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

Tetsu-to-Hagané Vol. 91 (2005), No. 4

  • Effect of Magnetic Field on Martensitic Transformation in Some Ferrous Alloys

    pp. 363-375

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    Magnetic field is one of external fields affecting martensitic transformations. In this paper, we review the change in transformation temperature and morphology by the application of magnetic field in some ferrous alloys with different magnetic properties, and explain their behavior thermodynamically. Besides, the magnetic field-induced strain in some ferromagnetic shape memory alloys is presented briefly. Moreover, kinetics of both isothermal and athermal martensitic transformations is explained based on a phenomenological theory.
  • Determination of the Ti2O3-CaO-Al2O3 Phase Diagram at Steelmaking Temperature

    pp. 376-382

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    In order to make the basis of oxide inclusion study containing titanium in the calcium treated steel, Ti2O3-CaO-Al2O3 phase diagram was investigated by diffusion couple experiments and high temperature equilibrium experiments. Ti2O3-CaO-Al2O3 phase diagram has been determined at 1600°C and 1550°C, under PO2=10-14-10-15 atm, which corresponds to dissolved oxygen content in deoxidized molten steel. In this system, liquid phase region, possibly forming plastic spherical inclusion, becomes narrower when Ti2O3 content is more than approximately 20 wt%. This region is also notably diminished when the temperature drops from 1600 to 1550°C. The reliability of the results measured in this work was confirmed by a good agreement of liquidus line and solid solubility with previous works.
  • Model Experiment and Analysis on the Motion of Non-metallic Inclusions

    pp. 383-389

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    The tiny non-metallic inclusion in a molten steel could be removed effectively when they collide and coalesce under the electromagnetic vibration. The viscosity resistance enforced on the particle is related to particles structure, surface status, size and movement velocity when inclusions are moving in the liquid. In order to study the collision and coalescence mechanism a water model experiment was conducted by using the porous particles made by glass fibers, which are simulated to dendritic inclusions. The falling process of the particles that was enforced by the gravity and the behavior when two particles that have the same diameter but difference solid fractions are approaching were observed by a high-speed camera, and then the velocity of the particles are calculated. According to the experiment results, the motion equation of the porous particles is derived. Moreover, the equation is examined by the model experiment. The approaching behavior of two particles is analyzed in the plane of the moving velocity and relative distance. The velocity change of the particles is very large when the large solid fractions are approaching, which means that strong liquid repelling resistance exists between the particles. The liquid repelling resistance is weak between the small solid fractions, which predicts that the particles are easy to collide and coalesce.
  • Gigacycle Fatigue Properties of Modified-ausformed V-added Steels

    pp. 390-396

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    This report reveals gigacycle fatigue properties for a modified-ausformed V-added steel with the chemical composition of 0.3C-0.3Si-1.0Cr-0.7Mo-0.3V in mass%. Modified-ausformed and oil-quenched steels were prepared for fatigue tests, followed by tempering at 400°C and 600°C. The tensile strengths of the 600°C tempered steels were almost equal to those of the 400°C tempered versions because of secondary hardening due to fine precipitation of vanadium carbides. The fatigue properties of the 600°C tempered steels oil-quenched steel (QT600) showed little difference from the 400°C tempered version (QT400) in spite of the fine precipitation of vanadium carbides. The modified-aus-formed steels (AF400 and AF600) revealed higher fatigue limits at 5×109 cycles than the oil-quenched versions (QT400 and QT600), although the difference between AF400 and AF600 was small. The remarkable difference between AF400 and AF600 was fatigue strengths at around 106 cycles, i.e. the fatigue strength of AF600 at those cycles was higher than that of AF400. Based on the above results, the effect of the fine precipitation of vanadium carbides was small on the gigacycle fatigue properties, while modified-ausforming could improve those properties. On the other hand, the multiple effects of the fine precipitation and modified-ausforming was large on the fatigue strength at around 106 cycles.
  • Effect of Ti and B on Microstructure of 780 MPa Class High Strength Steel Weld Metal

    pp. 397-402

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    The effect of Ti and B on the microstructure of 780 MPa class high strength steel weld metal was investigated. It was found that the morphology of bainitic ferrite of weld metal was changed from lath-like into acicular type by adding Ti. It was also revealed that the morphology of bainitic ferrite in the Ti bearing weld metal revested to lath-like by adding B. The change of microstructure by the Ti addition could be explained by the promotion of nucleation of acicular type bainitic ferrite, which was bainitic ferrite nucleated at Ti-oxides inside of austenite grains. It was supposed that segregation of free B around Ti-oxides restrained the nucleation of bainitic ferrite on Ti-oxides.
  • Cyclic Softening of the High-strength Steel HT780 Studied by Positron Annihilation Spectroscopy

    pp. 403-407

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    Cyclic softening mechanism of the high strength steel HT780 has been investigated using transmission electron microscopy (TEM) and positron annihilation lifetime spectroscopy. It has been found by the TEM observation that a high density of dislocation exists in the specimen before fatigue test, which moves from inside to the boundaries of ferrite grains in the rapid softening stage. The positron lifetime is found to increase rapidly in the rapid softening stage indicating that the positron lifetime of the mobile dislocation created by the fatigue test is longer than that of the dislocation which exists before the fatigue test. The positron lifetime becomes nearly constant as softening saturates. The positron lifetime at the saturation is longer as the strain amplitude is larger, showing that the density of the mobile dislocation depends on the strain amplitude while is kept constant during the cyclic deformation with a given strain amplitude.
  • Evaluation of Toughness and Creep Properties of Aged Main Valve CrMoV Casting Steel by Using Small Punch Specimens

    pp. 408-414

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    It has been required to evaluate material deterioration of plant components with high accuracy, because more than seventy percent of power plants in Japan have been operated for 100, 000 h or more. The small punch (SP) test method can directly determine mechanical properties of components with high accuracy because of a destructive test. Compared with the standard test method using large specimens, it can minimize the damage caused by removing samples from a component because of use of a small specimen. In this study, both the ductile-brittle transition temperature (DBTT) and the creep properties of CrMoV casting steel, which had been used as a main valve in a power plant for 100, 000 h, were estimated by using SP specimens. The conventional SP test results revealed that the SP-DBTT of the aged steel was higher than that of the virgin steel. The actual DBTT determined by Charpy impact tests with V-notched specimens was in relatively good agreement with the calculated one by the SP-DBTT. The results of SP creep test showed that the creep rupture strength of the aged steel was inferior to that of the virgin steel. This degradation of creep properties seemed to be attributed to the microstructural changes and the formation of cavities or micro cracks with the long-term operation. Good correlation was observed between the results of the SP creep test and the standard uniaxial creep test. Consequently, the SP testing method is expected to be an appropriate tool for evaluating material deterioration of plant components in-service.
  • Assessment of Fracture Toughness by CT and Round Bar Specimens in a HT780 Steel

    pp. 415-420

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    It is known that fracture toughness value of steels is affected by test temperature, specimen thickness and loading rate. In this research, it is attempted to investigate it by changing temperature and loading rate with the rate parameter then being applied. The fracture toughness value is also obtained by round bar specimen with a circular notch. This result has been compared with the results by the CT specimens, and the validity of the fracture toughness value that has been obtained from round bar specimen with a circular notch is examined. The sample material used is HT780 steel. The CT specimens were 1T, 2T and 4T-CT defined in ASTM E399, test temperature is varied from 77K to room temperature. The loading rate is also varied for the 1T-CT and the round bar specimen with a circular notch from static to 1 m/s. The fracture toughness value decreases as the test temperature decreases. It decreases with loading rate and specimen thickness. The fracture toughness test result is arranged using the stress intensity factor rate to obtain the rate parameter. Moreover, the fracture toughness value which has been obtained from the round bar specimen with a circular notch is lower than those by 1T-CT specimen, closer to 2T-CT specimen. The test temperature and the loading rate dependency of the fracture toughness value can be arranged by the rate parameter that is the function of temperature and stress intensity factor rate. Availability of the round bar specimen with a circular notch test specimen is discussed to obtain valid fracture toughness values.
  • Chlorine-containing Phases in CaO-SiO2-Al2O3 Slags and Their Dissolution Behavior into Aqueous Solution

    pp. 421-427

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    In order to clarify the possibility of utilization of blast furnace slag containing chlorine, chlorine bearing phases in the synthetic CaO-SiO2-Al2O3-Cl slags were characterized and their dissolution behavior was investigated. The synthetic slags with various crystalinity were identified by XRD and SEM-EDX. Chlorine was found to condense in the amorphous phase and 9CaO·6Al2O3·5SiO2·CaCl2, whereas it was hardly detected in the other crystallized phase, such as CaO·SiO2, 2CaO·Al2O3·SiO2, CaO·Al2O3·2SiO2. The dissolution behavior of chlorine into aqueous solution was studied to grasp the stability of chlorine in the slag. Experimental time (Shaking time) and pH dependences on the solute dissolved from the two main chlorine containing phase, amorphous phase and 9CaO·6Al2O3·5SiO2·CaCl2, were measured. The amount of chlorine dissolved from amorphous phase was smaller than that from 9Ca0·6Al2O3·5SiO2·CaCl2. The amount of solute dissolved from the slag tended to increase with the fraction of crystallization. Furthermore, the crystal phases in blast furnace slags were identified by XRD and SEM-EDX, and there were two main crystal phases, melilite (Ca2(Al, Mg)(Si, Al)2O7) and 9CaO·6SiO2·CaCl2 in it. The similarity between synthetic slag and BF slag was that the amount of Cl dissolved from slag increased with crystallizing.
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  • Organized Loading Schedule System for Batch Annealing Furnace at Kudamatsu Plant, Toyo Kohan Co., Ltd.

    pp. 428-432

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    T.O.C. (Theory Of Constraints) was first introduced at Kudamatsu Plant in 2001, when we launched the 3-year project to reform the production system and this project is still proceeding.
    This was aimed at constructing a competitive manufacturing structure in which our production line could be streamlined and require less resources, less reserved materials, and less inventory within a shorter lead-time than before, dealing with severe competition in manufacturing industries.
    We have promoted the realization of the production control system based on the belief that it will bring about overall benefit to our plant by maximizing the operation in the bottle neck and boosting the through-put on the whole.
    As the first step to establish the consistent production plan system, we have developed the organized loading schedule system for the B.A.(Batch Annealing) process. This system was brought into effect in 2002 and has been performing very well so far.
    This paper describes the advancement made by introducing this system, such as reducing lead-time and labor savings.
  • Mixing Time in a Cylindrical Bath Agitated by Off-centered Swirling Liquid Jet

    pp. 433-435

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