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

Tetsu-to-Hagané Vol. 73 (1987), No. 14

  • Technological Challenge for the Japanese Steel Industry

    pp. 1613-1621

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  • Description on Blast Furnace by U. HUGUENIN and Ohashi Blast Furnace, Kamaishi Iron Mine

    pp. 1622-1630

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  • The Recent Trend of Steel for Construction Machine and Earth Moving Equipment

    pp. 1631-1642

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  • Fatigue Life and Safety of Machine

    pp. 1643-1655

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  • Progress in Light Water Reactor Pressure Vessel Steels

    pp. 1656-1667

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  • Effects of Gaseous Sulphur and Calcia on Abnormal Swelling of Iron Oxide Pellets during the Reduction with Hydrogen

    pp. 1668-1675

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    Sulphur in reducing gas was found to be the only essential factor to cause abnormal swelling (volumetric increase of about 500 percentage) of hematite and magnetite pellets even in the reduction with hydrogen. This swelling brought about by the formation of iron whiskers was significant when the activity of sulphur relative to iron/iron sulphide equilibrium was in the range of 10-3 1 and the feed rate of reducing gas was so small as to control the reduction rates.
    The effects of reduction temperature, PH2O/PH2, ratio and indurating temperature of hematite pellets on this swelling due to sulphur was also investigated.
    The conditions indispensable to the formation of iron whiskers were found to be the presence of sulphur of low potential and the relatively slow rates of chemical reaction on the surface of wustite. This was independent of the kind of reducing gas.
    In the absence of sulphur, the addition of CaO into iron oxides can not induce the abnormal swelling but general swelling (volumetric increase of several tens of percentage), regardless of any reduction histories to wustite. But, the less uniform its distribution in iron oxides, the greater the abnormal swelling by sulphur.
  • Determination of Liquidus and Solidus Surfaces at Iron-rich Region of Fe-Cr-Ni System

    pp. 1676-1683

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    The liquidus and solidus surfaces of iron-rich corner of Fe-Cr-Ni system, which are closely related to the solidification behavior of commercial stainless steels, were determined.
    The tie-lines were measured with the concentration profile of planar liquid-solid interface obtained by stationary melting method, and the liquidus temperatures were measured by differential thermal analysis.
    These results, combined with the morphological analysis of unidirectionally solidified specimens, were used to clearly determine the α (ferrite) and the γ (austenite) regions of iron-rich corner and the liquidus and solidus surfaces including tie-lines.
    The results have shown good agreements with the work reported by SCHÜRMANN et al., except for the peritectic-eutectic line, which have found to shift slightly toward the Fe-Cr side between 10 and 15 wt%Cr. The peritectic-eutectic transition point was found to be at the composition about 15 wt%Cr-10 wt%Ni.
  • Desulphurization Behaviour of Liquid Iron in CaO Crucible by Adding Al and Al Alloys

    pp. 1684-1690

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    Experimental studies have been conducted on the desulphurization of molten iron, with different initial contents of both oxygen and carbon, in CaO crucible after adding Al or Al alloys such as Al-B, Al-Si, Al-Ba, and Al-Zr.
    Desulphurization rate is shown to be affected by initial oxygen and carbon concentrations and to be significantly accelerated by the addition of boron with Al. These experimental results are interpreted based on the slaging reaction on the crucible wall and by the thermodynamic equilibrium between the crucible wall and the iron melt.
  • Refining of High Purity Ni-base Superalloy Using Calcia Refractory

    pp. 1691-1697

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    Technical review and experimental study have been conducted on melting process for Ni-base superalloy using calcia refractory.
    Experiments were carried out first on denitrogenation for liquid iron, and secondly on reaction between calcia crucible wall and molten Ni containing Hf. Major experiments were carried out on producing Ni-base model alloy, and remelting of IN738 and MarM 247.
    These experimental results have revealed that Ni-base superalloy thus made has very low oxygen and nitrogen content below 10 ppm and superior cleanliness, and that calcia refractory has an excellent stability for melting and refining.
  • Computer Simulation of Macrosegregation in Ingots

    pp. 1698-1705

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    A direct simulation method of macrosegregation in ingots has been proposed, where the flow due to liquid density change by temperature and concentration variation during solidification and due to solidification contraction was postulated to be laminar and darcy flows in the liquid and the solid-liquid coexisting (mushy) regions, respectively. Since the conservation laws of thermal energy, mass and momentum are solved by the direct finite difference method developed by the authors, this method is applicable to ingots with complicated boundary condition. Some numerical examples such as unidirectional solidification of Al-Cu and Fe-C alloys including solidification of a stepped specimen and a large steel ingot showed that the proposed method can fairly accurately simulate at least the macrosegregation caused by the convection and solidification contraction in the mushy region, excluding the channel type segregation. Although the accuracy of simulation of the macrosegregation in large steel ingots should be further examined by comparing the simulations with experiments, the tendency of positive segregation could be simulated. Further, it was found that the accuracy of the simulation depends especially on the data of the liquid density and permeability in the mushy region.
  • Estimation of Forming Condition of Center Porosity in Forging Ingot

    pp. 1706-1713

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    Porosities are often found in the center of forging ingot together with “V” segregation. For the production of sound ingot, therefore, it is essential to develop a method to estimate the size and the location of the porosity. For this purpose, four forging ingots were examined by ultrasonic testing to evaluate the size and location of the porosity. Computer calculation of solidification was also carried out on these ingots to study factors influencing the formation of the porosity.
    As a result, it was found that the size of porosity was not determined by such parameters as temperature gradient and solidification rate but by a new parameter L/D, where L and D are height and width, respectively, of semi-solid region formed during solidification in the center of ingot. The parameter L/D is a function of solidification condition and the grade of steel. By calculating the distribution of L/D along the axis of ingot by computer, porosity zone can be predicted for each porosity size.
  • Development of High Shape Factor Rolling Technology and Its Application to Manufacturing Thick Steel Plates with 50 kgf/mm2 Grade High Tensile Strength for Arctic Service

    pp. 1714-1721

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    Improvement of toughness at the mid-thickness of thick rolled steel plate (more than 50 mm) and manufacturing procedure for getting uniform properties over the whole thickness position were studied.
    High shape factor rolling (large roll diameter and large reduction per pass) at non-recrystallization region brought about excellent toughness at the mid-thickness. We studied by simulation experiment and rigid plastic finite element method (FEM) analysis, and showed that high shape factor rolling increased rolling effect and resulted in fine ferrite grain size at the mid-thickness.
    Excessive high shape factor rolling made recrystallization of austenite grain, and toughness deteriorated. Consequently, choice of appropriate rolling temperature and rolling pass schedule is important.
    The thick steel plates with 50 kgf/mm2 grade high tensile strength made by applying high shape factor rolling technology have excellent toughness at base plate over the whole thickness position and at welded joints, and can be used for arctic service.
  • Superplastic Deformation Mechanism of δ/γ Duplex Stainless Steels

    pp. 1722-1729

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    Superplasticity of δ/γ duplex stainless steels has been studied in relation to the microstructural change during deformation in order to elucidate the role of the second phase particles. In the case of deformation in the δ/γ duplex phase region, local strain concentration within the δ-ferrite matrix due to dispersion of relatively hard γ particles and the subsequent recrystallization occur repeatedly. When the alloys containing high Cr and Mo are deformed at temperatures around 900°C, σ phase particles precipitate via eutectoid decomposition of δ-ferrite into new γ and σ phases, and the γ/σ duplex phase structure forms. The dynamic recrystallization of γ phase matrix occurs locally and intermittently, and extremely large superplasticity is also obtained. Prior cold work largely accelerates these processes, and leads equiaxied δ/γ or γ/σ duplex structure in the early stage of deformation. The superplasticity in both cases can be obtained by delicate balance between the local strain hardening and the subsequent recrystallization, and thus the flow stress exhibits large strain rate dependence. This model also explains granular appearance of the fracture surface as a coalescence of microvoids induced by the individual hard phase particles. In order to obtain large superplasticity, the microstructure should consist of hard particles embeded within a soft matrix and the amount of hard particles should be at least greater than 10% in the case of σ in γ/σ duplex structure. The structure with hard phase matrix within which the soft second phase particles disperse does not exhibit superplasticity.
  • Corrosion Process of Zn-Co, Zn-Fe and Zn-Ni Alloy Electroplatings

    pp. 1730-1737

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    The corrosion behavior of electroplatings of Zn-Co, Zn-Fe and Zn-Ni alloys containing about 10% alloying elements in pH 6 solutions was investigated. At the biginning of immersion, corrosion rate of the Zn alloy platings was larger than that of pure Zn plating, because the alloying elements (Co, Fe and Ni) promoted cathodic reaction. As corrosion proceeded, corrosion potential of the Zn alloy platings in pH 6 buffer solutions shifted to noble potential in a complex manner. The shift of the potential is characterized by the following corrosion process. In the early stage of the corrosion, a corrosion product with low electrical conductivity (Zn(OH)2) is formed on the surface of the alloy platings by the dissolution of Zn. The development of corrosion induces the formation of corrosion groove reaching to the underlying steel and the increase of relative content of the alloying elements to Zn in the corrosion products and/or on the alloy plating layers. As the area of exposed underlying steel and the relative content of the alloying elements increase, the power of galvanic protection of the plating decreases, leading to corrosion of the underlying steel.
    When the solution contains NaCl, a compound ZnCl2·4Zn(OH)2 is formed as a corrosion product. The qualitative nature of corrosion process, however, does not change by the addition of NaCl to the solution.
  • Effects of Alloying Elements and Cooling Rate on Austenite Grain Growth in Solidification and the Subsequent Cooling Processes of Low Alloy Steels

    pp. 1738-1745

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    Effects of alloying elements and cooling rate on γ grain growth behavior in the solidification and subsequent cooling processes of low alloy steels have been studied in relation to surface cracking of continuously cast (CC) slabs.
    Grain growth of γ phase occurs rapidly below a completion temperature of transformation into γ phase (Tγ ), since strong pinning effect of the second phase such as δ-ferrite and/or liquid phase on γ grain boundary migration disappears. Thus γ grain size of as-cast steels can mainly be determined by Tγ, i.e., the maximum grain size is obtained at a peritectic composition, as expected from Fe-C phase diagram. The carbon concentration at the peritectic point is significantly shifted by the addition of alloying elements. The coefficient kx on the shifting was determined separately for Mn, Ni, Si, Cr and S. Using the kx for element X, carbon equivalent (Cp) for perifectic reaction of low alloy steels can be written additively as
    Cp= C+Σikxi·Xi
    In the same composition, the γ grains are largely refined by increasing the cooling rate because of the effects of decrease in Tγ and of the suppress of γ grain boundary migration below Tγ.
    x

    Readers Who Read This Article Also Read

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  • Effect of AlN Precipitation on the Secondary Recrystallization of Fe-3% Si Alloy

    pp. 1746-1753

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    In an attempt to clarify the mechanism of the secondary recrystallization in 3% Si steel containing AlN and MnS as inhibitors, the relationship between the sharpness of the secondary recrystallization texture and the precipitation behaviour of AlN and MnS was investigated through changing the dew point of primary annealing atmosphere and the dew point and the N2 partial pressure of secondary annealing atmosphere.
    1) The precipitation of AlN during secondary recrystallization annealing increases more when the dew point at primary annealing atmosphere is 69°C than when it is 50°C, in the case the N2 partial pressure of the secondary recrystallization annealing atmosphere is high.
    2) When the precipitation of AlN is adequately supressed during secondary recrystallization annealing by controlling either the dew point of the primary annealing atmosphere or the N2 partial pressure of the secondary recrystallization annealing atomsphere, the onset of the secondary recrystallization temperature is raised and the sharp secondary texture is obtained.
    3) The secondary recrystallization mentioned above can be successfully explained by the new mechanism of secondary recrystallization considering the special grain boudary migration characteristics of coincidence boundaries under precipitates and the distribution of the coincidence boundaries in the primary matrix.
  • Application of the Electrical Potential Method to Measurement of Tunnelled Creep Crack Growth of 2.25Cr-1Mo Steel

    pp. 1754-1761

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    The applicability of the electrical potential method to measuring tunnelled creep crack growth of 2.25Cr-1Mo steel at 540°C was investigated.
    By dividing the changes in creep crack area with CT specimen thickness, through-the-thickness average crack extensions were obtained. The predicted crack extensions from electrical potential were equivalent to the three point averages of the measured crack extensions across the thickness on the fracture surfaces.
    Crack growth rates of the tunnelled creep cracks were underestimated in comparison with the growth rates on the CT specimens with side grooves.
    It was found that adjusting by the maximum measured extension of the tunnelled creep crack improved the relationship between the crack growth rate and C* integral.
  • Effect of Molybdenum on Creep-rupture Strength and Toughness of Low C-10Cr-Mo-V-Nb Heat Resisting Steels

    pp. 1762-1769

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    The effect of molybdenum on creep-rupture properties and room-temperature toughness of 10Cr-Mo-0.1V-0.05Nb heat resisting steels was investigated. The amount of molybdenum content was varied from 0 wt% to 3 wt%. The influence of molybdenum content on creep-rupture strength and Charpy absorbed energy was investigated with respect to the ratio of delta ferrite to tempered martensite, the precipitates, the microstructure, and the lattice parameter.
    The results indicated that the 10Cr-0.1V-0.05Nb steel with Mo-content less than 1.5 wt% had good toughness, and higher long term creep-rupture strength as compared to steels containing more than 1.5 wt%Mo. Charpy absorbed energy was analyzed in relation to the amount of the extracted residue, Vickers hardness, and delta ferrite content. It was concluded that the optimum amount of delta ferrite for creeprupture strength and Charpy absorbed energy was 10-20%, and the associated optimum molybdenum content was about 1.5 wt%.
  • Mechanical Properties and Low Cycle Fatigue Strength at 4 and 300 K of Welded Alloy A286

    pp. 1770-1777

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    The tensile, Charpy impact and fatigue properties of TIG welded alloy A286 have been investigated at 4 and 300 K. The base material was forged plates of 35 mm thick of electroslag remelted A286 in which the composition of minor elements such as C, Si and B was tightly controlled. The plates were welded by using A286 filler metal without fusion zone hot cracking and HAZ fissuring except for a small amount of micro-defects dispersed in the weld metal. The yield and tensile strengths, ductility and fatigue strength of the weldment were lower than those of the base material owing to strain localization at the softened weld metal zone. The post-weld heat-treatment which consists of homogenization followed by aging restored the lowered strengths, ductility and the fatigue strength of notched specimen near to those of the base material. The absorbed energy at 4 K of the base material, weldment and heat-treated weldment was almost the same, about 60 J. Though the micro-defects in the weld metal slightly decreased the ductility and absorbed energy, they did not cause any harmful effects on the yield and tensile strengths of the weldment and heattreated weldment. The fatigue strength of smooth specimens after the post-weld heat-treatment was, however, sensitive to the size or the number of the micro-defects and the S-N data were dispersed among those for the smooth specimens of the base material at 4 and 300 K.
  • Effect of Al, Ti, B and N on Hydrogen Attack of Simulated HAZ of Cr-Mo Steel

    pp. 1778-1785

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    Effects of Al, Ti, B and N on hydrogen attack were examined by using simulated HAZ specimens of Cr-Mo steel. The hydrogen attack resistance was evaluated by the ratio of Charpy absorbed energy measured after exposure to hydrogen atmosphere and that measured after aging in air. The hydrogen attack resistance increased with sol.Al content more than 0.01% for simulated HAZ of 10 ppm B bearing Cr-Mo steels. The addition of Ti and B also improved the resistance to hydrogen attack. It was found that M23C6 type carbide precipitated preferentially in the simulated HAZ of B bearing Cr-Mo steel. On the other hand, only the carbide of M7C3 type was observed when B was not added. The carbide of M23C6 type precipitation was promoted by free B in solution when N was fixed by Al and Ti.
    It was recognized that M23C6 was more stable than M7C3 at high temperature and high pressure in hydrogen atmosphere. The carbide of M7C3 type reacts with hydrogen to form methane and metal. The reason why the additions of Al and B improve the resistance to hydrogen attack is that the precipitation of M23C6 type carbide is accelerated by free B in solution which is more stable at high temperature and high pressure of hydrogen.
    x

    Readers Who Read This Article Also Read

    1. Hydrogen Induced Cracking Observation by “in situ HIC Measurement Method” Zairyo-to-Kankyo Vol.40(1991), No.9
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    3. Research on hydrogen embrittlement by electrochemical hydrogen permeation technique Zairyo-to-Kankyo Vol.49(2000), No.4
  • 鉄鋼協会の過去,現状と未来/小たたら製鉄への挑戦-生徒とともに鉄の再認識を求めて-

    pp. 1786-1790

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  • 生産加工システムの知能化へ向けて/「不易」研究と「流行」研究

    pp. 1788-1788,1802

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