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
  • 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
  • C21C7/072—Treatment with gases
• • 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
• • 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
  • C21C7/0037—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by injecting powdered material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
• • 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

• the blowing start when the metal is still solid and continue through the melting stage. While the metal is still solid, the blown gas should be an inert gas containing a small amount of oxygen; however, once the meta is melted the presence of oxygen is excluded.
• the invention is concerned with a method for refining a metal.
• the invention is based upon the known method for degassing a molten metal which is disclosed in British Patent No. 772,515 and which comprises blowing one or several streams of a nonreactive gas onto the surface of the molten metal, said nonreactive gas acting as a vacuum for gases dissolved in the molten metal.
• It is a particular object of the invention to provide a refining method for stainless steel, allowing a reduction of its molybdenum content.
• the method of the invention comprises heating the metal in solid form up to its melting point, blowing during said heating a stream of an inert gas onto the solid metal, said inert gas containing 0.005-10 percent by volume of oxygen, continuing the heating until the metal has become molten, and blowing a stream of an inert gas onto the surface of the molten metal.
• the inert gas should be one of the gases belonging to class 0 of the periodic system of the elements, or a mixture of such gases. We prefer to use argon.
• the oxygen content of the inert gas shall be 0.00510 percent by volume, preferably 05-10 percent by volume.
• the blowing of the inert gas onto the solid metal should preferably begin when the metal is at normal temperature.
• the metal may be heated continuously up to its melting point.
• said solid material may be supplied as a fine powder to the stream of inert gas.
• the above-described refining process when applied to the refining of molybdenum-containing stainless steel scrap proceeds as follows:
• the solid scrap metal is heated whilst there is blown onto its surface a gas mixture consisting essentially of an inert gas 99-98% by volume and oxygen 12% by volume.
• This treatment is continued until the temperature of the scrap metal reaches 750- 850 C., whereupon the progressive heating is interrupted to allow molybdenum to escape from the steel.
• the heating is continued, with continued blowing of the inert gas-oxygen gas mixture, until the steel melts and the melt attains a temperature within the range 1600- 1700 C.
• the composition of the gas being blown onto the surface of the melt-to remove gaseous impurities therefrom is altered in such manner that the gas contains less than 0.01% by volume of oxygen.
• EXAMPLE The example is concerned with the refining of stainless scrap steel for the production of valuable stainless steel.
• the scrap steel had the composition:
• the scrap steel was heated in an electric high frequency furnace. Argon containing 1.2 percent by volume of oxygen was blown through a plurality of tubes towards the solid scrap steel. When the temperature reached approximately 650 C. the solid steel started emitting a brown smoke. The formation of smoke was most intense at approximately 800 -C., and this temperature was maintained until no smoke was formed. The temperature was now increased until the steel began to melt. The percentage of oxygen in the argon was now reduced to 0.005 percent by volume. The temperature was increased to 1650 C. and was maintained at this value for 8 minutes, while the argon-oxygen mixture was continuously blown onto the surface of the molten steel. While still being protected by argon the steel was poured into an ingot mould and allowed to solidify. The finished steel contained no hydrogen or other gaseous impurities and less than 0.5% molybdenum.
• the smoke emitted by the steel was condensed, forming'needle-shaped crystals consisting of M00
• the molybdenum atoms lying on the surface of the solid steel are oxidized to form M00 by the oxygen in the inert gas.
• the oxide has a certain volatility, and is therefore swept away from the surface of the steel by the inert gas which is vigorously blown onto the steel surface.
• a concentration difference is thus created between the molybdenum in the surface layer of the steel and that in the interior of the steel. Said concentration difference causes the molybdenum atoms to move by diffusion to the surface of the steel, where they are oxidized and removed from the steel as described. It is to be emphasized that molybdenum cannot be removed in a corresponding way from molten steel.
• a method for refining molybdenum-containing stainless scrap steel comprising heating the solid scrap steel while blowing onto its surface a mixture of an inert gas and 1-2% by volume of oxygen, interrupting the heating at 750-850" C. to allow molybdenum to escape from the steel, resuming the heating until the steel has become molten and the molten steel has reached a temperature of 1600-1700 C., and blowing an inert gas containing less than 0.01% by volume of oxygen onto the surface of the molten steel to remove gaseous impurities therefrom.
• a method for refining a metal containing a normally solid impurity having a vaporizing temperature lower than the melting temperature of the metal comprising progressively heating the metal, by high frequency heating, in solid form up to its melting point, blowing during said heating a stream of a gas mixture onto the solid metal, said gas mixture consisting of an inert gas containing 0.005-10 percent by volume of oxygen, continuing the heating until the metal has become molten, and blowing a stream of a pure inert gas onto the surface 4 of the molten metal to remove gaseous impurities therefrom.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Manufacture And Refinement Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=20262454

Family Applications (1)

Country Status (5)

Cited By (2)

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Citations (2)

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• 1966
  • 1966-03-14 DE DEN28202A patent/DE1281465B/de active Pending
  • 1966-03-16 US US3468657D patent/US3468657A/en not_active Expired - Lifetime
  • 1966-03-17 AT AT256466A patent/AT296360B/de not_active IP Right Cessation
  • 1966-03-17 BE BE678013D patent/BE678013A/xx unknown
  • 1966-03-17 GB GB1188466A patent/GB1137092A/en not_active Expired

Patent Citations (2)

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