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2013 Vol. 48 No. 9
Published: 2013-09-15
Technical Reviews
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technical Reviews
1
WANG Xin-hua
Non-Metallic Inclusion Control Technology for High Quality Cold Rolled Steel Sheets
The non-metallic inclusions which can create surface defects of the cold rolled sheets mainly are the large sized Al2O3 clusters, “Ar+Al2O3” typed inclusions and the entrapped mold powder particles. Nowadays, under normal and stable casting conditions, the inclusions formed due to the mold powder entrapment can be well controlled. Among various types of unsteady cast slabs, the quality of the first slab of the cast is deteriorated most severely. In the bottom slab of the cast, inclusions from the mold powder entrapment are much more than the normal cast slabs. Also, the inclusions from mold powders are more in the slabs cast during heat/heat ladle exchange and during SEN quick change than the normal cast slabs. It is noted that, in Shougang Jingtang Iron and Steel Co., Ltd., the number density of the large inclusions decreases with increasing the casting speed when the casting speed is 1.0-2.0m/min. The harmful inclusions larger than 100μm were found mostly in 0-2mm sub-surface layers of the slabs. To produce surface defects free sheets for automotives, slab surface conditioning treatment should be adopted.
2013 Vol. 48 (9): 1-7 [
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Raw Materials and Ironmaking
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SHI Shi-zhuang， WU Qiong，BI Xue-gong，ZHANG Hui-xuan,SUN Chao-qi, LU Shuai
Prediction of Coke Thermal Properties and Analysis of Influencing Factors
In order to predict, improve and regulate the thermal properties of coke in accordance with the demands, and also to make clear the effect of various factors on the thermal properties, prediction models of coke thermal properties were proposed on the basis of analysis of influence rules of the various factors and by means of ninety six runs of test for sixteen blending schemes, using bulk density (d), coalification degree index (Vdaf), caking property indices (G and Y) and mineral catalytic index (MCI) as input variables. The models simultaneously concern the two kinds of coke making processes, i.e. coal top-charging and coal side-charging, reveal intrinsic rules of influencing coke thermal properties by various factors, determine the optimal value of various factors and the best attainable value of coke thermal properties. The models make prediction with higher accuracies, apply to wider areas, and could be used not only to the traditional coke making process but also to the tamping coke making process. The impact of various factors, ways to improve coke thermal properties and the method of ferro-coke development were also analyzed.
2013 Vol. 48 (9): 8-15 [
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JIN Ke, FENG Yan-hui , ZHANG Xin-xin, WANG Ming-deng, YANG Jun-feng , MA Xiao-bo
Numerical Analysis on Flow Distribution in Regenerator of Coke Oven Heating System
According to the structure and process characteristics of regenerator in coking oven, a three dimension mathematical model was built to describe the flowing process in the flue and ramp area, the model was numerical solved and the law of the gas flow in regenerator was revealed, the pressure, flow distribution of the oulet in the flue and ramp area were obtained. The results show that the relative pressure along the length direction of the coking oven increases gradually; when the structure size is the same, the outlet flow of the grate brick which is nearer to the center of regenerator was greater. As the symmetry of the structure, law of the gas flow at the coke side in regenerator is the same as the machine side; it is good for the temperature uniformity along the length direction to adjust the size of grate brick legitimately. From machine to coke side, the gas flow at the outlet of the ramp area is increasing gradually except the furnace end; they are larger than others because of the greater heat dissipation.
2013 Vol. 48 (9): 16-20 [
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XIANG Ru, XUE Gai-feng, ZHAN Li-zhi, CHEN Peng, BAO Jun-fang
Technology of Increasing Blending Ratio of Weak Caking Coking Coal
By comparing microstructure of coke coked from different size gas coal and lean coal, the mechanism of coal grain size adjustment was deeply discussed. The results show that the grain size of gas coal cannot oversize and also cannot undersize, it should be controlled in a reasonable size, which can improve coke quality when it participated in blending. The coke quality also can be improved by reasonable comminuting lean coal. The optimization blending of increasing weak caking coal was also discussed. The good coke quality can be obtained through using the technique when the blending ratio of gas coal and lean coal is up to more than 30%.
2013 Vol. 48 (9): 21-25 [
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Steelmaking
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WANG Chao,,ZHANG Hui ,,WANG Ming-lin,,PEI Hong-bin,MA Zhong-wei,,ZHAO Pei
Physical Simulation of Flow Field in the Round Mould With EMS
A physical model was established with 1∶1 ratio, taking a 500mm round billet continuous casting mould in a plant as prototype. The effect of EMS on the flow field and inclusion behavior in the mould was studied. Mechanical agitation was applied with a stirring paddle to simulate electromagnetism generated by M-EMS. The results shows that M-EMS makes the molten steel gets a certain tangential velocity that improves the distribution uniformity of steel temperature of stir zone and also promotes the slag melting and moving. The flow at the outlet is turned to be radial from axial direction which helps decrease the impact depth of the steel flow, then the inclusions are better removed and the high temperature zone moves up. The increase extent of the inclusion remove rate is not linear with the increase of stirring strength. The highest of inclusion remove rate was obtained with the stirring strength of 48r/min.
2013 Vol. 48 (9): 26-30 [
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GAO Zhong,HAN Chuan-ji,TAO Jin-ming,QIAN Liang,LIU Tai-xin,XU Hong-liang
Analysis and Improvement of the Center Segregation in Continuous Casting Slab Based on QES
Aimed at the situation that the class A center segregation appeared in slab of Tangshan Medium-Thick Plate Co., Ltd., dynamic cooling system and QES that CCTEC developed were applied online. Based on QES, the impact of production process, composition of molten steel and equipments running status on center segregation of class A were investigated. The results show that the class A center segregation has little influence in the content of S, P, C and tundish temperature. But it closely relates to the variation of roll gap, roll gap control and water of secondary cooling zone. Finally, the incidence of center segregation of class A on slab decreases obviously after raising and using the improvement measures.
2013 Vol. 48 (9): 31-36 [
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GUO Jing, CHENG Shu-sen,CHENG Zi-jian,, ZHANG Ying-wei
Effects of Collision Behavior on Al2O3 Based Inclusion Modification After Calcium Treatment for Aluminium-Killed Steel
The steel samples were taken out at different time after calcium-treatment, and the inclusion information in them was monitored by SEM combined with EDS to understand how Al2O3 inclusions were modified during LF refining especially after calcium-treatment for aluminium-killed steel. Another collision mechanism for Al2O3 inclusion modification was proposed: CaO based inclusions precipitate after calcium treatment due to higher calcium concentration around calcium bubble, and then CaO based inclusions and Al 2O3 based inclusion collide together and further react with each other and finally form liquid calcium aluminates. In addition, it points out theoretically that Al2O3 based inclusion could be modified by colliding with CaO based on phase diagram analysis and the mechanism. And the mechanism and rate-controlling step differ from that of Al2O3 based inclusion modification by reduced reaction with calcium. The modification rate of this manner is much fast that Al2O3 based inclusion could be modified well in several minutes. Approximating 21% of Al2O3 based inclusion is modified in this manner in present trials. Finally, it is verified by laboratorial experiment and other researchers′ industrial trials that blowing CaO based powder can also modify Al2O3 based inclusion during secondary refining.
2013 Vol. 48 (9): 37-44 [
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Metal Forming
45
XU Jiang-hua,LI Shan-qing
Flatness Control Algorithm Based on Fuzzy Inference and Its Application
In order to improve the strip flatness quality, flatness control system was developed and applied in the skin pass mill of the continuous annealing line. The flatness control algorithm based on fuzzy inference was used in control system, which can tune the gain factor according to flatness deviation magnitude and variation. When flatness deviation magnitude or variation is big, control algorithm can adjust flatness to set point value rapidly，which can ensure flatness deviation to be always limited to a less extent. Up to now, flatness control algorithm has been applied to two continuous annealing lines in Baosteel, both of them achieve desired control effects.
2013 Vol. 48 (9): 45-49 [
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ZHENG Fu-yin，DI Quan-kang，ZHOU Yu-li，WANG Xiao-chen，CHAO Yue-lin，HOU Dong
Control Method of Four-Slitting Line-Difference of Ribbed Bars
The finishing process of four-slitting rolling of 12mm hot rolled ribbed steel bars was simulated to resolve the lines-difference of 1500-2000mm by tri-dimensional finite element simulation software Deform. The parameters of K6, K5, K4, K3 finishing passes were optimized after the study of the full degree impact on the lines-difference. The result shows that the difference between four lines can be controlled below 200mm in the 90m length.
2013 Vol. 48 (9): 50-53 [
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Materials
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MI Zhen-li,DUAN Lu-zhao,LI Zhi-chao,JIANG Hai-tao,DAI Le-le
Effect of Continuous Annealing Temperature on Microstructure and Mechanical Properties of a High Silicon Dual-Phase Steel
High silicon 590MPa grade cold rolling dual phase steels were trial-developed in laboratory with continuous annealing simulation tester. The effect of different annealing temperature(735 to 835℃) on the microstructure and mechanical properties were research by the SEM, EBSD , TEM and mechanical performance test. The results indicate that annealing temperature has important influence on strength and plasticity. When the annealing temperature is 785℃, material has the well mechanical properties. The microstructures of different annealing temperatures are the same. All of them are ferrite and uniformly distributed martensite on the grain boundaries of ferrite; discrete distribution of austenite in ferrite and martensite grain boundaries is clearly observed used EBSD technology. In addition, dislocation and dislocation roll around the martensite is found by TEM. And it is the important guarantee of continuous yield characteristic of dual phase steels.
2013 Vol. 48 (9): 54-57 [
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YAN Tao,, YU En-lin,, ZHAO Yu-qian
Constitutive Equation for High Temperature Flow Behavior of 55SiMnMo Bainite Steel
The high temperature flow behavior of 55SiMnMo bainite steel was studied by hot compression test at temperatures of 950-1100℃ with strain rates of 0.01-10s-1 using Gleeble-3500 thermal-simulation machine. Experimental results show that peak stress increases with decreasing of deformation temperature and increasing of strain rate; dynamic recrystallization of 55SiMnMo steel occurs with strain rate=0.01s-1 and=0.1s-1, deformation temperature t≥1000℃. According to the experimental results, the influence of hot deformation processing parameter (strain, strain rate and deformation temperature) on flow stress was analyzed. A constitutive equation of 55SiMnMo bainite steel during high temperature deformation was established to describe the stress-strain relationship by considering compensation of strain rate. The reliability of the model was verified by the comparison between the predicted flow stress curves by the model and the experimental data.
2013 Vol. 48 (9): 58-63 [
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NIU Jian-qing, LIU Dong-sheng, CHEN Huan-de
Microstructure and Mechanical Properties of TMCP Processed ABS-EQ47 Plate Steel for Offshore Platform
Continuous cooling transformation behavior of commercial ABS-EQ47 grade platform plate steel was investigated under various austenitizing scenarios, i.e., under the non-deformed, deformed, and simulated heat-affected zone (HAZ) conditions. Plates ranged from 35 to 40mm in thickness were rolled from blocks sectioned from the industrially cast EQ47 steel slab during test-scale rolling trials employing thermo-mechanical control processing (TMCP). Single pass welding processes were also simulated on the TMCP treated plates. The microstructures of the plates consist of mainly acicular ferrite (AF) + refined granular bainite (GB). An excellent combination of strength and toughness is achieved showing yield strength (Rp0.2) greater than 500MPa, tensile strength (Rm) greater than 630MPa, and Charpy impact toughness (KV2) greater than 200J even at -60℃. In comparison with a commercial steel plate with the same composition and, however, treated by conventional quenching and tempering (QT) process, the TMCP plates exhibit better yield ratio and higher tensile strength. The KV2 of the simulated coarse-grained HAZ is higher then 40J at -40℃ as long as the heat input of the simulated heat input is less than 30kJ/cm.
2013 Vol. 48 (9): 64-70 [
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GUO Hui-ying，ZHANG Yu，HE Yu-chun， XU Hong-mei
Development of Low Alloy Seawater Corrosion Resistant Steel
Three kinds of Cu-Mo and Cu-Mo-Cr alloyed steels were designed and melted, and then hot rolled into 20mm thick plates, and finally mechanical property, seawater corrosion resistance and weldability of the rolled plates were evaluated. Salt spray tests with 96, 240, 336 and 500 hours were conducted, and all tested steels shows improved corrosion resistance as compared to SM490A, and the superior corrosion resistance is more pronounced with elongation of testing period. Corrosion resistance increases with increasing Cr content, and the corrosion resistance of the steel with 0.85% Cr increases 59.1% as compared to SM490A. The Cr enriched at inner rust layer can effectively withstands diffusion of Cl-, and thus improves corrosion resistance. Gleeble simulation was executed to evaluate steel weldability without preheating and postweld heat treatment, and the impact toughness of the simulated CGHAZ ≥ 57J with cooling rates of 5-60℃/s, which implies the good weldability of the designed steel.
2013 Vol. 48 (9): 71-76 [
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LIN Teng-chang,ZHU Rong,WANG Cheng-jie,LI Ming-gang
Effect of Trace Bi on Inclusion Morphology in Free-Cutting Steel
The influence of trace element Bi on MnS inclusions aspect ratio in S-Bi free-cutting steel was investigated through using Q500 image analyzer and JSM6480LV SEM. The results show that there are three existing forms of Bi in free-cutting steel: exist alone in steel, be packaged by sulfide and between steel and sulfide. The aspect ratio of MnS in S-Bi free-cutting steel ingot, with w（TO） = 0.032%, 0.022% and 0.024%, w(Bi) = 0.0002%, 0.0010% and 0.0020%, is during 1.0-1.6, which is lower than 1.2-3.2 in w（TO）=0.030% S free-cutting steel. The growth rate of inclusion aspect ratio is less than 1.0 when forging ratio is 2.25. Deformation rate MnS inclusions will decrease when Bi content rising up. It is found that Bi in steel can prevent MnS deformation during forging process.
2013 Vol. 48 (9): 77-80 [
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Environmental Protection and Energy
81
ZHANG Jian-liang,TANG Yun-teng,WANG Guang-wei, ZUO Hai-bin
Effect of CeO2 and Its Composite Catalyst on Combustion of Pulverized Coal
The effect of CeO2 and its composite catalyst on combustion characteristics of pulverized coal was investigated by thermogravimetric analysis. The experiments of different catalyst additive amount and components were conducted from room temperature to 900℃ in air. The results show that CeO2 can promote precipitation and combustion of volatiles and combustion characteristics of bituminous varied in different additive amount of CeO2. The combustion characteristics of bituminous with 4% CeO2 are improved obviously. Different catalysts can play different roles in combustion of anthracite. MnO2 promotes combustion of volatiles and CeO2 performs well in residue carbon combustion. Ce-Fe-Mn series composite catalyst shows better performance than the single one and the composite catalyst CeFeMn(3∶1∶1) performed best. Kinetic parameters were calculated by Coats-Redfern model. The value of reaction rate constant of pulverized coal with CeFeMn(3∶1∶1) is higher than others.
2013 Vol. 48 (9): 81-86 [
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