Classifications

• • 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
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
  • C21C5/5264—Manufacture of alloyed steels including ferro-alloys
• • 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
  • C21C7/068—Decarburising
  • C21C7/0685—Decarburising of stainless steel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• ABSTRACT Chrome steels are made by blowing an oxidising gas into an electric furnace containing a bath of molten metal containing chromium to decarburise the metal, the oxidising gas being blown in below the surface of the metal and passing through the bath from the bottom upwards.
• the or each jet of oxidising gas is peripherally surrounded at its point of entry into the metal by a fluid refractoryprotectant such as fuel oil.
• a fluid refractoryprotectant such as fuel oil.
• the metal bath initially ,contains more than 0.7% carbon, and can contain more than 1.2% carbon. The absence of any upper limit on the initial carbon content allows the use of carburised ferro-alloys, and the refining of relatively high carbon content baths.
• the partial pressure of the carbon monoxide product of the decarburization is reduced by placing under vacuum a ladle of chrome steel and blowing into the steel a jet of pure oxygen by means of a lance.
• the metal treated by these methods has first been refined in an electric furnace and hence the carbon content is limited for the reasons of safety explained above.
• the consumption of argon becomes greatly increased and hence the refining costs are high.
• a high initial carbon content necessitates the use of very powerful vacuum pumps and the procedure is difficult in practice.
• a principal advantage of the method of the invention is to be able to treat, under good technical and economic conditions, charges more highly carburized than usual and thus, by using carburized ferro-alloys, to reduce very significantly the consumption of the more expensive refined and over-refined ferro-alloys.
• the invention provides a method of making a chrome steel which includes the step of blowing oxidising gas into a molten steel-makin charge steel-making chr0- mium, in an electric arc furnace to decarburise the charge, wherein the charge initially has a carbon content of above 0.7 percent, and at least one drowned jet of oxidising gas is blown into the charge below the surface thereof and passes through the bath from the bottom upwards, the or each said jet being surrounded at its periphery, at its point of entry into the charge, by a fluid refractory protectant.
• the distance from tip of the drowned blast-pipe up to the surface of the molten charge is at least 300 mm.
• the method of the invention is particularly advantageous in the hitherto difficult case of electric furnace charges containing chromium and having a carbon content higher than 1.2 percent.
• the oxidizing gas employed may advantageously be pure oxygen.
• the method of the present invention can constitute one particular way of carrying out the general method, as applied to chrome steels.
• at least one jet of oxidizing gas is blown into the electric furnace by blastpipes passing through the hearth or the wall of the furnace, and each jet is surrounded at its periphery by an agent which protects the refractories against wear, this protective agent opening into the bath round each jet of oxidizing gas (which may be pure oxygen).
• the present invention can also, however, be applied to oxidizing jet means of another nature, for example, of air enriched with oxygen or a mixture of oxygen and steam, protected at its periphery by an auxiliary fluid.
• the oxidizing gas is either technically pure oxygen or is oxygen containing a small quantity of a gas such as nitrogen or argon or steam, for example, in the ratio of up to 5 percent of said gas to 95 percent oxygen, the said gas having the effect of accentuating the stirring of the bath in the cases or in the phases in which the natural mixing by the carbon monoxide produced is not sufficient.
• a gas such as nitrogen or argon or steam
• the oxidizing gas blown in at depth consists of a mixture of oxygen and a fluid diluent for the carbon monoxide by-product, which diluent fluid can be, for example, argon, nitrogen, steam or water atomized into a carrier gas, in a major proportion, for example 50 to 70 percent of the total flow.
• blowing in of pure oxygen by lance at the surface can be combined with blowing in at depth in accordance with the invention.
• one of the main advantages of the method of the invention is to force the oxygen to react at depth with the carbon in the bath and so form, within the whole mass of the metal bath, bubbles of carbon monoxide which ensure good stirring of the whole bath and also between the surface metal layer and the slag.
• Another advantage of the invention is a shortening of the duration of the operation, because a greater gas flow rate can be used at the bottom of the bath than can be used in top-blown lance procedures.
• Another advantage of the invention is a smaller consumption of refractories, firstly because the zones of superheat are embedded in the bath, next because the splashing and spattering are less violent than with top blowing by lance, and finally because the operation is shorter.
• the loss of Cr brought was 5 kg/t of liquid steel during the blow. (From the point of view of the Cr content of the bath, the scorification of the chromium had been compensated by a reduction in weight of the bath, whence a quasi-conservation of the Cr content.)
• the metal thus refined was poured into a ladle for supplementary refining by oxygen under vacuumto a carbon content of 0.012 percent (in order to limit the scorification of the chromium).
• the loss of Cr in this last phase was 13 kg/t of liquid steel, reduced to 4 kg/t of liquid steel by reduction of the ladle slag.
• the invention is useful for the production of chrome ferrites.
• the oxidizing gas is introduced into the molten metal charge from the bottom region thereof, rather than from the top as in conventional top blown electric arc furnaces.
• This may conveniently be achieved by introducing the gas through blast pipes which pass into the furnace through the bottom or the lower part of a wall thereof, and from which the gas is released into the bottom region of the molten metal.
• a method of making a chrome steel which includes the step of blowing oxidizing gas into a molten steel-making charge containing chromium, the steps of introducing the charge in an electric arc furnace, to decarburise the charge, the charge initially having a carbon content of above 0.7 percent, blowing at least one submerged jet of oxidizing gas into the charge below the surface thereof and passing through the bath from the bottom of said furnace upwards, each said jet being surrounded at its periphery, at its point of entry into the charge, by a fluid protectant for the refractory lining of said furnace.
• the oxidizmg gas is selected from the group consisting of pure oxygen, air enriched with oxygen, mixtures of oxygen and a neutral gas, and mixtures of oxygen and steam, and may contain atomized water in suspension therein.
• the diluent fluid is selected from the group consisting of argon, nitrogen, steam and atomized water in a carrier gas.

Landscapes

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

Applications Claiming Priority (1)

Publications (1)

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Citations (4)

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• 1973
  • 1973-02-07 FR FR7304266A patent/FR2216362B1/fr not_active Expired
  • 1973-12-31 DE DE19732365258 patent/DE2365258B2/de not_active Ceased
• 1974
  • 1974-01-07 GB GB64174A patent/GB1423634A/en not_active Expired
  • 1974-01-08 IT IT67031/74A patent/IT1009087B/it active
  • 1974-01-10 US US432309A patent/US3929458A/en not_active Expired - Lifetime
  • 1974-01-11 JP JP49006943A patent/JPS49111811A/ja active Pending
  • 1974-01-15 IN IN96/CAL/74A patent/IN139479B/en unknown
  • 1974-01-15 AU AU64503/74A patent/AU6450374A/en not_active Expired
  • 1974-01-16 ES ES422325A patent/ES422325A1/es not_active Expired
  • 1974-02-05 DD DD176384A patent/DD109664A5/xx unknown
  • 1974-02-05 LU LU69322A patent/LU69322A1/xx unknown
  • 1974-02-06 BE BE140606A patent/BE810675A/xx unknown
  • 1974-02-06 CA CA191,881A patent/CA1016754A/fr not_active Expired

Patent Citations (4)

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