Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
  • B22D11/11—Treating the molten metal
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
  • C21C7/04—Removing impurities by adding a treating agent
  • C21C7/06—Deoxidising, e.g. killing

Definitions

• This invention relates to the continuous casting of steel and, more particularly, to the continuous casting of rimming steel.
• molten steel is poured into the upper end of a mold open at its bottom.
• the mold is cooled by a liquid, such as water, circulated in the mold walls.
• a liquid such as water
• the bottom of the mold is closed with a metal plug.
• the plug cools the molten metal and the metal fuses to the plug.
• the cooled mold cools the metal in contact with the mold causing the molten metal to solidify and form a skin or sheath around the molten metal in the mold.
• the plug is withdrawn from the bottom of the mold and the steel, fused to the plug, follows. A continuous slab or casting of steel is thus formed.
• the plug is later removed from the end of the slab.
• the skin or sheath formed around the molten metal in the mold is relatively thin at the time the cast slab emerges from the bottom of the mold.
• the metal, still molten in the center of the slab, is contained in the slab by this skin.
• the slab is supported by rollers which contact the slab below the mold. Some of the rollers are driven to regulate the speed at which the slab leaves the mold.
• the cast slab After leaving the mold, the cast slab is cooled. As the slab is cooled, the molten metal in the slab progressively solidifies from the outer wall of the slab inwardly. The skin or wall of solid metal thickens until, finally, all the metal in the slab is cooled and solidified. The point where the entire slab is solidified is below the mold and may be thirty-five feet, or more, from the point where the slab leaves the mold. Thus, as the slab leaves the mold, and for a considerable distance below the mold, the skin of solid metal around the slab supports the molten metal in the slab. Obviously, if this skin should be ruptured, the molten metal will escape and considerable damage to operating equipment can result, to say nothing of failure to form the required slab.
• a substantial portion of the molten metal in continuous casting is cooled and solidified after the slab leaves the mold.
• the collecting gas can escape upward through the molten metal, the gas vigorously agitates, boils and froths the molten metal.
• Such vigorous agitation and boiling interferes with the desired cooling of the molten metal by the cooled mold wall and hinders proper formation of the skin of solid metal around the slab, vital to continuous casting. Failure of the skin to properly form results in a weak wall which cannot support the molten metal.
• the uncombined oxygen can be removed from the metal before the continuous cast is poured. This can be accomplished by the addition of materials to the molten metal which will react with, and absorb, all or substantially all of the uncombined oxygen.
• a controlled amount of uncombined oxygen is required.
• a certain amount of uncombined oxygen is desirable in the molten metal.
• This uncombined oxygen reacts to form a gas which moves through the molten metal and agitates the metal.
• the agitation or movement of the molten metal can be controlled so that the metal is agitated in a pattern in the mold.
• One of the objects of the instant invention is to provide an improved method for continuous casting of rimming steel.
• a further object is to provide such a method that will form a relatively thick rimmed area.
• a further object is to provide such a method wherein impurities in the cast are moved away from the surface of the cast.
• Still a further object is to provide a continuous cast which can be rolled into relatively thin sheets without impurities or flaws on the surfaces of the sheets.
• the metal for casting is prepared in the customary manner, is poured into a ladle and, from the ladle, is poured into the tundish of the continuous casting mold.
• the iron oxide content of the slag is measured in accordance with customary practices.
• the molten metal is poured into the ladle at a temperature of about 2950 to 3060 F. Difficulties in sampling, and the time available, do not allow precise measurement of the iron oxide content of the slag. However, and as will be more apparent from the following description, such measurement has been found sufficient for purposes of the instant invention.
• the carbon, manganese, phosphorus and sulfur content of the metal are also measured. These later measurements are primarily for the purpose of determining the additions to the metal which may be required to produce the desired steel but may have an indirect relationship to the oxygen content.
• the carbon content of the molten metal is controlled by the oxygen blowing of the metal. This blowing is adjusted so that the carbon content of the molten metal, when ready for pouring for low carbon rimming steel, does not substantially exceed 0.07%. Where higher carbon rimming steel is to be continuously cast, the blowing is adjusted for a higher carbon content. Where excess carbon is present, oxygen blowing is continued until the carbon content is reduced.
• carbon content of the metal is 0.07% or less
• Carbon added to the molten metal does, to a certain extent, react with and remove as a gas some of the uncombined oxygen in the molten metal.
• the amount of carbon that can be added is limited.
• the balance of the uncombined oxygen removed to attain a substantial uniform pattern of agitation in the molten metal during continuous casting and, at the same time, avoid excess agitation, boiling and froth in the mold and cast is removed by reaction with vanadium and aluminum additions to the molten metal.
• Aluminum is well-known as a deoxidant in steelmaking.
• the aluminum combines with the uncombined oxygen forming aluminum oxide.
• the aluminum oxide which when formed is an impurity, migrates to the top of the ingot and is cut from the ingot during rolling.
• Attempts, heretofore, to utilize aluminum as a deoxidant in continuous casting of rimming steel have resulted in erratic rimming, relatively thin rims, and the formation of relatively large agglomerates of aluminum oxide at or near the surface of the cast slab which, when the slab is rolled, resulted in streaks and flaws on the surfaces of the rolled sheet.
• the amount of deoxidant addition depends, of course, on the oxygen content of the metal for which the iron oxide content of the slag in the steelmaking furnace provides a satisfactory estimate for present purposes.
• Vanadium in the form of ferro vanadium, has been found to be acceptable.
• ferro vanadium having an average analysis of 55.00% vanadium, 4.00% silicon, 2.50% carbon, and the balance i on s emp y
• the amount of ferro vanadium and aluminum which can be added to the molten metal can be varied over a wide latitude.
• the ferro vanadium is added to stabilize the melt and the aluminum to control the rimming action.
• the amount of ferro vanadium to be added to a particular melt is determined from the iron oxide content of the slag and the chemistry of the metal. It is preferred to add the ferro vanadium in a fixed amount and to vary the aluminum addition to suit the needs of the particular melt. For example, seventy-five pounds of ferro vanadium are added to the 47 ton melt and suflicient aluminum is added to reduce the uncombined oxygen content of the melt to the desired level.
• the measured iron oxide content of the slag is measured as 16% or less
• seventy-five pounds of ferro vanadium is sutficient to maintain the required addition of aluminum well under the 50 pound limit.
• the ferro vanadium addition may be increased to one hundred pounds if it is desired to maintain the aluminum addition at a low level.
• the vanadium apparently acts as a buffer and lowers the uncombined oxygen content of the molten metal to a point where it can be effectively controlled by the aluminum addition.
• Final control of the uncombined oxygen content is regulated "by the aluminum addition. Because the measurement of the iron oxide content of the slag and the residual elements in the metal are not precise measurements, and the amount of uncombined oxygen in the metal may not have been precisely determined, the ferro vanadium, is first added to the ladle. The aluminum is then added and the amount of aluminum is determined, to some extent, by the activity of the tapping stream and the metal in the ladle.
• One method which has been found effective for regulating the aluminum addition and at the same time attaining the desired results of the instant invention, is to estimate the amount of aluminum required from the iron oxide measurement and the ferro vanadium addition and then add a portion of the estimated aluminum. If the metal in the ladle is relatively calm, is not excessively boiling and there is no frothing, the remaining portion is not added. If, on the other hand, the metal in the ladle remains wild, boils excessively and froths, the additional aluminum is then added. In some instances, even after the addition of the remaining portion further addition of aluminum may be required to reduce the activity of the metal in the ladle.
• the melt for continuous casting is prepared at a temperature of about 2950 to 3060 F.
• the temperature of the melt in the ladle is about 2850 to 3000 F. and the temperature in the tundish, as the molten metal is being delivered to the continuous casting mold is about 2800 to 2875 F.
• the molten metal may become more active and the activity may exceed that necessary for good and effective rimming. Where such activity occurs, additional aluminum may be added in the tundish.
• tundish addition is not necessary and it is preferred to add all of the required alumium to the ladle.
• a method of partially deoxidizing and continuously casting rimming steel comprising adding to molten steel not more than about 82.50 pounds of vanadium per 47 tons of molten steel, then adding not more than about 50 pounds of aluminum per 47 tons of molten steel, said aluminum being added a portion at a time to a point at which agitation of the molten steel is without vigorous boiling and frothing when poured, thereafter continuously casting the steel by pouring it in one end of an open-ended mold wherein the periphery of the steel is solidified to form a casting having a molten core, withdrawing the casting from the mold as a continuous strand, and subsequently cooling the casting to solidify it completely with a rimmed structure.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Priority Applications (10)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23929924

Family Applications (1)

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Citations (8)

Family Cites Families (1)

• 1965
  • 1965-09-08 US US485915A patent/US3411897A/en not_active Expired - Lifetime
• 1966
  • 1966-08-26 BE BE686037D patent/BE686037A/xx unknown
  • 1966-08-29 IL IL26401A patent/IL26401A/en unknown
  • 1966-08-30 NL NL6612215A patent/NL6612215A/xx unknown
  • 1966-09-01 DE DE19661508807 patent/DE1508807B1/de active Pending
  • 1966-09-05 AT AT838766A patent/AT270907B/de active
  • 1966-09-06 LU LU51883D patent/LU51883A1/xx unknown
  • 1966-09-06 GB GB39864/66A patent/GB1156036A/en not_active Expired
  • 1966-09-06 ES ES0331377A patent/ES331377A1/es not_active Expired
  • 1966-09-07 FR FR75500A patent/FR1491858A/fr not_active Expired

Patent Citations (8)

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