Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 66 (1980), No. 6

  • Interdiffusion of Chromium in Molten Fe-Cr and Fe-Cr-Ni Alloys

    pp. 601-607

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    Interdiffusion coefficients of chromium in molten Fe-Cr and Fe-Cr-Ni alloys have been determined at 1 550°C by the diffusion couple method with the following results:
    (1) Interdiffusion coefficient in molten Fe-Cr alloy, DFe-Cr, is expressed by the following empirical equation for chromium content up to 15 at%:
    DFe-Cr×105=3.36-20.9NCr+171N2Cr, cm2/s
    (2) In molten Fe-Cr-Ni alloy with the composition of 4 at%Ni and 0 to 12 at%Cr, the main (diagonal) diffusion coefficient of chromium, DCrCr, is 1.3 to 1.9 times as large as the binary diffusivity DFe-Cr, that is, an addition of nickel increases the diffusion rate of chromium. Cross diffusion coefficients, DCrNi and DNiCr, are estimated to be negative and smaller than the main coefficients by an order of magnitude.
  • The Effect of Surface Movement on the Evaporation Rates of Alloying Elements from Liquid Iron under Vacuum

    pp. 608-617

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    The rates of evaporation of alloying elements from Fe-Cu, Fe-Sn and Fe-Cr melts under vacuum have been investigated by using an experimental apparatus which was made up of a LANGMUIR'S evaporation cell and of target plates for collecting evaporated material. These melts were so heated as to change stirring conditions by resistance heater or high frequency induction.
    The evaporation rates are of first order with respect to all the alloying elements. The evaporation from Fe-Sn systems is mainly controlled by the evaporation step on the surface. However, in the cases of Fe-Cu and Fe-Cr systems, both the evaporation step and the diffusion step through the liquid boundary layer are rate controlling, i.e. in these systems, the total evaporation process is of mixed. controll.
    The surface concentration of these alloying elements was obtained by analyzing the condensed material on the target plates. The observed values are in good agreement with the theoretical values based on the model proposed by R. G. WARD. This agreement implys that the vaporization coefficients of these alloying elements are unity.
    When tin which is surface active element is evaporated from the specimen, surface movement due to surface pressure (Marangoni effect) is observed, and the mass transfer coefficient is increased.
  • Solidification Microstructure of Ingots and Continuously Cast Slabs Treated with Rare Earth Metal

    pp. 618-627

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    In order to evaluate theoretically and prove the effect of REM and Ca-sulphides on heterogeneous nucleation, investigations have been made to find how REM addition influences the solidication microstructure of ingots and continuously cast slabs.
    Some characteristics of REM-added steel compared with ordinary steel are as follows:
    1) Primary dendrite arm spacing is narrower.
    2) Primary dendrite arms are shorter, and they exist more in number.
    3) The growth direction of dendrite arms is less oriented.
    4) The micro-segregation of C, S, P, Si, and Mn is less.
    It is concluded that new primary dendrite arms are generated due to the hetrogeneous nucleation by REM addition in the region of comparatively small supercooling near liquid-solid interface.
  • Solidification Macrostructure of Ingots and Continuously Cast Slabs Treated with Rare Earth Metal

    pp. 628-637

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    Various characteristics were observed in the solidification macrostructure of ingots and continuously cast slabs treated with REM.
    The results are as follows:
    1) REM addition brings about diminition of macro-segregation, enlargement of equiaxed zone, and reduction of loose structure.
    2) The starting position of the formation of the inverse V-segregation moves toward the center of ingot and the segregated area expands. The length of segregation line and the segregation ratio are reduced.
    3) By autoradiographic observation, large differences in macrosolidification rate are not observed, however, mushy zone at the bottom of an ingot is formed earlier.
    4) REM-oxides, sulphides, and oxysulphides are mainly precipitated in dendrite arms. The constituents of inclusions are varied by the methods of REM addition.
    Non-metallic inclusions formed by REM addition seem to act as nucleation catalyst and thus improve not only the microstructure but also the macrostructure of the casts.
  • The Effects of Electromagnetic Stirring on Cast Structure of Continuously Cast SUS 430 Stainless Steel Slabs

    pp. 638-646

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    The effects of electromagnetic stirring on cast structure of continuously cast SUS 430 slabs have been investigated in order to improve ridging of sheets by grain refinement of cast structure.
    The results are summerized as follows:
    (1) As stirring intensity increases, equiaxed crystal zone enlarges. Grain refinement of cast structure is influenced considerably by super heat (ΔT) of molten metals and even if stirring intensity increases equiaxed crystal zone hardly enlarges when ΔT reaches a certain temperature. Alternate stirring mode is most suitable for stirring. The effect of super heat on grain refinement of cast structure can be relieved by falling position of stirrer, but ratio of equiaxed crystal zone decreases. Suitable stirring conditions for high ratio of equiaxed crystal zone above 60% are found.
    (2) As ratio of equiaxed crystal zone increases ridging of sheets from continuously cast SUS 430 slabs are improved. Ratio of equiaxed crystal zone above 50% is necessary to obtain almost the same ridging as sheets from ingots.
  • Formation of MnS-type Inclusion in Steel

    pp. 647-656

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    The formation mechanism of MnS-type inclusion in steel was investigated on the basis of the experimental results with the effects of sulfur content and cooling rate on the morphology of sulfide, the relation between the solidification structure and the distribution of sulfides, and the observation of formation process of sulfide in steel quenched from various temperatures.
    As the result, it became clear that the sulfide which formed an eutectic colony (type II according to SIMS' classification) was increased with the sulfur content in steel and the cooling rate, observed mostly in the region solidified lastly and formed in contact with the melt at the final period of solidification, and also that the non-colony type sulfide (type I, type III and so on) was hardly affected with the sulfur content in steel, decreased as an increase of cooling rate, observed mainly around a dendrite and increased remarkably after the finish of solidification.
    These results can be explained rationally by an idea that the colony type sulfide is formed by the eutectic reaction while the non-colony type sulfide is formed as the precipitate from the solid steel.
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  • Effect of Hot Rolling Process on Deep Drawability and Ridging Tendency of Ti Stabilized 17Cr Stainless Steel

    pp. 657-666

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    Hot rolling and hot-band annealing conditions seem to be very important factors to produce the final sheet having a better deep drawability and fewer surface defects for Ti stabilized 17Cr stainless steel.
    Two kinds of experiments were performed to investigate
    (1) the effect of finishing temperature with and without hot-band annealing on the plastic strain ratio (r value) of the final sheet,
    (2) the effect of finishing temperature and hot-band annealing condition on the ridging tendency of final sheet, and obtained the following results.
    Excellent r values are obtainable by decreasing the finishing temperature without hot-band annealing. But pronounced ridging is formed by omitting the hot-band annealing.
    Ridging can be diminished by eliminating the band structure which is formed in the center layer of the hot rolled sheet, and the elimination can be attained with a combination of low finishing temperature and propriate hot-band annealing temperature.
    The lower finishing temperature is favorable as it facilitates the recrystallization of the band structure with a lower annealing temperature.
    The hot-band annealing temperature must be high enough to complete the recrystallization of the band structure, but not be so high as the grain coarsens to become an origin of the orange peel.
    The appropriate annealing temperature depends on hot rolling condition and Ti contents.
  • Strength and Toughness of a Cold Rolled 13Ni-15Co-10Mo Maraging Steel

    pp. 667-676

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    A study was conducted to determine the effect of cold rolling prior to aging on the strength and toughness of an ultrahigh strength 13Ni-15Co-10Mo maraging steel. The smooth tensile strength of cold rolled and aged maraging steel increased continuously with increasing amount of cold reduction. The cold rolled maraging steel exhibited anisotropy in properties: the tensile strength in the transverse direction was higher than in the longitudinal direction, whereas the reduction of area and elongation showed lower values in the transverse direction. The notch tensile strength and plane strain fracture toughness KIC also increased with increasing amount of cold reduction, taking maximum values at the 60-70% reduction. For example, longitudinal KIC value increased from 34 MPa·m1/2 for 0% reduction to 63 MPa·m1/2 for 70% reduction. The large KIC increase was attributable to the formation of delamination cracks running parallel to the rolling plane. The KIC test specimen might behave as the sum of a number of thin plates in the presence of the delamination cracks and each thin plate might fracture under the plane stress condition. From these results, it was concluded that the good combination of the strength and toughness could be obtained at the 60% cold reduction.
  • Relation between Hydrogen Embrittlement and Strain Rate Sensitivity in the Tensile Properties of 245kg/mm2 Grade and 280kg/mm2 Grade Maraging Steels

    pp. 677-684

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    Tensile properties and their strain rate sensitivity have been investigated on 245kg/mm2 grade and 280kg/mm2 grade maraging steels as a function of testing temperature. Tensile test was carried out at temperatures ranging from -76°to 150°C, and a crosshead travel speed was varied from 0.005 to 30 mm/min. The strain rate sensitivity in the maraging steels was produced by selecting aging temperature and time.
    It was found that temperature range where the tensile properties were very sensitive to strain rate was from about -40°to about 75°C. As the strain rate decreased, tensile elongation decreased. Tensile elongation at a decreased strain rate was increased in tensile tests at temperatures where no strain rate sensitivity was observed. It was also found that tensile elongation at room temperature was increased by increasing the strain rate. Accordingly, hydrogen embrittlement is vitally concerned with the strain rate sensitivity of the tensile properties.
  • Effects of Cr and Zr on Yield Strength of Al-killed Steel

    pp. 685-692

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    A systematic study has been made of the effects of Cr and Zr on the yield strength of steels in order to develop super mild steels. The steels studied have almost the same chemical composition as commercial Al-killed mild steels except for the addition of Cr and Zr.
    The yield strength of the hot rolled steels decreases with Cr content and becomes the lowest at about 0.35wt%Cr. It also decreases with Zr content up to 0.12wt%.
    The relation of grain size and yield strength (σy) of the steels has been investigated in order to determine the parameters of σ0 and Ky in Hall-Petch relation expressed as σy=σ0+Kyd-1/2, where σ0, Ky and d have usual meanings. σ0 and Ky have been discussed in terms of Cr and Zr contents.
    Cr addition continuonsly increases Ky but decreases σ0. In contrast, Zr addition decreases Ky and provides little effect on σ0. The variations of σ0 and Ky can be attributed to the carbon and nitrogen contents in solution and to the area fraction of pearlite formed at the grain boundaries, respectively.
    It has been concluded that the proper combination of Cr and Zr decreases both σ0 and Ky and results in a super mild steel with an extremely low yield strength of about 10kg/mm2.
  • Probability Distribution of Failure Times of Stress Corrosion Cracking of 17Cr-11Ni Stainless Steel

    pp. 693-701

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    Probability distribution of failure times of stress corrosion cracking of 17Cr-11Ni stainless steel under constant stresses of 5 to 30 kg/mm2 in 25%, 35%, and 45% MgCl2 solutions at their boiling temperature has been analysed by using the Weibull probability paper which is widely used in reliability engineering. Probability distribution of failure times was found to be described as single or composite Weibull distributions. The composite distribution consisting of mode 1 and mode 2 distributions is found at the low stress conditions. Mode 1 is observed at the earlier failure time region and its shape parameter is larger than unity, depending on the stress and temperature examined. On the other hand, the shape parameter of mode 2 which is observed in the latter region of failure times shows almost a constant value of unity. The condition which gives the shape parameter of unity is likely to correspond to a chance failure or random occurence of crack initiation, while the shape parameter larger than unity indicates a wearout failure which seems to correspond to crack propagation. Thus, the type of distribution of failure times is likely to connect with the failure mode, i.e., crack initiation or propagation.
  • Thermal Stress Measurement of Explosive Austenitic Stainless Clad Steel with X-ray

    pp. 702-709

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    Since the method of X-ray stress measurement can be done by non-contact and non-destructive state, we can easily perform the measurement even if the temperature is high such as a few hundreds degree.
    In this paper the thermal stress on heated clad steel by X-ray was measured. The result was that we could perform good stress measurement and could find a clear thermal stress cycle at even such a high temperature as 560°C.
    Experimental results are as follows:
    1) The clad steel hearted up to a temperature of 560°C showed a fine X-ray profile and gave a good correlation on 2θ-sin2ψ diagrams, so we could perform thermal stress measurement by the usual method.
    2) In the heating process the thermal stress explained by thermal-expansion coefficient showed thermal stress explained by thermal-expansion coefficient showed thermal stress cycles, giving a terperature loop.
    3) The stress value varied by removal of oxide film.
  • Effects of Alloying Elements and Inoculators on Refining of Solidification Structures of Type 430 Stainless Steel

    pp. 710-716

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    In order to improve the solidification structure of type 430 steel, alloying and inoculation were tested.
    Among used alloying elements, Ti is most effective for formation of equiaxed zone, and this effect is considered to be attributed to TiN as nuclei. Ratio of equiaxed zone is related to quantity of TiN.
    Co-borate and other borates induce the local temperature drop by thermal decomposition in liquid steel, and then improve the solidification structure. So these inoculators must be used at casting stage.
  • Statistical Properties for Fatigue Strength of Steels

    pp. 717-723

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  • Origin of Iron Ores

    pp. 724-729

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  • 石油および天然ガス資源開発

    pp. 730-733

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  • 誌上討論

    pp. 734-736

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  • Ironmaking- and Steelmaking-Technology in 1980s/Japanese Steel Industry and Its Rate of Development

    pp. 737-754

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  • 抄録

    pp. 755-761

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