRC hardness.
2019 Vol. 54 (5): 73-77 [
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SUN Jian-liang， LI Shuo， JIAO Yun-jing， SUN Meng-qian， ZHANG Xin-you
Large cylinder induction heating process technology based on Curie point effect
In order to improve the insulation effect of the large cylinder induction heating device，a large cylinder induction heating resistor insulation device was designed. In order to improve the induction heating effect of large cylinder，the induction heating process route of large cylinder is studied by considering the Curie point effect of the metal during the induction heating，and an electromagnetic-thermal-stress coupling mathematical model of the large cylinder is established. The effect of the large cylinder induction heating and resistance insulation，the traditional heating process and the heating effect under the induction heating process considering Curie point effect are analyzed based on the finite element method. The results show that the double design of the induction heating resistor insulation device and the induction heating route considering the Curie point effect greatly shortens the thermal insulation time of the large cylinder at the high temperature stage. The maximum equivalent stress of the inner and outer surfaces of the large cylinder during heating is greatly reduced， and the heat treatment effect of the large cylinder is improved.
2019 Vol. 54 (5): 78-85 [
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YIN Bin， LI Wan-ming， WU Shao-peng， ZANG Xi-min， YU Hao-cen
Thermodynamic analysis of Al and Ti element loss in electroslag remelting Inconel718 superalloy
In order to study the influence of various components of slag system on the oxidizable elements Al and Ti in the alloy during the electroslag remelting process of the Inconel718 superalloy，based on the five-component slag CaF2-CaO-Al2O3-MgO-TiO2，through the molecular and ion coexistence theory，a thermodynamic model for the oxidation of Al and Ti in the slag-gold interface during the electroslag remelting process of Inconel718 superalloy was established according to the equilibrium reaction and the material conservation of each component in the slag-metal interface. By analyzing the model and performing slag-metal balance verification experiments on the model results，the validity of the model is verified. The results showed that the change of CaF2 and MgO percent in the slag has little effect on the Al and Ti elements in the alloy. The Al2O3 in the slag has the effect of burning Ti to increase Al，the TiO2 has the effect of burning Al to increase Ti，and the CaO can inhibit the burning of Al element. The slag ratio that can reduce the burning of Al and Ti during the electroslag remelting of the Inconel718 superalloy is：20%-25%CaO，4%-6%TiO2，1%-4%MgO，50%-60%CaF2，and 15%-20%Al2O3.
2019 Vol. 54 (5): 86-94 [
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WANG Chun-mei1， LI Zhi-liang2
Method for improving efficiency of cold rolling logistics
In order to improve the efficiency of cold rolling logistics，strengthen the automatic control ability of logistics equipment，and effectively reduce the invalid operation of logistics equipment. Unified dispatch of material warehouse，intermediate warehouse and finished product warehouse，coordinated control of logistics equipment. Through active acquisition of production scheduling plan and contract plan， pre-processing and manual intervention of cold rolling materials are carried out， which makes logistics scheduling full of planning and forward-looking. Unified control of logistics equipment. enhancing interaction between equipment. Strengthening the coordination and control ability of equipment.
2019 Vol. 54 (5): 95-99 [
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