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

Tetsu-to-Hagané Vol. 74 (1988), No. 1

  • Some Elementary Steps in the Thermomechanical Processing of Steels

    pp. 18-35

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  • Activity of ISO/TC 102-Iron Ores

    pp. 36-41

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  • The Latest Information of Electronic Iron and Steel Materials

    pp. 42-50

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  • Present Status of Rheocast Process

    pp. 51-60

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  • Oxidation Reaction of Silicon in Molten Iron of High Carbon Concentration by FeO Containing Slag

    pp. 61-68

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    The rate of oxidation reaction of silicon between Fe-4.4%C-Si melt and Li2O-CaO-SiO2-FeO slag has been investigated under the condition of mechanical stirring at 1 300°C. The initial concentrations of FeO in slag, (%FeO)0, and silicon in metal, [%Si]0, were 2.530 and 0.0080.1, respectively. The rotating speed of the stirrer was 50400 rpm.
    The activity of silica, aSiO2, in the slag has also been determined experimentally by measuring the concentration of Si in carbon saturated iron equilibrated with SiO2 in Li2O-CaO-SiO2 slag at PCO=1 atm and 1 300°C.
    In the explored concentration range of FeO in the slag, the apparent metal-side mass transfer coefficient of Si, k'si, increases with increasing (%FeO)0, while k'si does not change much with varying [%Si]0. It is found that k'si increases approximately in proportion to the 1/3 power of the rotating speed of the stirrer, but the effect of mechanical stirring on the mass transfer of FeO in the slag is negligible except at lower (%FeO). A mathematical model describing the simultaneous reactions of Si, C and FeO is developed. The reaction mechanism of the present slag-metal reactions is explained with the aid of the mathematical model.
  • Interfacial Resistance to Nitrogen Desorption from Molten Iron

    pp. 69-75

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    A study was made on the rate of nitrogen desorption from molten iron by Ar gas injection together with blowing onto the melt surface. Two types of crucible (Al2O3, MgO) and two types of deoxidation method (Al addition, C addition) were used. The flow rate of injected gas was about 80 Ncm3/min and that of blown gas was 1 100 Ncm3/min. The immersion depth of the nozzle was 3.3 to 4.5 cm. During the experiment, the bubble formation time was measured by using a pressure pulse technique.
    The kinetic data were compared with the calculations by a mixed control model of mass transfer of nitrogen and of interfacial chemical reaction. From the comparison between calculation and experiment, the interfacial resistance was quantitatively estimated. The interfacial resistance existed at the free surface while did not at the bubble-metal interface. Under the same deoxidation condition, the rate of nitrogen desorption with an Al2O3 crucible was lower than that with a MgO crucible. This comes from that the interfacial resistance exists at the free surface of the melt held in the Al2O3 crucible although the free surface appears clean. In the case of deoxidation with Al, Al2O3 layer behaves itself markedly as the interfacial resistance.
  • Mechanism of Fume Formation during the Decarburization of High Carbon Iron Melt

    pp. 76-83

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    Charactristics of fume formation during the decarburization of high carbon iron melt by O2, O2-Ar or O2-CO2 were studied using a 15 kg induction furnace. The results obtained are summarized as follows ;
    (1) Remarkable increase in the rate of fume evolution accompanied by fine iron droplets emission was observed when the oxygen flow rate and oxygen content of top blowing gas exceeded some critical values. This critical condition seemed to correspond to the onset of CO bubble formation beneath the bath surface.
    (2) It was found that the temperature of the jet impinging zone measured by a two-color pyrometer through the oxygen lance rose up to 2 200°C only when bubble bursting took place. Bubble bursting was supposed to be the main cause of fume formation both by bursting itself and by accelerating the vaporization of iron.
    (3) The effects of bath temperature and C, S, Si, Mn and Al contents of hot metal on the critical oxygen flow rate of bubble bursting were examined and it was made clear that they had significant effects on this critical condition.
  • The Development of an Operational Guide Model for Electric Furnace for Producing Silicomanganese

    pp. 84-90

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    For the operational guide of electric furnace for producing silicomanganese, a new simplified mathematical model suitable for online application has been developed on the following procedure.
    (1) Equations for the estimation of reaction rates are derived from material balance through the charge conditions and the exhaust gas compositions.
    (2) The ratio of transference of MnO, FeO, SiO2 into slag and the amount of permeation of carbon into metal are formulated as the functions of operational variables.
    (3) By using the above-stated formulated equations, the transition of metal formation rate and metal temperature can be estimated.
    At EF shop No. 2 in Kashima Works of Chuo Denki Kogyo Co., Ltd., the model is being used for the guidance of the operation and contributes to the reduction of electric power consumption.
  • Mini-slab Casting by Horizontal Continuous Caster

    pp. 91-98

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    Kawasaki-Technica type Horizontal Continuous Caster (COMPUTOCAST) was installed at YachiyoWorks of Kawasaki Heavy Industries, Ltd. in 1982, and various grades of steel has been cast in square and round billets. Recently, the caster equipped with new mold system for 40 mm×200 mm mini-slab has been in operation so as to establish thin slab casting technology.
    This new equipment was developed to be applied to thinner and wider sections with new devices of 1) divided break rings 2) combined plate mold 3) adjustable mold plates. In order to optimize the above devices, the lengths of each part of mold were decided according to the simulation of solidification and the analysis of bulging. The casting of manganese steel (SMn443) with this new mold system has been carried out, which proved that the mini-slab with accurate dimentions and desirable quality was obtained with this system.
    Furthermore, on the basis of the above technology, the equipments for 20 mm×200 mm section (stainless steel-SUS304) and cross-shape section (SMn443) were manufactured and it has also resulted in successful castings.
  • Development of Direct Quenching Method for Steel Plates

    pp. 99-106

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    Experimental studies have been made of the direct quenching method for steel plates, which demonstrate that slit jet cooling followed by pipe laminar cooling is most suitable for the upper surface of a steel plate, while slit jet cooling followed by spray cooling is useful for the bottom surface.
    A new water cooling equipment for direct quenching, designed without upper rollers, has been developed and added to the existing controlled cooling facility at Kobe Steel's Kakogawa Works. Production of SM58Q-grade steel plates made from Si-Mn-V steel of low carbon equivalent (0.37%) shows that the new water cooling equipment is highly effective for making high-strength steel plates with good flatness and mechanical properties.
  • Effect of Titanium on Metallurgical and Mechanical Properties of Controlled Rolled Steels

    pp. 107-114

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    The effects of titanium on metallurgical and mechanical properties of controlled rolled steels areinvestigated and compared with those of niobium. Large TiN particles, existing in high titanium content steels, have little ability to control austenite grain growth in slab reheating. In steels with micro amounts of titanium, finer austenite grain size is observed in slab reheating at high temperatures of above 1 200°C. Controlled rolled titanium steels have high strength and excellent toughness, because titanium, similarly to niobium, strongly retards recrystallization of austenite, and strengthens steel by precipitation of TiC. TiN with very low solubility hardly dissolves at all in slab reheating, and resultantly does not contribute to the strength of the steel. Therefore, an effective titanium content, which is defined by (Total Ti-3.4N), is useful for designing steels. Strengthening by 3 kgf/mm2 in tensile strength per 0.01% effective titanium was observed. Strengthening due to grain refinement and that by precipitation of TiC are almost equal in a 0.1% titanium steel. The value of vEs of 0.003%S-Ti steel with 60 kgf/mm2 in the tensile strength is higher than that of Nb-V steel by about 2 kgf-m, due to sulfide shape control effect by titanium.
  • Superplastic Behaviour and Optimum Work Processing of a Powderconsolidated and Extruded Ni-base Superalloy

    pp. 115-122

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    The powder of nickel-base suneralloy Mod. IN-100 was consolidated by hot isostatic pressing and recrystallized under the conditions of extrusion ratio of 72% at 1 373 K and subsequent annealing at 1 343 K×1h. The fine grain size of 1.5 μm in diameter was obtained.
    The superplastic behaviour of alloy bars mentioned above was investigated in the temperature range of 1 2231 423 K and in the range of strain rates from 2.5 × 10-4 to 10-1 s-1.
    The ln σ vs. ln ε curves were obtained. It was shown that the conditions obtaining the maximum strainrate sensitivity index, m changed from the constant strain rate of 10-2 s-1 at temperatures above 1 303 K to the constant flow stress of 150 MPa below 1 303 K. Therefore, it was possible to divide the ln σ vs. ln ε curves into six regions according to the deformation behaviour.
    Furthermore, it was desirable to decrease the temperature continuously for the purpose of keeping the maximum m during superplastic deformation in tensile test. In fact, the total elongation exceeded extremely as compared with the isothermal test.
  • Design of Titanium Alloys Suitable for Superplastic Forming

    pp. 123-129

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    Using four kinds of α+β titanium alloys (Ti-Al-V-Sn-Zr-Mo-Cr-Fe system), the effects of test temperature and volume fraction of α phase on superplastic properties were investigated.
    (1) Total elongation of each alloy was more than 400% in the temperature range between 1023 K and 1123 K at the strain rate of 6.7×10-4 s-1. Maximum flow stress increased with decreasing temperature rapidly in the temperature range lower than 1073 K. From these results, the temperature range between 1073 K and 1123 K was considered to be suitable for superplastic forming of these alloys at the strain rate of 6.7×10-4 s-1.
    (2) The effects of test temperature and volume fraction of α phase on the strain rate sensitivity, m, were examined by multiple regression analysis. Following regression equation was obtained.
    m=-17.128(Θ-1.095)2-0.514(Vα-0.426)2+0.422
    Θ : Test temperature K×10-3, Vα : Volume fraction of α phase
    From this equation, titanium alloys whose volume fraction of α phase is 0.426 at the temperature of 1095 K are considered to give the maximum m value and the best superplastic properties at a strain rate of 6.7×10-4 s-1.
    (3) α phase was formed at the surface of specimen due to the reaction with oxygen during high temperature tensile test in an argon atmosphere. Such α phase was expected to be detrimental for superplastic forming and to reduce ductility of the material.
  • Effect of pH and Stirring on the Electrodeposition Behavior of Zn-Fe Alloys from Sulfate Solutions

    pp. 130-136

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    Zn-Fe alloys were electrodeposited from sulfate solutions under galvanostatic conditions (0.01-250A/dm2) to investigate the effects of pH and stirring of the solution on the deposition behavior of the alloys. With a decrease in pH, the current density-alloy composition curve was shifted to higher current density region while the current efficiency of the alloys decreased over a wide range of current densities. Stirring of the solutions shifted the curves of both the current density-alloy composition and the current density-current efficiency to higher current density region. These phenomena are explained by considering the change in polarization curves for the alloy deposition by the effects of variation of pH and stirring.
    x

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    2. Surface Appearance of Electrodeposited Zn-Fe Alloys Tetsu-to-Hagané Vol.69(1983), No.8
  • Effects of Zinc Coating Layer on the Corrosion Properties of Weldable Prepainted Steel Sheets

    pp. 137-143

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    The effects of zinc coating layer upon steel substrates on corrosion properties of weldable prepainted steel sheets are investigated by means of salt spray test and galvanic coupling test.
    As the sacrificial corrosion prevention effect of zinc powders in the paint film is poor, it is difficult to completely prevent red rust if steels are used as substrates. In case that zinc coated steels are used, both zinc coating and zinc powders in the paint film sacrificially prevent corrosion of steel substrates, resulting in delaying red rusting to some extent depending upon the type of paint applied.
    If the paint containing zinc, stainless steel and aluminium powders in ratio of 43 : 37 : 20 is applied onto zinc coated steel, it is proved that corrosion resistance is superior in wide range of powder contents between 20 and 35 vol%. Based on these results, the weldable prepained steel sheet having excellent corrosion resistance, formability and weldability has been developed by applying 10 μm of paint film containing totally 30 vol% of zinc, stainless steel and aluminium powders onto 20 g/m2 of zinc coated steel sheet.
  • Development of Weldable Paint Coated Steel Sheet Having Superior Formability and Corrosion Resistance

    pp. 144-150

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    Application of zinc alloy coated steel sheets as the substrates of weldable prepainted steel sheets has been investigated.
    As zinc-nickel alloy coating improves corrosion resistance of the weldable prepainted steel sheets to agreat extent, thickness of electrically conductive paint film is able to be reduced to 5 μm. This results in improvement in their weldability and formability. The zinc alloy coating containing iron more than 9wt% is apt to form red rust.
    Based upon above results, the surface coated steel sheet having 5 μm of electrically conductive paint film containing totally 30 vol% of zinc, stainless steel and aluminium powders upon 10 g/m2 of zinc-nickel-chromium-iron alloy coating has been developed. This product is much superior in press formability, weldability and corrosion resistance to zincrometal and has been put into practical use in the automotive industries.
  • Effect of Notch Geometry on Hot Ductility of Low Alloy Steels

    pp. 151-158

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    In order to understand the effect of surface roughness of CC slabs such as oscillation mark on the surface cracking, hot deformation of some low carbon low alloy and austenitic stainless steels has been investigated by means of hot tensile tests using the specimens with round notch at temperatures from 800 to 1 100°C at average strain rates from 10-4 to 10-1 s-1.Although the total elongation of the parallel portion decreased with strengthening by the notches, such notch effects were markedly reduced by lowering either deformation temperature or the average strain rate or by Nb addition. This can be explained in terms of dynamic precipitation behavior of carbonitrides such as NbC and/or AlN, i.e., the precipitation can be suppressed by the increase of true strain rate which arises from local straining in the notched region, resulting in the ductility improvement. The ductility loss due to the notch is determined by the depth and does not depend on the initial sharpness, since the shape can easily change in the early stage of deformation. Therefore, control of the oscillation mark depth is the most important to prevent surface cracking of CC slabs.
  • Study of Over-ageing Process of Al-killed Low Carbon Steel Sheet by Measurements of Electrical Resistivity and Thermoelectric Power

    pp. 159-166

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    The following points are studied using Al-killed low carbon steel sheet for two ageing processes ; ageingafter quenching from 650-700°C to 0°C and reheating to 300-450°C (Q.A. process), and ageing after direct quenching from these annealing to ageing temperatures (D.A. process). The slope of thermoelectric power versus electrical conductivity plot is determined to be 295±5 μVK -1μ Ω cm, irrespectively of the processes. Residual solute carbon concentration after Q.A. is reconfirmed to be a little less than that after D.A.. Dependence of precipitation kinetics on grain sizes and quenched-in supersaturation of carbon is found to be different between the two processes, when the annealing temperature is low and the ageing temperature is high. A calculation based on a model of diffusion of carbon shows that the differences correspond to observed different distribution densities of carbides particles. The result indicates promotion of carbide nucleation by the reheating stage of the Q.A. process. Time to attain an equilibrium partition of carbon atoms to Mn-C dipole sites and to interstitial sites free from manganese atoms is estimated to discuss measured relative concentrations of carbon in the two sites. The estimation demonstrates difficulty of quenching for the equilibrium partition.
  • Relationship between Distribution of Boron and Quenching Hardenability of Boron-bearing 80 kgf/mm2 Grade Steel Plate in Direct Quenching and Tempering Process

    pp. 167-174

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    In the production of 80 kgf/mm2 grade steel plate with high toughtness by direct-quenching and tempering (DQ-T) process, optimum amounts of B in steel plate is indispensable. Because, if the plate does not contain that, the tensile strength of plate is not necessarily higher than that of reheat-quenched and tempered plate. And, optimum amounts of B are changed by parameters of DQ-T process such as slab reheat, and finish-rolling temperatures and plate chemistry.
    In this paper, an investigation has been made on the effect of B behavior and change in γ-grains during the period between finish-rolling and quenching on the plate tensile strength. In particular, existing state and distribution of B were observed by using modified autoradiography (modified FTE technique) which can clearly show B-distribution at the γ-grain boundary and γ-grain matrix.
    Boron-distribution and γ-grain structure dynamically change depending on the time from finish of rolling to quenching, and this results in change in the hardenability of plate. Enough segregation of solute B at recrystallized γ-grain boundaries increases the hardenability of plate. Whereas the formation of fine precipitate of B conpounds within recrystallized γ-grain and at grain boundaries lowers the hardenability of plate.
    The model showing relationships between γ-grain structure, B-distribution and hardenability of plates are schematically represented on the basis of experimental results.
  • Defects in Flash Welded Zone of High Strength Chain

    pp. 175-181

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    A high strength chain is manufactured by bending steel bars, flash welding and subsequent heat treatment. The defects in the flash welded zone have been investigated.
    1. The defects are detected in the flash welded zone by UST of 20 MHz. The defects are oxide clusters generated by welding.
    2. The defects are found more in the outer area than in the inner of the transverse section of a chain link. This is because the molten steel flows to the inner area from the outer by the electromagnetic force generated during welding, thus the molten steel layer becomes thin in the outer area, where oxide clusters are not ejected together with the molten steel and remain there.
    3. The defects can be eliminated by an increase of upsetting length in the weld process ; this is the most of the defect can be removed by cutting off the flash and oxide clusters are finely dispersed.
    4. With increasing the upsetting length, the average impact value of the welded zone decreases but the scatter of the value is improved.
  • Estimation of Fatigue Strength of Large Diameter Chain in Air and Sea-water

    pp. 182-189

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    It takes long time for fatigue test on an actual chain and the test is very difficult for large chains such as 100 mm over in diameter. This paper describes the relationship between the fatigue strength of an actual chain and those of the specimens cut out of the chain.
    The fatigue failure of a chain often occurs at the toe of stud-weld or at the corner of indentation produced by the stud other than the bend part of the link. In these cases, the fatigue strength of the chains was lower than that of the chains failed at the bend part. Moreover, it was found that the fatigue strength of the chain even failed at the bend part in air was lower than that estimated from the result of small specimens, because of the effects of decarburizing and roughness of the chain surface.
    In the artificial sea water, the fatigue strength of chains was rather close to that estimated from the results of small specimens. It is considered that this is due to the fact that the condition of the surface of chains and specimens becomes similar for the two cases by corrosion. Consequently, it is concluded that the result of small specimens may be applied to estimate the fatigue strength of chains in the sea-water.
  • 立体視をどうぞ/我が国における粗鋼生産量と輸出比率

    pp. 199-199,205

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