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
• • 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
  • C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle
• • 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
  • C21C7/005—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using exothermic reaction compositions
• • 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
  • C21C7/064—Dephosphorising; Desulfurising
• • 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

Definitions

• the present invention relates generally to a method of metallurgical treatments on a metal bath. It relates more particularly to such a method which comprises a first treatment involving the presence or the formation of an acid slag on the surface of a metal bath and a second treatment involving the presence or the formation of a basic slag on the surface of this bath metallic.
• a process of this kind is for example a process for treating crude steel in a ladle in which a heating of the steel bath is carried out by aluminothermy before carrying out a desulfurization treatment (that is to say a treatment to lower the sulfur content) and / or dephosphorization (that is to say a treatment for lowering the phosphorus content).
• a desulfurization treatment that is to say a treatment to lower the sulfur content
• dephosphorization that is to say a treatment for lowering the phosphorus content.
• aluminum is reacted with oxygen, which forms an acid slag of Al 2 O 3 on the surface of the steel bath.
• the desulfurization treatment, respectively dephosphorization which requires a basic slag on the surface of the steel bath, is inhibited by the presence of an acid slag of Al 2 O 3 on the surface of the steel bath. Therefore, the acid slag from AI203 must first be cleaned before the desulphurization and / or dephosphorization treatment can be started.
• Another process of the kind defined in the preamble is a process in which a pig-iron bath or a ferro-alloy bath must undergo both desiliconization by oxygen injection (i.e. treatment to lower silicon content) and desulfurization and / or dephosphorization.
• the desiliconization by oxygen injection produces an acid slag of SiO2 on the surface of the metal bath.
• the subsequent desulfurization treatment requires the presence of a basic slag on the surface of the steel bath and it is inhibited by an SiO 2 content greater than 10%. It follows that the acid slag formed during the silting-up must be descaled before starting the desulfurization treatment. As already explained, such an intermediate scouring significantly increases the duration of the process and is not possible in any metallurgical treatment stand.
• the object of the present invention is to optimize the progress of a metallurgical process in which a first treatment involves the presence or the formation of an acid slag on the surface of a metal bath and a second treatment involves the presence or the formation of a basic slag on the surface of this metal bath.
• this objective is achieved by carrying out the two treatments without intermediate scouring simultaneously or successively in two separate zones and by ensuring on the surface of the metal bath a physical separation between an acid slag zone and a basic slag zone.
• the two treatments will preferably take place simultaneously.
• one of the two treatments is carried out under a deep bell whose lower edge is immersed in the metal bath and the other treatment is carried out around this deep bell.
• This deep bell ensures physical separation between the two zones of slag on the surface of the bath, while making it possible to carry out one of the two treatments under a protected atmosphere, with a minimum of losses to the environment.
• a simple partition wall to ensure on the surface of the metal bath a physical separation between a zone of acid slag and a zone of basic slag.
• This partition wall can either cooperate with the edges of a metallurgical container to divide the surface of the metal bath into two juxtaposed zones, or form a sort of ring to delimit an "island" inside the surface of the metal bath. .
• the first treatment is for example a chemical reheating which is carried out under a deep bell under a protected atmosphere and which produces an acid slag under this bell.
• chemical heating is meant here a strongly exothermic oxidation of a generally metallic element, such as for example aluminum (aluminothermy) or silicon (silicothermic).
• the first treatment can also be a desiliconization treatment by oxygen injection, in particular within the framework of a treatment of cast irons or ferro-alloys (such as for example ferro-nickel) with high silicon contents.
• This desiliconization treatment by oxygen injection is also advantageously carried out under a deep bell whose lower edge is immersed in the metal bath.
• the second treatment is for example a desulphurization and / or dephosphorization treatment involving a basic slag, formed for example by adding lime, sodium carbonate, magnesium etc. This treatment can be carried out around the deep bell under which the first treatment is carried out.
• the desulfurization and / or dephosphorization treatment advantageously comprises the addition of limestone, in particular of castine, to the metal bath. It is a cheap and very effective desulfurizing agent, but its decomposition in the metal bath gives rise to a strongly endothermic reaction which tends to cool the metal bath. However, in combination with a desiliconization by injection of oxygen, this cooling effect hardly causes any problem, since the desiliconization reaction, which is strongly exothermic, produces an excess of heat anyway.
• the procedure is advantageously as follows: first, by injection of an inert gas, a "window" in an initial layer of slag covering the surface of the metal bath; this "window” is covered with a deep bell whose lower edge is immersed in the metal bath; one of the two treatments is carried out under the deep bell and the other around the deep bell, by simultaneously carrying out stirring of the metal bath by injection of an inert gas; and at the end of the two treatments, we stop brewing, remove the deep bell and clean immediately after the two slags. Stopping the brewing before removing the deep bell prevents the two slags from mixing too much, which could be detrimental to the result of the process.
• FIG. 1 shows a schematic illustration of the implementation of a method according to the invention.
• Fig. 1 is used to describe in more detail, by way of illustration of the present invention, the progress of a metallurgical process which comprises a desulfurization treatment in a ladle of a crude steel bath, preceded by chemical heating in pocket of this steel bath.
• FIG. 1 shows a metallurgical pocket 10 in a metallurgical treatment stand during the implementation of the above process.
• this pocket 10 contained a crude steel bath 12 from the converter or the electric furnace, as well as a layer of basic residual slag covering the steel bath.
• a window 14 was first formed in the residual slag layer by injection of an inert gas, that is to say that an area of the surface of the bath was freed. steel 12 at least partially from the residual slag which covered it.
• a deep bell 16 was then positioned, so that its lower edge 18 is immersed in the metal bath 12 by at least 20 cm (the greater the bubbling of the metal bath 12, the greater the immersion depth of the lower edge of the bell 16).
• a possible execution of such a deep bell 16 is for example described in the patent application WO 98/31841, by specifying however that the bell used in the present process does not necessarily have to be a rotating bell.
• the steel bath is reheated by aluminothermy.
• aluminum is added and oxygen is blown under the bell 16, as indicated diagrammatically by the arrows 18 and 20.
• the metal bath 12 is stirred using a gas inert, which is injected, preferably using a side lance 22, into the metal bath 12.
• the aluminum reacts in a strongly exothermic reaction with oxygen. This reaction results in the formation of an acidic slag of Al 2 O 3 below the bell 16.
• this acid slag from AI203 is identified by reference 24.
• the bell 16 was raised at the end of the chemical heating to carry out a scrub of the residual slag highly contaminated with the slag AI203 formed under the bell 16. Then the desulfurization treatment was carried out on the steel released from slag.
• the Al 2 O 3 content of this slag must be less than 40%.
• the desulphurization and / or dephosphorization treatment is carried out around the bell 16 without performing an intermediate slag cleaning.
• a basic slag-forming agent 28 is injected with a lance 26 into the metal bath 12 around the bell 16.
• This basic slag-forming agent 28 can for example be of lime, limestone, limestone, soda ash, magnesium etc.
• Bell 16 prevents the acid slag of AI203 formed under bell 16 from mixing with the basic slag surrounding the pocket 16, which allows to carry out the two treatments simultaneously or successively without intermediate cleaning.
• heating by aluminothermic heating is started first and the desulphurization and / or dephosphorization treatment is started as soon as the steel bath has reached a sufficient temperature.
• the treatment carried out under the bell could, for example, also be a treatment for desiliconization of cast iron or ferro-alloys, in particular ferro-nickel, by injection of oxygen.
• the silicon reacts with the oxygen blown below the bell to form an acid slag of SiO2 below the bell.
• a desulphurization and / or dephosphorization treatment can then be carried out as described above.
• the bell prevents the acid slag of SiO 2 formed under the bell 16 from mixing with the basic slag surrounding the pocket 16, which makes it possible to carry out the two treatments simultaneously or successively without intermediate cleaning.
• the SiO 2 content of the basic slag must not be greater than 10%.
• This example relates to a ladle treatment of the raw steel of the converter with the objective of desulfurization to 80% of this steel.
• a metallurgical ladle contains 160 tonnes of raw converter steel and 600 kg of residual refining slag.
• the analysis results are as follows: 0.04% C, 600 ppm O, 0.010% S.
• the temperature of the steel bath is 1600 ° C.
• 200 kg of deoxidizing Al and 600 kg of CaO were added.
• Reheating by aluminothermy The first treatment is reheating by aluminothermy which takes place, as described in relation to FIG. 1, under a deep bell positioned above an area of the steel bath previously released from its layer of residual slag. An increase in the temperature of the steel bath is obtained of approximately 90 ° C. by injection of 530 kg of aluminum and 350 m3 of oxygen in 7 min (flow rate of 50 m3 / min of 02). The brewing below the bell is carried out by injection of argon using a lateral lance with a flow rate of 0.2 m3 / min.
• Desulfurization The second treatment is advanced desulfurization to
• slag agent a powder composed of 60% CaO and 35% Al 2 O 3 is used, the remainder being impurities.
• AI203 aims to regulate the fluidity of the slag obtained.
• Other slag agents can also be added.
• the desulphurizing agent is injected using a lance with a submerged head, using argon as the carrier gas.
• the injection lance is used to effect a prior mixing of the steel bath.
• the injection lance is supplied for 5 min with a flow rate of approximately 0.5 m3 / min of argon, the supply of the desulphurizing agent being cut off. This preliminary stirring makes it possible in particular to homogenize the temperature of the steel bath before its desulphurization.
• the residual slag which is found around the bell, may already contain a sufficient amount of desulphurizing agents to obtain moderate desulphurization of the steel. It then suffices to stir the steel bath around the bell to make it react with the residual slag floating on its surface and to add, if necessary, still slag agents to regulate in particular the consistency of the slag.
• This example concerns a ladle treatment of pig iron with the objective of desiliconization and desulfurization of the pig iron.
• a metallurgical ladle contains 100 t of pig iron, the analysis results of which are as follows: 4.5% C, 0.8% Si, 0.10% S.
• the temperature of the pig iron bath is 1350 ° C. .
• the cast iron is covered with a layer of residual slag with a basic character.
• Silicon treatment A silicon injection treatment is carried out, as described above, under a deep bell positioned above an area of the bath previously freed from its layer of residual slag. 450 m3 of oxygen are injected under the bell in 10 min (flow rate 45 m3 / min of 02). The brewing below the bell is carried out by injection of argon using a lateral lance with a flow rate of 0.2 m3 / min.
• Desulfurization takes place around the bell.
• desulphurizing agent a powder composed of 70% CaCO3 and 30% Na2CO3 is used.
• Other slag agents can also be added.
• the desulfurizing agent is injected using a submerged lance, using argon as the carrier gas. About 1000 kg of the abovementioned desulphurizing agent are injected over a period of approximately 20 minutes (solid flow rate approximately 50 kg / min) with approximately 1 m3 / min of argon as carrier gas. After stopping all brewing we can put the bell back up and unclog the two slags together.
• Pre-treated cast iron 4.3% C, 0.4% Si, 0.02% S, temperature approximately:
• an Mg-CaC2 or Mg-CaO mixture is most often used as desulphurizer. They are very effective desulfurizers, but also very expensive. They are mainly used because they produce limited cooling of the metal bath.
• a desulphurizing agent which is more cooling but cheaper, such as for example limestone (CaCO 3) or limestone.
• the decomposition of CaCO3 or Na2CO3 in the steel bath also generates oxygen, which contributes to the desiliconization of the cast iron (1 kg CaCO3 or Na2CO3 reduces the need for oxygen deiliconization by approximately 0.1 m3).
• a bath of ferro-alloys in particular a bath of ferro-nickel, can also be the subject of a combined treatment of desiliconization and desulfurization, as presented in Example 2 for pig iron.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Coating With Molten Metal (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)

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• 2002
  • 2002-05-24 LU LU90924A patent/LU90924B1/fr active
• 2003
  • 2003-05-21 JP JP2004507542A patent/JP4405381B2/ja not_active Expired - Fee Related
  • 2003-05-21 WO PCT/EP2003/050183 patent/WO2003100102A2/fr active IP Right Grant
  • 2003-05-21 CN CN038153289A patent/CN1665942B/zh not_active Expired - Fee Related
  • 2003-05-21 CA CA002485633A patent/CA2485633A1/fr not_active Abandoned
  • 2003-05-21 RU RU2004138075/02A patent/RU2289630C2/ru not_active IP Right Cessation
  • 2003-05-21 ES ES03740486T patent/ES2273014T3/es not_active Expired - Lifetime
  • 2003-05-21 BR BRPI0311295-0A patent/BR0311295B1/pt not_active IP Right Cessation
  • 2003-05-21 AU AU2003273150A patent/AU2003273150B2/en not_active Ceased
  • 2003-05-21 DE DE60308860T patent/DE60308860T2/de not_active Expired - Fee Related
  • 2003-05-21 EP EP03740486A patent/EP1507876B1/de not_active Expired - Lifetime
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