钢铁研究学报(英文版)
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2014 Vol. 21 No. 7
Published: 2014-07-15
Metallurgy and Metal Working
637
Dian-hua ZHANG,Jian-zhao CAO,Jiu-jing XU,Wen PENG,De-wen ZHAO
Simplified Weighted Velocity Field for Prediction of Hot Strip Rolling Force by Taking into Account Flattening of Rolls
The weighted velocity field was simplified for analysis of hot strip rolling. Using the field and GM (geometric midline) yield criterion, the deformation power, friction power and shear power were obtained respectively. Summing the partial power contributions, the total deformation power for strip rolling was presented. Then, by minimizing the power function, the rolling force was obtained; meanwhile, considering the effect of roll elastic flattening, iterative calculation of the roll radius was carried out until the radius was convergent. On-line data were compared with the calculated results to verify the model accuracy. It was indicated that the calculated rolling forces were basically in agreement with the measured ones since the maximum error was less than 10.0%. Moreover, the effects of various rolling conditions such as thickness reduction, friction factor and shape factor, upon separating force, location of neutral angle, and stress state coefficient were discussed systematically.
2014 Vol. 21 (7): 637-643 [
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644
Lei RAO,Jian-hua ZHAO,Zhan-xi ZHAO,Gang DING,Mao-peng GENG
Macro- and Microstructure Evolution of 5CrNiMo Steel Ingots during Electroslag Remelting Process
A comprehensive mathematical model was established and used to simulate the macro- and microstructure evolution during the production process of 5CrNiMo steel ingot by electroslag remelting (ESR) method. Along the ingot height, the macrostructure distribution characteristics changed from vertical, fine columnar grains to tilted, coarse columnar grains, and this transformation process occurred at the very beginning of ESR. In the cross section of the ingot, there were three grain morphology regions and two grain type transition regions from the outside to the center of the ingot. These regions were the fine columnar grain region, columnar competitive growth transition region, coarse columnar grain region, columnar to equiaxed grain transition (CET) region, and coarse equiaxed grain region. The influence of the remelting rate on the macrostructure and microstructure was investigated using a series of experiments and simulations. The results showed that a low remelting rate could produce a small grain growth angle (GGA); the average secondary dendrite arm spacing (SDAS) firstly decreased and then increased as the remelting rate increased. An excessively high or low remelting rate can increase the GGA and average SDAS in ingots. Thus, the remelting rate should be controlled within a suitable range to reduce composition microsegregation and microshrinkage in the ingot to produce an ESR ingot with satisfactory hot forging performance.
2014 Vol. 21 (7): 644-652 [
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653
Xiang-dong XING,,Jian-liang ZHANG,Zhen-yang WANG,Ke-xin JIAO,Xing-le LIU,Shan REN
Reduction of Pyrite Cinder Pellets Mixed with Coal Powder
Direct reduction of pyrite cinder in a rotary hearth furnace (RHF) was studied under the condition of laboratory simulation. Effects of reduction temperature, reduction time, molar ratio of carbon to oxygen, and CaO addition on metallization rate as well as compressive strength of the pellets after reduction were discussed. The results showed that the metallization rate and compressive strength were 93.9% and 2160 N per pellet respectively under the conditions of the reduction temperature of 1200 ℃, the reduction time of 16 min, and the molar ratio of carbon to oxygen (xC/xO) of 1.0; adding 2.5% CaO was beneficial to sulfur enrichment in slag phase of pellet, and metallization rate increased slightly while compressive strength decreased.
2014 Vol. 21 (7): 653-659 [
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660
Jian-hua LIU,Chang-ling ZHUANG,Xiao-ning CUI,Guo-xuan WANG,Quan-de GAO,Yan YANG
Inclusion Distribution in Ingots Investigated by Dissection
Inclusion distribution in ingots was studied by dissection of a 16.8 t P12 ingot and a 5.0 t H13 ingot, with the analysis of T［O］, original position statistic distribution analysis (OPA), metallographic microscope static analysis and small sample electrolysis. The results showed that the inclusions in ingots were uneven; a positive segregation area was found in the center and lower part of the ingot, while a negative segregation area was present in the central part of ingot top; inclusion segregation in a large size ingot was severer than that in a small one. A new concept, named inclusion segregation index, was put forward to quantify the segregation degree of inclusion. It was found that the segregation indexes drawn from T［O］ analysis and OPA fit well, but they were different from those obtained by metallographic microscope static analysis and small sample electrolysis in the investigation of P12 ingot, which contained a higher sulfur content; while the segregation index drawn from T［O］ analysis was close to that from metallographic microscope static analysis in the H13 ingot with a lower sulfur content.
2014 Vol. 21 (7): 660-665 [
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666
Azza Ahmed,Hossam Halfa,Mohamed K. El-Fawakhry,Hoda El-Faramawy,Mamdouh Eissa
Parameters Affecting Energy Consumption for Producing High Carbon Ferromanganese in a Closed Submerged Arc Furnace
The power consumption is considered to be the most important factor affecting the production cost of ferromanganese alloy. Different parameters affecting the energy consumption for industrial production of high carbon ferromanganese HCFeMn were investigated in a closed submerged arc furnace. The analysis of industrial data revealed that the most energy-consumed factors were the direct reduction by solid carbon, Boudouard reaction, metal and slag formation, and decomposition of fluxing materials (limestone and dolomite). To reduce the energy consumption and minimize the energy losses in the production process of HCFeMn, it was recommended to use Mn blend with minimum Mn to Fe ratio of 6 and lower SiO2 content or higher basicity. The added coke must be adjusted according to the material balance to prevent the over-coke and to minimize the highly endothermic “Boudouard reaction”. In addition, it was recommended to work at basic slags with the ratio of (CaO+MgO) to SiO2 equal to 1.0-1.2 instead of much higher slag basicity. Furthermore, the mass losses had to be minimized through adjusting the handling and charging process and to take care of all metal produced.
2014 Vol. 21 (7): 666-672 [
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673
H. P. Tiwari,P. K. Banerjee,V. K. Saxena,S. K. Haldar
Effect of Indian Medium Coking Coal on Coke Quality in Non-recovery Stamp Charged Coke Oven
The maximum possibility of utilizing the Indian coking coals and inferior grade coking coal for producing metallurgical coke through non-recovery stamp charging technology was investigated. Indian indigenous coals contained low percent of vitrinite (＜50%) and higher content of ash (＞15%) compared to imported coking coal. Therefore, the selection of appropriate proportion of different types of coals was a major challenge for coke makers. Coal blend selection criterion based on a single coefficient, named as composite coking potential (CCP), was developed. The use of increased proportion of semi-soft coal (crucible swelling number of 2.5) and high ash (≥15%) indigenous coal in the range of 20%-35% and 20%-65% respectively in the blends resulted in good quality of coke. Plant data of a non-recovery coke oven were used for developing and validating the model. The results showed that the coke strength after reaction (CSR) varied in the range of 63.7%-67.7% and the M40 value was between 81.8 and 89.3 in both the cases.
2014 Vol. 21 (7): 673-678 [
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Material
679
Hao WANG,Chang-sheng LI,Rui-bin MEI,Gang HUO
Effect of Ball Scribing on Magnetic Shielding Efficiency of Grain-oriented Silicon Steel
Magnetic shielding of grain-oriented silicon steel was investigated. Ball scribing with spacing of 2 to 16 mm was performed at peak flux densities of 8.0 mT to 1.3 T. Magnetic shielding efficiency was calculated, including absorption, reflection and inner multi-reflection shielding efficiencies. Magnetic shielding efficiency (MSE) increase ratios after different scribing spacing were compared, and thickness requirement to achieve absorption shielding of 50 dB was also calculated. The results show that magnetic shielding efficiencies of C711 and H668 silicon steels increase by 4.79 and 3.15 dB respectively after scribing of 16 mm. Before scribing, shielding efficiency of H668 steel was higher than that of C711 steel, while after scribing, both absorption and shielding efficiency gaps were largely abridged between C711 and H668 steels. Plate thickness of C711 steel could be reduced from 3.18 mm without scribing to 2.20 mm after scribing of 16 mm. There is no apparent thickness reduction at lower flux densities; while the peak flux density is above 0.3 T, the shielding effect becomes apparent, and the thickness could be reduced from 2.28 mm without scribing to 1.70 mm with scribing spacing of 16 mm. Magnetizing process and its effect on variation of magnetic shielding were also analyzed.
2014 Vol. 21 (7): 679-684 [
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685
Yu-guang ZHAO,Jia-tao ZHANG,Juan TAN,Bing-dong MA
Microstructure Refinement and Property Improvement of Metastable Austenitic Manganese Steel Induced by Electropulsing
Grain refinement efficiency of electropulsing treatment (EPT) for metastable austenitic manganese steel was investigated. The mean grain size of original austenite is 300 μm. However, after EPT, the microstructure exhibits a bimodal grain size distribution, and nearly 70vol.% grains are less than 60 μm. The refined austenite results in ultrafine martensitic microstructure. The tensile strengths of refined austenitic and martensitic microstructures were improved from 495 to 670, and 794 to 900 MPa respectively. The fine grained materials possess better fracture toughness. The work-hardening capacity and wear resistance of the refined austenitic microstructure are improved. The reasonable mechanism of grain refinement is the combination of accelerating new phase nucleation and restraining the growth of neonatal austenitic grain during reverse transformation and rapid recrystallization induced by electropulsing.
2014 Vol. 21 (7): 685-689 [
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690
Chen LING,Li XIANG,Sheng-tao QIU,Yong GAN
Effects of Normalizing Annealing on Grain-oriented Silicon Steel
The grain-oriented silicon steel is a kind of important magnetic materials with low iron loss and high induction. Hot band normalizing annealing is an important process which influences the microstructure and the development of the inhibitors. The effects of different annealing temperatures and cooling conditions on the inhibitors and microstructures of normalizing annealing band were investigated. The microstructure and different kinds of the inhibitors, i.e., AlN, AlN+CuxS+MnS, and TiN, were discovered. The result shows that a suitable cooling condition leads to more nano-scale inhibitors and uniform microstructure of the normalizing annealing band and consequently results in better magnetic properties.
2014 Vol. 21 (7): 690-694 [
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695
Zi-cheng ZHANG,Ken-ichi MANABE
Influence of Heat Treatment on Hydroformability of TRIP Seamless Steel Tube
A low-carbon TRIP seamless steel tube, which is expected to be used in the hydroforming process, was successfully fabricated using piercing, cold-drawing and two-stage heat treatment process. The two-stage heat treatment is one crucial step because it significantly affects the microstructure and mechanical properties of TRIP seamless steel tube. In order to obtain the TRIP seamless steel tube with high hydroformability, several different heat treatment processes were conducted. The effects of heat treatment conditions (intercritical annealing (IA) and isothermal bainite treatment (IBT)) on the TRIP seamless steel tube hydroformability which was determined by free hydraulic bulge test were analyzed. Two different internal pressure boosting velocities of 0.2 and 0.5 MPa/s of free hydraulic bulge tests were adopted to determine the effective stress vs. effective strain curve of TRIP seamless steel tube. The results showed that for the predetermined IA condition, the maximum bulge height increased, but the maximum burst internal pressure decreased, with the increase of IBT holding time from 4 to 6 min. For the predetermined IBT condition, the maximum bulge height decreased, but the maximum burst internal pressure increased, with the increase of IA holding time from 5 to 10 min. By analyzing the free hydraulic bulge test results, it was found that the maximum bulge heights of TRIP seamless steel tubes with the internal pressure boosting velocity of 0.5 MPa/s were higher than those when the internal pressure boosting velocity was 0.2 MPa/s. This means that an appropriate deformation rate should be chosen to obtain the optimal hydroformability of TRIP seamless steel tube. In addition, the effective stress vs. effective strain curves of TRIP seamless steel tubes were obtained with free hydraulic bulge test.
2014 Vol. 21 (7): 695-701 [
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702
Han MA,Shu-lun LIAO,Shi-fang WANG
Effect of Ti on Austenite Grain Growth Behavior in High Carbon Steels
Austenite grain growth behavior of two high carbon steels was observed using Confocal Laser Scanning Microscope (CLSM). Apparent austenite grain sizes for different holding time under a series of temperatures were measured by employing linear intercept method. Experimental results showed that Ti-bearing steel exhibited a much sluggish growth rate compared with Ti-free counterpart, which was attributed to the pinning effect of Ti(C,N) nanoparticles with the size of 20 to 40 nm on austenite grain boundaries. Based on the research conducted by using Transmission Electron Microscope (TEM) observation and Thermo-Calc calculation, Ti(C,N) was confirmed to be the dominant phase at elevated temperature. Some models were introduced to predict the grain sizes of both steels. By comparison, the results predicted by the modified Gladman equation are found to be closest to the experimental results, which could be employed to predict accurately the austenite grain growth of high carbon steels.
2014 Vol. 21 (7): 702-709 [
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710
He-ping LIU,,Bin LIU,Da-zhao LI,Hu-er SUN,Feng-er SUN,Xue-jun JIN
Microstructural Characterization of Welded Joint in Duplex Stainless Steel by Laser Continuous Heat Treatment
Microstructural characterization in fusion zone of the laser continuous heat treatment welded joint was investigated. The results showed that the martensite-like microstructure is the face centered cubic (FCC) crystal structure so that it can be identified as the secondary austenite. The dislocation is observed inside and outside the secondary austenite, whereas inclusion is not found in the vicinity of the secondary austenite. In the fusion zone, there is a kind of carbide precipitate which is identified as M23C6 by the means of transmission electron microscope (TEM). The carbide precipitate is a representative mode of transformation, which can be generated by the eutectoid reaction. Furthermore, the formation mechanisms of the secondary austenite and chromium carbide are analyzed.
2014 Vol. 21 (7): 710-714 [
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715
Gulcan TOKTAS,Alaaddin TOKTAS,Aslan Deniz KARAOGLAN
Mathematical Modeling of Carbon Content and Intercritical Annealing Temperature in DP Steels by Factorial Design Method
2k factorial design is employed to find the mathematical relation between the carbon content and intercritical annealing temperature (IAT) in order to predict the responses namely martensite volume fraction (MVF), microhardness (H), yield strength (YS), ultimate tensile strength (UTS), total elongation (TEL), yield ratio (YR) and Charpy impact energy (CIE) in dual phase (DP) steels. Steels containing different carbon contents (0.085% C and 0.380% C) had been chosen for this purpose. The main advantages of factorial design are its easy implementation and the effective computation compared with the other optimization techniques, which were employed for predicting mentioned responses in the literature. To verify the proposed approach based on factorial design, experiments for verification were performed. The results of the verification experiments and the mathematical models are in accordance with each other and the literature.
2014 Vol. 21 (7): 715-722 [
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