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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 83 (1997), No. 10

  • The Effect of Atmosphere Gas on Hot Erosion Properties of the Materials Applied to PFBC Boiler

    pp. 605-610

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    Three kinds of materials applied to PFBC boiler have been examined in the atmosphere of the mixed gas (N2-O2-SO2), and the effect of atmosphere gas on hot erosion waste of the materials was studyed. The results obtained are as follows.
    (1) The erosion waste of materials is accelerated by SO2, and is restrained by O2.
    (2) The erosion waste is small on the condition of low testing velocity below 7m/s.
    The erosion waste becomes larger in proportion to the increase of the testing velocity on the condition of the high velocity beyond 7m/s.
    (3) The erosion waste becomes smaller at larger Cr content because of a formation of Cr oxide at the most inner layer of an oxide scale.
  • Influence of Oxide Scale on Heat Transfer Properties of Ni Bearing Low-alloy Steel

    pp. 611-616

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    The effect of surface oxidation on heat transfer of a low-alloy steel with Ni of 0-4.9mass% was investigated. Cooling curves were obtained by means of 10mm thick plate heated and oxidized by induction heating in air at 1473K for 300 sec. The results obtained are summarized as follows.
    Heat transfer properties change noticeably depending on Ni content. As the Ni content increases, transition boiling begins at higher temperature. At temperatures below the breakdown temperature of film boiling, i.e. the lower limit temperature of film boiling, the heat transfer coefficient has risen with Ni increase, while above that temperature it is independent of Ni content.
    During the heating and cooling scale layer adheres to Ni bearing steel surface. The adherent scale layer becomes thicker with increase in Ni content.
    The scale layer consists of oxide and Ni enriched metal, and seems to be a subscale peculiar to Ni bearing steel. Change of the heat transfer properties depending on Ni content is due to the adherent scale layer. The scale layer has low effective thermal conductivity, and produces a steep temperature gradient in it during cooling. As a result true surface temperature is lowered, and transition boiling begins at higher temperature.
  • Combustion and Gasification Behaviors of Plastics Injected into Raceway of Blast Furnace

    pp. 617-622

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    The combustion and gasification behaviors of plastics have been investigated with the drop tube furnace, raceway hot model and scrap melting shaft furnace. From the observation of a single plastic combustion by the drop tube furnace experiments under around 1200°C, the burning rate of coarse plastic was slower than that of pulverized coal. On the contrary, in the raceway hot model and scrap melting shaft furnace with the plastics injection, the combustion efficiency of plastics was much higher than that of pulverized coal in spite of coarse particle. Moreover, the gas composition and temperature distribution in the raceway during the plastics injection were similar to those of all coke operation. Thus, it was concluded that the combustion mechanism of coarse plastics was different from that of pulverized coal. On the basis of these results, it was estimated that the residence time of coarse plastics in the raceway was longer than that of pulverized coal or fine particle. The circulation model of coarse plastic particle in the raceway was newly investigated, and the combustion efficiency of plastics was theoretically evaluated. The results calculated by the circulation model agreed with those of the hot model experiments.
  • Deoxidation Equilibrium of Magnesium in Liquid Iron

    pp. 623-628

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    Magnesium has very strong affinities with oxygen and sulphur. Therefore, it is necessary to know the exactly thermodynamic values on deoxidation of magnesium in liquid iron for ultra high quality steel production and composition control of non-metallic inclusion. However, the proposed deoxidation equilibrium relation shows a loop in the figure which shows the relation between magnesium and oxygen dissolved in liquid iron. This means one concentration of magnesium corresponds to two concentration of oxygen and vice versa. Therefore, it is impossible theoretically to control the oxygen content with magnesium. It causes by use of only 1st order interaction parameters to express the activities of magnesium and oxygen. In the present work, the deoxidation equilibrium of magnesium was studied on the viewpoint that the thermodynamic values concerning very strong deoxidation such as magnesium have to be evaluated by 1st and 2nd order interaction parameters including cross products too. As the result, the temperature dependence of thermodynamic values on magnesium deoxidation was obtained, and it was in good agreement with the observed values in the present work.
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  • Effect of Oxide Film on Solid Phase Bonding of Aluminum Sheet to Steel Sheet

    pp. 629-634

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    In order to clarify the solid phase bonding mechanism of aluminum to steel, the bonding characteristics of steel/aluminum(CS/Al) and stainless steel/aluminum(SS/Al) bonding sheets were investigated. The bonding sheets were produced by hot rolling. From the results of diffusion bonding, it was found that iron oxide film was the barrier of aluminum sheet to steel sheet bonding, however, chromium oxide film and aluminum oxide film were not always the barrier of aluminum sheet to stainless steel sheet bonding. The peel strength of the bonding sheets increased with the increase of the aluminum sheet reduction and the rolling temperature. Amorphase aluminum oxide film or chromium oxide film were observed at the interface of the CS/Al and SS/Al bonding sheet. Intermetallic compound were formed in area where oxide film was not observed. Diffusion zones of iron and aluminum were not recognized at the interface of the bonding sheets.
  • Effect of Crystal Orientation of Steel Substrate on the Morphology of Zinc Electrodeposit

    pp. 635-640

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    The effect of crystal orientation of steel substrate on the morphology of zinc electrodeposit was investigated by using the polycrystal commercial low carbon Al-killed steel sheet and the sulfate bath under the current density of 50-150 A/dm2. The morphology of zinc deposit changes according to the crystal orientation of steel sheet, and the morphology can be classified into 3 types by the angle α between the sheet surface plane and the {110} Fe plane. When α is less than about 20°, zinc electrodeposits grow heteroepitaxially with Burgers' orientation relationshp, i.e. (0001) Zn//(110) Fe up to the coating weight of 20g/m2 (Type I). When α is between about 20°and 30°, secondary random zinc electrodeposits begin to grow on the initial heteroepitaxial Zn basal plane that follows the Burgers' relationship (Type II). When α is larger than about 30°, Burgers' relationship doesn't meet the case. Flat (0001) Zn plane initially grows parallel to the sheet surface plane, then separate Zn basal planes grow randomly on the initial plane on the slant (Type III).
  • Formation and Growth of Intermetallic Compound at Interface of Steel/Aluminum Bonding Sheet

    pp. 641-646

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    This paper deals with the formation and growth of intermetallic compound (IMC) at the interface of steel/aluminum bonding sheet. The bonding sheets were produced by hot rolling and diffusion bonding.
    The heating conditions which let to the formation of the IMC depended on the combinations of steel and aluminum sheets. The growth of the IMC layer was obeyed by parabolic law and the activation energy in the growth of the IMC layer were estimated to be 116 to 235k J/mol. The growth rate of the IMC increased with the increase of magnesium content and the reduction of aluminum sheet. However, it decreased in case of using stainless steel sheet. The peel strength decreased with the increase of the IMC layer thickness (heating temperature) and the bonding sheets were peeled easily at the IMC/aluminum interface when the IMC layer thickness were more than 2μm. The IMC formed at the interface were FeAl3. Fe2Al5 and FeAl2.
  • Effects of Dissolved Oxygen Content on Microstructure and Room Temperature Tensile Properties of Cast TiAl-Fe-V-B Alloy

    pp. 647-652

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    We examined the effects of dissolved oxygen content on room temperature tensile properties of a gamma TiAl alloy, Ti-46.7 Al-1.3Fe-1.1 V-0.35B (mol%) developed as a casting material for turbine components, for replacing superal- loys. The ductility and the tensile strength were reduced with the increase of dissolved oxygen content. Then, we focused on the relationship between dissolved oxygen content and microstructure. Oxygen had a significant effect on the amount of lamella phase and the presence of the beta phase. According to composition analysis by using EPMA, as compared that of TiAl-Fe-V-B alloy with approximately 500ppm oxygen, the alpha and gamma two-phase field was extended with an increase in the oxygen content. On the basis of these experimental results, we discussed the allowable content of oxygen to avoid the decrease of the room temperature ductility and tensile strength and to meet the design requirements.
  • Effect of Grain Boundary Cr Concentration Profiles on Stress Corrosion Cracking Susceptibility in 304 Stainless Steel

    pp. 653-658

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    Very narrow chromium (Cr) depletions with widths below 10nm were produced by a heat treatment which controlled a growth of Cr carbides at a grain boundary (GB) in type 304 stainless steel. A Correlation between the Cr depletion profile and intergranular stress corrosion cracking (IGSCC) susceptibility in a high temperature water was investigated. IGSCC susceptibility was affected especially by the Cr concentration as compared with the Cr depletion width at GB. The susceptibility increased at the Cr concentration below about 15mass%. No IGSCC susceptibility was observed when there was no Cr depletion at GB. The above mentioned results in heat treated materials almost corresponded with that in neutron irradiated materials.
  • Effects of Carbon, Silicon and Molybdenum on Torsional Strength of Induction Hardened Steel for Automotive Shafts

    pp. 659-664

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    An increase in the torsional strength of automotive shafts has been a subject of particular interest. Induction hardening can afford a medium-carbon steel shaft desirable torsional strength. When case hardness exceeded a certain level, the fracture mode of some test-pieces changed from mode III to mode I with intergranular fracture. The purpose of this study is to establish a method of increasing strength of shaft steels to mode I fracture. The effects of carbon, silicon and molybdenum on torsional strength in mode I fracture were investigated.
    The strength in mode I fracture of induction hardened steel decreased with increasing carbon content. The precipitation of fine cementite in the prior austenite grain boundary was recognized. The amount of cementite in the grain boundary was increased by increasing carbon content. The reduction of the strength with increasing carbon content was due to two causes: large amount of grain boundary cementite and high hardness. The magnitude of effect of grain boundary cementite on strength was almost the same as the effect of hardness.
    The strength in mode I fracture was increased by increasing silicon or molybdenum contents. This was because the size of grain boundary cementite was refined by the addition of silicon or molybdenum.
  • Effects of Phosphorus and Boron on Torsional Strength of Induction Hardened Steel for Automotive Shafts

    pp. 665-670

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    The purpose of this study is to establish a method of increasing strength of shaft steels in mode I fracture associated with intergranular fracture. The effects of phosphorus and boron on the torsional strength in mode I fracture were investigated.
    The strength in mode I fracture of induction hardened steel was increased by the addition of boron. The beneficial effect of the addition of boron on the torsional strength was larger than that of lowering phosphorus content from 0.013% to 0.002%. In the boron bearing steel, the segregation of boron in prior austenitic grain boundary was recognized and the amount of phosphorus segregation was one half that of boron-free steel. This was because the segregation of boron and phosphorus occurred concurrently at the induction heating and boron scavenged phosphorus in prior austenitic grain boundary.
    It is concluded that the increasing strength by the addition of boron was due to two causes: lowering the amount of phosphorus segregation by the effect of scavenging phosphorus in grain boundary and the increase in the grain boundary strength by the unique effect of boron. The effect of the latter on the strength was larger than the former.
  • Effect of B Contents on Toughening by the Solution Treatment under Unrecrystallized Austenite in 18%Ni Maraging Steel

    pp. 671-676

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    Effects of B contents on strengthening and toughening by the solution treatment under unrecrystallized austenite were examined in 2.1GPa grade 18%Ni maraging steels. Because addition of B retarded the recovery process, and further to the suppression of recrystallization, when B was added in 18%Ni maraging steels, recrystallization temperature of the reverse-transformed γ increased with B contents. In addition of B more than 0.0020mass%, however, toughness decreased on the solution treatment under unrecrystallized austenite of a higher temperature side at 1123K. This decrease of toughness is a phenomenon called thermal embrittlement. The thermal embrittlement was caused by the precipitation and growth of borides at the prior austenite grain boundaries. The optimum amounts of B addition is about 0.0010mass% for strengthening and toughening due to the solution treatment under unrecrystallized austenite as well as avoiding the thermal embrittlement.
  • Analysis of Environmental Burden of Steel Making Process by the Use of I/O Table

    pp. 677-682

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    Recycle of steel is expected to conserve natural resources, such as ores, and reduce environmental burden which accompanies steel production. However, the difference of environmental burden caused by blast furnace process and electric furnace process, which are used for steel recycling, is not quantitatively clear. In this study, we combine monetary data from I/O table and quantitative data from steel statistics, and estimate total CO2 emission from each steel making process. According to the result, total CO2 emission is 458kgC/t for BF process and 136kgC/t for EF process. We also evaluate the change of CO2 emission from EF process in the case where more pig iron is added to EF process in order to lower the concentration of impurities. The result shows that the difference in CO2 emission between both methods disappears when pig iron input exceeds 75% of the total charge of iron materials to EF process.
  • An Analysis Overseas Investment of Steel Industry Using Input-Output Table

    pp. 683-688

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    Due to the rapid change of appreciation of yen, many Japanese companies have been making intensive overseas investment since 1980s. However, while automobile and electronic industries have been aggressive about their overseas production, steel and other several industrial have made relatively small overseas investment. This difference is thought to be attributed to their cost structure and market structure. In order to evaluate the difference totally, we have to consider not only on the single industry base, but also on the total industry base including all the related industries. In this study, we used I/O table and calculated the comprehensive structure of cost and market for the steel and other major industries in Japan. The results show that as regards the labor cost ratio and the overseas market dependence calculated in this method there are a strong correlation the with investment overseas.

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