Tetsu-to-Hagane

Gasification and Combustion Behavior of Combustibles Injected into Coke Bed

Hideharu SHIBAIKE, Ken TAKAMIYA, Masaaki NAITO

2003 Volume 89 Issue 11 Pages 1093-1098
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1093

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From the viewpoint of preventing global warming and reducing maintenance costs, the reduction of coke consumption in the direct melting furnace for municipal solid waste is strongly called for. Accordingly, the authors have developed technology for injecting combustibles through the tuyeres of the direct melting furnace. This paper reports on the gasification and combustion behavior of combustibles injected into coke bed in a high-temperature combustion experiment.
The main results obtained are as follows:
(1) Combustibles such as plastics, combustible dust and LPG injected through tuyeres gasify and burn with priority over coke even under the combustion conditions of a direct melting furnace that has no raceway space.
(2) Combustible injection through tuyeres is effective in reducing the coke consumption in the direct melting furnace.

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Formation Behavior of Iron Carbide in a Pellet with Pressurized H₂-CH₄ Gas Mixtures Containing Traces of H₂S

Shoji HAYASHI, Yoshiaki IGUCHI

2003 Volume 89 Issue 11 Pages 1099-1106
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1099

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Using a thermobalance, industrial hematite pellets were reacted with pressurized H₂-CH₄ mixtures (1-3 atm) at 800-900°C to produce iron carbide in the pellets. H₂S having low pressures unable to form FeS was added to the mixtures. First, reduction of iron oxides proceeded and meanwhile carbidization of metallic iron took place. The addition of traces of H₂S into gas promoted iron carbides (Fe₃C, Orthorhombic) rather than free carbon (soot) or metallic iron as final products with nearly complete carbide conversion. The higher the temperature and the pressurization, the larger the carbidization rates. The tests without H₂S gave lower iron carbide contents with much soot or metallic iron. The addition of oxidant CO₂or H₂O into gas suppressed iron carbides and soot. Initial carbidization rates of a reduced iron pellet coincided with a reaction rate model proposed earlier by Grabke.

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Effect of Core Ore Type, CaO Content and Shell Ratio of Quasi-particle on the Structural Changes of Packed Bed in the Sintering Process

Takaho OTOMO, Yasushi TAKASAKI

2003 Volume 89 Issue 11 Pages 1107-1112
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1107

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Model sintering experiments were carried out in order to control the sinter cake structure under lowering slag ratio and using a large amount of limonite ore in the sinter mixture. In experiments, the influences of combined water content in core ore, and of CaO content and shell ratio of quasi-particles on the structural changes in packed bed of quasi-particles were examined by measuring compressive strength of sinter as an index. The results obtained were summarized as follows:
The void fraction in packed bed of quasi-particles decreased and compressive strength increased by the melt formation during heating. Because of a negative correlation was found between the compressive strength and void fraction of sinter, it was necessary to decrease the void fraction of the sinter in order to produce the sinter having high strength. The void fraction of sinter increased by increasing in the combined water content in core ore and by decreasing in the CaO content of quasi-particle. Whereas the void fraction of sinter decreased by increasing in shell ratio of quasi-particle. However, the effect of shell ratio is small when combined water content in core ore is high. The compressive strength has been improved by mixing two types of quasi-particles, which use limonite ore and hematite ore as core ore. Therefore it is thought to be key factor to control the arrangement of CaO constituent and the mixing ratio of core ore appropriately, in order to lower the slag ratio and to use large amount of limonite ore.

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Rate Enhancement of the Degassing Reaction by the Enlargement of RH and DH Reactors

Hideki ONO-NAKAZATO, Hiroyuki TAJIRI, Tateo USUI, Toshihiro TANAKA, Ka ...

2003 Volume 89 Issue 11 Pages 1113-1119
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1113

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Many techniques have been developed on the vacuum degassing of molten steel. The RH and DH reactors, which are suitable to the high productivity of converter, have occupied the mainstream. The DH process had constantly been installed until the latter half in 1970's, but has not been set up since 1980's. On the other hand, the RH process has continually been installed up to the present. The reason why RH has occupied the mainstream and has been developed further is examined from the viewpoint of the rate enhancement of the degassing reaction by the enlargement of RH and DH reactors. With the enlargement of the RH and DH reactors, the ratio of the upper surface area of steel in vacuum vessel to total reaction area decreases. On the other hand, the surface area of bubbles by Ar injection increases. Accordingly, the contribution of bubbles to the A/V (reaction area/metal volume) value becomes larger than that of the upper surface of steel in vacuum vessel. Although the argon gas can be also injected in the DH process, it is rather difficult to conduct the Ar injection in comparison with the RH process. It is not possible to sufficiently demonstrate the rate enhancement effect of the bubbles on the degassing reaction in DH reactor. Accordingly, from the viewpoint of the A/V value, the enlargement of the reactor is more advantageous to RH reactor. On the other hand, the circulation mass flow rate of steel similarly increases with increasing the heat size in both RH and DH reactors. It can be concluded that, with the enlargement of the RH and DH reactors, the Ar injection plays more important role on the rate enhancement of degassing reaction. In RH reactor, the molten steel is continuously circulated by the Ar injection. On the other hand, in DH reactor, the vacuum vessel repeats the periodic (uncontinuous) up and down. In this respect, the RH process is superior to the DH process. It can be considered that this is one of the reasons why the RH process has been more developed.

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State of Segregation with Bubble in Continuously Cast Slab of Ultra Low Carbon Steel

Norifumi KASAI, Hideo MIZUKAMI, Akifumi MUTOU

2003 Volume 89 Issue 11 Pages 1120-1127
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1120

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The phosphorus segregation adjoined to pin-hole between primary dendrite arms in continuously casting slab of ultra low carbon steel was clarified. The segregation regions of phosphorus were formed in both growth and anti-growth direction of primary dendrite arm based on the pin-hole. The maximum invaded distances of the pin-hole into primary dendrite arms corresponded to the position at fraction solid of 0.2. The critical velocity of interface between liquid and solid for trapping pin-hole was proportional to -1.1 power of pin-hole diameter. The pin-hole was easy to be trapped between primary dendrite arms of ultra low carbon steel, because the amount of shrinkage during solidification per unit temperature was thought to increase with decreasing the carbon concentration.

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Determination of Arsenic in Steels by Automated Extraction with a Recycled Solvent and Gravity Phase Separation

Tetsuyuki TANIAI, Akio SAKURAGAWA, Atsushi UZAWA, Hideichi FURUYAMA

2003 Volume 89 Issue 11 Pages 1128-1133
Published: November 01, 2003
Released on J-STAGE: January 15, 2010

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1128

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An automated on-line solvent extraction system has been developed for the determination of arsenic in steels by electrothermal atomic absorption spectrometry (ET-AAS). It is based on the reaction of As(III) with iodide ion in the concentrated hydrochloric acid medium to produce AsI₃, which is extracted into benzene and back-extracted into water. Improved gravitational phase separator based on the previously proposed was developed for the recycling of organic solvent used in the automated on-line solvent extraction system. Using the proposed automated on-line solvent extraction system, arsenic contained in the acid decomposed steel sample solution was automatically extracted into the benzene phase and it was back-extracted into the water phase. Then, the back-extracted water phase was used for the determination of arsenic by ET-AAS. When the ET-AAS method was used for the determination of arsenic, 800 mg dm^-3 of cobalt solution had to be used as the matrix modifier to remove an effect of coexisted substances such as iodide ion. In this method, a determination limit of As is 0.2μg in the 0.1g of steel sample.

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Influence of Si and Ni on Surface Hot-shortness of Cu-Sn Containing Steel Heated in Water Vapor Containing Atmosphere

Masaharu HATANO, Kazutoshi KUNISHIGE

2003 Volume 89 Issue 11 Pages 1134-1141
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1134

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This paper describes the influence of Si and Ni on surface hot-shortness of 0.3%Cu-0.04%Sn containing steel heated in water vapor containing atmosphere, where the atmosphere was changed in a manner of x%H₂O-1%O₂-bal.N₂ (x=0, 10, 20, 30). Surface hot-shortness was assessed by measuring the surface cracking depth occurring in the 1100°C hot-deformed specimens after 1250°C heating in the water vapor atmosphere. The microstructure at the scale/steel interface was closely observed and the effect of the mass gain on surface cracking depth was investigated.
For lower than 0.01% Si steel, the surface cracking depth increased largely with the mass gain, while an addition of 0.1% Si seems to suppress the surface cracking, especially at increased mass gains and the change with the mass gain was small. Steels with 0.14%Ni-Si<0.01% and 0.14%Ni-0.02%Si contained showed unexpectedly a marked surface cracking even in as low as 0.6 kg/m² mass gain of 0%H₂O-1%O₂-bal.N₂ and the surface cracking decreased considerably with an increase in the mass gain.
Si and Ni were found to be favorable alloying elements for suppression of the surface hot-shortness at increased mass gains in water vapor containing atmosphere. The mechanism of the suppression was discussed in terms of the unevenness of scale/steel interface and occlusion of Cu-Sn-Ni or Cu-Sn enriched liquid alloy into the scale.

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Deformation Analysis of Surface Defect on Plate Rolling

Takashi ISHIKAWA, Nobuki YUKAWA, Yoshinori YOSHIDA, Yuhi TONOHATA

2003 Volume 89 Issue 11 Pages 1142-1149
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1142

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Micro-defects sometimes appear on the surface of rolled plate and they affect the surface quality and cause the breakdown and cracks in the rolled sheet and strip. It is very difficult to make defect free products now. The shape of defect after rolling changes variously due to the rolling conditions. If the relation between the shape of the defect before rolling and that after rolling is clear, it leads to the effective method to predict the reason of the surface defect and to develop the process to remove the defect. The finite element analysis seems to be an influential technique, but it is difficult to calculate the deformation of micro-defects since the size of the defect is very small and the deformation is concentrates in small area. In this study, finite element analysis with an effective meshing and adaptive remeshing system was newly applied to calculate the change of surface micro-defects in plate rolling. A small mesh under sub-millimeter size was used around the defects. Rolling of plate with several types of surface defects, for instance V-shaped and rectangle scratch or denticle was calculated and the existing defect after rolling was investigated. The validity of simulated results was checked by experiments. There were mainly two cases in the change of defect shape in rolling i.e. opening type and closing type. The influence of rolling condition (roll diameter, lubrication and pass schedule etc.) on existing defects after rolling was revealed and the optimum condition to eliminate defects was discussed.

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A Roll-bonding Technology of Sheet Bars by Hot Strip Mill Rolling

Masaru MIYAKE, Yasuhiro SODANI, Sunao TANIMOTO, Fumio FUJITA

2003 Volume 89 Issue 11 Pages 1150-1157
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1150

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A roll-bonding technology of sheet bars aimed at fully continuous hot strip rolling was studied. Rolling of two piled up sheet bars at the entry of roll-bite was modeled and roll biting conditions were discussed in conjunction with friction coefficient between a work roll and a sheet bar as well as friction coefficient at the interface of two sheet bars. Pushing force by sheet bar's inertia was estimated by a spring-mass system model and the influence of the pushing force on roll biting conditions were examined. To examine the influence of the oxide layer at the interface of two sheet bars on biting and bonding phenomena, rolling experiments were performed by both laboratory rolling mill and production hot strip mill. If the thickness of oxide layer at the interface of sheet bars is thin enough, both biting and bonding can be achieved. It appeared that sheet bar's inertia force has great influence on roll-biting of two pile up sheet bars.

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Effect of B in Low Carbon Steels on the Si and Mn Selective Surface Oxidation Behavior during Continuous Recrystallization Annealing

Yoshitsugu SUZUKI, Kazuaki KYONO

2003 Volume 89 Issue 11 Pages 1158-1164
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1158

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Effect of B addition on the Si and Mn selective surface oxidation behavior of low carbon steels was investigated, by glow discharged spectroscopy, secondary electron microscopy, transmission electron microscopy, and auger electron spectroscopy, after recrystallization annealing. The oxides composed mainly of Si and Mn for B-free steel, and of B, Si and Mn for B-added steel. For B-free steel, fine selective surface oxides, which covered most of the steel surface, were observed. For B-added steel, gross globular selective surface oxides were observed on the steel surface, with partially bare Fe surface. For B-added steel, B-Si-Mn compound oxide is considered to be in molten phase in annealing, because the melting point of the compound oxide is lowered than the annealing temperature. As a result, the compound oxide is considered to coagulate and grow during annealing, due to the surface tension effect. The amount of Si and Mn selective surface oxidation was suppressed about 1/3 for B-free steel, compared with that of B-added steel, because of insufficient oxygen supply through the protective oxidation layer. For B-added steel, the selective surface oxidation was promoted, because oxidation layer was considered to be non protective. Only B addition of 5 ppm was enough, for the promotion of the Si and Mn selective surface oxidation.

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A Protective Film Component among Corrosion Products on Galvanized Steels Estimated by Solubility Calculations

Hiroki TAMURA

2003 Volume 89 Issue 11 Pages 1165-1169
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1165

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Galvanized steels are used extensively in atmospheric environments because of their high resistance to corrosion as well as their low cost of production. The corrosion resistance arises from the slow corrosion rate of the zinc layer that covers the steel (coating and shielding effect) and the low corrosion potential of zinc which keeps the steel under a reducing condition as long as zinc remains (sacrifice effect). However, detailed examination of the corrosion processes has shown that galvanized steels exhibit some corrosion resistance after the disappearance of metal zinc by corrosion. This effect has been ascribed to a protective nature of corrosion products from the zinc layer. It is important to establish the protective components of corrosion products for the elucidation of corrosion mechanisms and for the development and improvement of corrosion protection technologies. In this investigation, zinc oxide, zinc carbonate, basic zinc carbonate, and zinc ferrite were chosen as model corrosion products, it was noted that protective films must have very low solubilities and very low dissolution rates for them to persist, and their dissolution properties were examined by solubility calculations. The solubilities of zinc oxide, zinc carbonate, and basic zinc carbonate are similar and very large, indicating that these would be dissolved away in atmospheric environments. A further corrosion product, zinc ferrite, is not a major component, but can be formed as a thin layer by the corrosion of the zinc-steel alloy phase. The solubility product of zinc ferrite was estimated from thermodynamic data and its solubility was calculated. The solubility is very small and it can be concluded that zinc ferrite is the most likely protective film component among the zinc compounds described above.

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Tensile Properties Obtained by Static Tensile Tests in Ultrafine-grained Ferrite-Cementite Steels

Noriyuki TSUCHIDA, Yo TOMOTA, Kotobu NAGAI

2003 Volume 89 Issue 11 Pages 1170-1177
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1170

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We conducted static tensile tests below room temperature for ultrafine-grained ferrite-cementite (FC) steels with ferrite grain sizes between 0.47 and 1.5 μm. The change in flow stress (σ) for the FC steels as a function of ferrite grain size (D) follows the Hall-Petch equation: σ= σ₀+kD^-1/2, where σ₀ and k are constants. The effects of temperature and strain rate on flow stress for the FC steels are scarcely influenced by ferrite grain size and the effect of ferrite grain size on flow stress is almost independent of temperature and strain rate. When the results of the FC steels are compared with those of the ferrite-pearlite (FP) steels, little difference is found in the effects of temperature and strain rate on flow stress. However, the effect of ferrite grain size on flow stress and the work-hardening rate are different from each other.

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Two Body Abrasive Wear of Fe-Al Intermetallic Compounds

Takao YAKOU, Tomohiro SASAKI, Shigeaki KOBAYASHI

2003 Volume 89 Issue 11 Pages 1178-1182
Published: November 01, 2003
Released on J-STAGE: May 29, 2009

DOIhttps://doi.org/10.2355/tetsutohagane1955.89.11_1178

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The abrasive wear behavior of specimens of Fe-Al intermetallic compounds (Fe₃Al, FeAl, FeAl₂, Fe₂Al₅ and FeAl₃) on SiC abrasive papers having an abrasive grain diameter ranging from 10 to 48 μm were investigated. The relationship between the wear rate and the material hardness is classified into two cases. In the first case, the wear rate increases with decreasing specimen hardness when the specimen is worn using an applied force of less than 0.31 MPa and an abrasive grain diameter finer than 30 μm. In this case, ductile wear is observed in all specimens. In the second case, the wear rate increases with increasing specimen hardness when the specimens are worn using an abrasive grain diameter coarser than 30 μm. In this case, brittle wear is observed in the FeAl₂, Fe₂Al₅ and FeAl₃ specimens.

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