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

• the invention relates to a method for the production of killed, unalloyed or low-alloy, aluminum containing steel having a low carbon content, according to the continuous casting method, wherein aluminum is added to the liquid metal in two portions, the first portion being added at a period before the liquid steel is cast into the tundish and being of a quantity sufficient to bind the major amount of oxygen present in the liquid steel, with the provision that the casting stream coming into contact with air contains only between 0.005 and 0.01% of metallic aluminum, and the second portion being added at a stage when the casting stream will no longer get into contact with the atmosphere and being of a quantity sufiicient to obtain the desired analysis.
• a material is obtained whose surface is largely free from aluminum oxides and thus is suitable for deep-drawing purposes.
• the present invention relates to a method for the production of killed, unalloyed or low-alloy, aluminum containing steel having a low carbon content, according to the continuous casting method under addition of aluminum as deoxidizing agent, the liquid steel being cast under contact with the oxygen containing atmosphere into a tundish, and from said tundish into a cooled mould whereupon the solidifying bar is drawn and subjected to further cooling.
• Killed, aluminum containing steels with low carbon content are primarily processed to cold rolled sheets capable of being deep-drawn and meeting the highest demands regarding surface quality. Such sheets are destined primarily for the manufacture of car bodies.
• a cast processing material is necessary which is deoxidized by means of aluminum and whose surface zone is very clean, i.e. largely free from non-metallic inclusions, especially from macroscopic inclusions, which otherwise would get to the surface of the rolling stock during rolling and would lead to the formation of linear flaws, so-called bands, in the surface of the sheets.
• the obtained product representing the material to be processed in the rolling mill, does not meet the requirements mentioned.
• the marginal zone of the cast product deoxidized' with aluminum is greatly impurified by non-metallic inclusions, especially macroscopic ones.
• the invention is aimed at avoiding these disadvantages and difficulties by attempting to prevent the formation of a layer rich in inclusions. It has been found that in continuous casting there is a connection between the casting speed, which in general is lower than in conventional casting of ingots (rapid casting), and the frequency of surface flaws occurring as bands on the sheet: a reduction of the casting speed leads to an increase in the number of bands in the surface.
• the aluminum oxides are formed under the influence of the atmospheric oxygen on the dissolved aluminum in the casting stream and unite to macroscopic agglomerations which are deposited primarily in the marginal zone of the slabs when it is no longer possible to eliminate them.
• a number of methods have become known for reducing the content of non-metallic inclusions in the steel, including degassing in vacuum, flushing the steel melt with inert gas, or the use of special deoxidizing agents. These measures are, however, employed prior to casting the steel melt. Whereas they diminish the frequency of inclusions contained in the steel, they are not capable of preventing the formation af aluminum oxides in the casting stream on account of the influence of air.
• the liquid steel On its path from the metallurgical refining vessel to the mould the liquid steel has to pass an oxidizing atmosphere at least twice.
• the second passage of the liquid steel through the oxidizing atmosphere takes place at the continuous casting plant when the ladle is emptied, in correspondence with the lowering speed of the bar, into the tundish serving as a butter. It is here that the undesired oxidation of the aluminum in the casting stream occurs. Owing to the fact that the pouring rate employed in continuous casting is very low and fixed within a very narrow range on account of the technological conditions it is not possible to eliminate the influence of the oxidizing atmosphere on the casting stream by increasing the casting speed. It has been proposed to pour the steel from the ladle under a protective gas atmosphere. A realization of such proposals is obviated, however, by constructional difliculties and the incurrence of high costs so that until now such method has not been employed on large scale in steel works.
• the steel may come into contact with the oxidizing atmosphere a third time.
• the method according to the invention solves the given problems in that the aluminum is added in two portions, the first portion being added at a stage before the liquid steel is poured into the tundish and being of a quantity sufficient to bind most of the oxygen present in the liquid steel, with the provision that the casting stream coming into contact with air contains only between about 0.005 and 0.01% of metallic aluminum, and the second portion being added only when the casting stream will no longer get into contact with the atmosphere and being of a quantity suflicient to obtain the desired analysis.
• the first portion of aluminum may be added at any moment before the steel is poured into the tundish, so e.g. while the hot metal is tapped from the refining vessel or while the steel is in the ladle.
• the second portion of aluminum may be added continuously into the mould.
• the second portion may be added into the tundish.
• the casting stream being in contact with the atmosphere contains only a negligible amount of metallic aluminum.
• EXAMPLE 1 In a 50 mt. converter pig iron of the following composition: 4.16% C., 0.73% Si, 1.11% Mm, 0.126% P, 0.036% S, remainder substantially iron was converted to steel by top-blowing oxygen. The amount of steel produced was 50.4 mt. The tapping temperature was 1610 C. The steel contained 0.071% of dissolved oxygen. The first aluminum portion of 51 kg. was added into the ladle in the form of billets. The steel was poured from the ladle into the tundish. The steel temperature in the tundish was 1540 C. During pouring a sample of the steel was taken and its aluminum content was determined to amount to 0.007%. The sample contained 0.014% of oxygen. 36 kg.
• the aluminum wire was fed into the tundish at a rate of 5.64 m./rnin.
• the cast finished product had the following analysis: 0.05% C., 0.28% Mn, 0.017% P, 0.022% S, 0.056% of metallic aluminum dissolved in the steel, lbalance iron; the measures employed for casting were the following:
• the slabs were flame scarfed with 2.5% loss of material.
• the waste owing to linear surface flaws amounted only to 014%.
• EXAMPLE 2 In a 50 mt. converter pig iron of the following composition: 3.97% C, 0.81% Si, 1.21% Mn, 0.103% P. 0.030%
• Example 2 was added as described in Example 1 into the tundish with a feeding speed of 6.25 m./min.
• the cast finished product had the following analysis: 0.04% C, 0.34% Mn, 0.015% P, 0.02% S, 0.062% of metallic aluminum, dissolved in the steel, remainder substantially iron; the measures employed for casting were the following:
• a method for the production of aluminum-containing killed steel for continuous casting wherein the liquid steel is conveyed as a first casting stream which is in contact with the atmosphere from the ladle into a tundish and thereafter as a second casting stream from the tundish into a mold, comprising adding a first predetermined portion of aluminum to the liquid steel before the steel reaches the tundish to substantially kill the steel, the quantity of said added aluminum being sufiicient to give a metallic aluminum content substantially homogeneously distributed throughout the steei in the tundish of about 0.005% to 0.010% by weight of the steel adding a second predetermined portion of aluminum to the liquid steel at a stage when the second casting stream will no longer contact the atmosphere to alloy the steel and to obtain a final aluminum content of at least 0.20% by weight of the steel, and thereafter continuously casting the steel to produce a casting with improved surface characteristics.
• a tundish comprising a casting tube extending into said mould and terminating below casting level and said second portion of aluminum is continuously added into said tundish.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Continuous Casting (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Investigating And Analyzing Materials By Characteristic Methods (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=3500637

Family Applications (1)

Country Status (12)

Cited By (1)

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Family Cites Families (2)

• 1969
  • 1969-01-28 AT AT82669A patent/AT310215B/de not_active IP Right Cessation
• 1970
  • 1970-01-13 SE SE00369/70A patent/SE354294B/xx unknown
  • 1970-01-14 JP JP45003583A patent/JPS5210802B1/ja active Pending
  • 1970-01-16 SU SU1394854A patent/SU405192A3/ru active
  • 1970-01-20 DE DE19702002283 patent/DE2002283A1/de active Pending
  • 1970-01-20 ES ES375695A patent/ES375695A1/es not_active Expired
  • 1970-01-22 CH CH102870A patent/CH544153A/de not_active IP Right Cessation
  • 1970-01-26 US US00005912A patent/US3730704A/en not_active Expired - Lifetime
  • 1970-01-26 FR FR707002565A patent/FR2029535B1/fr not_active Expired
  • 1970-01-27 CS CS577A patent/CS161870B2/cs unknown
  • 1970-01-27 GB GB3892/70A patent/GB1291375A/en not_active Expired
  • 1970-01-28 BE BE745020D patent/BE745020A/xx unknown

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