Journal of the Japan Society of Powder and Powder Metallurgy
Online ISSN : 1880-9014
Print ISSN : 0532-8799
ISSN-L : 0532-8799
Volume 29, Issue 3
Displaying 1-5 of 5 articles from this issue
  • Katsushi Kusaka
    1982 Volume 29 Issue 3 Pages 71-78
    Published: April 25, 1982
    Released on J-STAGE: December 04, 2009
    JOURNAL FREE ACCESS
    An investigation was made on pressing and sintering behavior of water-atomized 13%Cr, 17%Cr and 23%Cr-steel powders having 0.25% or less of nitrogen.
    The results were summarized as follows:
    (1) Excess nitrogen was mostly retained in powders as a state of solid-solution on account of rapid solidi-fication obtained by quench-atomization of melt and the powder-compressibility was inclined to get lowered with a solid-solution hardening proportional to the amount of nitrogen plus carbon dissolved in particle matrix.
    (2) Especially for nitrogen-rich 13%Cr steel powders, the powder compressibility was more deteriorated under the added influence of γ→α' phase transformation which occurred on cooling to room temperature during quench-atomization. On the other hand, the situation was appreciably improved by annealing the powders at the temperature around Al, because of the precipitation of nitride from α'.
    (3) Nitrogen in powders (compacts) was found to affect the rate constant K (ΔL/L=K(T, D)⋅tn) in relation to the isothermal transformation (γ→α) arising from denitrogenization during vacuum sintering for lower Cr steel powders.
    Consequently, the same level of densification rates for all powders were obtained in the middle stage of sintering (approximately at the temperature above 1100°C), irrespectively of original amount of nitrogen.
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  • Hidenori Kuroki, Katsura Hayashi
    1982 Volume 29 Issue 3 Pages 79-83
    Published: April 25, 1982
    Released on J-STAGE: May 22, 2009
    JOURNAL FREE ACCESS
    The dimensional changes in the axial direction of iron powder compacts (10 mm diameter, 10 mm height) pressed under 2-8 t/cm2 (196-784 MPa) were measured along the process of production; these are, after unloading, ejecting, dewaxing at 600°C (873 K) for 30 min and sintering at 1100°C (1373 K) for 60 min in cracked-ammonia.
    When 0.7 wt% of powder lubricant was added to iron powder, the magnitude of the axial spring-back was larger than that observed when die-wall was lubricated. But, each powder lubricant did not give appreciable difference in magnitude.
    Some compacts swelled in dewaxing. Greater swelling was observed on compacts pressed under high pressure using lubricants which were viscous in the molten state.
    Shrinkage by sintering grew large with the increase of the sum of spring-back and swelling. But, this tendency disappeared when the sum surpassed 3%.
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  • Influence of infiltration teperature and time
    Kunio Okimoto, Tomio Sato
    1982 Volume 29 Issue 3 Pages 84-89
    Published: April 25, 1982
    Released on J-STAGE: December 04, 2009
    JOURNAL FREE ACCESS
    Influence of infiltration temperature and time upon the mechanical properties of the joined sintered products was studied. The optimum condition for joining by infiltration was 60 min. at 1140°C, or a few min. at 1200°C. In this joining condition, tensile strength was improved by 3 kg/mm2, and impact value and reduction of area were doubled to the products treated by the previously reported condition of at 1140°C for 30 min.
    As an example of application of this joining method, joining of sintered iron compact and wrought metal was carried out. The strength of the joint was superior to that of both the sintered iron compact and wrought metal. As another example, joined hollow products were made successfully by compacting the iron powder within a pre-compacted block.
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  • Tadatoshi Honda
    1982 Volume 29 Issue 3 Pages 90-94
    Published: April 25, 1982
    Released on J-STAGE: May 22, 2009
    JOURNAL FREE ACCESS
    The effects of the boronizing temperature and time, the sintered density, and the addition of alloying elements on the formation of the boride layer in sintered irons treated with the mixed powder of 80 wt% Ferroboron and 20 wt% Na2CO3 were investigated by microscopic and SEM's examinations, X-ray diffraction and EPMA's analysis. The following results were obtained.
    (1) The microscopic examination and X-ray diffraction showed that the boride layer consisted of two phases of FeB in the outer layer and Fe2B in the inner one.
    The thickness of boride layer was independent of the density of sintered iron compact.
    (2) The boride layer of sintered Fe and Fe-alloyed compacts increased with increasing boronizing temperatures and times in according with parabolic law.
    (3) The rate of growth of the boride layer in sintered Fe-C, Fe-Mo and Fe-Ni compacts was inhibited with increasing the addition of alloying elements.
    The EPMA's analysis showed that a very considerable concentration of such as C, Mo and Ni occurred at the interface zone between the boride layer and the matrix.
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  • Hiroshi Nagai, Yoshiki Takebayashi
    1982 Volume 29 Issue 3 Pages 95-99
    Published: April 25, 1982
    Released on J-STAGE: May 22, 2009
    JOURNAL FREE ACCESS
    The isothermal oxidation behavior in air at 1000, 1050 and 1100°C of Fe-20Cr alloys with 1 wt% dispersion of Y2O3, La2O3, Al2O3, TiO2, SiO2 and Cr2O3 prepared by a conventional sintering and rolling procedure was examined. It was found that the dispersion of SiO2, TiO2 and Cr2O3 reduced the oxidation resistance, while the dispersion of La2O3 and Y2O3 excellently improved the oxidation resistance of Fe-20Cr alloy. The oxidation rates during the early stage of oxidation were apparently dependent on the type of the dispersed oxides, while the grain size of the alloys was not dependent on the type of the dispersed oxides. There was no evidence that the dispersed particles accumulated at the alloy-scale interface. Ion microanalyses of the Cr2O3 scales formed after 1 hr oxidation at 1100°C revealed that all the dispersed elements were incorporated in the scale and the iron content of the scale was lower on the alloys which exhibited better oxidation resistance.
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