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

Tetsu-to-Hagané Vol. 56 (1970), No. 9

  • A Study on the Reaction between Chromium Ore and Alkali during Roasting in Rotary Kiln

    Toyoshi ASANO

    pp. 1157-1164

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    Abstract

    The reactions between Cr are and Na2CO3 during roasting were studied using a rotary kiln (10000mm in length and 700mm in diameter). The followings are results obtained.
    Both of the optimum roasting temperature and the optimum basicity of the raw material were quitesimilar to those of the laboratory experiments. The conversion rate of Cr (III) to Cr (VI) was raisedby increasing revolving speed of the kiln. The best conversion of Cr (III) to Cr (VI) was obtained whenthe weight ratio of filler to Cr are being 4 to 1. Considerations on heat balance was made for producingone ton of Na2Cr2O7·2H20 by the rotary kiln.
    Among the many items of heat output, it was recognized obviously that the loss of heat by radiationand convection from the surface of kiln depended largely upon the capacity.
    The following equation represents the relation between the loss of heat per ton of Na2Cr2O7·2H20 by radiation or convention and dimensions of kiln.
    where E: Loss of heat per ton of Na2Cr2O7·2H20 by radiation and convection from the surfaceof a kiln with inner diameter c2, and outer diameter d2.
    E= {(c1/ d1)/(c2/ d2)} E0
    E0: Loss of heat per ton of Na2Cr2O7·2H20 by radiation and convection from the surfaceof a kiln with inner diameter c1, and outer diameter d1.

  • Theoretical Analysis on the Degassing Process in Upper Leg of R-H Degassing Plant

    Tetsuya FUJII, Iwao MUCHI

    pp. 1165-1171

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    Abstract

    It may be considered that the degassing rate in R-H degassing plant is mainly determined the rateof each the following processes, i. e., degassing process by inert gas bubbles in upper leg and one fromthe splash and the free surface of molten steel in vacuum chamber, and that these processes are affectedby circulation flow rate of molten steel.
    To obtain the fundamental informations on the design of this plant and on the determination of theoperating conditions, a particular attention is devoted to the degassing process by inert gas bubbles inupper leg, and a mathematical model of this degassing process in two-phase flow including gas bubblesand molten steel is developed in this paper. And, this model consists of material and momentum balancein metal phase, material balance in bubble phase and equation of continuity for two-phase flow.
    Numerical calculations on the degassing rate in upper leg and the circulation flow rate of moltensteel have been conducted with the aid of digital computer. Longitudinal distributions of process variablessuch as bubble size, pressure, concentrations of CO and H2 in bubble phase and that of C, O and H in metal phase have been obtained over the range from the blowing point of inert gas tothe exit of upper leg under various blowing rates of inert gas. Calculated results on the circulationflow rate of molten steel were found reasonable by comparing them the comparison with previous datareported by other investigators.

  • Effect of Nonmetallic Inclusions on the Bending Property and the Surface Defects of Cold Rolled Stainless Steel Sheets

    Ichiro TAKAHASHI, Masayoshi OGAYA, Takeshi YOSHIDA

    pp. 1172-1181

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    Abstract

    The effects of oxide and sulphide inclusions on the bending property and the surface defects of cold rolledsheet of 18-8 and 18 Cr stainless steels were investigated. The results are summarized as follows:
    (1) The bending property of the sheet containing chromium-oxide as a main constituent of oxide inclusionsis far superior to that of the sheet containing silicate.
    (2) An increase in the sulphide quantity in the range of this experiment causes a decline in the bendingproperty, but hardly affects other mechanical properties, with the exception of a slight deterioration of theErichsen value on 18-8 stainless steel sheet.
    (3) When the sulphide quantity is equal, chromium-oxide coexisting with sulphide inclusion improves thebending property far more than the other-oxide. This is due to the fact that the particles of chromium-oxideincluded in sulphides prevent the sulphides from the string-like elongation.Consequently, in order to improve the bending property both in 18-8 and 18 Cr stainless steels, it isessential to reduce the amount of sulphide inclusion by lowering the sulphur content in metal and toprovide oxide Inclusions which are reluctant to take a stringer shape such as chromium-oxide formedby lowering the silicon content and increasing the manganese content in metal within the limit of specifications.
    (4) Independent of the main constituent of oxide inclusions, chromium-oxide or silicate, surfacedefects and sand marks are formed whenever the oxide inclusions crowd locally, however, the defectsoccurring due to chromium-oxide can be removed not more easily than those due to silicate by mechanicalsurface conditionings.
    Thus, while chromium-oxide formed by lowering the silicon content in metal considerably improvesthe bending property, it affects deterioratively on the removal of the surface defects.

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  • Study on the Deoxidation of Stainless Steel with Aluminium

    Ichiro TAKAHASHI, Masayoshi OGAYA, Takeshi YOSHIDA

    pp. 1182-1193

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    Abstract

    A study was carried out on the deoxidation with aluminum instead of with silicon and manganese, aiming to improve the quality of 18-8 stainless steel, and its practical utilization was discussed.
    Experimental results are as follows:
    (1) 18-8 stainless steel deoxidized with Si and with Mn in a 10-kg induction furnace was thentreated with Al (0.5 to 1.0kg/t), resulting in a fairly well reduction of oxygen content. By holdingthe melt decrease of Al and increase of oxygen are recognized
    (2) Experiments in an 8-t Heroult furnace have shown that, even when aluminum is added at anearly finishing stage, the recovery of oxygen before tapping takes place remarkably. Aluminum additionin ladle should also be avoided because residual alumina might give rise to surface seams.
    Accordingly it is most suitable, to add aluminum at an intermediate stage.
    (3) By the well-timed aluminum addition the surface defects of cold rolled sheet are far less thanthose by conventional deoxidation. A little addition of titanium along with aluminum further diminishesthe surface defects.
    (4) For fine grain austenitic steel treated with titanium the pre-oxidation with Al is more effective, since the reduced oxygen content leads to a high yield of titanium available for the grain refinement.

  • The Decarburization Mechanism in Rimming Steel

    Toshiharu SHIMAZAKI, Yozo TAKEMURA, Shigeyoshi FUKUDA

    pp. 1194-1200

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    Abstract

    There are many studies on rimming steel but very few of which are quantitative.
    We have examined both the progress of solidification and the variation of composition in 10-22t low-carbon rimming steel melts during the time from pouring to capping. From these results, we made an unique quantitative investigation on the decarburization mechanism for rimming steel after pouring.
    From this study, the infiuence of oxygen coming from air on the decarburization reaction was clarified, and the decarburization reaction was classified to two types. One is the decarburization reaction which arises from the reaction of the carbon and oxygen discharged, during solidification, due to the difference of the solubity for melt and solid steel. The other is the decarburization reaction which arises from oxygen introduced from air which makes the oxygen concentration in melt deviate from the C-O equilibrium.

  • Some Investigations on the Fatigue Layer and Dressing Programme of Plate Finisher Mill Backup-Roll

    Mitruo NAGASE, Shigenari SHIMIZU, Hideaki SHIMIZU, Hirosuke TABE, Koichi KUDO, Hiroshi GOTO

    pp. 1201-1209

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    Abstract

    This report described the results of our two years' joint research between Nippon Kokan Kabushiki Kaisha and The Japan Steel Works, Ltd. On the plate finisher mill backup roll at N. K. K. Keihin Plant. The problems examined here were the fatigue layer of backup roll bycyclic loading, suitable dressing programme and the wear patterns and surface temperature of work rolls.
    The main results obtained were as follows:
    (1) The wear patterns of top backup roll were concave and those of bottom backup roll were almost flat. The affected layer of top rolls extended within 1.0 mm depth from the surface, while that of bottom rolls somewhat deeper than 1.0mm. Hardness measurement of the roll surface is considered to be one of the suitable means to ascertain the degree of fatigue.
    (4) The suitable dressing programme of this plate mill backup roll is 2.0 mm in dia. Everytime for top rolls and 2.Omm in dia. at initial 3 times and 8.0mm in dia. at the 4th time for bottom roll.

  • On the Phosphorizing and Phospho-carburizing of Steel

    Imao TAMURA, Yukio YAMAOKA, Yasutaka OKADA

    pp. 1210-1218

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    Abstract

    Phosphorizing of steels was studied by utilizing the treatment in ferro-phosphorous grains or in molten salts containing NaPO3 at various temperatures. Some properties of phosphorized steels were also examined. The results were summarized as follows:
    1. When steels were treated in ferro-phosphorous grains containing several percent of charcoal at about 1000°C, the phosphorized layer was uniform and smooth. In molten salts containing NaPO3, the specimen of steel was corroded and the phosphorized layer was porous. However, if the molten salts containing not only NaPO3 but also several percent of NaCN, a uniform phosphorized layer was obtained.
    2. The phosphorized steel was rapidly attacked by chemical corrosion in acidic solutions, but showed excellent resistant to weathering.
    3. Phospho-carburizing in molten salts containing NaPO3 and about 15% of NaCN was studied. Martensite in phospho-carburized and quenched specimens was harder than iron-carbon martensite in usual carburized steel. The hardness of P-C martensite reached to about Hv 1000.

  • Effects of Ni, Cr, and Cooling Rate of Quenching on the Properties of 3%Cr-Mo Steels

    Tadataka GOTOU, Masatosi MAEDA, Akira SUZUKI, Taira NAKANO

    pp. 1219-1230

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    Abstract

    In the 3% Cr-Mo and 2.5% Ni-Cr-Mo steels which are to be used for large blower rotor and low-pressure turbine rotor shafts, were studied the effects of Ni contents (0-2.5%) in the former and Cr contents (1.75 and 3%) in the latter on the continuous cooling transformation, and on the mass effect and mechanical properties when quenched at the cooling rate equivalent to the quenching of large rotor shaft. Results are summarized as follows:
    1) The ferrite transformation curve is shifted to longer time and lower temperature with increase in Ni contents. The bainite transformation curve is also shifted to longer time and lower temperature with increase in Ni and Cr contents, the latter shift being negligibly small for Ni contents below 1.75%.
    2) The transition temperature of the martensite and/or bainite with the tensile strength of 80-90kg/mm3, increases as the quenching rate decreases. This tendency is much pronouced especially at a very slow cooling rate.
    Increase in Ni contents tends to lower the transition temperature, but this change is very little between 1% and 1.75%. The transition temperature is increased with lowering quenching rate, especially at smaller Cr contents.
    3) The transition temperatures of the test pieces quenched equivalently to large forgings agreeded fairly well with those of large rotor shafts.

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  • Influence of C, B, and N on Creep-Rupture Strength and Structural Changes in Creep of 18 Cr-10 Ni Stainless Steel

    Takayuki SHINODA, Ryohei TANAKA, Tomoyuki ISHII, Tohru MIMINO, Kazuhisa KINOSHITA

    pp. 1231-1244

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    Abstract

    The influence of carbon, boron, and nitrogen on the creep-rupture strength and the structural changes, especially the morphological changes of carbides precipitated during creep of 18 Cr-10 Ni austenitic steel have been studied, and the relationships between the strength and the structures in the steel have been discussed.
    Following results were obtained.
    1) The addition of carbon up to 0.32% increases the 103 hr rupture strength of the steel at temperature of 600°C, but at 650°C and 700°C, the strength reaches the maximum at the carbon content of 0.23%. The reason is that, by the coalescence of carbides precipitated, the solid solution strengthening of carbon and the dispersion strengthening of carbides decrease with rising temperature.
    2) The addition of boron up to 0.009% maintains the high creep-rupture strength, especially at high temperatures and for long time. Boron prevents the carbide precipitation on grain boundaries or the precipitation of the grain boundary reaction type and makes carbides precipitated within grains fine and uniform.
    3) The addition of nitrogen up to 0.15% to the steel increases the 103 hr creep-rupture strength at 600°C, where the steel is effectively strengthened by finely dispersed precipitates, but nitrogen is not effective on the long time creep-rupture strength at 800°C, where the coalecence of the carbide is accelerated on grain boundaries and within grains.

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  • The Relationship between Wear Phenomena and Wear Particles of Cast Iron

    Kazuo KITAGAWA, Fumio SEKI, Masuzo UEDA

    pp. 1245-1252

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    Abstract

    The wear test of the pair of plain cast irons was performed in air atmosphere, and it was found that the formation of oxide film took place on their frictional surfaces and oxide mixed metallic particles always existed on frictional surface and gave a big effect on wear phenomena.
    Therefore, in this work, the composition change of wear particles produced under some frictional conditions was studied by using X-ray diffraction method. And then, the wear phenomena were investigated by employing grooved frictional surfaces by which particles could be removed easily.
    Results obtained were as follows;
    1) At lower frictional velocity when Fe2O3 film was formed, the oxide film were not good under heavy load.
    2) The amount of Fe2O3, particles decreased with increasing frictional velocity and had a minimum value at 1m/sec. And then considering these facts, the wear loss will increase rapidly on the condition that the equilibrium between repairing and tearing rates of oxide film is broken.
    3) In general, wear loss decreased when grooves were made along the frictional surface, however it did not always decrease at relatively high frictional velocity.
    4) It was found that hardened wear thin metallic flakes (Hv; 800) were torn off from hardened surface layers (Hv; 1000) and transformed to ledeburite structure by melting at too high temperature.

  • On the Durabilities of Special Cast Steels against Abrasive Wear

    Naotsugu INAKAZU, Shozo YOSHIOKA, Hisashi YAMAMOTO

    pp. 1253-1261

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    Abstract

    A study was made on fatigue layer of the backup roll surface by cyclic loading in rolling and its suitable dressing program in 4 high plate finisher mill at Keihin Plant, Nippon Kokan. An examination was also made on patterns and surface temperature of the work roll after rolling operation.
    The results obtained were as follows:
    1) The wear patterns of top backup roll were concave and those of bottom backup roll were almost flat.
    2) The layer affected by fatigue of the backup roll surface was examined by X-ray reflection method. The affected layer of top rolls extended within 1.0mm depth from the surface, while that of bottom rolls somewhat deeper than 1.0mm. Hardness measurement of the roll surface is considered to be one of the suitable means to estimate the degree of fatigue.
    3) The suitable dressing program of the plate mill backup roll is 2.0mm in dia. every time for top rolls and 2.0mm in dia. at initial 3 times and 8.0mm in dia. at 4th time for bottom roll.

  • Analytical Method of Carbon in Martensite in Steel with X-Ray Microanalyzer

    Minoru SASAKI, Kenichi SUZUKI, Ohiko KAMIMORI

    pp. 1262-1267

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    Abstract

    Analytical conditions and data treatment method for determining carbon content in martensite in low carbon steel were investigated by using an X-ray microanalyzer. The results were summarized as follows:
    1) The influence of polishing method on the X-ray intensity of C Kα line was eliminated by carefull buffing at finish polishing. In the analysis of martensite phase revealed by etching, abnormal high carbon value was obtained owing to the accelerated carbon deposition on the sample surface. The position of analyzed phase was required to be directed by microvickers indentions.
    2) Almost of the coarse grained martensite phase in the steel with 0.4% Ccontained 0.4-0.5%C. The phase containing 0.2-0.3% C were characteristic in particle shape.
    3) In the fine phases of which size were closely to the resolution limit of the used X-ray microanalyzer, the marking of objective phase and the stabilization of experimental equipment were particularly important. To correct the low analytical values which were inducedby simultaneous analysis of the ferrite phase surrounding the objective martensite, a trial of data treatment was made.

  • Study on Determination of Low Content of Calcium in Steels

    Kazuo KAWAMURA, Shiro WATANABE, Takeshi FURUKAWA

    pp. 1268-1279

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    Abstract

    An experiment was carried out to establish an accurate spectrophotometric method for the determination of very little amount of calcium in steels by glyoxal-bis (2-hydroxyanil). The forms of calcium compounds in steel were examined by an electron microscopic observation and an electron diffraction.
    The results obtained are as follows;
    (1) The interfering elements were completely isolated by extraction with β-diketones in benzene at pH (2) Very low content of calcium in steel even in ppm order was made possible to be determined by the present method.
    (3) Calcium in steels normally exists as non-metallic inclusions. The calcium compounds in the steels for this experiment were identified to be crystalline types CaO SiO2 (α), 2CaO SiO2 (α), and CaO SiO2 (β).(4) However, calcium in the experimental steels containing 1% to 5% soluble Al was found to be in solid solution predominantly.

  • Emission Spectrographic Analysis of Trace of Calcium in Steel

    Mutsumi IHIDA, Mamoru NAGAI, Yoshihiko KAWAI

    pp. 1280-1285

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    Abstract

    A solution method using a rotating graphite electrode and a direct emission spectrographic method has been studied to determine trace of calcium in steel. The experiment was performed with a 3.4m Ebert type plane grating spectrograph. In the case of the solution method, after dissolution, of a steel sample by dilute sulfuric acid, its solution is directly excited by high voltage spark discharge without separation of iron. The counter electrode is a graphite rod and the iron spectral line can be used as the internal standard. Lower detection limit of this method is 5ppm and the coefficient of variation is 2.5-7.9% in the range of 14-172ppm Ca. In the case of the direct emission spectrographic method, a steel rod sample is excited in the argon atmosphere by the low voltage spark discharge using a copper rod as a counter electrode with plus polarity. Lower detection limit of this method is 5ppm and the coefficient of variatiop is 2.5-11.7% in the range of 12-125ppm Ca.

  • Effect of Chromium and Molybdenum on the Temper Brittleness of Ni-Cr-Mo-V Steel for Large Turbine Rotor Shaft Forgings

    Hidemitsu TAKEUCHI, Ikujiro KITAGAWA

    pp. 1286-1294

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    Abstract

    The effects of chromium and molybdenum contents on the temper brittleness of Ni-Cr-Mo-V steel, used for turbine rotor shaft forgings, have been investigated. The steels alloyed with 0.52-1.73%Cr and 0.3-0.6%Mo were subjected to embrittling treatment at 500°C for 100hr. The degree of temper brittleness was estimated and compared by the 50% fracture appearance transition temperature (50% FATT) obtained by Charpy impact test (2mm V motch Charpy), and the fracture appearance of each test piece was observed by scanning electron microscope.
    The results are as follows:
    (1) The degree of temper brittleness increases with the content of chromium and molybdenum.
    (2) The embrittled steels have a tendency increasing the ratio of intergranular fracture, however, there is no clear quantitative relationship between the degree of embrittlement and the ratio of intergranular fracture. This tendency is greatly influenced by the austenite grain size, and fine grain steel shows considerable low values in the ratio of the intergranular fracture, even in embrittled speciments.

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    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • © 1970 The Iron and Steel Institute of Japan

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