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

Tetsu-to-Hagané Vol. 92 (2006), No. 4

  • Efforts to Save Nickel in Austenitic Stainless Steels

    pp. 233-238

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    The price of nickel is maintaining high level due to the demand continuing to outstrip supply, therefore the stainless steel, which is the largest consumer of nickel, has been maintaining a high-price.
    In this paper, the way of nickel saving by more than half and the comparison of properties between the nickel saving stainless steels and the SUS304 were reviewed, and the problem caused by the use of the nickel saving stainless steels were discussed.
    Nickel saving stainless steels have the following 4 types; martensitic stainless steels, ferritic stainless steels, duplex stainless steels and Cr-Mn-Ni austenitic stainless steels. Nickel saving stainless steels have both superior and inferior points as compared to SUS304, however they have a large possibility of substitution for SUS304. Further expansion of the use of nickel saving stainless steels is expected if the properties required for the stainless steel are reconsidered for proper demands.
  • Mechanism of Aluminothermic Reduction of MgO

    pp. 239-245

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    Desulfurization and deoxidation of molten iron with magnesium vapor produced in-situ by aluminothermic reduction of magnesium oxide has been developed. In the present study, the mechanism of aluminothermic reduction of magnesium oxide by use of pellets composed of magnesium oxide and aluminum powders was discussed. SEM observation of the pellet at different reduction stages for various temperatures showed that fracture and disappearance of the alumina film on the aluminum particles were stimulated above 1473K, and thus the reduction of magnesium oxide was greatly accelerated.
    From in-situ observation of the aluminothermic reduction of magnesium oxide using a high temperature optical microscope (HTOM), it is found that the reduction proceeded after the penetration of molten aluminum into the magnesium oxide phase. The penetration began at 1273K, and it was accelerated above 1373K. The reduction took place violently at 1473K. SEM observation and EDS analysis of the cooled sample revealed that the penetration took place only through cracks of the alumina film.
    In-situ observation of the melting process of aluminum particles together with SEM observation of the cooled sample showed that the thermal stress could break up the alumina film and the outflow of molten aluminum did take place at the elevated temperature.
  • Effect of Operating Parameters on Resulfurization in Desulfurization Process of Molten Iron with in Situ Produced Magnesium Vapor

    pp. 246-253

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    The mechanism of resulfurization in the desulfurization process with magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide was clarified in the present work. The influences of various operating parameters on the resulfurization were studied and the methods for preventing the resulfurization were proposed.
    There are two kinds of mechanisms of resulfurization in the desulfurization process with magnesium. One is decomposition of the desulfurization product of MgS under the inert atmosphere. The other is oxidation of MgS under the oxidative atmosphere.
    Under the present experimental conditions, lowering operating temperature and oxygen partial pressure in the atmosphere, and adding more pellets containing magnesium oxide and aluminum could effectively prevent the resulfurization. The resufurization took place more markedly by using Al2O3 crucible than by using MgO or graphite crucible.
    Adding CaO onto the melt surface was an effective method for preventing the resulfurization due to transformation of the desulfurization product of MgS into the more stable compound of CaS. For prevention of the resulfurization, using the CaO-Al2O3 mixture is less effective than using only CaO. Since addition of the activated charcoal powders greatly decreased the transfer rate of oxygen in the atmosphere to the melt surface and the oxygen partial pressure on the melt surface, it also prevented the resulfurization effectively.
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    Readers Who Read This Article Also Read

    1. Mechanism of Aluminothermic Reduction of MgO Tetsu-to-Hagané Vol.92(2006), No.4
    2. Resulfurization Rate in Magnesium Desulfurization Process of Molten Iron Tetsu-to-Hagané Vol.92(2006), No.4
  • Resulfurization Rate in Magnesium Desulfurization Process of Molten Iron

    pp. 254-261

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    During magnesium desulfurization of molten iron, the desulfurization product of MgS floats up to the melt surface. After magnesium supply terminates, resulfurization tends to take place because of the transfer of sulfur from MgS into the melt. In the present study, a simplified experiment was designed to clarify this resulfurization mechanism. With MgS powders added onto the melt surface, the transfer rate of sulfur from MgS into the melt was measured.
    Two kinds of mechanisms are revealed to be responsible for the resulfurization in the magnesium desulfurization process. One is decomposition of MgS under the inert atmosphere; the other is oxidation of MgS under the oxidative atmosphere.
    It is also found that increasing temperature and oxygen partial pressure in the atmosphere increased the transfer rate of sulfur into the melt and the resulfurization ratio. But the increase in the added amount of MgS did not change the resulfurization ratio largely under the present experimental conditions. The resulfurization rate was smaller by using MgO crucible than that by using Al2O3 crucible. Addition of Ca0 and the activated charcoal powders onto the melt surface could significantly prevent sulfur of MgS on the melt surface from transferring into the melt.
    With a simplified first-order rate equation, the calculated capacity coefficient for transfer of sulfur from MgS to the melt is increased with increasing the temperature and the oxygen partial pressure in the atmosphere, but does not change very much with adding different amounts of MgS onto the melt surface.
  • Development of Real Time Monitoring Apparatus Based on Jet-REMPI Technique for the Determination of Hazardous Organic Compounds

    pp. 262-267

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    For monitoring of hazardous organic compounds, we have been developing an on-line analytical instrument based on a supersonic jet resonance enhanced multi-photon laser ionization (Jet-REMPI) mass spectrometry. We have attempted to apply this technique to monitor transient attitudes of hazardous organic compounds, e.g. in the exhaust gas.
    It becomes possible that the real time monitoring of the gaseous compounds in atmosphere by our instrument with a continuous sample introduction. We demonstrated that the signals of mono-chlorinated benzene in the air could be detected with 150 s interval through a 23m stainless steel pipe, which kept 200 degree of centigrade. Our instrument has a very high vacuum pumping system to keep the difference of the vacuum level between in atmosphere and in ionization chamber. It has been proved that monitored molecules were well cooled as the result of REMPI spectra. It is strongly advantageous for the selective detection of a specific molecular species.
    The emission mechanism of chlorinated aromatic compounds is discussed by monitoring 2 different kinds of compounds, simultaneously.
  • Prediction of Carbon Profiles in Vacuum-carburized Steels Based on Carburizing Mechanism

    pp. 268-273

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    In order to develop effective ways to estimate carbon distribution in vacuum carburized steel, the surface interaction during vacuum carburizing was investigated. 0.1 mm thick specimens were vacuum carburized for sufficiently long time. The carbon content and carbide area fraction of specimens proved to be the value in equilibrium with graphite. This result shows that the graphite exists while vacuum carburizing on the surface of specimens, and that the local equilibrium between specimens and graphite is dominant factor. Carbon profile of carburized round bar was calculated on the basis of diffusion equation, on the assumption that surface carbon content is as much as the value in equilibrium with graphite. The calculatuied carbon profiles correspond to measured ones for some materials and carburizing conditions.
  • Micro Etching Process of Metals Using Microbial Metabolic Reaction (I)

    pp. 274-279

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    The possibility of new material processing using microorganism has been studied. In these studies, it was investigated new techniques to utilize bacteria as processing tools and to apply microbial metabolic reaction to material processing.
    This method originated from the proposal of using the iron oxiding bacteria, Thiohachillus felloaxidans, focusing on the possibility of applying its supreme ability of corroding iron to material processing. However, T. ferrooxidans is not always suitable for material processing because it prefers a strong sour environment, and usual materials are easily damaged by these sour solutions. Therefore, bacteria that live in a neutral environment and their biochemical is more suitable for this processing. Therefore, Microbiologically Influenced Corrosion (MIC) is a good candidate for this processing because MIC involves high corrosion rates in a mild environment.
    A study on this new etching process for metals, applying the microbial metabolic reaction related to MIC, is reported here. The process is called "Bio-etching" and it is investigated by the following experiments. First, Staphylococcus sp., detected as the cause of the corrosion of copper was selected as the test strain. The situations of the adhesion area of Staphylococcus sp. and the occurrence of the corrosion on each culture condition were evaluated, and the optimal conditions for processing were examined. Secondly, an experiment for bio-etching to metallic copper using Staphylococcus sp. was carried out, the creation of the processing pattern corresponding to the shape provided by resist was observed.
  • Micro Etching Process of Metals Using Microbial Metabolic Reaction (II)

    pp. 280-286

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    The authors have been applying a microbial metabolic reaction that induces Microbiologically Influenced Corrosion (MIC) to develop a biological metal etching process (Bio-etching). Some kinds of bacteria that have the ability to induce corrosion on metals were detected through MIC failure case analysis. For example, Staphylococcus sp. is known to be able to induce corrosion on copper.
    The mechanism of MIC of copper, related to Staphylococcus sp., is described in the following. First, the adhesion of Staphylococcus sp. on the surface of copper takes place. The bacteria then multiply and begin to form small patch colonies. At this point lactic acid, related to the beginning of the MIC process of copper, is produced. With further bacterial multiplication a bio-film is formed on the surface of copper and ammonia, which has a strong causticity to copper, is also produced, showing that further corrosion of the copper surface takes place.
    In this paper, a study has been performed to investigate the effective application of the metabolic reaction of Staphylococcus sp. to bioetching, by forcing microorganism to stick to the materials. It was confirmed that the formation speed of the adhesion area on copper, which has antibacterial function, had improved and that the processed area of the target zone could be defined with good accuracy. It was also observed that the corrosion takes place only in the small areas not covered by the protection resist. These results show that Bio-etching of metallic copper by Staphylococcus sp. is a very effective process.
  • Micro Etching Process of Metals Using Microbial Metabolic Reaction (III)

    pp. 287-294

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    Bacteria having the ability to produce corrosive pits on metal surfaces were detected from Microbiologically Influenced Corrosion (MIC) failure case analysis. The target of this study is to apply the corrosive ability of these bacteria to material processing.
    In previous reports, the authors focused on Staphylococcus sp. and its ability to corrode copper. Those studies showed the possibility of bio-etching with Staphylococcus sp. by defining the processing area with a protective resist.
    In this report, another strategy of bio-etching is described, i.e., to define the processing area by controlling the phase of the material.
    One of the characteristics of MIC is that in stainless steel welds the corrosive attacks occur preferentially on certain phases. Applying this phase-preferential corrosion property to material processing lead to the new method of bio-etching, namely, the location of the processing area can be defined by controlling the metal structure.
    The following experiments were designed to verify this idea. Bacillus sp. and Pseudomonas sp. were selected as the test strains. The optimal bio-etching parameters, the adhesion area of the bacteria as well as the change of pH of the culture medium were evaluated. A processing bioreactor prototype was then designed based on these results. Finally an experiment for bio-etching of stainless steel welds was carried out.
    This study confirmed that bio-etching process is suitable for position selective etching, by controlling the metallic phase of the material.

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