ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Volume 52 , Issue 6
Showing 1-29 articles out of 29 articles from the selected issue
Fundamentals of High Temperature Processes
Regular Article
  • Jiang Diao, Bing Xie, Yonghong Wang, Xu Guo
    2012 Volume 52 Issue 6 Pages 955-959
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Phosphate rock is a vital nonrenewable resource. In order to find new source of phosphorus, the recovery of phosphorus from dephosphorization slag produced by duplex steelmaking process (De–P slag in De–P_De–C steelmaking process) was investigated in the present paper. It was demonstrated that the P-rich phase in dephosphorization slag is difficult to recover effectively by magnetic separation as the reason of P enriched phase inlay in the Fe enriched phase in the slag. The relationship between P recovery ratio and magnetic intensity and slag particle size were also obtained. A series of slag modification experiments were designed to investigate the recovery of phosphorus from high P2O5 content dephosphorization slag produced by duplex high phosphorus hot metal refining. It was found that the addition of SiO2, Al2O3 and TiO2 has a positive influence on the P recovery ratio. However, the P recovery ratio and the concentration of P2O5 in unmagnetized slag showed a reciprocal relationship with increasing SiO2 and Al2O3 content. The P recovery ratio was little affected by the addition of FetO and MnO. Furthermore, the P recovery ratio increased under the stirring condition. 74% and 87% P were recovered in the unmagnetized phases with adding 10% SiO2 and Al2O3, respectively. The results demonstrated that most of the phosphorus in the slag could be recovered through slag modification and magnetic separation.
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  • Yoshinao Kobayashi, Shinji Kodama
    2012 Volume 52 Issue 6 Pages 960-966
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Recent proposal of utilisation of impurities in steel requires preservation of phosphorus in molten steel during its refining process. To know the phosphorus absorbing ability of deoxidation by-product slag having CaO, the phosphorus partition has been investigated between the MnO–SiO2–FetO–CaO–MgO–P2O5 slag and molten iron in this study. The phosphate capacities (CPO43–) for the present slag having CaO content from 4.73 to 19.6 mass% have been determined to be from 2.22×1015 to 1.25×1017 at temperatures from 1843 to 1923 K. Focused on the slag basicity, a thermodynamic discussion gives the capacity as functions of optical basicity (Λ) and temperature (T) as follows;
    logCPO43– = (11300Λ + 54560)/T + 18.30Λ –27.43
    Estimated values of phosphorus distribution ratio ranges from 0.0003 to 0.008 between the present slags and molten iron in practical operations according to empirical phosphate capacities. CaO is useful to improve phosphate capacity of this system to some extent.
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  • Chin Eng Loo, Nigel Tame, Gareth Carlson Penny
    2012 Volume 52 Issue 6 Pages 967-976
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    In iron ore sintering, the properties of the flame front are clearly critical as they determine the heat imparted to the particulate bed and, hence, the strength of the formed sinter. This study explores the factors that influence flame front temperature and also the speed at which it descends down a bed. These two properties are dependent on post-ignition airflow rate and the properties of the sinter mix. Post-ignition airflow rate is a strong function of the pre-ignition airflow rate and the flow resistance of the flame front. This study reiterates the strong dependence of flame front resistance on gas flow velocity, flame front temperature and applied suction. Dense ores produce higher bulk density and lower porosity beds and, as a consequence, they have the effect of slowing down and broadening the flame front. The influence of flame front speed on flame front properties for different ores was also established. For comparable flame front properties results show that sinter basicity has a large influence on sinter strength and yield. Studies of coke combustion efficiency show decreasing values with increasing flame front speed and values increased significantly when sintering YANDI ore. Many of the obtained quantitative dependences will be used to verify a sintering mathematical model that is under development.
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  • Shengping He, Guoxing Zhang, Qian Wang
    2012 Volume 52 Issue 6 Pages 977-983
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    This study introduces the desulphurisation process in RH (Vacuum Recycling Degassing) degasser developed for the soft-killed ultra-low-carbon electrical steels. A CaO–Al2O3–CaF2–based desulphuriser with high sulphide capacity was developed by laboratory experiments of steel desulphurisation and by considering the floatation of Al2O3 (the deoxidation product). The optimum composition of the desulphuriser was found to be mass%CaO/mass%Al2O3=2.5–4, SiO2<5% and F<8% with the melting point lower than 1350°C. To prevent the resulphurisation of steel, the effect of components in the top slag on sulphur partition between slag and steel was calculated using the thermodynamic package FACTSAGE and the range of the components in the top slag was proposed to control the oxygen potential. It was found that FeO+MnO content in the top slag should be controlled below 15% before RH and 10% after RH degassing treatment. Industrial trials were carried out by controlling the FeO+MnO content in the top slag via slag modification and adding RH desulphuriser after final deoxidation. The results from industrial trials showed that resulphurisation was effectively prevented by controlling the FeO+MnO content in top slag below 15% via slag modification. The combination of the top slag modification and the addition of RH desulphuriser consistently produced the ultra-low-carbon steel with sulphur content less than 0.005%.
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  • Shan Ren, Jianliang Zhang, Liushun Wu, Weijian Liu, Yanan Bai, Xiangdo ...
    2012 Volume 52 Issue 6 Pages 984-991
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The influence of B2O3 on the viscosity of high Ti-bearing BF slag is studied under Ar atmosphere from 1773 K (1500°C) to about 1593 K (1320°C). The results show that the addition of B2O3 can decrease the viscosity of high Ti-bearing BF Slag containing UPC, consequently improve its fluidity. With the existence of 1.5% UPC, when the content of B2O3 increased from 0 to 4.1%, the volume fraction of perovskite decreased from 7.7% to 1.6% at 1610 K. Meanwhile, the liquidus temperatures decreased from 1619 K to 1613 K. At a lower temperature, B2O3 was easy to form a eutectic and decreased the viscosity of molten slag. At a higher temperature, some tetrahedron [BO4]5– changed into triangle [BO3]3– which would disintegrate the chains/molecules of molten matrix and decreased its viscosity.
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  • Rita Khanna, Somyote Kongkarat, Seshadri Seetharaman, Veena Sahajwalla
    2012 Volume 52 Issue 6 Pages 992-999
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The carbothermic reduction of alumina was investigated at 1823 K in the presence of molten steel in argon atmosphere for time periods up to 6 hours. A sessile-drop study was carried out to investigate the influence of operating parameters such as carbon/alumina ratio in the substrate, solute carbon level in the melt and reaction time. With molten steel acting both as a reducing agent and a metallic solvent, we report significant reduction reactions in the Al2O3–22.82 pct C/Fe (0.6 pct C) system, associated generation of CO gas and carbon pick-up by molten steel. The refractory substrate thickness was seen to decrease with time and the metal droplet started to flatten out and spread over the substrate after 5.5 hours. The chemical composition of metal deposited on the substrate was determined to be iron-aluminide; small levels of unreduced alumina and residual carbon were also observed. The carbon level in the metal droplet increased steadily to 1.5 wt pct during initial 3 hours and then decreased to 0.6 wt pct after 6 hours indicating carbon consumption; a small step increase in CO gas generation was also observed after 5.5 hours. While the metal droplet was still predominantly iron after 5 hours, it had completely transformed to iron aluminide after 6 hours of contact. The molten metal was also seen to penetrate deep in the substrate. These experimental results provide unambiguous evidence for a macroscopic carbothermic reduction of alumina occurring at 1823 K in the presence of molten steel and for the dissolution of product aluminium in molten steel.
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  • Hitoshi Tsuji
    2012 Volume 52 Issue 6 Pages 1000-1009
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The sampling of raw materials in the rotary kiln, firing experiment by the experimental kiln, and water quenching experiment have been performed, and the clarification of behavior of the reduction and the growth of metal has been attempted by SEM-EDS. In the amorphous serpentine region, NiO has very high reducibility than FeO. The increase in heating temperature above 1273 K allows the fine reduced metal to be confined in the silicate, which causes the extraction by the bromine methyl alcoholic solution to be difficult. This allows the degree of reduction to enter apparently the depression region. However, the increase in heating temperature above 1525 K allows melt to occur, which causes the fine metal to coalesce with each other. Therefore, the degree of reduction leaves the depression region, and approaches the equilibrium values. Low-MgO and high-FeO·NiO silicate is enriched by the fractional crystallization, and thereafter reduction reaction is enhanced. From the result of SEM observation that metals occur from the lower temperature in the low-MgO and high-FeO ore containing much point defect, NiO and FeO in the crystal lattice are reduced via cationic and electronic defect species, the oxygen occurred diffuses toward the crystal surface via vacancies. However, the lack of experimental data of defect chemistry in Ni-ore requires the further investigation. From the fact that the temperature of the melt occurrence coincides with the temperature of metal beginning to grow largely in SEM observation, it is confirmed that the fine metals coalesce with each other via melt to grow.
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Ironmaking
Regular Article
  • Hiroyuki Kurosawa, Shouhei Matsuhashi, Shungo Natsui, Tatsuya Kon, Shi ...
    2012 Volume 52 Issue 6 Pages 1010-1017
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Since the cohesive zone has a great influence on the gas flow in the blast furnace, modeling of the cohesive zone is considered to be an important subject. In the cohesive zone, the softening and melting behavior of ore particles is affected by the load from the upper layer and the temperature distribution, and the pressure drop of the ore layer increases remarkably due to shrinkage of the ore particles. In this study, a model of the cohesive zone considering physical properties such as Young's modulus was developed on the basis of the discrete element method, which can track the individual motions of the numerous particles in a packed bed. To determine the appropriate Young's modulus of ore particles for the cohesive zone, element model calculations for a softening test under load were carried out, with particular attention to change in the void fraction. The optimized value of Young's modulus value was then introduced in the discrete element method and computational fluid dynamics (DEM-CFD) model. The changes of gas flow in the vicinity of the cohesive zone were visually expressed by this model. These results were similar to those of cold model experiments and the burden structure observed in the dissected blast furnace. The influence of the coke rate on the gas flow was also analyzed using the above model. The change in the gas flow under a low coke rate condition could be well recognized.
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Steelmaking
Regular Article
  • Duk-Yong Song, Nobuhiro Maruoka, Govind Sharan Gupta, Hiroyuki Shibata ...
    2012 Volume 52 Issue 6 Pages 1018-1025
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    In steel refining process, an increase of interfacial area between the metal and slag through the metal droplets emulsified into the slag, so-called “metal emulsion”, is one prevailing view for improving the reaction rate. The formation of metal emulsion was experimentally evaluated using Al–Cu alloy as metal phase and chloride salt as slag phase under the bottom bubbling condition. Samples were collected from the center of the salt phase in the container. Large number of metal droplets were separated from the salt by dissolving it into water. The number, surface area, and weight of the droplets increased with the gas flow rate and have local maximum values. The formation and sedimentation rates of metal droplets were estimated using a mathematical model. The formation rate increased with the gas flow rate and has a local maximum value as a function of gas flow rate, while the sedimentation rate is independent of the gas flow rate under the bottom bubbling condition. Three types of formation mode of metal emulsion, which occurred by the rupture of metal film around the bubble, were observed using high speed camera. During the process, an elongated column covered with metal film was observed with the increasing gas flow rate. This elongated column sometimes reached to the top surface of the salt phase. In this case, it is considered that fine droplets were not formed and in consequence, the weight of metal emulsion decreased at higher gas flow rate.
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  • Morshed Alam, Jamal Naser, Geoffrey Brooks, Andrea Fontana
    2012 Volume 52 Issue 6 Pages 1026-1035
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    A computational fluid dynamics (CFD) model was developed to simulate the liquid flow field and surface deformation caused by an impinging shrouded supersonic jet on a liquid bath from the top as used in oxygen steelmaking. Two different computational domains were used to avoid the difficulties that arise from the simultaneous solution of compressible gas phase and incompressible liquid phase. The results were validated against the experimental data and the reasons for any deviation were described accordingly. The effect of shrouding gas flow rates on the axial jet velocity distribution, depth of penetration and velocity distribution of liquid phase were investigated. A high shrouding gas flow rate was found to increase the depth of penetration and liquid free surface velocity which in turn contributes in reducing the mixing time. The mechanism of droplets generation was investigated in detail. The CFD model successfully predicted the formation of surface waves inside the cavity and consequent liquid fingers from the edge of the cavity which were experimentally observed by the previous researchers.1,2) It was shown that the Blowing number theory (NB) fails to predict the droplet generation rate if the cavity operates in the deep penetrating mode. The possible reasons behind this limitation have been discussed using the Blowing number equation and CFD results. Finally, the cavity surface area was found to be the most influencing factor in the generation of droplets.
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  • Dian-Qiao Geng, Hong Lei, Ji-Cheng He
    2012 Volume 52 Issue 6 Pages 1036-1044
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    In order to improve productivity during RH refining, the traveling magnetic field was imposed around the snorkels. The numerical method was employed to investigate the flow, mixing, decarburization and inclusion removal in RH degasser. Numerical results showed that the predicted results agree well with the experimental data. With the increasing current, the circulation flow rate increases and the mixing time decreases. If the current frequency lies in the range of 10–30 Hz, with the increasing current frequency, the circulation flow rate increases while the mixing time decreases. If the current frequency lies in the range of 30–60 Hz, with the increasing current frequency, the circulation flow rate decreases while the mixing time increases. In order to increase circulation flow rate and shorten mixing time, the most effective measure is to apply the traveling magnetic field around the up snorkel, and the second choice is to apply the traveling magnetic field around the down snorkel if the gas flow rate is smaller than the saturation value. Applying the traveling magnetic field can accelerate the decarburization rate during the process, but can not decrease the final carbon mass concentration. For inclusion removal, the most effective measure is to apply the traveling magnetic field around the up snorkel and down snorkel, and to apply the traveling magnetic field around the up snorkel has the minor effect. Furthermore, the application of traveling magnetic field can decrease the maximum inclusion characteristic radius and the related peak value time.
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  • Yuta Hino, Yoshisato Kiyota
    2012 Volume 52 Issue 6 Pages 1045-1053
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The fatigue failure behaviors of high-alumina brick, agalmatolite brick and silica brick refractory materials were investigated at room temperature and high temperature. As a result, fatigue fracture lives at room temperature are almost the same with the order of high-alumina > agalmatolite > silica. In comparison with other inorganic materials, fatigue failure life in this work was slightly higher than that of silica glass and alumina ceramic.
    At high temperatures, it should be noticed that fatigue failure lives of the agalmatolite and silica bricks showed significant increases at the temperatures over 1473 K. On the other hand, the high-alumina brick showed slight increase. The behavior of strain rate at high temperatures proved that the strain rate of the silica brick mainly increased as a result of crack growth, while crack growth in the high-alumina and agalmatolite bricks increased as a result of creep deformation.
    Moreover, the reason why fatigue fracture at high temperatures increased in the agalmatolite and silica bricks was examined in more detail. It was deduced that the longer fatigue fracture lives at high temperatures were related to the generation of a slight amount of liquid phase. The degree, of how long fatigue fracture life would be, was estimated to be dependent on the wettability between the solid phase and liquid phase; poor wettability elongated fatigue fracture life.
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Casting and Solidification
Regular Article
  • Marcelo Aquino Martorano, Caio Fazzioli Tavares, Angelo Fernando Padil ...
    2012 Volume 52 Issue 6 Pages 1054-1065
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The distribution of delta ferrite fraction was measured with the magnetic method in specimens of different stainless steel compositions cast by the investment casting (lost wax) process. Ferrite fraction measurements published in the literature for stainless steel cast samples were added to the present work data, enabling an extensive analysis about practical methods to calculate delta ferrite fractions in stainless steel castings. Nineteen different versions of practical methods were formed using Schaeffler, DeLong, and Siewert diagrams and the nickel and chromium equivalent indexes suggested by several authors. These methods were evaluated by a detailed statistical analysis, showing that the Siewert diagram, including its equivalent indexes and iso-ferrite lines, gives the lowest relative errors between calculated and measured delta ferrite fractions. Although originally created for stainless steel welds, this diagram gives relative errors lower than those for the current ASTM standard method (800/A 800M-01), developed to predict ferrite fractions in stainless steel castings. Practical methods originated from a combination of different chromium/nickel equivalent indexes and the iso-ferrite lines from Schaeffler diagram give the lowest relative errors when compared with combinations using other iso-ferrite line diagrams. For the samples cast in the present work, an increase in cooling rate from 0.78 to 2.7 K/s caused a decrease in the delta ferrite fraction, but a statistical hypothesis test revealed that this effect is significant in only 50% of the samples that have ferrite in their microstructures.
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  • Zhe Tan, Mikael Ersson, Pär G. Jönsson
    2012 Volume 52 Issue 6 Pages 1066-1071
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The flow pattern in the uphill teeming process has been found to be closely related to the quality of ingots regarding the formation of non-metallic inclusions and entrapment of mold flux. The filling conditions can be improved by the utilization of a swirl blade in the runner. The emphasis of this study is to investigate the flow pattern of steel in the gating system and molds with swirl blades implemented at the bottom of the vertical runners during the initial stage of the mold filling process based on the authors' previous study. A two-mold gating system was adopted in the study and different orientations of the swirl blade were studied. In addition, same calculation method and boundary conditions were used to study the flow pattern in the uphill teeming. The results show that more calm filling conditions with less fluctuations are achieved in the molds with the implementation of swirl blades. However, a chaotic initial filling condition with a considerable amount of droplets is created when steel enters the molds. In addition, the orientation of the swirl blades affects the flow pattern of the steel. From the current results it is clear that a parallel placement of the swirl blade is better than a perpendicular placement of the swirl blade. Moreover, the fluctuations of the hump height decrease as the filling proceeds. In addition, the implementation of swirl blades can decrease and stabilize the wall shear stress value in the gating system.
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Instrumentation, Control and System Engineering
Regular Article
  • Jian Li, Yun-Hui Yan, Xing-Hui Guo, Yan-Qing Wang
    2012 Volume 52 Issue 6 Pages 1072-1079
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Nonlinear vibration of axially moving steel strip with tension near the air knife box during continuous hot-dip galvanizing process is investigated. A model of strip vibration for cooling section is established. Governing equations of the model are derived through the Hamilton's principle. Effect of speed, tension, molten zinc, oscillation of touch rolls and nonlinear wind load on strip vibration is considered. The reasonability of boundary conditions of the model is confirmed by comparison of results from theoretical method and numerical simulation. Averaging method is employed in solving the equations and obtaining displacement response. The relation between amplitude near the air knife and production parameters is studied and further solutions of vibration control is presented. The research reveals that speed of strip has noticeable effect on amplitude near the air knife. It will be more difficult to reduce vibration with the increase of speed. Larger tension is in favor of keeping away from peaks of amplitude by using speed adjustment. A scheme of vibration control based upon averaging method can meet the requirement of production. A vibration suppression proposal by improving support stiffness of touch rolls is suggested.
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  • Il Seouk Park
    2012 Volume 52 Issue 6 Pages 1080-1085
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The design of cooling systems for running hot steel plates has received much attention because the mechanical and/or metallurgical properties of final products are greatly influenced by the cooling capacity of the system. Thus many steel makers have largely concentrated on simply increasing the cooling water supply capacity of the system. Some researchers believe that plate cooling is a type of thermal communication between the hot plate and the cooling water or the atmosphere, so they have emphasized the importance of thermal conditions such as the cooling water temperature or air humidity. Actually the cooling process is governed by the basic physics of boiling heat transfer between the hot steel plate and the cooling water. Therefore steel makers should be more concerned about the influence of the design parameters of cooling facilities on the boiling phenomenon rather than the simple increase of the cooling water flow rate. In this study, when the diameter of the nozzle supplying cooling water is changed, its effect on boiling heat transfer has been investigated numerically. The average heat flux, the Leidenfrost-steam-layer thickness, the temperature drop and so on were investigated according to nozzle diameter.
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  • Sho Sonoda, Noboru Murata, Hideitsu Hino, Hiroshi Kitada, Manabu Kano
    2012 Volume 52 Issue 6 Pages 1086-1091
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    A statistical model for predicting the liquid steel temperature in the ladle and in the tundish is developed. Given a large data set in a steelmaking process, the proposed model predicts the temperature in a seconds with a good accuracy. The data are divided into four phases at the mediation of five temperature measurements: before tapping from the converter (CV), after throwing ferroalloys into the ladle, before and after the Ruhrstahl-Heraeus (RH) processing, and after casting into the tundish in the continuous casting (CC) machine. Based on the general state space modeling, the bootstrap filter predicts the temperature phase by phase. The particle approximation technique enables to compute general-shaped probability distributions. The proposed model gives a prediction not as a point but as a probability distribution, or a predictive distribution. It evaluates both uncertainty of the prediction and ununiformity of the temperature. It is applicable to sensitivity analysis, process scheduling and temperature control.
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  • Ilhwan Noh, Sangchul Won, Yu Jin Jang
    2012 Volume 52 Issue 6 Pages 1092-1100
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    In this paper, we propose a non-interactive looper and strip tension control method for a hot finishing mill based on the nonlinear dynamic model. Using the NDOB (nonlinear disturbance observer), the nonlinear looper-tension dynamic system is decoupled into two independent SISO (single-input, single-output) subsystems, and moreover, the model uncertainties and the external disturbances generated from forward slip, strip thickness variation and outgoing strip speed are compensated. A modified TSM (terminal sliding mode) controller is utilized to control the looper angle while the output-feedback controller regulates the strip tension by adjusting the incoming roll speed. Hardware experiment with the 2-stand hardware looper simulator was performed to verify the effectiveness of the proposed approach.
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Chemical and Physical Analysis
Regular Article
  • Mikko Mäkelä, Timo Paananen, Jyrki Heino, Tommi Kokkonen, Sa ...
    2012 Volume 52 Issue 6 Pages 1101-1108
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The utilization of fly ash and ground granulated blast furnace slag (GGBFS) as supplementary cementing materials in cold-agglomerated blast furnace briquetting was investigated. Sample analysis included chemical and mineralogical composition, particle size, and scanning electron microscopy and the produced briquettes were evaluated for mechanical durability (2, 7, and 28 day tumble strength), mineralogy, thermal decomposition (DSC–TG–MS), and disintegration under reducing conditions at 800°C (LTD). Based on the data, only the use of GGBFS with or without fly ash led to satisfactory 28 day mechanical durability compared to the 28 day reference mean value. The most promising series, where 20% of Portland cement was replaced by a three-fold amount of GGBFS, attested to a 30% strength increase at 28 day compared to the respective reference mean value. However, the 48 hour durability values proved inferior to respective references due to the comparatively larger particle size (one fly ash sample) and slower strength development provided by the supplements. The LTD (800°C) values determined by isothermal reduction at 800°C were strongly correlated (R2 = 0.694) with briquette mechanical durability governed by the dehydration of the C–S–H phase at approximately 320–360°C established by DSC–TG–MS. Subsequent to the dehydration of C–S–H, briquette durability was possibly maintained by the formation of an intermediate carbonated phase prior to final breakdown under the conditions of the LTD (800°C) test. Briquette moisture optimization was encouraged by the variation in detected levels, prospectively emphasized by the ability of industrial-scale briquetting plants to operate on comparatively lower moisture levels.
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Forming Processing and Thermomechanical Treatment
Regular Article
  • Duckjoong Yun, Donghun Lee, Jaeboo Kim, Sangmoo Hwang
    2012 Volume 52 Issue 6 Pages 1109-1117
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Precision control of the width of slabs, plates and strips, is vital for product quality and production economy in steel mills. A common practice in the production line is to perform vertical rolling and reduce the width in the roughing mill. However, the formation of so called ‘dog-bone’ at the edge of the slab would affect the final width after horizontal rolling that follows. Therefore, it is essential to predict and control the dog-bone shape. In this paper we present a new model for the prediction of the dog-bone shape during vertical rolling in roughing mills. The model is developed on the basis of the minimum energy principle for a rigid-plastic material and a three-dimensional admissible velocity field. The predictions accuracy of the proposed model is examined via comparison with predictions from finite element simulation and also with experimental data.
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Surface Treatment and Corrosion
Regular Article
  • Jun Wang, Yuanhua Lin, Jing Yan, Dezhi Zeng, Runbo Huang, Zejing Hu
    2012 Volume 52 Issue 6 Pages 1118-1123
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Salt bath nitriding of type 304 austenite stainless steels conducted at low temperature, 430°C, using a complex salt bath heat-treatment. Microstructure and the properties of the nitrided surface were systematically evaluated. Experimental results revealed that when 304 stainless steel subjected to complex salt bathing nitrided at such temperature less than 4 hours, the main phase of the nitrided modify layer was the expanded austenite (S phase) generally. When the treatment times prolonged up to 8 hours and more, S phase was formed and subsequently transformed partially into CrN, and then the secondary CrN phase precipitated. All treatments can effectively increase the surface hardness. And the nitrided layer depth thickened intensively with the increasing nitriding time. The growth of the nitrided layers took place mainly by nitrogen diffusion according to the expected parabolic rate law. Low temperature nitriding can improve the corrosion resistance against diluted hydrochloric acid. After nitriding for 16 hours, the sample has the best corrosion resistance than others though there are many CrN transformed in the layer.
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Transformations and Microstructures
Regular Article
  • Junya Kobayashi, Sung-Moo Song, Koh-ichi Sugimoto
    2012 Volume 52 Issue 6 Pages 1124-1129
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    A new type of 0.2%C–1.5%Si–1.5%Mn ultra high-strength low alloy TRIP-aided steel consisting of lath martensite structure matrix and metastable retained austenite films, “TRIP-aided martensitic steel; TM steel”, was developed by means of quenching and partitioning process. In addition, effects of partitioning temperature and time on the microstructure and retained austenite characteristics were investigated. The matrix structure was composed of two kinds of lath martensite structures, or wide and narrow lath martensite structures. Most of the retained austenite of about 3 vol% was located along the narrow martensite lath boundary. On the other hand, a small amount of fine and needle-like carbides precipitated only in wider lath martensite structure. Partitioning at temperatures lower than 250°C for 1000 s after quenching in oil or ice brine considerably increased carbon concentration of the retained austenite phase to about 1.0 mass%, maintaining volume fractions of retained austenite and carbide. Also, the carbon-enrichment mechanism in the retained austenite was proposed through TEM observation, as well as the carbide precipitation and coarsening mechanisms.
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  • Alejandro Basso, Martín Caldera, Graciela Rivera, Jorge Sikora
    2012 Volume 52 Issue 6 Pages 1130-1134
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The aim of this paper is to study the advantages and disadvantages of using high silicon ductile iron to produce cast parts with “Dual Phase ADI” microstructure. In this study, four ductile irons with different percentages of silicon: 2.4, 3.1, 3.5, and 4.2%, respectively, were used. Samples from each cast were subjected to heat treatment in order to determine the intercritical interval. Significant increase in the upper and lower critical temperatures was found as the amount of silicon incremented. However, the difference between the lower and upper critical temperatures (intercritical interval amplitude) remained nearly constant for all ductile irons.
    The materials were metallographically and mechanically characterized in the as-cast conditions and after full annealing heat treatments. Tensile, hardness and impact properties were determined as a function of the silicon level.
    The results suggest that high silicon ductile iron (Si content ranging from 3.0 to 3.6%) can be used in the manufacture of cast parts with “Dual Phase ADI” microstructures, yielding undeniable advantages in the production process if compared to low and medium silicon ductile irons.
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Mechanical Properties
Regular Article
  • Youngdeuk Kim, Hyunchul Park, Seoung Soo Lee, Chang-Wan Kim
    2012 Volume 52 Issue 6 Pages 1135-1144
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    To date, a variety of analytical and mathematical dynamic models of a rolling mill have been developed, but they were simplified models involving the vertical vibration of the rolls and were not enough to be compatible with actual chatter vibration. In this paper, a mathematical model of a cold rolling mill including the driving system is proposed. The model is reliable enough to be compatible with experimental and theoretical analysis. It took into account the frictional forces between the rolls and the stiffness caused by the roller bearings and the contact between rolls. The joint forces of the spindle were computed from the force equilibrium equations in which the contact stiffness between the gears was approximated in a Fourier series form. To solve the model efficiently, a novel combination of the direct integration method and quasistatic analysis was proposed. The principal frequencies, including the gear mesh and chatter frequencies, predicted by the model were very similar to that determined by experimental and theoretical analysis. Not only the vertical, but also the horizontal vibration was investigated to study the added effect of the horizontal rolling force, frictional forces, and joint forces. The horizontal chatter vibration had a strong effect on the dynamic characteristics, although the chatter frequency was generated both in the vertical and horizontal directions.
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  • Xavier Quelennec, John Joseph Jonas
    2012 Volume 52 Issue 6 Pages 1145-1152
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    Hot compression tests were carried out on three steels: i) a 0.038% Nb-0.11%C microalloyed grade; ii) a Nb-modified TRIP steel; and iii) a Ti-stabilized low carbon steel. The tests were performed at strain rates up to 1 s–1 and over the temperature range 880–1200°C. The initiation of dynamic recrystallization (DRX) was observed under all testing conditions. Two sets of equations were derived from the experimental curves: i) a work hardening relation pertaining to the grains in which DRX has not yet nucleated; and ii) a separate work hardening expression describing the mean flow stress applicable to the grains in which DRX is taking place. With the aid of the temperature and strain rate dependences determined from the data, and using the law of mixtures, extrapolated flow curves were calculated applicable to strain rates up to 100 s–1, i.e. to those involved in strip mill rolling. The simulations show that, once DRX has been initiated, the flow stress is controlled by the kinetics of the softening mechanisms.
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  • Motoaki Morita, Osamu Umezawa
    2012 Volume 52 Issue 6 Pages 1153-1161
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    An accommodation deformation model to relax incompatibility between soft (yielded) and hard (non-yielded) grains was proposed. Dislocation arrays were installed in the soft grain to investigate the effect of secondary slips on accommodating the displacement incompatibility due to the grain interaction at the grain boundary. When a secondary slip in the soft grain is active on the same plane as the dislocation arrays, it can accommodate the displacement incompatibility in almost all orientations. However, a dislocation reflection on the primary slip plane is difficult to adopt for accommodation deformation. When the secondary slip in the soft grain is restricted to a plane without the primary slip, accommodation deformation in the soft grain does not occur. To accommodate the displacement incompatibility at the grain boundary, slip systems in the adjacent grain are required in almost all orientations. Around the orientation at which the secondary plastic deformation is the hardest to achieve, three slip systems are operating in areas of accumulation with high displacement incompatibility. Thus, the three slip systems should operate on different octahedral slip planes. However, the displacement incompatibility is not fully accommodated, and a stress field remains near the normal to {111}. The combination of sufficient stress concentration to open the grain boundary and the assembly of dislocations on the three slip systems at the grain boundary may be the cause of intergranular cracking.
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Physical Properties
Regular Article
  • Seil Lee, Bruno Charles De Cooman
    2012 Volume 52 Issue 6 Pages 1162-1170
    Published: 2012
    Released: June 15, 2012
    JOURNALS OPEN ACCESS
    The effect of P, ranging from 0.0 to 0.10 mass%, on the core losses of electrical steels containing 2.0 mass% silicon has been investigated. The core losses were separated into hysteresis losses, classical eddy current losses and anomalous losses. The hysteresis losses were found to decrease with increasing P content due to a larger grain size brought about by P additions. The anomalous losses were proportional to the square root of the grain size, and decreased with increasing volume fraction of grains with a ND || <111> orientation. The lowest anomalous losses were obtained at 0.05 mass% P content.
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