Materials Transactions, JIM
Online ISSN : 2432-471X
Print ISSN : 0916-1821
ISSN-L : 0916-1821
Volume 33 , Issue 6
Showing 1-13 articles out of 13 articles from the selected issue
  • Hiroyuki Katayama
    1992 Volume 33 Issue 6 Pages 531-542
    Published: 1992
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    A flexible manufacturing system for the production of iron and steel is required. One of the potential technologies for this purpose is the smelting reduction process with a thick layer of slag. A feature of the process is that an oxygen jet is separated from the metal bath by a thick layer of slag. This is realized by the coexistence of carbonaceous materials for controlling slag foaming, and it allows high post combustion operation without disturbing the reducing reaction.
    Experiments using furnaces of 100 kg, 600 kg, 3 t and 100 t for the production of Cr–Fe–C (Cr≤58%), Mn–Fe–C (Mn≤65%) and Fe–C by smelting reduction were done successfully. The procedure of experiments is reviewed and the phenomena of slag foaming and its control by the coexistence of carbonaceous materials, the physical properties of the slag layer, the reducing reaction, the method for supplying fine ore from the top without agglomeration, the limit of post combustion, the mechanism of heat transfer particularly by the circulation of carbonaceous materials in the slag layer, and the behavior of impurities during smelting reduction are discussed. There would be no problems in enlarging except that post combustion decreases when carbonaceous materials of high volatile matter are used, and coal consumption does not decrease as much as expected from the decrease of heat loss by enlarging.
    This process can also be applied for scrap melting. An interesting phenomenon found in scrap melting with a thick layer of slag is the accelaration of Sn removal as SnS.
    In the production of ferroalloys and hot metal, features of this process are (1) heating without electricity, (2) high post combustion, (3) decrease of dust formation which is a common problem in the use of oxygen gas, and (4) effective removal of some impurities.
    Though there are some problems particularly on how to use high volatile matter coal effectively, this process shows a new direction for future iron and ferroalloy production, particularly for increasing the flexibility.
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  • Yuichi Tanaka, Hidehiko Kage
    1992 Volume 33 Issue 6 Pages 543-557
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The superior combination of attainable properties has caused austempered spheroidal graphite cast iron to emerge as a new class of cast iron. The metallurgy of austempered spheroidal graphite cast iron is presented with the purpose of clarifying the mechanical properties. It is emphasized that segregation of alloying elements can cause an iron to behave differently than might be expected. The role of the graphite nodule count on the strength and the toughness of this iron is discussed from the standpoint of the matrix structure, because segregation can be controlled by varying the nodule count, i.e. solidification rate during casting process. High carbon-reacted austenite increases with increasing nodule count, but instable unreacted austenite decreases. With increasing nodule count, the tensile and fatigue properties are improved, but the elasto-plastic fracture toughness decreases. This behaviour is explained without contradiction by the microstructures including the reacted and unreacted retained austenites and the notch effect of the graphite. The austempered spheroidal graphite cast iron has very desirable characteristics for a wide range of applications as component parts of automobiles, construction machinery, railroad, etc.
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  • T. Mohri, Y. Sugawara, K. Watanabe, J. M. Sanchez
    1992 Volume 33 Issue 6 Pages 558-564
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    A study synthesizing the kinetic and equilibrium aspects of order-disorder phase transitions is attempted for an fcc system at 50 at% using the Cluster Variation Method and the Path Probability Method. The disorder-L12-L10 phase diagram is calculated using the tetrahedron approximation of the CVM. A perturbation expansion of the free energy functional, followed by a Fourier transformation, provides a concentration wave description of the system, from which the ⟨100⟩ instability locus in the phase diagram and the short range order diffuse intensity are obtained. By employing the Path Probability Method, the time evolution of the pair and the tetrahedron correlation functions as well as fluctuations from the most probable path during an isothermal aging process following a quenching operation are calculated for a system at 1:1 stoichiometry. Finally, the most probable path followed by the system during an isothermal aging process is placed in a thermodynamic configuration space.
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  • Takeshi Kawabata, Daisuke Shindo, Kenji Hiraga
    1992 Volume 33 Issue 6 Pages 565-570
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    End-on images of dislocations in Ni3(Al, Ti) single crystals deformed at 683 and 293 K were observed by high-resolution transmission electron microscopy. They showed a superlattice intrinsic stacking fault (SISF) type of dissociation on a {111} plane and an antiphase boundary (APB) type of dissociation on a {001} plane. SISF and APB energies were calculated to be 133 and 560 mJ/m2, respectively, using an isotropic elasticity theory, and they were compared with the other results obtained by field ion microscopy, weak-beam technique and high-resolution electron microscopy. It is considered that a decrease of dissociation distance due to the Ti addition results in an increase of strength anomaly.
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  • K. Yamada, K. Sato, C. B. Boothroyd
    1992 Volume 33 Issue 6 Pages 571-576
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The purpose of this work is to detect and quantify nitrogen which is dissolved in steels using parallel detection Electron Energy Loss Spectroscopy (PEELS). PEELS in the Transmission Electron Microscope (TEM) has a high detection efficiency and is potentially powerful for studying the behaviour of light elements in commercial steels with a high spatial resolution.
    Type 316 stainless steels (SUS316) and high nitrogen austenitic stainless steels having a range of nitrogen (0.04–0.40 mass%) content were used. We also used a duplex stainless steel as a test specimen where partitioning of nitrogen between ferrite (α) and austenite (γ) phases was present. Typically nine spectra were recorded from the same area of the specimen and then were processed using the iterative averaging method described. This method efficiently removes the noise due to the channel gain variation in the parallel detection and allows the detection of small peaks. The intensity ratios of (INICr) or (INIFe) are correlated with the atomic concentration ratios (CNCCr) or (CNCFe) where I and C denote the intensity and atomic concentration, respectively.
    The measured intensity ratio and the concentration ratio have a good correlation and a common calibration curve is obtained regardless of the matrix composition which are different between type 316 and high nitrogen austenitic stainless steels. By using the calibration curve, the nitrogen content can be determined as 0.26±0.04 mass% in the γ-phase of the duplex stainless steel, while that of α-phase is close to or below the detection limit of 0.04 mass%.
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  • Setsuo Takaki, Shunji Iizuka, Kouki Tomimura, Youichi Tokunaga
    1992 Volume 33 Issue 6 Pages 577-584
    Published: 1992
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    The effect of cold working on the recovery and recrystallization behavior of lath martensite has been investigated in a 0.2% C low alloy steel by means of optical and transmission electron microscopy. Cold working in the lath martensitic steel causes an intrusion of slip bands into the matrix and this results in the destruction of lath martensitic structure and the formation of dislocation cell structure around slip bands. The volume fraction of such a damaged martensite increases with increasing deformation. In the specimens subjected to heavy cold rolling above 80% reduction, the undamaged lath martensitic structure could rarely be observed and dislocation density becomes one order of magnitude higher.
    On the annealing at 973 K (below AC1 temperature), there is a large difference in the recovery and recrystallization behavior between the damaged and undamaged areas. Recrystallized ferrite grains preferentially nucleate within the damaged area and grow to encroach into the undamaged area where the recovery rate is slower than that in the damaged area. With increasing prior deformation, the recovery and recrystallization of the matrix are markedly promoted, corresponding to an increase in the volume fraction of the damaged martensite and in the density of dislocations.
    Thus, it is concluded that cold working before annealing plays a role to destroy the lath martensitic structure and to increase the dislocation density, leading to an increase in both nucleation and growth rate of the recrystallized ferrite grains.
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  • Tadashi Furuhara, Hideyuki Nakamori, Tadashi Maki
    1992 Volume 33 Issue 6 Pages 585-595
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Crystallographic orientation relationships of α phases precipitated on dislocations and deformation twin boundaries in the β matrix have been investigated in a Ti–15V–3Cr–3Sn–3Al alloy, by means of transmission electron microscopy (TEM).
    Planar and widely spaced, {112}⟨111⟩β slip bands are formed by weak rolling at room temperature after being solutionized. By the subsequent aging at 933 K, α plates precipitate preferentially on the dislocations in the slip bands. In the same slip bands, α plates select particular variants of the Burgers orientation relationship. The selectivity of variants was discussed in terms of the effective relaxation of the transformation strain by the stress field associated with the dislocation.
    By subzero rolling at 77 K, {332}⟨113⟩β deformation twins are produced. By the subsequent aging at 933 K, α phases precipitate on the twin boundaries, holding the Burgers orientation relationships with respect to both of the β matrix and the twin. It is considered that the α nucleus forms coherently with both of the β phases to reduce the energy of the α⁄β interface newly formed.
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  • D. S. Sarma, K. M. Al-Otaibi, K. L. Murty
    1992 Volume 33 Issue 6 Pages 596-603
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The tensile properties and deformed microstructures of zirconium in the annealed condition have been investigated in both the rolling (RD) and transverse (TD) directions at three strain rates of 10−4, 10−3 and 10−2 s−1 at different temperatures in the range 298–673 K in order to understand the extent of anisotropy in mechanical properties, discontinuous yielding behaviour, dynamic strain aging (DSA) and mechanisms of deformation. It is shown that zirconium does not exhibit sharp yield points in either RD or TD in the temperature and strain rate ranges studied. While the yield strength (YS) and the ultimate tensile strength (UTS) values are not influenced by the direction of testing or strain rate at any temperature of testing, the tensile ductility is superior in the RD to that in the TD, and the YS and UTS decreased gradually with increasing temperature. The strain rate sensitivity (m) values are very small in all the conditions studied and but show a slightly decreasing trend after 473 K, which indicates an extremely weak DSA effect, if any. The transmission electron microscopy studies performed after 2.5% tensile strain as well as on the uniform gage portion of the broken tensile specimens indicate that zirconium deforms by a mixed mode of prismatic slip and twinning in both RD and TD.
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  • Kazuo Yamanaka
    1992 Volume 33 Issue 6 Pages 604-610
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The initial repassivation processes of anodic reaction on newly created surfaces of high nickel alloys containing 0–30 mass% chromium were investigated by a rapid straining electrode technique in a 10%Na2SO4+H2SO4 (pH 3.0 at room temperature) aqueous solution at 553 K at constant anodic potentials. The results obtained are as follows:
    (1) The decrease in current density with time after rapid straining consists of two stages. Namely, the current density in a short period (within around 20 ms) after rapid straining decays to the formula of i∝exp(−tn) (i: current density, t: time, n: constant), and then the density at least up to 1000 ms decays to the formula of itn.
    (2) The repassivation rate increased with increasing chromium content, and so the amounts of charge caused by the metal dissolution decreased with increasing chromium content.
    (3) It was considered that the reason for which nickel-base alloys containing high chromium content such as Alloy 690 (60%Ni-30%Cr-10%Fe) had high SCC resistance in a high temperature acidic solution containing sulfate ions is due to both the promotion of the repassivation and the suppression of the film dissolution by the formation of the chromium oxide film.
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  • Hidekazu Sueyoshi, Yoshihisa Ohzono
    1992 Volume 33 Issue 6 Pages 611-617
    Published: 1992
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    In Japan, Sn–Pb alloys have been used as materials for utensils and vessels. However, Pb is undesirable in the utensils and vessels because of its toxicity. For developing Pb-free Sn alloys having excellent machinability, high strength, and pear-like surface morphology, Sn–Bi alloys were studied from the viewpoints of hardness, microstructure, surface morphology, and machinability.
    The hardness equivalent to that of Sn–Pb alloys is obtained by the addition of 1 mass% Bi. Hardness of Sn–Bi alloys is attributable to solid-solution hardening up to 2 mass% Bi, but thereafter to dispersion hardening. Microstructure of Sn–Bi alloys depends upon solidification rate. In rapid cooling fine Bi particles crystallize out uniformly, while in slow cooling Bi particles crystallize out along grain boundaries. When the Sn–Bi alloys solidified under the latter condition are etched with HNO3, the etched surface results in pear-like morphology. Sn–Bi alloys exhibited an excellent chip-disposability because Bi particles promote the crack propagation in chip. Surface roughness decreases as Bi content increases up to 2 mass%, but thereafter yields to a saturation behavior. The decrease in surface roughness is caused by matrix-embrittlement due to the addition of Bi.
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  • Kazumi Tani, Hiroshi Nakahira, Kiyoshi Miyajima, Yoshio Harada
    1992 Volume 33 Issue 6 Pages 618-626
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The dependency of the physical property of thermally sprayed coatings on the microstructure which is characterized by a composite of lamellae was examined. The thermal and elastic properties determined parallel to the coating plane have been proved to be different from those determined perpendicularly to it, which indicates that the thermally sprayed coatings have an anisotropy. The thermal conductivities of copper, molybdenum, Type 316 austenitic stainless steel, alumina and WC-20 mass%Cr-7 mass%Ni cermet coatings are discussed. The values parallel to the coating plane were 1 to 2.27 times larger than those perpendicular to it. The behavior of anisotropy can be explained by the rule of mixture. Young’s moduli in the two directions of WC-12 mass%Co cermet coatings were measured and the value parallel to the coating plane was about twice as large as that perpendicular to it. The thermally sprayed coatings may be characterized by a composite of rapidly solidified lamellae between which there is only limited real contact and they also contain pores and oxides. It is clear that the directionality characteristic of the thermal barrier behavior or the less cohesion among the lamellae is dominant over the anisotropy of thermally sprayed coatings.
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  • Yoshitaka Iwabuchi
    1992 Volume 33 Issue 6 Pages 627-631
    Published: 1992
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    The microstructural features and mechanical properties of SCS 13 steel castings were correlated with nitrogen contents together with the varying concentrations of nickel and other compositions. Delta-ferrite contents varied with the compositions, however, showing relatively lower contents than those predicted by Delong plot. Regression equations were developed among various properties. Tensile strength and abrasive wear were also linearly related to the hardness. Electrochemical measurements showed that the varying chemical compositions and delta-ferrite contents have only a minor effect on the corrosion resistance. Multiple regression analysis was made to explain the contribution of nitrogen, and delta-ferrite, which satisfactorily predicted the yield strength, tensile strength, impact energy and abrasive wear. It was shown that nitrogen causes well-known strengthening effect, and also delta-ferrite is a powerful strengthening element.
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  • Naoya Hasegawa, Noriyuki Kataoka, Kenji Hiraga, Hiroyasu Fujimori
    1992 Volume 33 Issue 6 Pages 632-635
    Published: 1992
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Nanocrystalline structure of soft magnetic Fe–Ta–C films crystallized from an amorphous state has been investigated. High-resolution transmission electron microscopy (HRTEM) revealed that tantalum carbide particles much smaller than iron grains are dispersed at the grain boundaries (mostly at tripple junctions) of iron grains. Such a configuration of the carbides hardly interrupts the intergranular magnetic coupling which reduces the effective magnetocrystalline anisotropy. It was also found by both HRTEM and temperature dependence of magnetization and coercivity that there is no distinct residual amorphous phase in the nanocrystalline Fe–Ta–C films, unlike the Fe–Cu–Nb–Si–B alloys. It was proved that the substance stabilizing the nanocrystallites in the Fe–Ta–C films is not an amorphous phase but the tantalum carbide which is thermally more stable.
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