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

Tetsu-to-Hagané Vol. 67 (1981), No. 8

  • General Review of Recent Progress in Continuous Casting Epuipment

    pp. 1043-1055

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  • Instrumentation and Control System on Recent Continuous Casting

    pp. 1056-1065

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  • Development of Production and Operation for Slabcaster

    pp. 1066-1079

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  • Current Status of Improvement of Quality and Application of Continuously Cast Slabs

    pp. 1080-1100

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  • Continous Bloom and Billet Casters and Quality of It's Product

    pp. 1101-1113

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  • Development of Slab Continuous Casting Technology in N. K. K.

    pp. 1114-1120

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    Nippon Kokan K. K. has constructed 7 continuous casting machines for slabs. At present, about 70% of production is produced continuous casting process. In this report, particulars and features of NKK slab continuous casting technology are described.
  • The Characteristics of Walking Bar Type Curvilinear Continuous Caster

    pp. 1121-1127

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    Walking Bar type curvilinear continuous caster holds the slab by surface contact with W. B. and straightens it with low-strain and low-strain rate. The slab bulging and its thermal stress are analyzed by the elasto-plastic finite element method which is supported by the results of the mechanical properties of metals at high temperatures, the composite driven rivet tests and the analytical simulation of the slab internal temperature distributions.
    The slab supported with W. B. has only about 1/2-1/7 bulging compared with the slab supported with rolls.
    As the observation of the casting stop test, it is confirmed that the parts of the slab supported with W. B. have extremely small deflection but the one of the slab supported with rolls have much deflection.
    It is recognized that W. B., indirect cooling system is rather excellent in thermal stress prevention than spray cooling system.
    W. B.: Walking Bar
  • Automatic Casting System Using Electromagnetic Mold Temperature Detector

    pp. 1128-1134

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    This paper describes the newly developed mold level control system and the ladle valve control system, both of which are greatly contributing to the automatic operation of the continuous casting machine.
    (1) New type of mold level control system
    The new type of mold level control system employs the non-contact type thermo-sensors instead of the conventional thermocouples to detect the steel level in the mold. The steel level change in the mold is detected by a permeability change of the thermo-sensitive magnetic materials attached to the mold wall; Easy maintenance of the mold is now possible without taking care of the thermo-couples.
    (2) Withdrawal speed control system
    The flow rate of molten steel through the slide valve of the ladle is calculated and controlled by means of micro-computer taking the withdrawal speed of cast strand as an input. Thus, in comparison with the conventional ladle slide valve control, this system can avoid the load cells on the tundish car, and brings about an advantage on both of the maintenance and the cost.
  • The Technique for High Speed Casting with High Availability in Slab Caster

    pp. 1135-1144

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    A new equipment has been developed for wide range slab width changing during casting with considerably high moving speed of narrow face by utilizing suitable taper setting of narrow faces in mold. Combination of this technique and sequence casting of different chemical compositions has realized high availability of up to 85% constantly.
    On the other hand, the improvement of some equipments and establishment of suitable casting condition have assured satisfactory surface and internal qualities of slab in high casting speed with superior machine characteristics such as multi bending and/or unbending and divided rolls of small diameter. Thus, almost all the casts are directly charged into reheating furnace without any conditioning for the purpose of saving fuel consumption in rolling mill shop. Additionally, typical operational accidents such as break out and nozzle-clogging have been overcome by the improvement of casting technique.
    Therefore, Kawasaki Steel Corp. has succeeded in increasing productivity of slab caster remarkably at Mizushima and Chiba Works.
  • New Continuous Slab and Bloom Caster at Kashima Steel Works

    pp. 1145-1151

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    The new continuous caster at No. 1 steel-making shop in Kashima Steel Works is the low head typemultiunbending machine (SH-CCM).
    Kashima Steel Works already has two units of big S-type continuous caster with two strands. And the production ratio of slabs by these two casters reaches approximately 60 percent of the total production in Kashima.
    One of the main purposes to develop SH-CCM is to utilize the old top pouring deck for the conventional ingot making process, which is not used recently. The other is to produce rather inefficent lots for a big caster, such as the one with small amount or with a special size, in order to maintain high productivity of the main conventional casters.
    The construction of this machine is more economical than that of a conventional caster since it is possible to utilize various facilities of the old ingot-making deck.
    SH-CCM has many features, such as approximately 5.8 m in machine height, which is far smaller than that of the conventional caster, five successive unbending points, wide range in size and single strand which is applicable to both slab and twin-bloom casting.
    The new caster has been running satisfactorily since its start-up in July 1979 and the quality of products is by no means inferior to that of conventional casters.
  • Source of Exogeneous Inclusions and Reduction of Their Amount in Continuous Casting Process

    pp. 1152-1161

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    Investigations to produce clean steel for draw and ironing cans in continuous casting process were carried out.
    Results obtained are as follows:
    (1) Inclusions which cause flange cracks in manufacturing draw and ironing cans are 50150 μm in size and CaO-Al2O3 in compositions, which can be fairly well detected by the magna-flux method.
    (2) CaO-Al2O3 inclusions are originated from slag which is deoxidized by Al in molten steel, the content being about 0.005% or above.
    (3) Main source of the above-mentioned inclusions is tundish-slag, which is spattered into molten steel by the stream of the next ladle in continuous casting.
    (4) Good clean steel for draw and ironing cans can be produced by means of either large tundish with dams or reladling method (LLTM process)
    (5) The theoretical model to explain the effect appointed out in (4) was proposed.
  • A Numerical Analysis of Strains in Slabs and Forces on Rollers in the Straightening Zone of Continuous Casting Machine

    pp. 1162-1171

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    A numerical method has been developed to improve mechanical analysis of straightening process in continuous casting, preceded by discussion on shortcomings involved in forgoing methods.
    Characteristics of the straightening revealed by this method are
    (1) Starting end of slab strand exerts excessive force on rollers in the straightening zone,
    (2) The above force becomes much smaller in the steady state of casting,
    (3) Curvature of the strand is largely in agreement with that of roller alignment but with some offalignment in the steady state of casting,
    (4) Straightening of the starting end cannot completely be made, leaving complicated deformation of the end slab.
  • Analysis of Bulging in Continuously Cast Slabs by the Creep Model

    pp. 1172-1179

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    The creep test on steels and the bulging test by plasticine were carried out to confirm the validity of equation derived by introducing creep concept to calculate the bulging of continuously cast slabs. At the same time, bulging was measured of the slab completely solidified in a 10.5 m R bow-type machine. The results obtained are summarized as follows:
    1) At temperatures experienced in continuous casting, defomation of steel slabs is characterized by creeping. Only the transient creep was observed in a short creep time up to 30 sec during when the slabs travel a half of supporting roll spacing.
    2) When the transient creep was expressed as
    ε=a0σtn, (ε; Strain, σ;Stress, t; Creep time)
    the creep constant a0 was expressed by an Arrhenius equation, and the value of n changed in the range of 0.40.6 depending on temperature.
    3) The observed values of bulging of the slab completely solidified in the machine corresponded well with the calculated ones.
    x

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  • Hot Ductility in Steels in the Temperature Range between 900 and 600°C

    pp. 1180-1189

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    The embrittlement of carbon steels in the temperature range from 900 to 600°C was studied by the hotstage tensile test as well as fractographic analyses, and the mechanism of formation of transverse facial cracks in the continuously cast steels was discussed in terms of this embrittlement. Factors affecting the embritlement are the austenite grain size, the precipitates such as sulfide and oxide and the film-like proeutectoid ferrite formed along the austenite grain boundary. Thus, lowering the impurity content, refinement of the austenite grain and also slower rate of cooling are effective to minimize this embrittlement. However, the best way to have sound slabs is to avoid this poor ductility temperature region at the benching point.
  • Fundamental Study and Its Application of Surface Defects of Powder Cast Strands

    pp. 1190-1199

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    Simulation experiments using Mould Simulator developed by the authors and plant trials have been carried out to investigate the formation mechanism of oscillation marks and the factors affecting powder consumption rate in continuous casting.
    Following results were obtained through the experiments.
    1) Oscillation marks are formed as a result of interaction between solidified shell and very viscous layer of mould powder at the circumference of molten steel surface in a mould.
    2) Depth of oscillation marks increases as the negative strip time of the mould oscillation cycle increases.
    3) Consumption rate of mould powder, q is proportional to the positive strip time.
    Low frequency mould oscillation mode with decreased amplitude has been proposed to obtain shallow oscillation marks and high consumption rate of powder for a fixed powder property.
    Besides the above stated proposal, several measures which were not well documented have been studied in order to produce slabs without surface defects such as slag spots, transverse corner cracks and longitudinal facial cracks.
    The results obtained are listed below.
    1) Proposed mould oscillation mode is effective for reducing both slag spots and transverse corner cracks.
    2) Stable molten steel level in a mould during casting is very important for decreasing both slag spots and longitudinal facial cracks.
    3) A suitable viscosity range of the powder exists for minimizing the frequency of longitudinal facial cracks.
    x

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  • Factors Affecting the Formation of Shell and Longitudinal Cracks in Mold during High Speed Continuous Casting of Slabs

    pp. 1200-1209

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    Factors affecting the formation of the shell and longitudinal cracks on the shell have been investigated for high speed continuous casting of slabs.
    Withdrawal speed of slab, melt stream velocity coming out of submerged nozzle, mold taper, and mold oscillation have shown respective influence on the formation and their effects have been analyzed quantitatively. Also, characteristics of the heat extraction from and resulting stress in the shell have been examined with respect to the crack formation.
    These observations have resulted in countermeasures to enhance uniform shell formation in mold and prevent the cracks on the slabs.
  • Influence of the Molten Powder Pool on the Longitudinal Surface Cracks in Continuously Cast Steel Slabs

    pp. 1210-1219

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    The thickness of the molten powder pool on the molten steel in a mold and its formation process have been investigated from a viewpoint of the prevention of the longitudinal surface cracks in continuously cast steel slabs.
    The results obtained are summarized as follows:
    (1) It is important to control the thickness of the molten powder pool in the optimum range in order to prevent the longitudinal surface cracks in continuously cast slabs.
    (2) The necessary minimum pool thickness is decided by the oscillation conditions of the mold and the surface rippling characteristics of the molten steel in the mold, which correspond to casting conditions.
    (3) There is a characteristic incubation period of the mold powder before the heat flux starts to increase from the surface of powder layer which is formed on the molten steel. This incubation period can be used to evaluate the ability of the mold powder to form the pool.
  • Prevention of the Formation of Longitudinal Facial Cracks on Continuously Cast Slabs by Improving Mold Powder and Mold Oscillation

    pp. 1220-1228

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    Improving mold powders and optimizing mold oscillation have been made to decrease longitudinal facial cracks occurring on continuously cast slabs, aiming at direct reheating of slabs without surface conditioning.
    Controlling the melting characteristics of mold powders to avoid fluctuation in the thickness of molten slag of appropriate viscosity on the meniscus of steel melt has proved to be much effective. Optimized melting characteristics have been determined for casting speeds of up to 1.8 m/min. Also, oscillation of mold has been so adjusted as to give suitable flow of slag film in mold and solidified steel shell boundary by making negative stripping time tN to fall in the range between 0.2 and 0.3 s.
    These countermeasures followed by decreased water cooling intensity just below the mold have enabled us to increase the fraction of direct reheatable slabs free from surface defects up to 200000 ton/mo., about 40%. of crude steel production.
    x

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    1. Factors Affecting the Formation of Shell and Longitudinal Cracks in Mold during High Speed Continuous Casting of Slabs Tetsu-to-Hagané Vol.67(1981), No.8
  • Improvement of Continuously Cast Slab Surface and Performance of Rolling the Slab Free from Surface Conditioning

    pp. 1229-1235

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    Refinement in operating practice and technical development such as degassing, Ar gas shrouding, mould fluxes, tundish refractories, slab surface temperature control in the secondary cooling zone and so on, made it possible to improve slab surface quality and hence reheat the slab without surface conditioning.
    Recently, 80% of the slabs for plates and 50% for sheets are charged directly into the reheating furnaces by this process, with excellent results. On the basis of this development, continuous casting of high grade steels such as API-70 and deep drawing quality steels have been made possible.
  • Hot Charge of Continuously Cast Slabs

    pp. 1236-1240

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    Kashima Steel Works has three casters. The products quality of these casters are very high and approximately 150000 tons of products are monthly hot-charged into reheating furnaces to improve energy consumption.
    In this paper, the following items are described.
    (1) Hot charge of low carbon aluminum killed steel.
    Decrease in sub-surface Al2O3 inclusion and development of the deburring equipment of slabs.
    (2) Hot charge of 40 kg/mm2 grade steel.
    Decrease in longitudinal cracks of slabs and development of the optical inspection system for hot slabs.
  • Pseudo-rimmed Steel by Strand Casting

    pp. 1241-1247

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    In order to manufacture pseudo-rimmed steel by continuous casting, which has been strongly required, a stable production system is established by improving continuous casting process together with BOF and RH processes as one totalized process.
    In the BOF, oxygen blowing is ended at the constant carbon content of 0.10% for the reduction of FeO content in slag. Precise composition adjustment is made in the following RH process. Furthermore, the constant high speed casting under non-oxidizing condition is employed to ensure the good surface quality of cast slabs.
  • Qualities of Pseudo-rimmed Steel Sheet Manufactured by Strand Casting

    pp. 1248-1254

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    New pseudo-rimmed steel has been developed in order to improve the performance of conventional low carbon Al-killed and Si-killed steels.
    This paper describes the operability, formability, surface treatability, surface properties, welding properties, etc., of hot strip, cold strip and surface-treated sheet.
    The performance of pseudo-rimmed steel is found almost satisfactory. The deoxidation of molten steel with a minimum amount of Al without using Si has a significant effect on the improvement of the product performance.
  • The Technical Developement of a Large Cross-sectional Bloom Caster for Seamless Tubular Products

    pp. 1255-1261

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    A four strand vertical bloom caster was started up at Ohgishima in April, 1979. The caster is producing 100000 metric tons per month of 400 mm × 520 mm blooms for seamless tubular products. New technology has been developed as follows:
    (1) Automatic ladle pouring system with NKK rotary nozzle for labor saving and stabilization of cast products quality.
    (2) Automatic mold level control system with NKK eddy-current mold level meter.
    (3) Optimum rolling schedule of cast products.
    (4) Improvement of the continuous-continuous casting operation technology.
    (5) Improvement of qualities for cast products and rolling products.
    The caster began charging unscarfed hot blooms into the rolling and billetting mill in July, 1979 for all of cast products.
  • Operation and Quality Aspects of Large Section Mono-size Bloom Caster at Wakayama Steel Works

    pp. 1262-1268

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    The new bloom caster at Wakayama Steel Works has been very successfully commissioned in January 1979. It took only eleven months to build this machine. Owing to the experience of twin bloom casting operation at No. 2 slab caster prior to the new caster installation, the monthly production of new caster has increased rapidly since start up. The nominal production capacity of 80000 ton has already been reached in the second month from start up and the stable operation has established international record of long sequence casting of 775 heats in September 1980.
    The quality of the products is much better and more stable than conventional ingot and twin materials, so the application of cast bloom has been extended quickly to A.P.I. P-110 seamless tube production.
  • Influence of Operating Conditions on Internal Quality of Large Cross Section Continuously Cast Blooms

    pp. 1269-1277

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    The No. 1 Steelmaking Shop of Kawasaki Steel Corp. Mizushima Works has two circular arc type bloom casters with mold size ranging from 200 × 220 mm to 400 × 560 mm.
    In this paper, the influence of casting conditions on internal defects of large cross section bloom casts has been studied, especially the molten steel flow in the pool caused by immersed nozzle and elctromagnetic stirrer.
    The multi-pore immersed nozzle has been proved to be superior to the single-pore nozzle, in increasing aercal percentage of equiaxed crystals of casts and in decreasing accumulation of inclusions. The amount of large inclusions in large cross section bloom is less than in the case of smaller ones. A mathematical model to predict the amount of large inclusions accumulated in the upper side of bloom casts is presented. The influence of electromagnetic stirring on the center segregation and negative segragation at the part of white band is made clear, and low segregation casts can be obtained by choosing a proper electromagnetic stirring condition.
  • Influence of Electro-magnetic Stirring at Mold on Negative Segregation in Continuously Cast Bloom

    pp. 1278-1286

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    The fluid flow induced by electro-magnetic stirrer at the mold and the negative segregation caused by the fluid flow were investigated. The surface velocity of molten steel was obtained from the analysis of movie film taken by a high speed camera, and the flow velocity below the meniscus was estimated as compared with the fluid flow of low melting temperature metal. The experiment was carried out for low, middle and high carbon steels (0.13%C0.64%C).
    From the experimental result, it has been found that the degree of the negative segregation increases with the increase of flow velocity and with the decrease of carbon content of steel. The maximum depth in the mushy zone washed by bulk liquid and the width of the mushy zone are calculated, and the reason of the increase of the degree of negative segregation with the decrease of carbon content of steel is considered.
  • Quality Improvement by the Application of a Stirrer (Direct Current and Static Magnetic Field Method) to Continuous Casting Bloom

    pp. 1287-1296

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    In order to improve the inner quality of continuous casting bloom, especially for the increase of the ratio of the equiaxed crystal zone and the reduction of center segregation and center porosity, a study was made of the application of the stirrer (Direct Current and Static Magnetic Field Method) to the bloom caster.
    From experiments in the laboratory and at a 300 × 400 m/m bloom caster, the following results were obtained,
    (1) The ratio of the equiaxed crystal zone increased when long stirring time with low stirring force was applied.
    (2) The degree of white band was related to the maximum stirring force and was not influenced by the stirring time. A direct current and static magnetic field method was suitable to the bloom caster. Application of the stirrer to the 300 × 400 m/m Caster made it possible to improve the inner quality of the cast bloom and to expand the applications of caster products.
    x

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  • Improving Solidification Structure of Continuously Cast Steel by Electromagnetic Stirring

    pp. 1297-1306

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    The electromagnetic stirring is applied to continuous casting process of steel. A set of linear motor type stirrers is used for slab caster. High promotive force is fit for equiaxed crystallization of slab. The rotary motor type stirrer with 2 poles by 2 phases is used for bloom caster. Equiaxed crystallization of bloom is saturated in relatively low promotive force. Double stirrers system is more effective for equiaxed crystallization without heavy white band. Equiaxed crystallization by electromagnetic stirring reduces the centerline segregation of strand. The quality of products through continuous casting with electromagnetic stirring is therefore better than that through ingot casting.
  • Effect of Deformation on the Formation of Internal Cracks in Continuously Cast Blooms

    pp. 1307-1316

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    The effect of deformation on the formation of internal cracks in a solidifying continuously cast bloom has been investigated on the basis of two kinds of deformation tests, i.e., squeezing test of 300 mm square bloom and bending test of 300 × 400 mm bloom carried out on bloom caster.
    The relation between the amount of squeezing or bending and the roll load at the initiation of internal cracks was obtained for various grades of steels. Temperature range for the occurrence of internal cracks was also estimated from melting behavior of a composite rivet (Ni-embedded steel rivet) driven into a solidifying bloom together with heat transfer calculation for the solidifying shell. The internal cracks were observed to occur at temperatures of 30-40°C lower to slightly higher than the solidus. This indicates that formation of the internal cracks is closely related to the embrittlement occurring at this temperature range.
    The strain caused at the internal cracks by the squeezing test was calculated by the finite element analysis, and the strain leading to the formation of internal cracks was found to be 0.3 to 0.8%, depending on the steel grades.
  • Round Billet Casting by Slab Caster for High Quality Seamless Tube Application

    pp. 1317-1323

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    At Wakayama Steel Works of Sumitomo Metal Industries, tube rounds have been supplied by break down process of concast blooms. For the further drastic rationalization of the process, direct tube round casting trials have been carried out.
    (1) Round billet casting trials have been carried out by minor changes of the existing curved and vertical type slab casters.
    (2) Surface and internal quality of round billet have been found excellent.
    (3) Round billets may be rolled to seamless tubes without surface conditioning.
    (4) To reduce the center porocity, enough care must be taken, especially for super heat in tundish and casting speed.
    (5) Equiaxed crystal zone of cast round billet have greatly increased by newly developed R.M.S. (Rotating Magnet Stirrer).
  • Continuous Casting of Beam Blanks

    pp. 1324-1330

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    No. 3 continuous casting machine at No. 1 steel-making shop in Mizushima Works of Kawasaki Steel Corp. has capability of casting both large section blooms (300 × 400 mm, 400 × 560 mm) and beam blanks. It has been successfully operated since October, 1973. In continuous casting of beam blanks, various kinds of defects are liable to occur because of its complicated section. However, the adoption of suitable operating condition such as mold powder selection, cooling condition, and complete maintenance of machine have made it possible to roll almost all cast blanks without any surface conditioning. Casting speed has also been increased with good quality by preventing flange deformation of cast blanks.
  • Electric Arc Furnace, Ladle Refining Furnace and all-Bloom Continuous Casting Process

    pp. 1331-1337

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    Since November 1978, a ladle refining furnace with 100 t capacity has been operating at Sendai Works of Azuma Steel Corp. Through the EF-LF-Bloom CC process, high quality rod and wire for cold-drawing, cold-heading, heat-treatment or machining have been produced successfully instead of using the conventional ingot casting process. The process is very effective for deoxidation, desulfurization, lowering of inclusion content and precise control of chemical composition and temperature.
    Application of Ar-sealing, electromagnetic stirrer and super heat control technique to the large section and bending radius CC machine, combined with EF-LF process, gives clean, good-surface and homogeneous steel. EF-LF-all CC process gives a higher alloy yield, productivity and a lower cost (electricpower. electrode, refractories and fuel), compared with the conventional EF-CC process.
  • Continuous Casting for Wire Rods and Its Quality Problems

    pp. 1338-1344

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    For the production of high quality high carbon steel wire rods at reasonable cost, Sumitomo Electric has designed and installed a C.C. machine for both small size bloom and large size billet together with a break down mill.
    Investigations before designing are as follows:
    (1) Influences, on centerline segregation, of such factors as casting temperature, E.M.S., size and shape of bloom and billet, and diffusion during soaking have been made clear.
    (2) Evaluation of hot-workability of C.C. blooms by using a wedge specimen with fin was developed and criteria of hot workability were made clear to several grades of steel. These results were applied to design new C.C. machine, reheating furnace and break down mill, and wire rods having good drawability, cleanliness and surface were produced.
  • Continuous Casting of Special Steel Slabs

    pp. 1345-1353

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    Recent developments of continuous casting of special steel slabs are described.
    High carbon steel has been found susceptible to the formation of internal cracks and corner longitudinal cracks owing to low strength at elevated temperatures. The effect of cooling condition on the crack formation has been studied using finite element stress analysis. The formation of these cracks was prevented by increasing the stiffness of solid shell and decreasing the cooling intensity on narrow face just below the mold. The center-line segregation in continuously cast slab has been decreased without causing appreciable white bands by the improvement of electromagnetic stirring.
    The use of low SiO2 tundish powder was effective to reduce the oxygen content of SUS 430. The ridging of SUS 430 of continuously cast process was reduced to the same value as that of ingot process by the application of electromagnetic stirring.
    The crack sensitivity of 9% Ni steel was extremely high owing to the low ductility between 600°C and 900°C and large thermal expansion with transformation. The uniform cooling, prevention of reheating, and unbending over 950°C were cleared to be important to avoid the surface transverse cracks and subsurface cracks in the continuous casting of 9% Ni steel.
  • Refining of the Solidification Structure of Continuously Cast 18%Cr Stainless Steel by Electromagnetic Stirring

    pp. 1354-1362

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    The electromagnetic stirring (EMS) was applied in the secondary cooling zone in order to refine the solidification structure of continuously cast 18% Cr stainless steel slabs, in order to improve the ridging of the cold rolled sheets.
    So as to obtain the most suitable operational condition for refining the solidification structure, the casting and EMS conditions were varied systematically. The solidification structures of tested slabs were examined, and the flow pattern during EMS was studied on the basis of the growth direction of columnar crystals in order to clarify the mechanism for the formation of the banded equiaxed grains which were observed at high temperature casting. The results thus obtained are as follows:
    1) The effect of decreasing the superheat for increasing the ratio of equiaxed zone (REZ) is greater with the application of EMS than without it.
    2) Ridging of cold rolled sheets from the continuously cast slabs is fairly improved by increasing REZ which is achieved by application of EMS.
    3) It is supposed that the banded equiaxed grains form at the stagnant portion in the molten pool.
  • Continuous Casting of Small-size Austenitic Stainless Steel Billets

    pp. 1363-1369

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    A process was established in which AOD-refined austenitic stainless steel melts produced from homemade molten ferronickel and ferrochromium as main raw materials were continuously cast into smallsize billets of 115 to 175 mm square. The billets were then rolled into wire rods, round bars, etc. in a single heating manner.
    This paper deals with the following factors contributing to obtaining very sound small-size billets.
    1) The mold level control system employing a sliding nozzle.
    2) The non-oxidation casting comprizing of a long nozzle and a powder casting.
    3) The electromagnetic stirring.
    The causes and prevention of billet defects generated in the continuous casting of difficult-to-cast grades, Ti containing SUS 321, Cu containing XM7 and fully austenitic SUS 310, were also discussed.
  • The Equipment and Operation of Rotative Continuous Casting

    pp. 1370-1376

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    Rotative continuous caster, which was only one in service in Japan, was operated at Kciliin Works of Nippon Kokan K. K. from March 1974 to December 1977. In total, 1.5 millon tons of billets have been cast in the four years operation. During this period, various modifications of equipments and improvement of billet quality were carried out and contributed to the high productivity, over 40000 tons/month.
    Advantages of RCC process over the conventional ingotmaking-billetting process are;
    (1) Conditioning of billet is eliminated.
    (2) Total yield through all the processes of pipemaking increases by approximately 17%.
    (3) Energy saving of 3 × 105kcal/ton is achieved.
    (4) Total processing time required is shortened by 80%.
  • Effects of Various Factors on the Stability of Casting in Horizontal Continuous Casting

    pp. 1377-1386

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    The horizontal continuous casting machine of 2 ton laboratory scale was installed to investigate the basic problems associated with casting round billets of carbon steels and stainless steels.
    The main results obtained are as follows:
    (1) Intermittent withdrawal is essential for the prevention of break out during the casting of the billets in the operation of the horizontal continuous casting without mould oscillation.
    (2) For joining the mould to the tundish, the gap between the mould and the refractory nozzle of the tundish has to be minimized to prevent the molten steel penetration into the gap forming fin shape solidification shell which results in break out. Nitride refractories, e.g. boron nitride refractory, has been found to give satisfactory results.
    (3) The difference of the inner diameter of the mould and the refractory nozzle has to be minimized to decrease the discontinuity of solidification morphology beneath the surface of the pull mark.
    (4) The friction force between mould and solidified shell of stainless steel is larger than that of carbon steel. Nickel plating with solid particle dispersion as a lubricating agent enormously decreases the friction force between the mould and the solidified shell, which enabled casting 150260 mmφ stainless steel billets.
  • Development of Horizontal Continuous Caster for Steel Billet

    pp. 1387-1393

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    Nippon Kokan (NKK) installed the test plant in Fukuyama Works to commercialize the holizontal continuous casting process of steel for billet, developed in cooperation with Davy-Loewy Co. (DL), and started the operation test from Nov. in 1978.
    The various improvements of the Davy-Basic-Process and the additional developments of process technology have been done. That is:
    1) Use of special refractory made from Si3N4 with dispersed BN for break ring.
    2) Use of Cr-Zr-Cu alloy for mold material and control of cooling water pressure of mold.
    3) Adoption of intermittent withdrawal mode with high speed frequency cycle and proper push-back force.
    These enabled the continuous-continuous and high speed casting operations by the multi-strands. The billets with 115 mm square and 120 to 210 mm rounds, cast by this process were successfully rolled to Dbar, angle, rod bar and seamless pipe.
    This improved horizontal continuous casting process named "HORICAST" is now used on a commercial base.
  • Solidification of Steel Billets in the Mold of a Synchronized Rotary Type Continuous Caster

    pp. 1394-1400

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    A high speed continuous billet caster where casting speed matches the rolling speed has been developed. The caster consists of a copper wheel with a groove and an endless steel belt, both strongly cooled by water. There is almost no friction between mold and billet because of the mold moving simultaneously with the billet. In the course of development two studies were performed to establish the optimum casting and operating conditions. The first was to investigate the effect of casting temperature on the shell thickness. The second was with heat transfer characteristics of rotating wheel. The results are summarized as follows.
    (1) The shell thickness of belt side was smaller than that of wheel side when the molten steel with large superheat was poured.
    (2) Water modelling test revealed that downward flow with high velocity existed along belt side and upward flow along wheel side.
    (3) The allowable superheat was estimated to be 50 C by computer calculation on solidification.
    (4) Tension casting where the pinch rollers were controlled at a slightly higher rate than the wheel was effective to straighten the billets without any trouble.
    From these results the optimum conditions were established and the belt wheel type continuous caster was finally practised.
  • 抄録

    pp. 1401-1405

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