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

Tetsu-to-Hagané Vol. 100 (2014), No. 8

  • Trickle Flow Behaviors of Liquid Iron and Molten Slag in the Lower Part of Blast Furnace

    pp. 925-934

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    DOI:10.2355/tetsutohagane.100.925

    In-situ observations of the liquid high carbon iron (HCI) and slag flows in the packed coke bed was carried out by using high temperature X-ray fluoroscopy at 1773 K. Along with the observation, 2-dimensional multiphase computational simulations of the liquid HCI and slag flows in the coke bed was carried out to investigate the effect of the slag on the HCI flow in the coke bed. It is found that the liquid HCI or slag could not pass through the coke bed with the coke diameter of 3-5 mm, however, the HCI can pass through the same size coke bed if the HCI is contacted with the slag through the X-ray fluoroscopic observation and the computational flow simulation. When the HCI and slag contacted each other on the coke surface, the contact angle of the HCI with slag decreased and the initially non-wettable characteristic of the HCI changed to wettable one. On the other hand, the slag’s contact angle is increased and changed to non-wettable. Based on the experimental and simulated results, it is confirmed that the contact angle change due to the HCI-slag contact make it possible for the liquid HCI and slag to pass though the narrow coke slit that is small enough to prevent each liquid’s flow down if they are not contacted. Based on the capillary rise model, the driving force of the HCI penetration into the coke bed will be the energy reduction by extending area of the coke surface covered with the liquid HCI.
  • Development of High Efficiency Dephosphorization System in Decarburization Converter Utilizing FetO Dynamic Control

    pp. 935-942

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    DOI:10.2355/tetsutohagane.100.935

    Laboratory experiments were carried out with the aim of adapting a (FetO) dynamic control technique, in which (FetO) is estimated by calculating the oxygen balance during blowing, to the hot metal decarburization process. The rephosphorization condition in the higher decarburization rate period was then clarified based on those experiments. Next, (FetO) control experiments were carried out in a commercial-scale plant converter. (FetO) generation was promoted by increasing the oxygen flow rate and raising the lance height in the early stage of blowing, and the amount of dephosphorization during blowing was increased. Finally, a dephosphorization model was constructed by combining the coupled reaction model and the (FetO) estimation model. This model suggested an increase of the amount of dephosphorization during blowing, and the effect was confirmed by an experiment with a commercial 240 ton converter.
  • Effect of Nitrogen Content on Cold Working Properties of High Strength Mn-Cr-N Steel Made by Pressurized ESR

    pp. 943-950

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    DOI:10.2355/tetsutohagane.100.943

    High strength Mn-Cr-N steels containing high nitrogen contents were manufactured using a lab-scale pressurized electro-slag remelting furnace to determine the deformability of the steels. Melting experiments were performed under a condition of 1.0 MPa pressure N2 gas to have various N contents. Gas porosity and severe macrosegregation were not observed in the remelted ingots. Microstructure observation revealed that nitrides and non-metallic inclusions were small enough without affecting the mechanical properties. After the ESR ingots were heat-treated and forged, mechanical properties of the steels at a room temperature were measured. The grain sizes were measured as the range from 50 to 300 μm. The results of 0.2% proof stress showed that the steel became stronger with increasing N content according to solid solution hardening mechanism. In addition, with various strain rates, tensile work hardening exponents were determined to be almost constant values between 0.20 and 0.25. These results suggest that the method of cold working for the 18Mn-18Cr-0.7N steel is applicable to the Mn-Cr-N steels containing nitrogen over 1.0 mass%.
  • Influence of Basicity of Mold Flux on its Crystallization Rate

    pp. 951-957

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    DOI:10.2355/tetsutohagane.100.951

    Crystallization of mold flux was observed with confocal laser microscope. Crystallization temperature, CCT curve and crystallization rate were evaluated from the observed images. The evaluated results were compared between two kinds of mold flux, and influence of basicity on crystallization rate was discussed. Crystallization temperature increased with basicity. Crystallization rate also increased with basicity, but its dependency on cooling rate was differed by basicity. The difference could be explained by the viscosity of mold flux at crystallization temperature. Crystallization rate has clear relation to the viscosity at crystallization temperature, and the rate increased with decrease of the viscosity. Two kinds of mold flux were unified in this relationship. Crystallization is controlled with basicity in terms of not only equilibrium but also kinetics through viscosity.
  • Evaluation of Cooling Performance in Intensive Cooling with High Water Flow Rate and Effect of Controlled Rolling just after Cooling on Mechanical Properties

    pp. 958-965

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    DOI:10.2355/tetsutohagane.100.958

    Laboratory tests were conducted in order to quantify the cooling performance of intensive inter-pass water cooling, which was introduced as an effective method for increasing productivity in the manufacture of high strength steel plates.
    The range of flow rates was extended to 0.17-0.39 m3/m2 s. Pipe nozzles with inner diameters of 3 mm or 6 mm were used in addition to the original hole-type nozzle. The influences on cooling performance on the type of nozzle, nozzle pitch and injection distance were investigated. In the water cooling tests with the φ6 pipe nozzles, temperature drop in the specimens increased with higher water flow rates. The upper limit of cooling performance was found to be around 0.25 m3/m2 s in upper side cooling, whereas an upper limit was not seen in lower side cooling. In tests with the φ3 hole nozzles, temperature drop decreased with longer injection distance, and that tendency is larger in lower side cooling. A nozzle arrangement with a shorter installation pitch results in higher cooling performance. The influence of the inner diameter of the pipe nozzles on cooling performance is small.
    After water cooling, controlled rolling of specimens of Si-Mn steel, which is used widely as high tensile steel, was performed with a laboratory mill. As a result, it was found that total rolling time can be reduced with inter-pass water cooling, and water cooling does not affect the microstructure nor mechanical properties.
    Intensive inter-pass cooling, which has high cooling performance, has the potential to realize efficient production of high strength steel plates in controlled rolling.
  • PET-Hair Generating Mechanism of Laminated Steel in Forming Process of DI Can

    pp. 966-973

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    DOI:10.2355/tetsutohagane.100.966

    On application of polyethylene terephthalate (PET) film laminated steel to Drawn and Ironing (DI) process, it is necessary to control the PET-hair that we named shaving or breaking film at formed can edge due to no flange making in process. We previously reported the PET-hair was controllable with lower yield stress of steel substrate and stronger adhesion between PET film and the substrate. In this study, to demonstrate cause and mechanism of the PET-hair generation, we investigated the film adhesion to the substrate and the film peeled-off length at upper edge of formed can, and found a correlation between the two properties. The film peeled-off strength over 15N gets the film peeled-off length considerably shorten, resulting in difficulty in the PET-hair generation. Furthermore, we checked effects of ironing rate on the strain in the film during can-forming, and found the following mechanism. While ironing rate of 10% provides fracture strain in the film, strong adhesion could achieve no PET-hair generation even at the rate of over 10%. However, in case of the rate of over 15%, fracture of the film can’t be avoided, resulting in the PET-hair generation.
  • Influence of Hydrogen on Fatigue Property of Suspension Spring Steel with Artificial Corrosion Pit after Multi-Step Shot Peening

    pp. 974-983

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    DOI:10.2355/tetsutohagane.100.974

    In order to reduce the weight of the suspension springs by increasing the strength level of the steels used, improvement of the corrosion fatigue property is the most important issue. This study investigated, the effect of residual stress, artificial corrosion pit depth and diffusible hydrogen on rotary bending fatigue properties of specimens after double shot and triple shot peening. The following conclusions were obtained:
    (1) Fatigue limits of specimens having the artificial corrosion pit of 250 μm depth with and without the charged hydrogen are improved remarkably by the triple shot peening.
    (2) Fish-eye fatigue fracture with an inclusion as the fatigue crack initiation site occurs frequently due to the charged hydrogen.
    (3) A good relationship between fatigue limit after shot peening and compressive residual stress at the bottom of the artificial corrosion pit is obtained regardless of the depth of the artificial corrosion pit.
  • Pit Growth Behavior of SUS443J1 in Atmospheric Environment

    pp. 984-991

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    DOI:10.2355/tetsutohagane.100.984

    It is significant to evaluate the corrosion resistance of a new stainless steel, SUS443J1, in atmospheric environment. In this study, the growth behavior of pits on the surface of a ferritic stainless steel, SUS443J1, and an austenitic stainless steel, SUS304, were compared by field exposure tests and electrochemical measurements.
    It is known that the pit growth rate can be approximated as X = atn, where X is pit depth, t is time, a and n are constants. As a result of field exposure tests, it was obtained that the pit growth rate values, n, were 0.2 for both 2B and HL surfaces of SUS443J1 and SUS304. It could be predicted that the pit growth behavior of SUS443J1 and SUS304 were equivalent to each other.
    The pitting potential values, V’c10, of SUS443J1 and SUS304 were almost equivalent to each other, and the repassivation potential showed the same tendency. Pitting potential was reduced with increasing maximum valley depth, Rv., of the surface. The repassivation potential was affected by the turning current density, where the sweep of potential was reversed. The turning current density would represent a degree of pit growth. It was suggested that a deep pit would expand with larger growth rate than that of a shallow pit because a pit could growth easily and repassivation would hardly occur within a deep pit.
  • Fundamental Study of the Flow Stability in Reverse Roll Coating

    pp. 992-998

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    DOI:10.2355/tetsutohagane.100.992

    Reverse roll coating is widely used to coat a thin liquid layer onto a moving substrate. The metered liquid layer is created within the gap between a pair of co-rotating rolls. To avoid roll damage due to roll run-out, substrate caliper change or splice passage, when gap between rolls is small, one of the rolls will have a compliant polymer cover. The existence of a deformable cover in the gap between metal roll and rubber roll creates a elastrohydrodynamic flow field in that region. As the liquid passes through the coverging-diverging section within the gap it generates pressure, this pressure can deform the elastic roll surface, which in turn, alters the geometry of the gap and the flow. Therefore the uniformity of coating is effected differently than what is observed in the case, when only rigid rolls are used.
    In this study, visualizations of the flow between a reverse deformable roll and solid stainless steel roll are done to determine how the uniformity of coating is effected by operating parameters: the speed ratio, roll diameter and liquid properties. The wavelength of ribbing is investigated to verify the effect of speed ratio, wet thickness and viscosity. The roll coating apparatus is used with 4 inch diameter rolls installed one above the other for these experiments. The ribbing wavelength is measured from images. The uniformity of coating and its dependence on capillary number is evaluated. Numerical simulation of the flow between 2rolls leading to prediction of ribbing wavelength is conducted.
  • Effect of Trace Amount Tungsten on Long-term Material Properties of High Cr Steels

    pp. 999-1005

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    DOI:10.2355/tetsutohagane.100.999

    The applicability of high chromium (Cr) steel as the main structural material in fast breeder reactors (FBR) has been explored to enhance the safety, the credibility and the economic competitiveness of FBR power plants. Tungsten (W) is believed to improve the high temperature strength of high Cr steels by solid-solution strengthening mechanism, although the long-term effectiveness and stability of such a strengthening mechanism has not fully been understood yet. High Cr steels controlling W content are produced and tensile tests, creep tests, aging tests and charpy impact tests were conducted to investigate the long-term material properties. It was observed that the short-term creep strength could be improved by W. However, there is almost no influence of W on the long-term creep strength. And it was observed that the impact properties after aging could be improved by decreasing of W. It was found that the optimal W content for excellent high Cr steel of FBR grade are < 0.1 wt. %, under FBR operating conditions.
  • Novel Fabrication Process of Micro Components by Viscous Flowing of Iron Based Metallic Glassy Monodispersed Particles

    pp. 1006-1013

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    DOI:10.2355/tetsutohagane.100.1006

    Since Fe based metallic glasses have many attractive properties, i.e. high mechanical strength, high wear resistance, excellent soft magnetic properties, they’ve been expected to be utilized as raw materials for micro components. However, there are some difficulties and limitations in processing the Fe based metallic glass supercooled liquid into a final product due to its low thermal stability. Thus, the fabrication of Fe based metallic glassy micro components have yet to be achieved so far.
    In this work, we focused on fabricating metallic glassy micro components by using a novel microfabrication process which was previously proposed by our group. In the process, single spherical metallic glassy particle with several hundred micrometers in diameter was used as a raw material. A micro viscous flow processing was carried out using two types of dies with different shape, i.e. one is prism shape and another one is gear shape.
    In our study, two kinds of metallic glassy particles with different composition of [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 and Pd42.5Cu30Ni7.5P20, whose glass forming ability and thermal stability are different from each other, were used to demonstrate the applicability of the process.
    The results showed that the [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glassy micro components with fully amorphous structure was successfully fabricated for the first time and Pd42.5Cu30Ni7.5P20 micro components was also fabricated by means of our proposed microfabrication process.
  • Fabrication of Equipments Treating Iron and Steel Slags with Highly-Pressurized Hot Water and Investigation of Leaching of Constituents from the Slags

    pp. 1014-1020

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    DOI:10.2355/tetsutohagane.100.1014

    Two types of apparatus to treat steel slags with highly pressurized hot water were fabricated and examined in terms of leaching of constituents from the slags. The batch-type apparatus was consisted with a stainless steel vessel and a sand bath; a flow-type apparatus was composed of a stainless steel column, a column oven, an HPLC pump, a backpressure valve, and a fraction collector. In the batch-treating system, the concentrations of the elements leached from slags tended to increase as increase in the treating temperature while pH of the solution shows no obvious relations to the solution temperature. In the case of flow-treating system, on the other hand, a unique dependency of pH of the leachate on the treating temperature was observed in the obtained flow profiles. The flow profiles of the pH highly related to those of the concentration of calcium ion and sulfate. Treating 5.1 g of blast-furnace slag with 350 mL of water by the flow system at 250 ºC enabled to leach 22.5% of phosphorus, 97.1% of sulfur, and 0.89% of calcium from the slag. New depositions without sulfur on the treated slags were observed in SEM images, indicating that not only dissolution but also deposition occurred simultaneously during the treatment with highly pressurized hot water in the column. Thus, using highly pressurized hot water is promising method to treat steel slags for reuse of steel slags as environmental-friendly materials.
  • Antimicrobiability of Cu Contained Stainless Steels

    pp. 1021-1028

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    DOI:10.2355/tetsutohagane.100.1021

    Antimicrobial ability of Cu contained stainless steels was investigated. Antimicrobial ability increased with elute fraction of Cu ion from stainless steel surface into antimicrobial test medium. It is necessary to promote eluting fraction of Cu ion, that is, to achieve giving antimicrobial ability to Cu contained stainless steel that sub-micron order or larger size ε-Cu phases are dispersed in stainless steel, surface of stainless steel has high electrode potential and dissolved oxygen exist in the test medium.
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  • Utilization of Waste Organic Substances for Biological Denitrification

    pp. 1029-1035

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    DOI:10.2355/tetsutohagane.100.1029

    Waste organic substances were evaluated as an alternative nutrient source for biological denitrification in nitrogenous wastewater. In common, methanol is used as nutrient source for denitrifying bacterium. By using of organic wastewater discharged from steel making plant, substituting this wastewater for methanol is focused. In this study, four kinds of candidate steel industry wastewater were examined. In the first step, water quality analysis was conducted as simplified evaluation. BOD/CODcr was defined as the ratio of biological degradable organic substances to total organic substances, candidate wastewater were evaluated for BOD/CODcr. By this test, three kinds of candidate wastewater were selected. In the second step, continuous biological denitrification treatments were demonstrated. Two kinds of candidate wastewater were significantly effective for a nitrogen removal equivalent to methanol. By the water quality analysis and the continuous treatment test, the selection process of organic wastewater as alternative methanol was facilitated and it made possible to perform in a short period of time.
  • Dynamic Material Flow Analysis of World Steel Cycle in Machinery

    pp. 1036-1042

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    DOI:10.2355/tetsutohagane.100.1036

    In this work, a dynamic material flow analysis (MFA) was conducted to estimate the global flow and in-use stock of steel for 4 machines (engineering and construction equipment, agricultural machinery, fans and pumps, and conveyance machines) in 42 countries until 2050. Concerning 3 machines (engineering and construction equipment, fans and pumps, and conveyance machines), the growth of in-use stock and demand for steel was estimated based on the historical growth in Japan until now. For agricultural machinery, the growth of in-use stock and demand for steel was estimated based on the historical growth of steel in 42 countries until now. It was estimated that the in-use stock, demand and discard of steels for these machines would be 1.4-1.7 billion t, 100 million t and 80-100 million t, respectively.
  • Influence of Seawater Temperature and Organic Matter on Iron Elution from a Mixture of Steelmaking Slag and Composts

    pp. 1043-1047

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    DOI:10.2355/tetsutohagane.100.1043

    Seaweed depletions in coastal areas of barren grounds are serious problems in Japan and other parts of the world. The lack of dissolved iron is one of the possible reasons for barren grounds. We have developed a methods for restoration of seaweed beds using the mixture of steel making slag, and composts including humic substances. The influences of seawater temperature and organic matter on the iron elution from the mixture were investigated by iron elution test in seawater in this study. It was found that the iron elution rate from the mixture accelerated as temperature increased. Meanwhile, the powdered bamboo and powdered bamboo coal char were mixed with steelmaking slag and composts used for iron elution test. The amount and the rate of iron elution in seawater became larger by mixing bamboo and its coal char with the slag-composts sample. It was also confirmed that the addition of organic matter could promote iron elution from steelmaking slag.

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