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
  • C21C7/068—Decarburising
  • C21C7/0685—Decarburising of stainless steel
• • 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
  • C21C5/005—Manufacture of stainless steel

Definitions

• the process which is the subject of the invention relates to the decarburization of chromium or chromium nickel cast irons, containing on the order of 1.5 to 8% by weight of carbon, from 10 to 30% of Cr, up to 30% Ni, and possibly additions of Co, Mn and Mo.
• the pig iron to be decarburized is treated in a vertical converter by means of a lance arranged above the level of the liquid pig iron. This lance sends a jet of oxygen which strikes the surface of the liquid metallic bath.
• the analyzes carried out have shown that, under conditions favorable to dephosphoration, the P content of the droplets is 100 times lower than that of the metal bath.
• An increase in the impact force of the oxygen jet on the metal bath promotes the decarburization reaction because it results in an increase in the flow rate of projected droplets which can then exceed, as we said above, the ton per second .
• the very rapid decarburization which then takes place is favored by the bursting of the metallic droplets which results from the formation of the bubbles of CO.
• the process according to the invention is applicable to chromium cast irons containing: C 1.5 to 8%, Cr 10 to 30%, Ni 0 to 30%, Co + Mn + Mo 0 to 20%, Si ⁇ 4% as well than the usual impurities. It consists in carrying out decarburization by means of an oxygen jet, comprising a supersonic zone, which is directed towards the surface of the liquid pig iron and which, at least in the final phase of decarburization, causes the formation of a gas-cast emulsion in which the carbon is oxidized directly by oxygen, this final phase starting when the carbon content of the chromium cast iron is equal to C D / n, n being between 1.5 and 2.5 and C D being the initial carbon content of the pig iron, by weight
• liquid pig iron containing C 1.5 to 8 %, C r 10 to 30%, Ni 0 to 30%, Co + Mn + Mo 0 to 20 Z, Si ⁇ 4%, and the impurities are introduced.
• a vertical converter of a type comparable to those used for decarburization by the LD process is introduced.
• This converter has a basic lining resistant to very high temperatures. It is possible to use, in particular, bricks of the chrome magnesia type.
• the metal is covered with a limited amount of a lime-based slag.
• Decarburization is carried out by injecting high pressure oxygen using a lance which enters the converter from the top.
• This lance comprises a so-called supersonic nozzle which emits, in the direction of the surface of the metal bath, a jet of oxygen which comprises a small zone in which the speed of this gas is effectively supersonic.
• This zone extends along the axis of the jet on an ionizer which is a function of the oxygen pressure and the diameter of the nozzle at the neck, that is to say at the place where its diameter is the more reduced.
• the jet is oriented substantially vertically and the distance between the end of the nozzle and the initial surface of the metal bath is adjusted to a value substantially equal to that reached by the end of the supersonic zone of the oxygen jet.
• the distance between the lance and the bath varies between 5 and 30 times the diameter of the throat of the nozzle.
• the specific oxygen flow rate, per tonne of liquid iron must be approximately 3 Nm 3 / min under a pressure varying between 8 and 12 bar relative.
• a first reaction phase is observed during which the slag layer is gradually expelled from the surface of the bath by the gas jet, at the same time as rapid oxidation of the. most oxidizable elements contained in cast iron occurs.
• it is mainly the chromium which is oxidized.
• the temperature of the metal rises rapidly.
• the chromium oxidized at the start is reduced by the carbon, present at a still high content in the metal bath.
• the temperature continues to rise. Above a temperature of around 1700 to 1800 ° C., a third reaction phase begins, around which the boiling caused by the reaction of oxygen on the carbon of the bath no longer occurs.
• the quantity of oxygen present in the melt and the residual slag is sufficient to oxidize the residual carbon and it is easy to arrive at a final carbon content of less than 0.03%. Under these conditions the overall yield of chromium is excellent and close to 98%. As mentioned above, this result is obtained without the addition of one or more reducing elements or compounds.
• a cast iron is produced having the following composition: Cr 17%, C 6%, Si 0.3 X, Mn 0.3%, S ⁇ 0.03%, P ⁇ 0.03
• a quantity of 60 kg of this cast iron is brought to 1430 ° C. in an oven comprising induction heating, the surface of the liquid cast iron being covered with approximately 0.5 kg of lime.
• Oxygen is then injected by means of a vertical lance with a flow rate of 168 Nl / min under a pressure of 9 relative bars.
• the diameter at the neck of the nozzle is 2 mm and the vertical distance between the end of the lance and the bath is 30 mm. The oxygen thus injected reacts with the bath and three successive reaction phases can be observed.
• the oxygen reacts mainly on the surface of the iron bath, preferably oxidizing Cr, Si and Fe; as the oxides formed which mainly contain Cr 2 0 3 accumulate on the surface of the bath, a secondary reaction of reduction of these oxides by carbon begins.
• the speed of this reduction reaction increases gradually at the same time as the temperature rises to about 1650 ° C around the tenth minute.
• the CO formed is released during this time and burns giving flames.
• the reaction rates are high, which allows decarburization to continue at a rapid rate until a final carbon content of approximately 0.2% is reached at the 29th minute.
• the temperature is then around 1860 ° C. and the oxygen blowing is stopped.
• the analyzes carried out show that the yield of Cr is 97.5% by weight.
• the final decarburization is then carried out, in a known manner by placing the oven under vacuum by means of pumps making it possible to reach a pressure residual of about 2 torr in about twenty minutes. During this operation, the carbon content is lowered to around 0.02%, only thanks to the oxygen present in the liquid pig iron and the residual slag. At the end of this test, it is found that the chromium yield is 98%.
• the process can be applied not only to Cr cast iron without other significant additions, but also to Cr cast iron comprising additions of other metals such as Ni, Co, Mn or Mo. It is therefore possible by this process directly, from a Cr or NiCr cast iron, having undergone suitable additions, ferritic, semi-ferritic, austenitic or austenoferritic stainless steels.
• This nozzle is preferably made of copper cooled by water circulation and its surface is covered by projection of a layer of highly refractory oxides. This layer plays the double role of insulation and protection of the nozzle against the risks of breakthrough and therefore of water leakage.

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)
• Carbon Steel Or Casting Steel Manufacturing (AREA)
• Continuous Casting (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Mold Materials And Core Materials (AREA)
• Adornments (AREA)
• Devices For Post-Treatments, Processing, Supply, Discharge, And Other Processes (AREA)
• Pinball Game Machines (AREA)
• Medicines Containing Material From Animals Or Micro-Organisms (AREA)
• Control Of El Displays (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• High-Tension Arc-Extinguishing Switches Without Spraying Means (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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Citations (5)

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• 1980
  • 1980-01-24 FR FR8001809A patent/FR2474531B1/fr not_active Expired
  • 1980-12-04 PH PH24944A patent/PH16313A/en unknown
  • 1980-12-05 IN IN1349/CAL/80A patent/IN153729B/en unknown
  • 1980-12-31 US US06/221,903 patent/US4324584A/en not_active Expired - Fee Related
• 1981
  • 1981-01-13 TR TR21061A patent/TR21061A/xx unknown
  • 1981-01-16 YU YU00096/81A patent/YU9681A/xx unknown
  • 1981-01-19 AU AU66303/81A patent/AU531039B2/en not_active Ceased
  • 1981-01-19 SU SU813229959A patent/SU1170974A3/ru active
  • 1981-01-20 CA CA000368903A patent/CA1154967A/fr not_active Expired
  • 1981-01-20 DE DE8181420006T patent/DE3167358D1/de not_active Expired
  • 1981-01-20 AT AT81420006T patent/ATE10508T1/de not_active IP Right Cessation
  • 1981-01-20 EP EP81420006A patent/EP0033289B1/de not_active Expired
  • 1981-01-21 ZW ZW12/81A patent/ZW1281A1/xx unknown
  • 1981-01-21 BR BR8100314A patent/BR8100314A/pt not_active IP Right Cessation
  • 1981-01-21 ZA ZA00810411A patent/ZA81411B/xx unknown
  • 1981-01-22 JP JP855881A patent/JPS56116814A/ja active Pending
  • 1981-01-23 FI FI810188A patent/FI68862C/fi not_active IP Right Cessation
  • 1981-01-23 NO NO810242A patent/NO810242L/no unknown
  • 1981-01-23 ES ES498749A patent/ES498749A0/es active Granted

Patent Citations (5)

Non-Patent Citations (1)

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