US3621903A - Method of bottom casting steel ingots using low vacuum of from 610 to 310 mm. hg absolute - Google Patents

Method of bottom casting steel ingots using low vacuum of from 610 to 310 mm. hg absolute Download PDF

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Publication number
US3621903A
US3621903A US693376A US3621903DA US3621903A US 3621903 A US3621903 A US 3621903A US 693376 A US693376 A US 693376A US 3621903D A US3621903D A US 3621903DA US 3621903 A US3621903 A US 3621903A
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Prior art keywords
steel
mold
molten steel
present
pressure
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US693376A
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English (en)
Inventor
Yuzuru Doi
Kozo Yamada
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JFE Engineering Corp
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Nippon Kokan Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/003—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using inert gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/15—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using vacuum

Definitions

  • the mold When the molten steel in the mold reaches a certain height, the mold is sealed against further exhaust of gas. Molten steel is continued to be poured into the sealed mold until the mold is filled, volatile components in the molten steel being thereby prevented from escaping from the sealed mold.
  • the present invention relates to methods for reduced pressure casting of steel by a bottom pouring process, and particularly for production of low-carbon steel sheet suitable for press forming.
  • the main object of the present invention is to improve the mechanical properties of hotor cold-rolled steel sheets for press forming.
  • steel sheets for deep drawing with uniform quality can be produced, requiring no decarburization annealing, except in special cases.
  • Another object of this invention is to limit any cost increase in making steel ingots.
  • the process of the present invention is so simple that it imposes no burden on daily operations and has no ill efiect on productivity.
  • FIG. I is a graph of mechanical properties over the whole length of cold-rolled strip made by the process of the present invention.
  • FIGS. Za-Zd illustrate an apparatus for carrying out the present invention
  • FIG. 3 presents three graphs showing changes of exhaust gas volume with time by using the present invention in comparison with the usual process of pouring into a mold
  • FIG. 4 illustrates the variation in distribution of some elements throughout the height of an ingot made by the present invention in comparison with a conventional ingot
  • FIG. 5 shows the corresponding distribution of elements along the length of a coil rolled from the ingot of FIG. 4, indicating the portions of the ingot from which the various test positions along the length of the coil have been derived;
  • FIGS. 6a-6c show various test results which are explained hereinbelow.
  • FIGS. 7a-7bl show sulfur prints of a middle slab from the ingot of FIG. 4 and microstructures of the final product made from said ingot.
  • FIG. 6a indicates the summarized results regarding the effect of oxygen content on grain size.
  • FIG. 3(0) shows the change of exhaust gas volume in the progress in time under experimental conditions as follows.
  • the mold is sealed by mechanical closure means at the upper part of the casting mold.
  • the molten steel is forced against the cap containing the above closure means.
  • the first advantage is that the tubular blowhole, quite common to ordinary capped steel (i.e., that cast at atmospheric pressure), is extremely small and dispersed.
  • the second is the absence of any tendency for said fine inclusions to cohere around said blowhole.
  • the third is the formation of sound rim layers, with no skin holes.
  • Another advantage of the present invention lies in the easy and stable improvement in aging properties of steel sheets. That is, at the mechanical closure of mold outlet, the amount of free oxygen dissolved in the steel is already substantially reduced, so that if at this period V, B, Zr, Ti and Al are added, the nitrogen in the steel is most effectively fixed because of the oxidation loss being kept to a minimum.
  • FIGS. 2a-2d A preferred embodiment of the present invention is illustrated in FIGS. 2a-2d.
  • FIG. 2a is a plan view of a system for exhausting gas from each mold using the stools shown in Japanese Utility Model Publication 1 1,517/1962.
  • FIG. 2b is a layout of a complete exhausting system in the present invention, and
  • FIGS. 20 and 2d are enlarged views of the molds of FIGS. 2a and 2b and show diagrammatically the flow of molten steel in the molds during the exhausting of the gases.
  • FIGS. 2a-2d the stools l are assembled with the required number of smaller stools which are radially arranged around the center runner 2 stool and are fixed on a truck 23.
  • Molds 4 are placed on each of the above smaller stools and each are provided with caps 5 having exhaust pipes 6 to be coupled to flexible tubes 9 by means of flanges.
  • Flexible tubes 9 placed on each mold are, singly or by groups, collected to a main exhaust pipe 10.
  • the relation between exhaust pipe 6 and caps 5 is illustrated in a vertical section in FIG. 2b, and includes a bell-type plug 7 and a peephole 8. In each cap 5, a hole is made to accept the exhaust pipe 6 and the lower part of this hole is shaped to fit the belltype plug 7.
  • the cap 5 and a pipe 6 are connected together by suitable means such as a flange joint.
  • the plug 7 is hung on a rod which passes through a suitable hole and pipe 6, in order to move freely vertically.
  • Molten steel poured into the center runner 2 goes through the runner 3 into the mold 4.
  • the bell-type plug 7 is raised up to meet the cap 5, so that the exhaust is shut off.
  • the main pipe 10 of the exhaust air system is connected with cyclone 11, in which dust of comparatively coarse particle size is eliminated.
  • Cyclone 11 leads to a shutoff valve 12 and a vacuum tank 13.
  • the gas exhaust process of the present invention is principally characterized by its low degree of vacuum, so that the vacuum tank does not require an especially high vacuum. A pressure reduction to about 600 mm. Hg absolute at most is sufficient. Accordingly, a steam ejector 14 of rather low capacity suffices. The steam for the ejector 14 is properly reduced through pressure-reducing mechanism 16.
  • bypass line 17 is added, which is desirable in daily operation.
  • Exhaust gas from which fine dust has been removed by cooling water from pipe 19 in condenser 18, is removed through line 20 into the outer air.
  • the present invention can be easily designed and manufactured, and in practice, various modifications can be made.
  • the most important feature is to keep constant all the conditions prior to the vacuum tank 13 to obtain stable operation. In other words, it is essential to maintain the steam pressure prior to ejector 14 at a definite value, so that the degree of vacuum within the vacuum tank 13 is maintained at a constant level. According to experiments, it has been found that the control of the amount of pressure reduction by means of said steam pressure, is not always adequate. To meet this difficulty. a
  • pressure reduction control device is provided by introducing air at proper points before cyclone l1 and after each mold.
  • the vacuum control within each mold can be carried out smoothly and the response of the vacuum level to the change of air input was more rapid and stable than had been expected.
  • the pressure-reducing control to each mold is easily carried out according to the rimming action observed from the peephole 8.
  • 21 represents an air introductionline, having a regulating valve 27 with a gauge 22 for main exhaust pipe 10. This can be used to adjust the pressure for the molds as a whole.
  • each mold has a branch pipe 28 equipped with its own regulating valve 29 and reducing pressure gauge 30.
  • the interior of vacuum tank 13 be maintained at the required degree of vacuum, by closing valve 12 and the respective regulating valve 29 for each mold, while opening the main regulating valve 27 for exhausting gas. Then, if on pouring the molten steel, the valve 12 is opened and air-regulating valve 27 is gradually closed, it is easy to control the pressure reduction. At the same time, it is preferable to make adjustments by opening regulating valve 29 according to the rimming action in the mold.
  • the exhaust outlet of a mold may be placed in any position in relation to cap 5. As shown in FIG. 2b, such an outlet is located at the center of said cap 5. From observations through the peephole 8, the molten steel can be expected to follow the path indicated by arrows in FIG. after it is poured through sprue runner 3 into mold 4.
  • FIG. 2d is an example of an exhaust outlet placed to one side of the longitudinal centerline of the mold.
  • the molten steel in the mold follows the path shown by arrows in said figure. The path can be observed from the peephole 8.
  • the inclination of the sprue runner 3 and introduction of inert gas 24 indicated in FIG. 2d are intended to accelerate said convection current (or movement).
  • Said convection current is an ideal path of agitation for molten steel, and is superior to the backflow shown in FIG. 2c.
  • the ordinary steel casting process was employed in two of the molds, while the molten steel poured into three of the molds was processed by the present inventive process.
  • casting weight 16.5 tons casting speed: about 1 ton/min.
  • the exhaust outlet of the cap was fixed as illustrated in FIG. 2d.
  • the vacuum within the vacuum tank is 260 mm. Hg absolute before commencement of the pour.
  • FIG. 3a indicates the actual pressure curve for any one of said three molds, as measured at minute intervals.
  • FIG. 3b shows the exhaust volume per minute of CO CO and 0 again for one of said three molds.
  • the similarity of the curve of FIG. 3b and the curve of FIG. 30, which shows the exhaust volume of said three components in the conventional casting operation at atmospheric pressure, is due to the fact that the degree of pressure reduction reached at 4 minutes after starting the pour in, maintained substantially constant until the finish of casting.
  • FIG. 4 shows the component contents for an ordinary capped steel ingot (solid line) and a steel ingot made by present invention (broken line), both of which were cast from the same molten steel at the same time in the presently described example.
  • the present invention in spite of its low degree of pressure reduction, ensures far better uniformity than the ordinary casting process for capped steel.
  • the oxygen content of 0.060 percent is quite uniformly distributed from top to bottom of the steel ingot and is maintained within a range of 0.022 to 0.028 percent. Therefore, it is not necessary to maintain the high vacuum (of about 30-160 mm. Hg absolute) asis required in German Pat. No. l,171,l 18.
  • the excellent uniformity, as shown by dotted lines in FIG. 4, is entirely due to the effect of the molten steel hitting the cap after closure of the exhaust outlet at reduced pressure.
  • FIG. 4 covers analysis values measured at seven points spaced at the same interval along the centerline from top to bottom of the steel ingot.
  • FIG. 7a is a sulfur print of a slab made by the present process and FIG. 7 is a print of one made by the conventional process.
  • the rim layer by the present process is of almost the same thickness (50-60 mm. equivalent of steel ingot) as in a usual capped process of the prior art.
  • the thickness of the rim layer may be reduced to about half of that of the usual one.
  • the successful maintenance of the rim thickness is the effect of molten steel hitting the cap after mechanically closing the exhaust outlet at low-pressure reduction to force the reaction to stop.
  • the second advantage observed from said prints is the good uniformity of the core.
  • the central part of the core frequently presents some wrinkles due to shrinkage.
  • these wrinkles are entirely removed, with a uniformity and good properties, which are exemplified in the print of FIG. 7al
  • FIGS. 1 and 5-7 show the results of tests and measurements of the properties of the above-mentioned ordinary capped steel and the capped steel produced according to the present invention.
  • r represents thickness of the strip and the hardness relates to Rockwell hardness test results.
  • FIG. shows the analysis value of the three components corresponding to those of FIG. 4.
  • FIG. 6c indicates the degree of cleanliness corresponding to FIG. 6a, where cleanliness relates to the number offine particles in an ingot per unit;
  • FIG. 1 shows the mechanical properties;
  • FIGS. 7al) and 7bl) show the ferrite structures corresponding to FIGS. 7a and 7b.
  • the present invention may be summarized as follows.
  • a treatment under a pressure reduction to 610-310 mm. Hg absolute at which low pressure a cap for the molten steel is provided having means for mechanically closing the exhaust outlet of the mold.
  • the final annealing is carried out at comparatively low temperature of 720 C. for 10 hours, very favorable results were obtained with a yield point of about 18 kg./mm. and the yield ratio of about 55 percent.
  • annealed at 730750 C. the ordinary temperature for deep drawing steel sheets, the mechanical properties listed in FIG. I are further improved, almost without requiring decarburization annealing.
  • a molten steel was prepared including the following composition in the ladle: C, 0.06; 0 0.055; N 0.0010. After a similar treatment as given in said above embodiment at a pressure reduction of 400 mm. Hg at maximum, 0.3 kg. ofan iron alloy containing 21 percent Boron (B) per ton was continuously added into the molten steel from the center runner 2, from about 3 minutes before closing of the exhaust outlet by the bell-type plug. This proved quite effective, because in this period the free oxygen dissolved in the molten steel was reduced to less than 0.030 percent. As a result, the cold-rolled steel sheets contained 0.004 percent boron. Said steel sheets aging index was 2.1 kg. at 100 C. X 1 hr., which was a satisfactory delayed aging property. Other mechanical properties showed the same good values as mentioned hereinabove. Other addition agents mentioned earlier ensure similar good effects.
  • the process and apparatus according to the present invention are significant enough to break down the conventional concept of vacuum treatment, for providing the most suitable steel ingot for press forming. Taking into consideration the fact that steel sheets for press forming are items of mass production, the present invention is useful and beneficial to the industry concerned, and involves almost no cost increase.
  • a method of bottom casting steel ingots suitable for press forming steel sheets comprising:
  • a method'according to claim 1 comprising:
  • a method according to claim 1 comprising:

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)
  • Continuous Casting (AREA)
  • Forging (AREA)
US693376A 1966-12-26 1967-12-26 Method of bottom casting steel ingots using low vacuum of from 610 to 310 mm. hg absolute Expired - Lifetime US3621903A (en)

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JP8448866 1966-12-26

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US (1) US3621903A (enrdf_load_stackoverflow)
DE (1) DE1583679C3 (enrdf_load_stackoverflow)
FR (1) FR1562889A (enrdf_load_stackoverflow)
GB (2) GB1217517A (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3998261A (en) * 1974-06-18 1976-12-21 British Steel Corporation Casting steel ingots
US4817700A (en) * 1982-05-07 1989-04-04 Milov Vladimir N Squeeze-out casting machine

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB834909A (en) * 1955-10-28 1960-05-11 Demag Ag Method of casting steel and cast iron and mould for carrying out the method
US2958104A (en) * 1958-04-21 1960-11-01 Charles W Ohse Vacuum die casting process and apparatus
DE1132296B (de) * 1957-05-17 1962-06-28 Hoesch Ag Verfahren und Vorrichtung zum Giessen unberuhigter Staehle
GB937898A (en) * 1961-04-01 1963-09-25 Hoesch Ag Improvements in or relating to the sub-atmospheric treatment of molten steels
US3336970A (en) * 1966-02-28 1967-08-22 Prec Metalsmiths Inc Methods of casting

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB834909A (en) * 1955-10-28 1960-05-11 Demag Ag Method of casting steel and cast iron and mould for carrying out the method
DE1132296B (de) * 1957-05-17 1962-06-28 Hoesch Ag Verfahren und Vorrichtung zum Giessen unberuhigter Staehle
US2958104A (en) * 1958-04-21 1960-11-01 Charles W Ohse Vacuum die casting process and apparatus
GB937898A (en) * 1961-04-01 1963-09-25 Hoesch Ag Improvements in or relating to the sub-atmospheric treatment of molten steels
US3336970A (en) * 1966-02-28 1967-08-22 Prec Metalsmiths Inc Methods of casting

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3998261A (en) * 1974-06-18 1976-12-21 British Steel Corporation Casting steel ingots
US4817700A (en) * 1982-05-07 1989-04-04 Milov Vladimir N Squeeze-out casting machine

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Publication number Publication date
GB1217518A (en) 1970-12-31
DE1583679B2 (de) 1973-03-29
DE1583679C3 (de) 1973-10-18
DE1583679A1 (de) 1970-08-20
GB1217517A (en) 1970-12-31
FR1562889A (enrdf_load_stackoverflow) 1969-04-11

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