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

Tetsu-to-Hagané Vol. 104 (2018), No. 8

  • Influence of Low-temperature Oxidation on Structure of Coke Making Coal

    pp. 401-408

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    DOI:10.2355/tetsutohagane.TETSU-2017-090

    Self-exothermic reaction of coal is initiated by the reaction of coal in a pile with oxygen in the air to be oxidized. Then, the heat generated by the oxidation promotes further oxidation, resulting in ignition. In order to prevent this phenomenon, it is necessary to understand the initial stage of oxidation of coal in the condition of heat-accumulation. Conventionally, there are very few researches to understand the early stage of coal oxidation. In this study, we aimed at to elucidate the earlier oxidation stage of coals by employing low temperature oxidation of a mass of coals and several instrumental analysis techniques. The oxidation we used were heating 50 g of coal charged in a stainless steel closed container at 80°C for 24 h by flowing hot air to simulate the self-exothermic reaction condition. XRD and Raman spectroscopic measurements showed that the carbon skeleton structure of coal did not change by the oxidation treatment, while FTIR, 1H NMR and 13C NMR measurements showed a decrease in aliphatic side chains and an increase in hydroxyl groups in coal. The information obtained here will help to understand the whole process of self-exothermic reaction of coal to prevent burning.
  • Causes of Pinhole Generation on Solidification of Low Carbon S-Pb Free-cutting Steel Cast Continuously

    pp. 426-435

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    DOI:10.2355/tetsutohagane.TETSU-2017-098

    In this study, in order to prevent occurrence of surface cracks caused by pinholes occurring in production of low-carbon S-Pb free-cutting steel using continuous casting, on the causes of pinholes generation in this steel, the generating behavior of bubbles in front of solid/liquid interface and engulfment behavior of bubbles by solidifying shell has been theoretically examined from the viewpoint of transport phenomena, thermodynamics, and interfacial science, and the cause of pinhole generation on solidification has been clarified.Since the oxygen concentration of molten steel is high for undeoxidization to ensure machinability, the CO partial pressure at solid/liquid interface is significantly high due to solute enrichment on solidification. And additionally it is presumed that bubbles tend to be generated at the interface because the total gas pressure increases due to evaporation of lead. Furthermore, it was estimated that this steels are extremely high in sulfur concentration, and the surface tension at solid/liquid interface greatly decreases due to the enrichment at the interface, which also promotes the generation of bubbles on solidification. The CO partial pressure of the total gas pressure accounted for about 90%, and it was estimated that decreasing the CO partial pressure is most important in suppressing bubble generation by proper control of carbon and oxygen content of molten steel and application of stirring of molten steel.Furthermore, it has been clarified that detachment of the bubbles from the solid/liquid interface is suppressed by the interfacial tension gradient caused by the concentration gradient of sulfur and/or oxygen.
  • Identifying Factors for Cu Contained in Carbon Steel Produced in Japan

    pp. 461-466

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    DOI:10.2355/tetsutohagane.TETSU-2018-009

    The steel industry has been concerned with contamination by tramp elements during repeated recycling of carbon steel. Increase of Cu content has never been observed at least by monitoring EAF steel bars from the late 1980s. However, the increase may happen in future. To surely avoid the increase which leads to ineffective recycling, mechanisms of Cu mixing in carbon steel should be understood. The factors for Cu in carbon steel produced in Japan were identified. We distinguished two sources of Cu in obsolete steel scrap: Cu alloyed in carbon steel which has been contaminated by previous recycling and Cu contained in materials beside carbon steel. We found that, by dynamic material flow analysis, the Cu content derived from the former source has gradually increased because of increasing shares of bar and section which have a relatively high Cu content, which leaded to 0.05% increase in Cu content during three decades. On the other hand, Cu derived from the latter has become smaller from the late 1990s. One of the reasons was thought as increase of exporting scrap-mixed metal (often termed “zappin scrap”) from around the year. In the near future, it is predicted that the substantial part of the export will be rapidly reduced by amendment of relevant regulations. We estimate that Cu content in steel bars will become 0.49% on the average, if scrap-mixed metal is domestically recycled in a commercial way. This result underlines the necessity of improving the separation of Cu materials from carbon steel scrap.
  • Critical Condition for Formation of Accretion at Gas-Injection Nozzle Tip and Cooling Capacity of Gas

    pp. 409-416

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    DOI:10.2355/tetsutohagane.TETSU-2018-004

    A study has been made on the formation of accretion at the nozzle tip during submerged gas injection into Fe-C liquid metal. Experiments in 1 ton heating furnace were carried out to obtain data required for the initiation of the accretion and the followings were resulted: The inner diameter of gas injection nozzle and the solidus temperature of Fe-C were found to be determining factors for the critical condition for the formation of the accretion. By using Ohguchi’s heat balance equation for the stability of the accretion, transfer coefficient of the heat from hot metal to the accretion was estimated to be 63 ε ˙ 0.3 . Furthermore, by using modified Ohguchi’s heat balance equation including reaction heat term, the effective rate of reaction heat was obtained, which is 0.03 for CO2 and 0.4~1 for C3H8. Plant scale experiments were also conducted in 270 LD convertor at Muroran Works in order to examine the effect of the blowing of CO2-C3H8 gas mixture on the cooling for the protection of bottom nozzle and it was found that almost all of the reaction heat of C3H8 is contributed to the cooling, which supports the above mentioned result of 1 ton scale experiments.
  • Effect of Oxygen and Sulfur in Molten Steel on the Agglomeration Property of Alumina Inclusions in Molten Steel

    pp. 417-425

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    DOI:10.2355/tetsutohagane.TETSU-2018-015

    The agglomeration force that acts between alumina cylinders in molten steel has been measured at different concentrations of oxygen and sulfur. Both oxygen and sulfur in molten steel reduce the agglomeration force between the alumina cylinders in molten steel and act as interfacial active elements. However, oxygen reduces the agglomeration force more significantly than sulfur. The agglomeration force that was obtained empirically has been analyzed by combining the formulated surface tension concerning molten steel containing oxygen and sulfur with a model representing the alumina interparticle interaction due to a cavity bridge force. Thus, this analysis enables the effect of oxygen and sulfur in the molten steel on the agglomeration property of the alumina inclusions in the molten steel to be evaluated. The agglomeration property of the alumina inclusions reduces with the increase in the concentration of oxygen and sulfur in molten steel. The reduction due to oxygen is much greater than that due to sulfur. Moreover, when the concentration of sulfur in molten steel increases, the alumina inclusions remain in an adhesion state due to the strong agglomeration force based on the cavity bridge force. However, because the agglomeration force markedly decreases when the concentration of oxygen in the molten steel increases, the alumina inclusions that have agglomerated once are likely to separate again due to the molten steel flow.
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    1. Evaluation of Solidified Shell Thickness by Thermocouple in Mold Tetsu-to-Hagané Vol.104(2018), No.8
    2. Causes of Pinhole Generation on Solidification of Low Carbon S-Pb Free-cutting Steel Cast Continuously Tetsu-to-Hagané Vol.104(2018), No.8
    3. The Growth of γ' and γ'' Precipitates in Nickel-base Superalloys Tetsu-to-Hagané Vol.76(1990), No.8
  • Evaluation of Solidified Shell Thickness by Thermocouple in Mold

    pp. 436-443

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    DOI:10.2355/tetsutohagane.TETSU-2018-008

    High speed continuous casting technology has been developed to improve productivity. The method of real-time calculation of the solidified shell thickness by using multiple thermocouples embedded in the mold copper plates was tested at JFE Steel Kurashiki No.4CCM, and the possibility of detecting various types of breakouts in high-speed casting was demonstrated. The main results are summarized as follows.(1) The real-time calculation of solidified shell thickness at mold outlet position was successfully achieved on the basis of the local heat flux calculated by two thermocouples, 5 mm apart in copper plate depth direction.(2) The calculated solidified shell thickness was in good agreement with that of the observed by FeS addition.(3) The retardation of solidification was evaluated by the calculation in consideration of heat input caused by the steel stream impingement from the submerged entry nozzle. The index on the narrow face was increased on high speed casting condition in narrow width slabs.(4) The instantaneous local heat flux drop on the thermocouple measurements was observed when the slag rim or scum entrapment to the solidified shell was occurred. The calculated solidified shell thickness at mold outlet position was reduced to about 2/3.
  • Effect of Crystal Structural Changes of PET in Can-making Process on Properties of Film Laminated Steel for Containers

    pp. 444-452

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    DOI:10.2355/tetsutohagane.TETSU-2018-006

    PET film laminated steel sheets with excellent properties have now widely used in beverage cans. In recent years, can-weight reduction has been advanced from the viewpoint of resource saving, so that deep-drawing and ironing are performed to the laminated steel sheets, which requires non-oriented PET films with excellent formability instead of BO (Biaxially Oriented) PET films. However, non-oriented PET films have the possibility of any effects on impact and corrosion resistance due to the lack of crystal structure.In this study, we investigated the effect of the crystallinity of PET film on various properties required for beverage and food cans. Steel sheets on which PET films with different crystallinities were laminated were formed into the can shape by stretch-drawing processing in order to evaluate formability, adhesion property, impact and corrosion resistance.Here we found that BO-PET film laminated sheet with high crystallinity was inferior in impact and corrosion resistance compared with BO-PET/IA and NO-PET/IA film laminated ones. Film cracks parallel to the can-height direction were observed only on the surface of BO-PET film after the heat treatment, which caused deterioration of the properties. The heat treatment increased crystallinity degree of PET and aligned (100) crystal face of PET parallel to the can-height direction, which resulted in the occurrence of the film cracks.The study concluded that crystal-structural changes of PET film in can-making process had a significant effect on corrosion and impact resistance, and that the control of crystallinity of PET was the key factor to obtain the excellent properties.
  • Effect of Hot-rolling Conditions on Texture and R-value of 16%Cr Ferritic Stainless Steel

    pp. 453-460

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    DOI:10.2355/tetsutohagane.TETSU-2017-072

    Effect of Nb or Ti addition on texture formation and r-value of 16%Cr stainless steels was investigated to clarify the reason for keeping r-value of Nb or Ti free type 430 stainless steel low. Hot rolling conditions were examined to improve r-value and riding property of type 430 stainless steel. {111} texture was developed when Nb or Ti/(C+N) (at%) was over 1.0, and {111} texture was not developed in Nb or Ti free type 430 stainless steel because carbides and nitrides were dissolved before recrystallization during a final annealing. Higher reduction up to 60%/pass in rough hot rolling made r-value and riding propety improved by increasing {111} and decreasing {001} textures in a cold-rolled and annealed type 430 stainless steel, however reduction of 70%/pass lowered r-value. It is supposed a crystal rotation toward {001} occurred during a rough hot rolling, and the {001} texture remained after a hot band annealing, cold rolling and final annealing.

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