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2017 Vol. 52 No. 3
Published: 2017-03-15
1
SUN Ji-quan，TANG Di，MI Zhen-li，WANG Yi-de
Service-oriented transitions boosting supply-side reform of steel industry
Steel material is the essential basic guarantee for national economy and national defense construction. In recent years the demand for steel material growth slowed down and the structural adjustment was in practice， because of worldwide economic crisis and new normal of China’s economy. Through analysis the plight of China’s iron and steel industry resulted from multiple pressures of resources， environment， and excess production capacity， and by referring to some successful transition cases of foreign enterprises， and by listing some transition modes and solutions of domestic enterprises， it is clarified that the service-oriented transition is an effective way for iron and steel industry to set difficulties， as an new strategic development direction and one of new profit growth points. It is also proposed in this paper some transition suggestions and measures which is helpful for that supply-side structural reforms of iron and steel enterprises.
2017 Vol. 52 (3): 1-8 [
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15
GUO Long，ZHANG Xing-zhong，YUE Li-tao，FENG Chang-xi
Improvement on burden distribution of bell-less top in blast furnace
A lot of complex factors were analyzed in the iron making productive on-site in order to deal with the fluctuation of burden distribution laps of bell-less top in blast furnace. The key reason of fluctuation that the feedback angle of selsyn could not correspond to the rotating angle of throttle valve accurately was confirmed in the current study. The mathematic model was built based on the control mode by means of the feedback angle of selsyn. The rotating angle of throttle valve was controlled by the feedback of selsyn instead of the linear displacement of hydro-cylinder. Magnetostrictive displacement transducer was assembled in the hydro-cylinder so as to keep the signal away from outside interference. The linearity error was less than 150 μm when the displacement range of Magnetostrictive displacement transducer was 300 mm. The stability of the burden distribution was improved significantly and the error range of laps between burden distribution and foreman requirement is less than ±0.5 after using the new controlled mode.
2017 Vol. 52 (3): 15-20 [
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20
WANG Yao-zu，ZHANG Jian-liang，LIU Zheng-jian，ZHANG Ya-peng，LIU Dong-hui，DU Cheng-bo
Effects of[w(TiO2)]on mineral structure and softening-melting property of sinter
In order to investigate the effect of[w(TiO2)]on the metallurgical properties of sinter，influences of[w(TiO2)]on mineral structure and softening-melting property were investigated through SEM-EDS and drop test. The results indicated that with the increase of[w(TiO2)]from 1.40% to 3.02% in sinter， the contents of hematite， perovskite， and silicate in sinter increased， while mass of magnetite and complex calcium ferrite gradually reduced. The hematite content increased from 20.69% to 26.05% with crystal phase changing from native hematite to secondary hematite， which had a negative effect on the tumbler strength and low temperature reduction degradation of sinter. Therefore， increase of[w(TiO2)]in sinter （＜2%） contributed to the development of liquid phase， the reduction of fuel consumption，and the increase of the sinter drum strength. Ti in sinter was mainly distributed in perovskite， but less in SFCA and secondary hematite. With the increase of[w(TiO2)]in the sinter， the soften temperature[（t10 and t40）]increased， which was above 1 130 ℃. The soften interval[ΔtA]of sinter containing 1.4%[w(TiO2)]is 195 ℃， while[ΔtA]are more than 200 ℃.
2017 Vol. 52 (3): 20-28 [
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21
ZOU Chang-fei，，YANG Jie-ming，WEI Xian-yi，，LIANG Yu，，YANG Ming，
Microstructure characteristics of spot segregation of 25CrMo steel ingot
The freckle type segregation area of CrMo steel ingot was analyzed in the current study， which show that the elements of segregation area were stretching along the direction of forging with smaller size， the segregation in the primary ingot casting would be called the similar size of the spot segregation but in three dimensions. In this segregation area， with the relatively high element concentration of Cr and Mo， the bainite structures were formed after cooling and distributed in cross with the structures of the ferrite and pearlite in the matrix structure. Besides， the enrichment of inclusions in segregation area was obvious and partial areas existed air hole existed in some areas. The emergence of spot segregation in steel mainly was due to reducing the degree of under cooling at the front of solidified shell. Under constitutional super cooling condition， highly melting point constituent element Cr and Mo will partially enrich on the surface of dendritic with the temperature decreasing， the MnS inclusion in liquid steel was gathered by physical absorption of the surface of dendritic. At the same time，the viscosity of liquid phase in dendritic area increased， leading to the difficult release of gas， which will partially form air hole after solidification. The formation of spot segregation in ingots will be effectively reduced by improving the solidification rate of liquid steel and reducing its retention time in solid-liquid phase region.
2017 Vol. 52 (3): 21-26 [
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27
YANG Wen-yuan，JIANG Xiao-fang，LI Lin，PENG Xiao-yan，WANG Ming-lin，SHI Xiao-qiang
Thermal simulation experiments on scrap melting
In order to find out the melting speed and mechanism of scrap melting， thermal simulation experiments were carried out in 250 kg induction furnace. Steel bars with diameter from 20 mm to 50 mm were adopted for measuring the melting speed with bath temperature of 1 300， 1 400 and 1 600 ℃. Soaking times were determined by the diameter of steel bars. According to the difference of weight and diameter of steel bars before and after soaking in steel bath， the mass melting rates are1.8-4.0，3.5-6.5 and 12.6 g/s， respectively. The radial meting rate are 0.012-0.026，0.035-0.045 and 0.06 mm/s at the temperature 1 300，1 400 and 1 600 ℃， respectively. Convective heat transfer coefficient between the bath and the test bars at 1 400 ℃ is 32 931 W/（m2·℃） and is 32 884 W/（m2·℃） at 1 600 ℃. Convective mass transfer coefficient of carbon is 6.3×10－5 m/s and 6.4×10－5 m/s at 1 300 ℃ and 1 400 ℃. The measured steel bar melting speed，onvective heat transfer coefficient between bath and steel bars and convective mass transfer coefficient of carbon in the thermal simulation experiments are similar to the results of foreign metallurgical workers. These can be treated as the basic data for calculating the scrap melting in steelmaking.
2017 Vol. 52 (3): 27-35 [
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36
CHEN Wei，，YU Xing-wang，，WANG Jia-qi，，WANG Bao-xiang，，CHEN Ying，，MA Jin-hong，
Initiation locations of longitudinal surface cracks on beam blank in mold of continuous casting
During beam blank continuous casting production，lots of longitudinal cracks easily appear on the surface. In order to study the initiation locations of longitudinal surface cracks in the mold，a coupled thermo-elasto-plastic finite element model was established to compute the temperature and stress using the software ABAQUS. The user subroutine DFLUX was applied to simulate the heat transfer and solidification field. The stress-strain field under the influence of thermal stress，the surface friction and the ferrostatic pressure were analyzed by the method of contact algorithm and the restart scheme. According to the results，it can be inferred that the forming locations of longitudinal surface cracks easily appear on the surface，such as the fillet，the web center， the flange tip and the flange center. Moreover，initiation locations forming longitudinal surface cracks should be： position at the fillet at a distance of 200 mm to the meniscus，and the other three sections at a distance of 180 mm to the meniscus.
2017 Vol. 52 (3): 36-41 [
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42
JIN Xin，MENG Zi-yao，REN Ting-zhi，LIU Zhi-wei，LI Jie
Level fluctuation in continuous casting mold based on theory of turbulent submerged jet
Level fluctuation in the mold has great influence on the quality of continuous casting slabs. In order to study the regularity of level fluctuation in the mold，prevent slag entrapment and enhance slab quality，based on the theory of turbulent submerged jet，a theoretical model was constructed to study the flow velocity and the position of impingement point when the flow jet impacted on the narrow face in the mold. An analytical formula was derived to describe the level fluctuation index whose calculated value was later compared with that of the experiment and the result verified the correctness of the established theoretical model. Numerical simulation was applied to investigate the wave under various level fluctuation indexes. It shows that the error between the theoretical value and experimental result ranged from －4% to 2.5%，which could be adopted to evaluate the intensity of level fluctuation in mold. According to the established theoretical model，1.4 m/min was the best casting speed for mold with cross section of 1 000 mm×130 mm. This research is of theoretical significance in the prediction of surface wave and can provide practical guidance in the slab continuous casting process.
2017 Vol. 52 (3): 42-48 [
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49
KANG Yong-lin，ZHU Guo-ming，TAO Gong-ming，ZHANG Si-xun
Digital technology and application of high precision section steel rolling
Advanced theory and technologies，parametric modeling，database management，finite element method and metal forming control，were applied in our study. Parametric pass design CAD system，whole process thermo-mechanical numerical simulation and optimizing CAE system and CAM system of rolls for section steel rolling were developed. All of the systems above were integrated based on the idea of pass parameterization. Thus，a CAD-CAE-CAM system of digital section steel rolling pass design and manufacturing with the database transmitting directly was achieved. The efficiency and accuracy of developing complex section steel were considerably improved and the problem of quality and precision during developing and manufacturing were effectively solved. High precision complex section steel rolling digital technology has been successfully applied in high precision rail rolling and pass optimizing practically，as well as in developing a gantry section steel (J-shaped steel).
2017 Vol. 52 (3): 49-57 [
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58
BAI Zhen-hua，，HOU Bin，SONG He-chuan，LI Bo-yang，DU Jiang-cheng，HUA Chang-chun
Comprehensive optimization setting technology of emulsion flow in cold rolling process
With reference to the problems of fixed emulsion flow distribution，being unble to be adjusted dynamically with the change of rolling speed，this study made a lot of field experiments and theoretical research to study the comprehensive optimization setting technology of emulsion in cold rolling process. The technology fully considered the mechanical and technological characteristics of cold rolling unit，and put forward a dynamic setting method of emulsion flow. The best overall cooling effect of cold rolling unit and uniform cooling capacity among stands were taken as the control targets，the maximum permissible emulsion flow and optimum emulsion flow in theory were taken as constraints，then the cooling capacity coefficient of emulsion was present for the first time. The method was developed to use in a sertain 1 220 five stands cold rolling unit，and obtained good results. The emulsion cooling capacity of each stand was fully utilized，the abnormal increase of the rolling force and rolling pressure upside down caused by inadequate emulsion flow were avoided，creating greater economic benefits for enterprises with further popularization and application values.
2017 Vol. 52 (3): 58-63 [
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64
LUO Zong-an，CHEN Xiao-feng，XIE Guang-ming，WANG Guo-dong，DANG Jun， WANG Guang-lei
Microstructure and mechanical property of vacuum hot-rolled 825 alloy/X65 pipeline steel clad plate
In order to ensure the requirement for H2S corrosion resistance pipeline in the oil and gas transportation fields， the 825 Ni-based alloy and X65 pipeline steel were combined successfully by vacuum rolling cladding （VRC） technique. The VRC is a new type cladding technique based on electron beam welding and hot rolling cladding. Under the condition of high vacuum level， elevated temperature and severe deformation， the excellent metallurgical bonding was performed on the clad interface. Four-layer symmetry rolling of X65-steel 825-steel 825-X65 was used and the microstructures and shear tension properties of the clad interfaces were investigated. The results indicated that the cladding interface was continuous and straight without any porosity and crack， and a thin continuous TiC layer with a small amount of Al2O3 particles was distributed on the interface. Besides， obvious inter-diffusions of Fe， Cr and Ni elements were detected at the interface. The average tension shear strength of the cladding interface reached 404 MPa， and the fracture located at the cladding interface.
2017 Vol. 52 (3): 64-69 [
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WANG Chun-fang，LI Yong，LI Nan，LU Yan， LI Ji-kang
Effect of heat treatment process on critical transformation and CCT curve of AISI4340 steel
The critical transformation temperature of AISI4340 steel was determined by thermal expansion method， and the microstructure and hardness were observed. The effects of heat treatment process on critical temperature and austenite continuous cooling transformation curve（CCT curve） were studied. The results show that the hardenability of the experimental steel is good. The austenite transformation product is bainite when the cooling rate is 0.03 ℃/s. The austenite transformation products are marensite and bainite when the cooling rates lie in range of 0.03-0.78 ℃/s and martensite when the cooling rate is greater than 0.78 ℃/s.[Ac1]and[Ac3]are different with different heat treatment processes and CCT curve is similar.[Ac1]of the unstability initial microstructure is lower than the equilibrium initial microstructure. Effect of different initial microstructure to[Ac1]is larger than[Ac3.]
2017 Vol. 52 (3): 70-75 [
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76
ZHOU Lei，WEI Gang-wu，GAO Yan-xiang，SUN Hua
Development of 30MnVS non-quenched and tempered steel
30MnVS non-quenched and tempered steel for direct cutting is produced by the following processes： 100 t electric arc furnace smelting→LF＋VD refining→320 mm×480 mm bloom continuous casting with soft reduction-controlled rolling and cooling process. The rational chemical composition has been formulated， Other measurements， such as the critical processes of the EAF end-point control， the deoxidization by producing white slag in LF， the addition of nitrogen and sulfur， the modification of sulphide and the casting with full protection at the low overheating temperature， etc. were proposed. The carbon difference on the cross section of steel bar was approximately 0.02%， and the grain size maitained No. 10 grade. Thus， the steel had an excellent combination of strength and toughness， as well as high thermal stability. The impact energy of as rolled steel bar was higher than 160 J. The yield strength was above 620 MPa， the impact energy was above 120 J， and the elongation was higher than 20% after normalizing at 1 160-1 200 ℃， which were much better than that of normal non-quenched and tempered steel.
2017 Vol. 52 (3): 76-81 [
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82
QI Qi-song，，XU An-jun，，HE Dong-feng，，PAN Jiang-tao，
Carbothermic reduction for recycling of iron and chromium from stainless steel slag
The high temperature carbothermic reduction test of domestic stainless steel slag was conducted， reducing valuable metals. The effects of carbon equivalent， basicity， reaction temperature and thermal insulation time on the reduction ratio of Fe and Cr were studied. Results show that the reduction ratio of Fe and Cr improved with the increase of carbon equivalent and reaction temperature and the reduction of basicity. The highest reduction ratio of Fe and Cr reached at 93.92% and 72.76%， respectively. The reduction ratio was low when the carbon equivalent was less， and with the increase of carbon equivalent， the reduction ratio of Cr raised sharply as the reduction ratio of Fe became stable. The reduction of Fe and Cr became less steep when the basicity ranged from 1.4 to 1.2. When the holding time was over 60 min， there was no significant effect on increasing the reduction ratio of Fe and Cr.
2017 Vol. 52 (3): 82-87 [
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88
HU Chang-qing，YAN Long-ge，ZHAO Kai
Model construction and control method for power generation system of parallel sintering waste heat boiler
Focusing on the issues of poor operation stability and higher outage rate for sintering waste heat power generation system，a mathematical model of multi waste heat boilers paralleling operation power system was constructed based on the theory of probability. The influence of the working status of waste heat boilers on the operation stability of the waste heat power generation system was analyzed. The operation program of waste heat boiler and system steady running，and regulation strategy of steam were put forward. Adopted the in situ steam flow data，the results showed that the operation stability of power generation system would be improved through parallel operation of multiple waste heat boilers. For the sintering waste heat power generation system of four sets of waste heat boilers in parallel shared a generator，the system stable operation probability would exceed 0.98 if three or more waste heat boilers were in normal work. When the system steam was insufficient，the stable operation probability of power generation system could reach above 0.96 through the import of steam from steam network.
2017 Vol. 52 (3): 88-92 [
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LIU Bin，PAN Gui-xiang，LI Peng，LIU Hao-ran， JIANG Jia-hao
Vibration analysis of roll system with nonlinear stiffness of hydraulic cylinde
A vertical vibration dynamic model with two degrees of freedom was established considering the nonlinear stiffness constraint action from hydraulic cylinder in the four-high rolling mill process. On the basis of D’Alembert’s principle， the study established the nonlinear vertical vibration equation of roll system contained nonlinear stiffness of hydraulic cylinder， and obtained the amplitude-frequency response of the vibration system by using the average method. According to the actual parameters of rolling mill， the influences of the nonlinear stiffness of the hydraulic cylinder and the external force on the amplitude-frequency response of the rolling mill were analyzed， the behavior of mill vibration under different nonlinear stiffness was investigated. The study indicated that the larger the nonlinear stiffness of the hydraulic cylinder， the more unstable the rolling mill system. The mill vibration behavior would gradually converge to stability when the nonlinear stiffness was weaker， the mill vibration would be in a state of instability and divergent when the nonlinear stiffness was stronger， which provided a theoretical basis to suppress the vibration of rolling mill rolls.
2017 Vol. 52 (3): 93-99 [
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CHEN Jin-shan，ZHOU Guo-ping
Development and application of mathematical model for process control in continuous pickling line
Functional modules of pickling and mathematical models for process control of continuous pickling line were studied in order to increase stability and pace of production for continuous pickling， together with good surface quality after pickling. According to the principle of statistics， mathematical models of free acid concentration， Fe2+ concentration， and total acid concentration were established with fitting and regression analytical method， and then the control accuracy of acid concentration has been effectively improved. Meanwhile， the combined method between fuzzy control and conventional PID control was adopted to control the acid temperature， which eliminated the oscillation and overshoot during the control process of the acid temperature， and so the control accuracy of acid temperature control was greatly increased. The application results showed that the developed mathematical models for process control of continuous pickling line had high computational accuracy and high reliability， and could completely satisfy the requirement of process control of pickling for the production of high strength steels for automobiles， and was suitable for practical production.
2017 Vol. 52 (3): 100-107 [
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