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

Tetsu-to-Hagané Vol. 86 (2000), No. 12

  • Circumstances of Environmental Analysis in Steel Industry

    pp. 785-792

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    By this time, environmental problems had been put firmly on the political agenda. A great deal of research is still being carried out on environmental analysis, for example endocrine disrupting chemicals. The steel industry is a large scale material manufacturer. To this end the Japanese steel industry has established to the construction of the society of environmental harmonization. It is necessary to know the actual state of environmental pollution for the protection of environmental circumstances. Techniques of environmental analysis and environmental measurement equipments are developed in the period of 1970's in Japan. It is well known the Japanese environmental analysis is the most advanced in the world. The steel industry applied these techniques to the determination of nitrogen oxide, chemical oxygen demand and so on in the waste water and exhaust gases. In future the steel industry should be done continuously on the environmental analysis for the harmonization to the earth circumstances.
  • Numerical Analysis of Plastic Strain Distribution through Multi-directional Deformation

    pp. 793-800

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    The plastic strain in a specimen introduced by compression with a pair of anvils is evaluated using a three-dimensional dynamic finite element analysis. The stress-strain relations depending on strain rate and temperature are used in the analysis. The contact condition between the anvil and the specimen is determined from the experimental result from an identically deformed screw set in the specimen. The plastic strain introduced by uni-directional compression is compared with that by bi-directional compression non-simultaneously given from different directions. The bi-directional deformation is proposed as a method to introduce large plastic strain widely in the specimen. The bi-directional deformation can be developed as a technique to obtain ultra-fine grain steels for thick plates.
  • Uniform Formation of Fine Grained Ferrite Structure through Multi-directional Deformation

    pp. 801-806

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    A multi-directional deformation thermo-mechanical treatment simulator was designed and developed to verify the prediction by the FE-analysis on the effect of bi-directional deformation which can introduce a large plastic strain widely in a specimen. Using this simulator, both uni-directional and bi-directional deformations were performed for a 0.16%C-0.4%Si-1.4%Mn steel with a prior austenite grain size of 300 μm at 1073K at a strain rate of 1/s. The microstructure was composed of polygonal ferrite and intragranular Widmanstätten ferrite in the uni-directional deformation specimen. On the other hand, the half thickness of the specimen was composed of fine polygonal ferrite in the bi-directional deformation specimen. This region corresponds well to the region having a plastic strain of more than 2. The uniform formation of the fine polygonal ferrite due to the wide introduction of the large plastic strain was verified for the bi-directional deformation.
  • Shape, Size and Crystallographic Orientation of the Ferrite Grains Formed at Grain Boundaries of Deformed Austenite in a Low Carbon Steel

    pp. 807-814

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    The influence of plastic strain on the shape, size and crystallographic orientation of ferrite (α) grains formed at the grain boundaries of the deformed austenite (γ) was studied in a 0.17C-0.3Si-1.5Mn steel. Specimens with a coarse γ grain size of 300 μm were compressed at 1023K and cooled at 10K/s. When the plastic strain increased to 0.4, the shape of α grains changed from plate like to equiaxed, and the average length of a grains decreased from 12 to 6 μm. However, the average length did not change in the larger plastic strains up to 1.1. On the other hand, the average thickness of α grains was constant regardless of the plastic strain. The crystallographic orientations of the α grains formed at one γ grain boundary were almost the same when the plastic strain was smaller than 0.2 and the α grain shape was plate like. However, the orientations were widely distributed, and most of the α/α boundaries were high angle ones, when the plastic strain was larger than 0.4 and the α grain shape was equiaxed. The shape change and α grain refinement by the deformation resulted from the wide distribution of crystallographic orientations of α grains rather than from the increase in the nucleation rate. The wide distribution of crystallographic orientation of α grains is closely associated with the serrated austenite grain boundaries induced by the deformation.
  • Strength Analysis of a Ferrite+Bainite Steel by AFM Ultra-micro Hardness Tester

    pp. 815-821

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    AFM ultra-micro hardness test, micro Vickers hardness test and TEM observation were conducted for a ferrite+bainite steel, which consists of bainite and polygonal ferrite. The results obtained are in the following. (1) AFM ultra-micro hardness tests show that nanoscopic hardness is 155 near the center of bainitic ferrite grain and increases closer to its boundary. Nanoscopic hardness is kept constant at 151 in the polygonal ferrite grain. (2) Micro-Vickers hardness tests show that macroscopic hardness is 251 and 147 for the bainite and polygonal ferrite regions, respectively. (3) TEM observations show that many carbides precipitated along the grain boundaries of bainitic ferrite and the dislocation density was almost same in both grains of bainitic and polygonal ferrite.
    It is suggested from the above results that the strengthening by grain boundaries is important in the bainitic ferrite and this strengthening effect is enhanced by carbides along grain boundaries.
  • Influence of Hot Rolling Temperature and Reduction on Mechanical Properties of Ti-bearing Extra Low Carbon Hot-rolled Steel Sheets

    pp. 822-829

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    The effects of hot rolling temperature and rolling reduction on the mechanical properties of Ti-bearing extra low carbon steel sheets have been studied. Conclusions obtained are as follows:
    1. The elongation of as-rolled steel sheet through conventional reduction decreased when the finishing rolling temperature was under 840°C. But the elongation, tensile strength and yield strength of the steel sheet after annealing had little change in the range of 650850°C.
    2. The difference of tensile strength between as-rolled and annealed steel sheet was thought to be due to the substantial strain energy which was stored by hot rolling. The substantial strain energy of the steel sheet rolled at 650°C through conventional reduction corresponds to about 37% cold reduction.
    3. The r-value of the annealed steel sheet rolled at 650°C was 0.8. But it increased to 1.14 by surface shaving. This value is approximately equal to that of about 37% cold reduction steel sheet. In these circumstances, the cause of the low r-value of steel sheet rolled in the ferrite region is the influence of surface shear strain.
    4. In the case of heating at 1250°C, average r-value of Ti-bearing exrta low carbon steel sheet is approximately 1.0, when the high-reduction rolling is achieved in the final three stands with a reduction more than 50% near the Ar3 temperature at each rolling pass.
  • Effect of Hardness Distribution on Propagation Behavior of Torsional Fatigue Crack of Induction Hardened Steels for Automotive Shafts

    pp. 830-836

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    The purpose of this study is to clarify the effect of hardness distribution on the propagation behavior of torsional fatigue crack of induction hardened steels for automotive shafts. The effect of hardness distribution on the propagation rate of mode III crack and fatigue fracture toughness were investigated.
    In the torsional fatigue test, mode III fatigue crack propagated in early stage after crack initiation. And, when fatigue crack length achieved a certain critical level, the fracture mode changed from mode III to mode I and static final fracture occurred with intergranular fracture at almost the same time.
    The propagation rate of mode III crack decreased with increasing the hardness of crack propagation region. On the other hand, the length of mode III crack propagation at the fracture was decreased by increasing case hardness. This indicates that increasing case hardness enhance the shift from fatigus crack propagating at mode III to static final fracture, namely decreased fatigue fracture toughness.
  • A Quantitative Macro Model of Steel Scrap Recycling Considering Copper Contamination for the Sustainable Society

    pp. 837-843

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    The macro model for analysis of the steel mass flow in Japan is proposed and the problems for realizing the environmentally sustainable society are analyzed. In the model, the steels are classified into four types; converter steel for machinery, converter steel for construction, electric furnace (EF) steel for machinery and EF steel for construction and they are assumed to be discharged from the society in accordance with lifetime distributions. The promotion of recycling increases the production of EF steel and its impurity concentration. Consequently, the amount of the EF steel supplied for machinery use is limited by the increase of copper concentration and it becomes necessity to reduce the copper contamination in post-consumer scraps in order to promote recycling. The goal contamination ratio is estimated from the calculation result on the scenario in which recycling ratio is assumed to be 100%. The reduction amount of CO2 emission by introducing the new technology to reduce copper contamination is calculated and it is converted to the cost assuming the CO2 international emission trading, which could be invested to the development of the new technology. It is shown that the investable cost is in the range from 8.3 to 30 billion yens par year.

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