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2019 Vol. 54 No. 11
Published: 2019-11-15
1
ZHANG Fu-Ming
Prospect and Development Achievements of Blast Furnace Ironmaking Technologies and Equipments in China
In the past 40 years, Chinese iron and steel industry has made great progress, the crude steel production output has ranked first in the world for many years. Chinese blast furnace ironmaking technological equipments have achieved outstanding achievements in large-scale, modernization, high-efficiency, long service life and so on. Since 2000, a batch of super large blast furnaces above 5000m3, large sintering machines above 500m2, large volume coke ovens with battery height 7.0 m and large pelletizing production lines with an annual output of 4 million t/a have been built and put into commissioning in succession, and a series of the key technologies of integrated innovation and independent research have been achieved great achievements in production practice. At the same time of the technical equipments large sizing, a lots of advanced technologies and equipments research and application have been achieved remarkable results, such as blast oxygen enrichment and pulverized coal injection, bell-less top equipment, BF gas dry dust removal, dome combustion hot blast stove and high blast temperature technology, high efficiency and low consumption sintering technology, large scale clean coking technology, and so on. These achievements promote the progress of ironmaking technologies and equipments. Up to the middle of this century, great changes will take place in the situation and steel manufacturing process structure of China’s iron and steel industry. Reduction, greennization, intelligentization and high efficiency will be the main development tendency of ironmaking technology and equipment in the coming period.
2019 Vol. 54 (11): 1-8 [
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Heat transfer characteristics in process of hot sinter vertical cooling
Compared with traditional circulating cooling process,sinter vertical cooling process has the advantages of low air leakage rate and high heat transfer efficiency.A study on the gassolid convection heat transfer characteristics in the process of sinter vertical cooling was carried out in a sintering plant which can offer the hot air and hot sinter using a vertical cooling device. The study shows that the main factors influencing the heat transfer characteristics in the sinter vertical cooling process are the flow rate and the temperature of cooling air. The convection heat transfer coefficient between sinter and cooling air increases with the increasing of the sinter temperature, and also increases with the increasing of the cooling air flow rate and the decreasing of the cooling air temperature. Based on Buckingham theorem, an experimental correlation for describing the heat transfer characteristics between sinter and cooling air is obtained by fitting the experimental data, which can give a good prediction and its average relative error is 7.25%.
2019 Vol. 54 (11): 9-15 [
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LIU Song1,LIU Fulong2，LIU Erhao3,L Qing1,SHI Quan1,LIU Xiaojie1
Optimization of blast furnace parameters based on #br# big data technology and process experience
In order to evaluate the operation of blast furnace more accurately, the guidelines of blast furnace are quantified. According to the characteristics of blast furnace production process, the big data technology to the datadriven analysis of blast furnace production parameters was applied, hot metal production and blast furnace energy consumption, and proposes a new method to optimize blast furnace production parameters. Firstly, the data collection, cleaning, filtering and integration of the historical data of blast furnace in a steel plant are carried out, and the data warehouse of the blast furnace is established. Then, a variety of clustering algorithms are combined to complete the detailed division of the blast furnace condition changes. The combination of process experience and recursive feature elimination algorithm is used to comprehensively select strong correlation variables that can reflect fluctuations in furnace conditions. The statistical method is applied to analyze the optimal range of core parameters corresponding to class a furnace conditions, which is of great significance for guiding onsite production and maintaining the longterm stable and smooth operation of the blast furnace.
2019 Vol. 54 (11): 16-26 [
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WANG Linzhu1,LI Junqi1,YANG Shufeng2,CHEN Chaoyi1,JIN Huixin1
Effect of calcium treatment on characteristics of nonmetallic #br# inclusions in steel containing high Al
The morphology and the composition of inclusion were observed by SEMEDS. The particle size distribution in threedimensional, the intersurface distance and the distribution of inclusions were analyzed by an image software based on the stereology method. The results indicate that there were mainly Al2O3CaO(CaS)complex inclusions and AlN inclusions in the high Al steel after the calcium treatment. As the mass percent of Ca increasing from 0.0004% to 0.0024%, the average size of inclusions decreased from 2.5 to 1.8μm, the number density of inclusions increased by about one time, and the average intersurface of inclusions decreased from 95 to 72μm. Besides, the transformation process of inclusion composition during the cooling process was studied by FactSage thermodynamic calculation and the calculated results were in agreement with the experimental results. The relationship between the nucleus size and the characteristics was analyzed based on the calculation of inclusion nucleation. The factors affecting the inclusion distribution in the steel containing high Al were also discussed.
2019 Vol. 54 (11): 27-32 [
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ZHAO Bin，WU Wei，WU Wei，WANG Chengyi，CUI Huaizhou
Application of top blowing oxygen and powder injection #br# stirring process for hot metal dephosphorization
In order to obtain the best oxygen supply and the relationship between powder consumption and temperature.A new onestep process of the stainless steel smelting with low phosphorus hot metal was realized in a domestic steel plant using a special top blowing oxygen + powder injection agitation dephosphorization process to provide AOD furnace with the highquality stainless steel smelting with low phosphorus hot metal. The production practice showed that the dephosphorization rate increased with the increasing of the dosage of passivated lime powder and iron balls. When the dosage of lime injection was 1012 kg/t, the consumption of iron balls was 25.037.5 kg/t and the oxygen supply was 300400 m3, the dephosphorization rate was above 85%, and the dephosphorization rate decreased with the increasing of w(CaO)/w(Fe2O3). The dephosphorization rate was the largest when w(CaO)/w(Fe2O3)=0.8, most of the dephosphorization rate was over 85% when the w(CaO)/w(Fe2O3) between 0.8 and 1.4, and when the w(CaO)/w(Fe2O3) more than 1.4,the effect was reduced.
2019 Vol. 54 (11): 33-39 [
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CHEN Xingrun1,HAN Shaowei2,GUO Jing2,PAN Jixiang1
Inclusion evolution of 304 stainless steel produced with #br# different LF refining slag basicity
In order to improve product quality of 304 stainless steel, the effect of LF slag basicity on inclusions in the Sikilled 304 austenitic stainless steel during the LF refining and continuous casting process was researched using SEM+EDS analytical methods and thermodynamic calculations combining with industrial practices. The results showed that the mass percent of total oxygen and the inclusion density decrease throughout the process. A highbasicity slag of 1.75 can obtain a lower mass percent of total oxygen and inclusion density, but a higher mass percent of Al2O3 of inclusion and melting temperature. A low basicity slag of 1.53 results in a higher total mass percent of oxygen compared with a highbasicity slag, but lowers the mass percent of Al2O3 and CaO in inclusions and raises the mass percent of SiO2 and MnO in inclusions, lowering the melting temperature of inclusions and improving the deformability of inclusions. For 304 stainless steel products, different production processes can be adopted to meet product requirements.
2019 Vol. 54 (11): 40-48 [
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49
WANG Weihua1,2,LI Zhanjun1,2,CHU Rensheng1,2,CHEN Xia1,2
Hydrogen diffusion in slab for stacking slowcooling
In order to investigate the removal effect of hydrogen element in the slab slow cooling process of a medium plate plant, and finally to prevent the occurrence of white spots and improve the qualified rate of flaw detection, eight slabs with 250 mm×1 600 mm cross section were selected as the research objects according to the Fick′s second law unsteady mass transfer equation, and a twodimensional hydrogen diffusion model for the stacking slowcooling process of medium and heavy slabs was established using the software ABAQUS. The calculation results show that the stacking slowcooling of continuous casting slab is a powerful dehydrogenation measure by utilizing the dehydrogenation peak effect during phase transformation. After 24 to 48 h of the stacking cooling, the dehydrogenation rate of offline continuous casting slab can reach over 84.6% when the stacking slowcooling conditions are reasonable. If the average w (H)= 0.000 1% is taken as the criterion to prevent the occurrence of "white spots", the hydrogen content in the slab can be considered to be in the safe range after 24 h of stacking cooling. If the maximum w (H)= 0.000 1% is taken as the criterion to prevent the occurrence of "white spots", the w (H) in the slab is considered to be in the safe range after 36 h of stacking.
2019 Vol. 54 (11): 49-55 [
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ZHAO Menghao1，LIU Nianfu2，AI Kenan1，ZHANG Dong1，FU Jianxun1
Analysis of rolled cracks on 38MnVS nonquenched and tempered steel
Aiming at the rolling cracks of 38MnVS nonquenched and tempered steel，the twodimensional and the threedimensional morphology of cracks were analyzed by metallographic microscope，scanning electron microscope，energy spectrum. The results showed that there were obvious decarburization layers on both sides of the crack，and a large number of silicomanganese inclusions distributed along the crack periphery and extension area. Small longitudinal cracks were emerged on the surface during the continuous casting，because of the presence of endogenous inclusions，long and irregular silicic manganate inclusions. In the heat transfer and rolling process， these cracks further expansion，forming perforated cracks and leading to the scrap of the whole rolled. According to the mechanism of crack generation，optimizing the slag during the continuous casting process，and canceling the hot transferring and hot charging during the rolling process can effectively control the crack generation and significantly improve the finished product rate.
2019 Vol. 54 (11): 56-62 [
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YU Huaxin1，WANG Dongcheng1，2，LIU Hongmin1，2，XU Yanghuan1，GUO Zijian3
Channel coupling and decoupling of seamless flatness #br# meter for cold rolling strip
Flatness detection is the basis and key to improving flatness quality. To ensure that the strip surface is not scratched，a seamless flatness meter is developed. Because of the structure particularity of the seamless flatness meter，when a certain channel is pressed，a significant interference signals in the adjacent channels will be found， which causes the flatness detection error and needs to be eliminated by decoupling. To solve this problem， a channel coupling concept and an influence matrix model are firstly proposed by mechanics analysis. Then the entries of the influence matrix are obtained through calibration experiments. Finally，the interferences among channels are eliminated using a decoupling equation. The simulation and experiment and industrial application prove that the theory and method proposed can effectively improve the accuracy of the flatness detection and control.
2019 Vol. 54 (11): 63-68 [
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ZHAO Xiaoli1，2，ZHANG Yongjian2，HUI Weijun2，WANG Cunyu1，DONG Han1，3
Hydrogen embrittlement of intercritically annealed mediumMn #br# steel (0.1C5Mn) under different rolling conditions
Although the mechanical properties of mediumMn steels， such as ultimate tensile strength (UTS) and total elongation (TEL) have been significantly enhanced in recent years， many issues related to industrial production and application， such as hydrogen related problems， should be explored further to make them commercially viable to manufacture automobile components. For this purpose，the susceptibility to hydrogen embrittlement (HE) of intercritically annealed medium Mn steel under different rolling conditions were investigated by using electrochemical hydrogen charging，thermal desorption spectrometry (TDS)，slow strain rate tensile (SSRT) test and scanning electron microscopy (SEM). For this reason，the hot rolled and warm rolled 0.1C5Mn steel sheets were annealed at 650 ℃ for 30 min (called the HRA and WRA specimens，respectively). The results show that the HRA and WRA specimens exhibit primarily lathy and lathy+globular duplex microstructures of ferrite and reverted austenite，respectively. UTS of WRA specimens are higher while TEL are lower than those of the HRA specimen，however，a strengthductility balance (UTS×TEL) as high as 33 GPa·% could be obtained for all the three kinds of specimens. Almost all the charged hydrogen is diffusible hydrogen，and the HE susceptibility of HRA is lower than，WRA. SEM analysis of fractured SSRT surfaces revealed that the HRA specimen showed a mixed transgranular plus intergranular fracture along prior austenite grain boundary，while the WRA specimens exhibited a predominant dimples fracture consisting both empty dimples and dimples filled grains，and the latter is basically a brittle intergranular cracking occurring along the boundaries of austenite and/or martensite (formerly RA) grains. The difference in HE susceptibility of the two kinds of specimens is mainly ascribed to the difference of the microstructure and the corresponding fracture characteristics.
2019 Vol. 54 (11): 69-79 [
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YANG Lifang1，WEI Huanjun2，SUN Li1，XIN Ruishan1，MA Cheng1，PAN Jin1
Effect of annealing temperatures on microstructures，mechanical #br# properties and fracture behavior of a coldrolled mediumMn steel
To systematically study the effects of intercritically annealing and austenite reverted transformation annealing on the properties of mediumMn steel and provide the theoretical basis for its practical application，effects of annealing temperature in a range of 650-900 ℃ on microstructures，mechanical properties and fracture behavior were studied for a coldrolled mediumMn steel. The results show that the comprehensive mechanical properties of specimen after intercritical annealing were obviously superior to the specimen by austenite reverted transformation annealing. When annealed at 650-750 ℃，the tensile strength of about 1 000 MPa and product of strength and ductility of above 30 GPa·% were obtained. The fracture exhibits distinct layerlike cracks and massive dimples. When the annealing temperatures were 800-900 ℃，the tensile strength fluctuates greatly in the range of 743-1 154 MPa while the products of strength and ductility were below 10 GPa·%. Meanwhile，the brittle intergranular fracture occurred due to the poor elongation and the fracture surfaces were flat. Annealed at 650 ℃，the microstructures consist of equiaxed/lamellar ferrite and austenite，as well as abundant cementite. With increasing temperature，the cementite gradually dissolved and disappeared，and the volume percent of austenite and equiaxed grains increased. When the annealing temperature was 750 ℃，52.2% austenite was obtained. Martensite was generated at 800 ℃. With further increasing annealing temperature，austenite volume percent decreased，and only 14.6% austenite was retained at 900 ℃.
2019 Vol. 54 (11): 80-87 [
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GONG Zhihua1，2，WANG Liwei3，YAO Bin3，HE Yudong3，
Effect of forging process on microstructure and property of#br# 2Cr11Mo1VNbN heatresistant steel
In order to solve the problem of large difference in transverse and longitudinal properties of 2Cr11Mo1VNbN steel， OM and SEM were used to investigate the evolution of microstructure and mechanical properties of 2Cr11Mo1VNbN martensitic heatresistant steel for super (super) critical blades under different forging processes. The results show that the increase number of upsetting and stretching has little effect on the longitudinal properties including strength，plasticity and toughness. The transverse properties including toughness and area reduction improved by double upsetting and stretching processes. The size of primary NbC decreased during deformation and heating treatment processes，which resulting the decrease rate of crack formation and expansion during impacting test.
2019 Vol. 54 (11): 88-93 [
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YU Xinping，PAN Guangyong，QI Yongjie，HUANG Qinghua，PAN Qiaoyu
Dynamic recrystallization behavior of steel for 17Cr2Ni2Mo gears
The thermal simulation test was carried out on the steel of hot rolled 17Cr2Ni2Mo gears. The dynamic recrystallization behavior of the materials were studied at strain rate=0.01~10 s-1 and hot deformation temperature t=1 050～1 150 ℃，which can provide theoretical guidance for exploring thermoplastic deformation processes of materials. The results show that the flow stress appears as a dynamic recovery or a continuous dynamic recrystallization softening phenomenon after the peak value at a higher strain rate. The flow stress exhibits multiple peaks in the wave and multiple dynamic recrystallization softening occurs at lower strain rates. The dynamic recrystallization critical characteristic strain εc is determined by the work hardening rate with strain curve (θε)，and the εc/εp ratio is statistically between 0.629 and 0.854. It can be seen that εc becomes smaller as the temperature increases as the strain rate is constant. When the temperature is constant，εc becomes larger as the strain rate becomes larger. At the same time，the constitutive equation of flow stress is established，and the average relative error of data verification is 1.705%. Finally，a dynamic recrystallization kinetics model was established，which can provide a theoretical reference for the formulation of related thermal processing processes.
2019 Vol. 54 (11): 94-100 [
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LIU Chenglin1，CAO Jianchun1，ZHOU Huang1，GAO Peng1，
Effect of niobium on transformation of high #br# carbon steel austenite to pearlite
Niobium can significantly ameliorate the structure and improve the performance of steel. At the same time，Nb was also segregation in the steel，which can effectively increase the steel hardenability，shifting the eutectoid point to the right. Therefore，the metallographic method and isothermal heat treatment experiments were used to analyze the microstructure of high carbon steel. It was found that the precipitation and solid solution of Nb would refine the grains，and the addition of Nb would delay the pearlite transformation of high carbon steel and make it. The incubation period was extended. Valence electron cells of two austenite alloys Nb free atoms and Nb atoms were constructed by using empirical electron theory (EET) of solids and molecules，to revealed the Nb on austenite influence from the electronic level. Theoretical results shown that the maximum covalent logarithmic logarithm nA of the two models under 0.86% carbon mass percent were 0.972 5 and 0.962 4，respectively. The addition of Nb would changes the composition of the bonds in the system and combine with C atoms to form new strongest bond C—Nb bonds，thus explained the principle of the formation of NbC. The precipitation of NbC hinders the diffusion process of C in austenite，which delays the formation and growth of pearlite，and directly delays the phase transformation of pearlite，resulted in the CCT moving to the right after the addition of Nb.
2019 Vol. 54 (11): 101-109 [
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SONG Weiming1,2，ZHOU Jianan1,2，LI Shu1,2，YANG Jian1,2
Experimen on coal char reductive decomposition and #br# sintering flue gas desulfurization gypsum
Aiming at the problem of comprehensive utilization of the flue gas desulfurization gypsum，a new method for preparing CaO and SO2 by using the coal char to reduce and decompose gypsum was proposed. The hightemperature reaction characteristics of coal char and desulfurization gypsum were calculated by FactSage 6.1，and the behavior of coal char reduction and decomposition gypsum was theoretically analyzed by a thermogravimetric analyzer. Effects of temperature，coal coke addition and holding time on the gypsum decomposition rate，solid product and gas SO2release were further studied by tubular resistance furnace experiments. The results show that increasing the temperature，increasing the amount of coal char and increasing the holding time can increase the decomposition rate of gypsum. When the amount of coal coke increases from 5% to 20%，the mass percent of CaO and SO2 increases first and then decreases，while the mass percent of CaS always increases. When the coal coke amount is 11%，the content of CaO and SO2 reaches the maximum value. The variation of CaO and SO2 components is mainly affected by the relative contents of CaS and CaSO4. The use of coal char to reduce and decompose gypsum can provide a theoretical guidance for the comprehensive utilization of gypsum.
2019 Vol. 54 (11): 110-115 [
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LI Xiaoming,WANG Yanjun,JIA Lifeng,XING Xiangdong
Effect of stainless steel pickling sludge on bond #br# phase and equilibrium phase of sinter
The most commonly used safety landfill disposal method of the stainless steel pickling sludge occupies land and cannot reuse the valuable components such as nickel and chromium that exist in the pickling sludge. A technical idea of using stainless steel pickling sludge as sintering burdens so as to recycle valuable metals of Fe, Cr, Ni and make full use of the flux components was proposed, expecting to realize the closedcircuit resource utilization of pickling sludge in metallurgical enterprises. The bond phase strength test of iron concentrate added with pickling sludge showed that the bond phase strength increased first and then decreased with the increase of pickling sludge, and the corresponding value decreased with the increase of basicity. When the iron concentrate was added with 10% pickling sludge with the basicity of 1.5 and heating at 1 280 ℃ for 4 min, the content of hematite and magnetite in the sample was the largest while the cuspidine content was the smallest, leading the bond phase strength to reach the largest(15.12 kN). The equilibrium phase sintering test showed that the addition of pickling sludge could improve the sinter quality, and the comprehensive performance of the sinter was the best when the iron concentrate was added with 10% pickling sludge with basicity of 1.5 sintering at 1 300 ℃ for 240 min.
2019 Vol. 54 (11): 116-122 [
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LING Qihui1，ZHANG Wei1，ZHAO Qiancheng1，
Dynamic parameter identification of rolling mill vertical system
An improved particle swarm optimization (IPSO) algorithm was proposed to identify the dynamic parameters of the vertical mill system. Firstly，the stiffness and damping of the vertical system were considered as the Duffing oscillators and Vanderpol oscillators，and the nonlinear dynamic model of the vertical system was constructed. Then the PSO algorithm was improved，and the dynamic parameters of the system were identified by numerical simulation examples with noise or not，which verified the effectiveness of the algorithm. Finally，the vertical system was taken as the research object，and the algorithm was used to identify the vertical mill system dynamics parameter based on the measured data. Comparing the measured displacement，velocity and acceleration signal respectively with the identified displacement，velocity and acceleration signal，reliability of the method to identify vertical system dynamics parameters has proved. Additionally, the method has certain value in the field of engineering applications.
2019 Vol. 54 (11): 123-129 [
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HAN Yi1，XIAO Yao1，MIN Xiangling2,YU Enlin1，LI Dalong1，GAO Ying3
Residual stress and microstructure evolution of high #br# frequency welding of longitudinal pipe
With the rapidly development of crossdisciplines such as steel，metallurgy and electromagnetics in China，the output and quality of welded steel pipes are increasing day by day. The longitudinal pipe induction welding is the key process for producing high frequency welded pipes. Obtaining the more accurate residual stress distribution and microstructure evolution of welded pipes is the key factor to further improve the quality of welded pipes and the concerns of researchers. The effects of heat transfer and microstructure transformation on the stress are considered. For the unique hourglass welding temperature field of the highfrequency longitudinal welded pipe，the evolution process and the residual stress distribution of microstructure in the heat affected zone are quantitatively analyzed. The residual stress distribution is obtained，considering the thermal stress and microstructural stress. The results show that the radial residual stress is smaller near the weld seam，and the axial residual stress is larger. The maximum equivalent residual stress appears in the heat affected zone about 1/2 of the wall thickness from the center of the weld，and the position is related to the shape of the hourglassshaped temperature distribution of the highfrequency induction welding. At the center of the weld，the equivalent residual stress value without considering the change of the microstructure is 1.3 times that of the microstructure change. The distribution of residual stress at the peak of heating temperature and heating range is further quantitatively analyzed. Mastering the characteristics and laws of the highfrequency welding stress and microstructure evolution of welded pipe can provide a theoretical basis for optimizing the design of highfrequency welding process，which is great significance to improving the quality of highfrequency welded pipe further.
2019 Vol. 54 (11): 130-139 [
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