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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 54 (1968), No. 4

  • Study on the Rete of Reduction of Solid Silica by Carbon in Liquid Iron

    pp. 261-265

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    The reduction of solid silica by carbon (about 4 and 2%) in liquid iron was investigated at tem-peratures between 1360 and 1550°C under an atmospheric pressure of carbon monoxide.
    In higher carbon melts, the silicon content of liquid iron increased linearly with time during the course of experiment, but not in lower carbon melts, and in the latter case a linear relation between [%Si] 32 and [Ft/v] was found.
    In each series, apparent activation energies for the reaction were 90 and 128 kcal, respectively.
    These results suggest that in higher carbon melt, the reaction may be controlled by the dissociation of silica and in lower carbon melt the oxygen diffusion may be the controlling step.
    Furthermore, the amount of CO evolved during the reaction was measured and the relation to the increase of silicon content was examined.
  • On the Fundamental Properties of High Basicity Pellets

    pp. 266-276

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    Fundamental properties of fluxed pellets having relatively high basicities (CaO/SiO2=0, 1.25, 1.5, 1.75 and 2.0) were studied with the samples indurated at 1150, 1200, 1250 and 1300°C, using electric furnace. And following results were obtained. The main structures of fluxed pellets were hematite and hemi-calciumferrite (CaO, 2Fe2O3). When indurated at 1300°C, however, hemi-calciumferrite disappeared and slag and magnetite were formed. In the pellets having basicities of 1.75 and 2.0, there existed calciumferrite which was considered 3CaO.EFeO.7Fe2O3, when indurated at 1300.
    Porosity of indurated pellets decreased with increasing induration temperature, this tendency was more remarkable in fluxed pellets than regular pellets. Crushing strength of indurated pellets increased with increasing temperature but slightly lowered at 1300°C with a exception.
    In order to examine the reducibility without the effect of porosity, reduction tests were performed with the samples crushed under 74μ. The reducibility of fluxed pellets was superior to that of regular pellets regardless of induration temperature.
  • Swelling of Pellet during Reduction

    pp. 277-295

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    Two different views were brought by previous works for the swelling of pellets during reduction.“The swelling refers intimately to the transformation of mineral phases during reduction” is the one, and“ The growth of whisker-like fibrous materials cause the swelling like cotton candy” is the another.
    The present authors carried out series of experiment on the swelling by various kinds of raw material, after the detailed review on the previous works.
    Following explanations are possible. 1. A generation of some kind of force is supposed to be possible in the relatively early stage of reduction, which will cut off the bonds between the constituent grains, and break the grains themselves down into minute fragments. 2. The growth of fibrous material is observed in later stage of reduction after the breaking down came to end, and is found to form cotton candy like body. The breaking down and growth of fibrous materials are absolutely independent in the stage of reduction. 3. Swellings can be prevented by taking the diameters of pellets small, even for the raw material with remarkable swelling nature, and for the pellets fired under such conditions that will cause swelling or preserve the nature of swelling, also.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • The Countercurrent Reduction of Sinter and Carbon Deposition

    pp. 296-299

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    The reduction tube which had a slit-typetuyere was used for the countercurrent reduction. The data of countercurrent reduction were plotted on the graph of the degree of reduction v. s. the gas utilization coefficient. This graph was advantageous to explain the countercurrent phenomena.
    On the countercurrent reduction of sinter, the gas utilization coefficient was depended on two factors; the first was a ratio of ore descending speed to gas flow rate and the second was a contact time. When the contact time was 8.5 sec, the H2 utilization coefficient was similar to that of CO, but when the contact time was shorter, the former was larger than the latter.
    With the countercurrent reduction by CO, carbon deposited fast when a ratio of are descending speed to gas flow rate was low and a contact time was long. And with that by N2+34% CO, carbon deposited little.
    The reduction velocity with N2+34% CO was mainly determined, between 600°C and 900°C.
  • On the Comminution of High Carbon Ferrochrome

    pp. 300-306

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    The particle size distribution and the specific surface area were measured on the comminution products of high carbon ferrochrome ground in rod-and ball-mill for 0.5 to 8 hr.
    It was found that the Gaudin-Schuhmann equation (Eq.1) can be applied for the particle size dis-tribution in their over-micron range. On the other hand, the Charles equation (Eq. 2) on the energysize reduction relationship did not cover the whole range of comminution carried out and the size modulus, k, and the inverse of specific surface area, 1/S, were found to converge to their limiting values. On the other hand, the Harris equation (Eqs. 5 and 6) based on a modified logistic function fit well the energy-size reduction relationships. The limiting value of the size modulus k and the specific surface area S, were estimated as 22 to 26μ and 2 to 5×104 cm2/cm3, respectively.
    The specific surface area estimated on the basis of size distribution did not coincide with that measuredby the air permeability method. At longer grinding times, the measured values become larger than the estimated ones. This difference was supposed to be due to possible flocculation or welding during comminution which also increases with grinding time.
  • A New Acoustic Method for Water Leak Detection of Blast Furnace Cooling Boxes

    pp. 307-313

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    A new method by which the detection of the damages of blast furnace cooling system is easily made was developed.
    This is an acoustical method which detects the abnormal sounds caused by the entry of gas bubbles into cooling box or tuyere from the blast furnace through the small damaged part.
    The result of the application of this method to the actual blast furnace was found to be quite satis-factory.
  • Activity of Silicon in Liquid Iron

    pp. 314-320

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    The activity of silicon in liquid iron has been studied at 1560°C by mean of the equilibrium, SiO(g)+H2(g)=[Si]+H2O(g).
    At concentrations up to Ns1=0.07 in Fe-Si System, the slope d In γsi/dNsi has aconstant value of ε(Si)Si=12.
    By use of free energy of formation of silica determined by Bowles et al. at high temperature, the activity coefficient γ°Si at infinite dilution of silicon has been derived, and γ°Siis 8.7×10-4.
    At concentrations up to Nv=0.05 in Fe-Si-V System, interaction parameter ε(V)Si has a value of 5.3.
  • Effects of Chromium, Copper and Tin on the Activity of Carbon in High Carbon Liquid Steel

    pp. 321-329

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    Relationship between the activity coefficient of carbon and the carbon concentration in Fe-C binary alloys has been determined by means of CO-CO2 gas mixtures at 1550°C. It was given as log γ′C=2.33 (2N′C-N′2C)-0.181 (N′C=0-0.207)
    The activity of carbon and the interaction parameters ε(C)C, e(C)C were calculated in the whole range of carbon concentration N′C=0-0.207.
    The values of ε(C)C and e(C)C were compared with those given by other authors. Fe-C-X ternary alloys were equilibrated with the CO-CO2 gas mixtures having a constant carbon activity at 1550°C and the effects of chromium, copper or tin on the activity of carbon in high carbon liquid steel were investigated.
    The interaction parameters at constant carbon concentration have been determined as follows:
    (Cr)C]NC=0.032=-3.9
    (Cu)C]NC=0.032=4.8
    (Sn)C]NC=0.032=9.8
    These values were compared with those at infinitely dilute carbon solutions and at graphite saturated solutions.
  • Study on the Activity and Solubility of Oxygen in Liquid Iron-Niobium Alloy

    pp. 330-335

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    The equilibrium of gaseous H2O-H2 mixture with liquid iron-niobium alloys contained in alumina crucible shows that the activity coefficient of oxygen is moderately deminished by niobium. The oxide in equilibrium with the melt is not including iron and aluminum and considered to be NbO2 (s). The equilibrium constant at 1600°C is [%Nb]·[fO·%O]2=2·3·10-4 where log fO=-0.06.[%Nb]. The deoxidizing power of niobium is comparable to that of vanadium.
  • On the Floation of Deoxidation Products by Calcium-Silicide addition

    pp. 335-340

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    The floatation of oxide inclusions in static liquid iron was studied using the complex deoxidizez, calcium-silicide.
    The obtained results are as follows;
    1) At the initial stage of reaction, oxygen content in liquid iron decreases rapidly, but at the next stage of reaction decreases slowly, when the melt was deoxidized by calcium-silicide addition.
    2) Deoxidation products become large during short time but the rate of floatation of fine particles are so slow that the cleanliness of liquid iron is not good.
    3) The rate of floatation of large oxide particler is greates than that of deoxidation products by metallic silicon.
  • Behavior of Silicon during Carbon Deoxidation in Pure Iron Melting

    pp. 340-345

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    During carbon deoxidation of pure iron in vacuum melting furnace with MgO crucible, it has been observed that silicon contents of the melts increases usually. This has been thought owing to reduction of silica in crucible by carbon added for deoxidation. So far, no quantitative data has been published in literatures. In order to confirm the decrease of silica in crucible, we examined the change of crucible composition before and after carbon deoxidation by chemical analysis.
  • On Oxidation Rate of Solid Graphite and Decarburization Rate of Liquid Iron

    pp. 345-351

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    A critical experiment was carried out on the gaseous diffusion mechanism in the decarburization from liquid iron in a crucible by oxiding gas. The solid graphite or the liquid iron-carbon alloy both in a crucible with the same size was oxidized by the gas mixture of carbon monoxide and dioxide.
    The results are as follows;
    (1) The apparent rates of oxidation of carbon were same both for the cases of graphite and a high carbon content iron alloy.
    (2) The apparent rate of graphite oxidation increased with the temperature.
    (3) The rate increased with the increase of carbon dioxide content in the reactant gas mixture.
    (4) The rate increased with the increase of the flow rate of the gas mixture.
    (5) From the observation of the surface after the reaction, it was found that the reaction does not take place uniformly all over the surface.
    (6) The fraction of carbon dioxide reacted is more than 70% at 1550°C.
    From the close checks of the above experimental results, it seems that the reaction hardly takes place in steady state with the rate-determining step of gaseous diffusion in the present experimental condi-tions.
  • Exchange Reactions of Elements between Molten Slag and Alloy

    pp. 351-359

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    Exchange reactions of iron, manganese and silicon between molten slag and alloy were studied using radioactive isotope of each element. Small amount of slag containing one or two radioactive elements was added to the previously epuilibrated slag-metal system, and the exchange rate of the elements was determined from the change of the specific radioactivity in the metal phase. The results are summarized as follows:
    (1) Amounts of elements which transfer from slag to alloy, or vice versa under equilibrium were determined as 2.3×10-2, 6.2×10-4 and 7.3×10-5g/cm2 sec for iron, manganese and silicon, respectively. These values were also valid for non-equilibrium states.
    (2) Mass transfer coefficients of iron or manganese in the system of FeO-MnO slag over Fe-OMn alloy were obtained as 1.1×10-2cm/sec in the slag layer and 3.2×10-2cm/sec in the alloy layer. This was enabled by the simultaneous employment of radioactive iron and mangenese in one melting.
    (3) Although the rate of the exchange reaction of silicon obtained in the system of CaO-SiO2 slag over Fe-O-Si alloy is small compared with that of iron or manganese, it is still larger than the rateof the reduction of SiO2 by carbon in blast-furnace-type slage. The small exchange rate of silicon can be attributed to the slow transfer of silicon ions in the slag phase.
  • Activities in the Iron-Oxide Lime Slag

    pp. 359-370

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    The experimental procedure to reduce contamination of the slag by reaction with crucible in a rotating crucible furnace has been described.
    The distribution of oxygen between molten iron and lime-iron oxide slags has been determined and used to calculated activities of FetO, CaO in the system.
    The solubility of oxygen in a molten iron at 1560°C under pure iron oxide slag or lime saturatediron oxide slag conforms to the results of other investigators.
    When the lime content is less than 0.23 mole fraction, the activity of iron oxide, which is defined as the ratio of the observed oxygen content of the metal to that under pure iron oxide slag, deviates slightly positive from Raoult's law.
    In the range of lime content more than 0.23 mole fraction, it reveals negative deviation, which is increased with lime content. Iron oxide activity in the lime saturated iron oxide slag is 0.45 at 1560°C.
    It has been determined that α-function for FetO defined as logγFetO/(1-NFeto) 2 is a linear func-tion of lime content, that is, αFeto=1.0-4.3 NCao.
    Taking the components of the system as FetO, CaO, the activity of lime has been calculated from the Gibbs-Duhem equation.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • On the Behavior of MnO, SiO2 or Cr2O3 Mixed with SolidIron during Heating in Reducing Atmosphere

    pp. 371-381

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    In the previous studies concerning the behavior of oxide inclusions in steels in the hot-rolling process, the steel specimens were made by the method of powder matallurgy: that is, the iron powder was mixed uniformly with a certain amount of synthetic oxide inclusions, shaped by pressing, and sintered in H2 atmosphere. It was found that a part of mixed oxide inclusions disappeared by reduction.
    This phenomenon suggested that a part of the synthetic oxide inclusions was reduced by H2, and the metallic elements produced by the reduction were then dissolved in solid iron. Consequently, the activity of those elements was lowered, and the reducibility of oxides increased considerably.
    The present investigation was carried out in order to make the behavior of oxides in steels clearer and know more about the reduction. The specimens made of the iron powder containing a certainamount of MnO, SiO2 or Cr2O3 respectively were held at the constant temperature of 800°C to 1100°C and in the H2-H2O gas under the constant PH2O/PH2, ratio. When the equilibrium state was attained, the change of weight of these specimens due to the reduction of oxides was measured by thermo-balance, and the reducibility of the oxides at each temperature was investigated.
    Furthermore, the activity and the activity coefficient of the Mn, Si and Cr elements in solid Fe-basealloys were calculated by combining the experimental value of Mn, Si and Cr concentrations and the thermochemical data concerning the reduction of the oxides.
  • Discussion of Oxidation Reaction in an Oxygen Top Blowing Converter

    pp. 381-392

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    The authors investigated the mechanism of oxidizing reaction in the 160 t oxygen top blowing converter, and discussed on the differrence of the mechanism of oxidizing reaction between open hearth furnace and oxygen converter. The conclusions obtained are summarized as follows;
    1. The direct oxidizing reactions take place between oxygen gas and carbon, manganese and phosphorus in steel at the fire point where oxygen gas contacts directly with molten steel, and the oxidizing reactions do not take place between ferrous oxide in slag and carbon, manganese, and phos-phorus in steel at the interface of slag-metal.
    2. The excess oxygen (ΔO) is determined by the composition of CO and CO2 in evolution gas at fire point without by ferrous oxide in slag.
    3. Phosphorus in steel is oxidized by blowing oxygen without by ferrous oxide, and ferrous oxide participates in the rephosphorization reaction which is the most important reaction at the dephosphorization.
    4. The difference of desulfurization reaction between at the last blowing period of low carbon steel and at the first blowing period of high carbon steel was proved.
  • On the Formation of Sound Solid Skin of Low Carbon Rimming Steel Ingot

    pp. 393-401

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    The ingotmaking process to obtain low carbon rimming steel ingot with sound solid skin were studied. The results obtained are as follows;
    1. It is possible to prevent the formation of skin holes in solid skin by rimming action during teeming. The addition of shot aluminum during teeming is effective to increase therimming action. It is considered that aluminum prevents the growth of bubbles which are brought into molten steel bulk in the mold by teeming stream, and intensifies the circulating flow of liquidsteel along the mold wall.
    2. Thickness of solid skin is influenced by both the teeming rate and the range free from lenticular blowhole of ingot. The latter of the teemed steel is determined mainly by manganese content in the range of 0.06-0.08% carbon. Manganese has little effect on the deoxidation of teeming steel, but it is considered that at the solidifying front manganese influences the deoxidation and CO gas evolution.
  • The Formation Mechanism of Inverse Segregation of Steel Ingots

    pp. 401-410

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    To understand the formation mechanism of inverse segreggation of steel ingots, thesolidification phenomenon of ammonium chloride-water solutions in glass molds were observed. Based on the observation, it is believed that the formation mechanism of the inverse segregation of steel ingots was due to trapping of the solute concentrated liquid between the solid shell and the equiaxed crystal zone, because the equiaxed crystals formed in the liquid ahead of the solid shell and beyond the solute concentrated zone.
    It is also believed that the settling of crystals in the lower part of the equiaxed crystal-and-liquid mixture zone resulted in streak type inverted V shape tears filled with solute concentrated liquid in the zone. Furthermore, the negative segregation is believed to be formed by crystals which were carried from the advancing solid-liquid interface by the convection in the early stage of the solidification process.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • Gas-Carburizing and Quenching of Sintered Ferrous Materials

    pp. 410-415

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    Fe-Cu and Fe-Ni compacts were prepared from the mixtures of reduced iron, electrolytic copper and carbonyl nickel powders. These compacts were sintered and gas-carburized. The effects of sintering time and carburizing time on the carburizing behavior were examined.
    Further, gas-carburized specimens were oil-quenched. Microstructures, toughness and hardness of quenched specimens were also examined.
    The results obtained are as follows:
    (1) The sintering time of sintered Fe-Cu has minor effect on the carburized depth as compared with that of sintered Fe-Ni.
    (2) Short carburizing time is suitable for sintered Fe-Cu because of porous structure.
    (3) By oil-quenching of carburized specimens, more developed and uniform hardened-case can be obtained with Cu addition than with Ni addition because diffusion of Cu into Fe is faster than that of Ni.
    (4) Owing to the porous structure of sintered Fe-Cu, hardness of hardened-case is lowered slightly, and toughness of quenched specimen decreases remarkably above 3% Cu.
  • Study on Mass Effect of Law Alloy Steels for Large Steel Parts

    pp. 416-426

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    A simple method is proposed to predict mechanical properties of heattreated large steel forgings. The method is based on the findings. Firstly, the main considerations for the strength and the ductility are the carbon content of the forging and the microstructures induced during quenching. Secondarily, the microstructures can be computed from available CCT diagrams and cooling rates of quenching in the temperature range of 600°C to 300°C. These findings are verified experimentally on carbon steels and lowalloyed steels containing such elements as Ni, Cr and/or Mo. Equations for the rapid estimates of the cooling rates of steel forgings of the maximum diameter of 1000mm are derived experimentally as follows:
    log D+0.513 log C=2.37 when quenched in water
    log D+0.699 log C=2.02 oil
    log D+0.954 log C=1.18 air
    where, D is the diameter of a steel forging in mm. and C the looling rate in the temperature range of 600°C to 300°C in °C/sec.
    Discussions are given on the validities of the findings and the equations.
    x

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  • Tensile Properties of Pure Irons Made by Various Melting Methods

    pp. 427-432

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    Pure irons made by three kinds of melting methods, i. e. vacuum melting, electron-beam melting and zone refining, were studied on their tensile properties, at several temperaturesfrom room temperature down to liquid nitrogen temperature, and at strain rates from 10-4 to 8 per second. The purity of iron affected to the friction term in Petch's grain size dependence equation on yieldstress, and there were no changes in the coefficient of grain size term. The stress for brittle fracture due to the intergranular type fracture was not almostly dependent upon strain rate and temperature, but markedly upon grain size. For the electron-beam melted iron which was materially fractured brittlely in intergranular mode, brittle fracture strength of about 16kg/mm2 per unit grain boundary area was obtained when coarse grain specimens were failured intergranularly at low temperature.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • Study on Ferrite-Pearlitic Steels with Some Mixture of Low Temperature Transformation Products

    pp. 433-443

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    Effects of low temperature transformation products such as bainite and martensite on the mechanical properties of normalized low alloy high strength steels were studied using specimens with ferrite-pearlite structures including some mixed structures formed by varying the Mo content and cooling rate on normalizing.
    It was shown that the presence of these products in the microstructure increased the tensile strength, but this led to a disappearence of the yield point on the stress-strain curve, and resulted in a marked decrease in the proof stress/tensile strength ratio. The tensile strength of the steels containing these products depended on their amounts. Charpy impact transition temperature was divided into two groups by the presence or absence of the low temperature transfomation products, and both of them were represented by straight lines against logarithm of ferrite grain size, and at any fixed grain size within the range studied, the transition temperature was raised about 50°C by the presence of low temperature transformation products regardless of their amounts. The fracture characteristics of specimens broken by impact were studied by microfractography.
  • Microscopic Observations of the Machining Behaviors of Mild Steels Containing Telluride etc

    pp. 444-454

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    Some metallurgical observation and discussion were made upon the machining behaviors of mild steel samples containing free-cutting additives: telluride, sulfide, selenide, lead and/or bismuth. A specially devised tool holder was employed in order to obtain the cutting part of work sample with built-up edge.
    A part of free-machining mechanism of the tellurided steel samples at the cutting speeds around 60m/min was discussed based on the results from the observation with the optical- and electron-microscope as well as from the measurements of mechanical properties at various temperatures. Observed electron-microscopic substructure of a cut chip of a sample showed a peculiar subcell feature presumably caused by fast dynamic recovery of extremely strained ferrite.
  • Aluminum Mono-oxy Carbide Existed in the Band Like Region of Slightly Pressed Sheet Steel

    pp. 455-458

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    The inclusions which exist in the band like region of slightly pressed sheet steel were identified by examination of a carbon-extraction replica with both an electron microscope and an electron probe microanalyzer. The results firstly identified Aluminum mono-oxy carbide Al2OC in the band like region. The fine crystals of Al2OC were dispersed all over in that region where is dotted with Al2O3 and Fe3C.
  • Study on Maraging Steels Containing Chromium and Niobium

    pp. 459-464

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    Fe-Ni-Cr maraging type steels with two different kinds of matrices were studied on their micro-substructures and aging behaviors.
    1) A kind of dissimilarity was observed in the micro-substructures of martensites annealed at different levels of temperatures.
    2) Increase of the annealing temperatures generally resulted in a retardation of the aging process and in higher peak hardness values which appeared to be associated with niobium.
    3) Steels with higher chromium matrix had a tendency of retarding the aging process, which was observed in many features. Particularly when directly quenched to a subzero temperature, they showed peculiar subcell structures and some higher strength values.
    4) In the case of higher nickel matrix the reverted austenite precipitated in a continuous manner by forming Widmanstatten figure, whereas in the higher chromium matrix rather massive austenite appeared preferentially nucleating on the sub-boundaries regardless of other precipitating substances.
  • Changes of Microstructures and Mechanical Properties of Types 304 and 316 Austenitic Steels after Long Aging

    pp. 464-472

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    18-8 series stainless steels, which being used widely for big boiler plants recently, reveal some changes of mechanical properties during their use at high temperatures, resulting from the change of structures, i. e., precipitation of carbide particles and their coalescence.
    Types 304 and 316 stainless steels were aged for up to 10, 000 hr at approximate service temperature in use of 650°C The changes of structure, especially, the changes of observed shapes of precipitated carbides, were examined by optical and electron microscopies and those of mechanical properties were also investigated.
    As results, there was no major change in microstructures of type 304L steel having carbide precipitates coalescing on the grain boundaries after aging for 10, 000 hr But much carbide precipitates which have many shapes were observed on grain boundaries and also within grains of type 304H steel. The Charpy impact values of both steels became lower.
    The carbides precipitated mainly on grain boundaries of type 316H steel and had many shapes for example hexagonal plate-like and needle-like.
  • The Strengthening Effects of B, N and Mo Additions on the High Temperature Strength of 18Cr-12Ni-0.2C Austenitic Heat Resisting Steel

    pp. 473-489

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    For the purpose of obtaining some knowledge about the effects of alloying elements on the high temperature strength of 18Cr-12Ni-0.2C steels, the testing temperature and rupture time dependences of the strengthening by B, N and Mo additions upon tensile and creep rupture strength at 600 to 800°were investigated.Also, age-hardening response and microstructures of those steels were observed.
    The improvement due to B addition increased at higher temperature and longer time, and that due to N addition increased at lower temperature and shorter time. This effect of B addition was ascribed mainly to the suppression of intergranular fracture, and the effect of N addition was ascribed principally to the decrease of creep rate due to the solid solution hardening of N. However, this strengthening effect caused by N addition deteriorated extremely with increasing test temperature, because N promoted the coagulation of carbide.
    The improvement due to Mo addition was persisted in constant for all temperature and time range tested
    However, B and N respectively, in combination with Mo, appeared to interact and produced a more improvement in creep rupture strength than the sum of the individual contributions. The contributions of those alloy interactions increased grenerally with increasing test temperature and rupture time.
  • The Effect of Nitrogen and Carbon on the High-Temperature Strength of 25Cr-20Ni Heat-Resisting Steel

    pp. 489-497

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    The effect of addition of nitrogen up to 0.66%, of carbon up to 0.20%, and of nitrogen plus carbon on the creep rupture strength of 25Cr-20Ni heat-resisting steel was studied, and some strengthening mechanisms in this kind of steel due to the addition of nitrogen and carbon were discussed. The stress rupture strength of the steels at 700°C was improved remarkably with increasing amount of nitrogen up to 0.36%, above which the strength decreased due probably to a discontinuous precipitation of Cr2N. Further improvementof the strength was obtained by combinated addition of carbon and nitrogen, while the improvement withaddition of carbon only was very small relative to that of nitrogen. It was deduced from the results that strengthening with addition of nitrogen may be attributed mainly to an action similar to the I-S effect (chemical interaction between interstitial atoms and substitutional atoms), which had been proposed for low alloy heat-resisting steels, and to the SUZUKI's effect, and in the case of addition of nitrogen pluscarbon, dispersion hardening with carbide M23C6, in addition to above two mechanisms, may become also to effective, since coagulation of the carbide retard by the coexisting nitrogen.
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    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • Observations on the Load-Time and Load-Deflection Curves in Charpy Impact Test

    pp. 497-500

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    Relationships between load-time and load-deflection curves during impact in Charpy impact test have been simultaneously observed on a reactor pressure vessel steel plate, a low carbon Al-killed grain-refined steel.
    A precision wire wound variable resistance is used for deflection detecting element, and satisfactory result on the resolution of deflection is obtained.
    Observed load-deflection curves are similar to load-time curves at each testing temperature. Absorved energy from area under the load-deflection curve is rather smaller than the one from indicator of tester.
    The result that the time axis of the load-time curves can convert linearly to the deflection axis is obtained from analysis of deflection-time curves which are composed of both curves.
  • The wear-Resistivity of Special Cast Steels

    pp. 501-506

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    The wear tests on several kinds of special cast steels, “Adamite” cast steel s and a “Ductile” cast iron were carried out, using a Nishihara's wear testing machine, the load being 20Kg, and the revolution slip 9.09% in the absence of lubricant.
    The wear resistivities of the normalized cast steels containing 0.56-0.91% carbon increased with increases in both the hardness and the carbon content of the steel. In these cases, it was found that for the lower carbon steel, adhesive were firstly occured and followed by oxidation wear, while only oxidation wear for the higher carbon steel.
    “Adamite” cast steels containing 1.46-2.26% carbon were mainly worn by abrasive wear, which resulted in less superior wear resistivities than those of the lower carbon cast steels. There was a contrary tendency such that their total wear loss increased with increases in the hardness and carbon content.
    A “Ductile” cast iron (3.38%C) was found to have a far superior property than the others, owing to the protective lubrication of free graphite contained within itself.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • On Electrolytic Method of Extracting Oxide (Complex Oxide) Inclusions in Steel

    pp. 507-514

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    In the study of non-metallic inclusions in steel, the methods of extracting them are recognized one of the important techniques of study. In the series of our investigation on the behavior of oxide inclusions in steel in hot-rolling process, we adopted the electrolytic extraction method using Koch-Sundermann (type) cells and with neutral sodium citrate solution as electrolyte. This is one of the methods by which it is possible to extract stably and reliably the oxide inclusions from steel. But, in our investigation, we thought that it was necessary to examine the adaptability of the electrolytic method in regard to extracting such inclusions as α-Al2O3, TiO2, SiO2, MnO2, FeO, (Mn, Fe) O, FeO·Al2O3, 2FeaTiO2, 2FeO-ESiO2, MnO-ESiO2 and 2MnO-ESiO2.
    Therefore, the steel specimens containing uniformly a certain amount of particular oxide inclusions were prepared by means of powder metallurgy, and these specimens were dissolvedanodically at definite conditions. The extracted inclusions were examined by weighing and chemical as well as X-ray analysis, and the degree of extraction of the different inclusions were observed quantitatively.
    The results were as follows:
    (1)α Al2O3, TiO2, SiO2 and FeO could be extracted almost to the full, but MnO could scarcely be extracted.
    (2) As for (Mn, Fe) O, oxides rich in MnO could not be extracted at all. What was extracted had changed their composition because MnO in (Mn, Fe) O dissolved selectively during the electrolytic extraction.
    (3) FeO·Al2O3 and 2FeO·TiO2 could be extracted perfectly. The extraction percentages of 2FeO·SiO2, MnO·SiO2 and 2MnO·SiO2 were between 60 and 80%, but these extracted inclusions had not changed in quality.
  • Spectrochemical Analysis of Oxide Inclusions in Steel with Solution Method

    pp. 514-519

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    Solution spectrochemical analysis using special electrode which is named simplified reservoir cupped conical electrode (simplified RCC electrode) was studied and the isolated oxide inclusions with Iodinemethanol, Hot nitric and acid Slime method etc. were determined with this method.
    The slight sample (100μg up) is fused by fusing mixture (Na2CO3-K2CO3-Borax) in atiny platinum crucible, dissolved by the aliquot volume solvent (Co-citric acid-hydrochloric acid), poured into the simplified RCC electrode, excited by the high voltage spark source and taken each spectrum on the dry plate with 3.4m-Ebart type spectrography.
    The simplified RCC electrode is made of the rod type carbon electrode (4.6-5mm ∅;) and polyethylene cup (stopper of a pound reagent bottle).
    The merits of this method are not to require an expensive electrode such as rotating disk electrode, to be able to determine eight elements simultaneously from slight sample, to be superior both repeatability and accuracy and to be take shorter time (1/2) and be cheaper (less than 1/2) the cost of analysis than usual chemical analysis.
  • On the Gas Absorption in Condensed Film Accompanied in Oxygen Determination of Steel by Vacuum Fusion Method

    pp. 520-529

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    Condensed elements in bath are evaporated during vacuum fusion, accomplishing the absorption of CO extracted from bath, and authors could exactly recognize through the use of the gas analyzer “Exhalograph” that high speed of pumping system is to be in avail for the decrease of above pheno-mena, as had already been presumed by many workers.
    In addition, to investigate on the behaviour of condensed element during vacuum fusion the further experiments were carried out with pure iron added condensed elements such as Al, Mn and Cr, of which the results obtained showed that the origin of evaporation of condensed elements should be caused in. physical state of bath. The decrease of determined value of oxygen attributable to condensed elements, therefore, would occur when the amount of these elements in bath rise above allowing limit, and be reduced in bath constituted from Ni, in which the evaporation of condensed elements is considerably defended. Whereas complete determination of oxygen would be accomplished if the fluidity of carbon-saturated bath, which corresponds to the form of graphite, is less viscous, in spite of the amount of condensed elements, and the form of graphite was transformed to less viscous one with simultaneous addition of Ce, but not with bath added previously Ce, because the effect of Ce is not continued.
  • The Measurement of the Composition of Surface Film on the Electrolytically Treated Steel Sheet in Chromic Acid Solution

    pp. 530-534

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    In order to determine the elemental Cr in the hydrated Cr oxide and the metallic Cr separately on the surface film of the electrolytically treated steel sheet in the chromic acid solution containing some catalyzer, we inuestigated the conditions of alkaline dissolution of the Cr oxide film and the metallic Cr using a fluorescent X-ray method and a coulometric method.
    Furthermore, we calculated the thickness of the Cr oxide film by the measurements of the weight and the specific gravity of the Cr oxide film. The following results were obtained:
    (1) A little metallic Cr is dissolved by immersion in NaOH solution containing H2O2.
    (2) Metallic Cr is scarcely dissolved by immersion in 7.5 N NaOH solution at 90 to100°C for 5 min.
    (3) In a coulometric method current efficiency in anodic dissolution of the metallic Cr is not affected by the NaOH concentration, anodic current density, interelectrode distance and thepresence of the Cr oxide, and shows about 100%.
    (4) The weight of the Cr oxide corresponds to about 3 times of the weight of the elemental Cr in the Cr oxide and the specific gravity of the Cr oxide is 2.1-2.2.
  • Microanalysis of Oxide Layers of Steels

    pp. 534-540

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    The scales formed on the steels are examined through the electron probe microanalysis. Examined steels are low carbon rimmed steel, silicon killed steel, weather-resistance steel, high strength steel, sulfer free-cutting steel, ferritic and austenitic stainless steels.
    Specimens were oxidized in air at 1000 to 1350°C for various periods. The results obtained in the present investigations are as follows.
    (1) Low carbon rimmed steel: three well-known types of iron oxides (hematite, magnetite and wustite) are determined and any other oxides is not observed.
    (2) Silicon killed steel: under the iron oxide layers, manganese-iron-silicates exist together with dendritic wustite.
    (3) Low alloy steels (weather-resistance steel and high strength steel): the scales consist of hematite, spinel type oxides, wustite, silicate and metallic particles in which nickel and copper are condensed due to preferred oxidation of steel.
    (4) Sulfer free-cutting steel: iron sulfide is detected in the oxide scale and theinternal oxidation of manganese sulfide inclusions are also observed.
    (5) Ferritic stainless steel: main part of the inner oxide layer is the spinel type oxide of Fe, Cr, Mn and thin layers of Cr2O3 and SiO1 exist between the spinel and the steel substrate.
    (6) Austenitic stainless steel: the scale formed at high temperature consists of hematite, spinel type oxide, silicates and metallic particles similar to the case of low alloy steels.
  • On the End Point Temperature and Carbon Control with Dropping Thermocouple and Carbon Detector in the Molten Bath of L. D. Converter during Blowing

    pp. 541-544

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    In order to improve the quality and to increase the production of steel ingot, it is essential to achieve the most accurate and the speediest control of end point temperature and C in L. D. converter. For this purpose homemade dropping thermoconple and carbon detector were tested 20 times atAmagasaki 30 t L.D. Furnace of Kobe Steel, and the results obtained were as follows:
    (1) Using the computer and dropping the temperature and C detector into the moltenbath at 3 to 5 min before blow off, the deviation from aimed end point values can be restricted within ±10°C and ±0.01%C.
    (2) Measuring the bath and its freeging temperature within 15 sec, bath carbon canbe presumed for very short time.
    (3) The measuring accuracy is mainly decided by the blow hole and aluminum killingmethod in the sample, measuring time and position in the L.D. furnace and measuring technique of temperatures.
    (4) Detector can be used repeatedly, so the actual cost of consumption can be minimized.
    (5) Samples obtained in the detector can be used for analysis.
  • 炭素鋼の地疵についての考察

    pp. 545-546

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  • Continuous Casting of Nut-Size Ferromanganese and Silicon-Manganese in Metal Mould

    pp. 547-550

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