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US20080302210A1 - Steel desulphurating agent and use thereof in the desulphuration of steel - Google Patents

Steel desulphurating agent and use thereof in the desulphuration of steel Download PDF

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Publication number
US20080302210A1
US20080302210A1 US12/176,698 US17669808A US2008302210A1 US 20080302210 A1 US20080302210 A1 US 20080302210A1 US 17669808 A US17669808 A US 17669808A US 2008302210 A1 US2008302210 A1 US 2008302210A1
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Prior art keywords
steel
desulphurating
agent
desulphuration
slag
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US12/176,698
Inventor
Francois Sorrentino
Michel Gimenez
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Lafarge SA
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Lafarge SA
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Priority to US12/176,698 priority Critical patent/US20080302210A1/en
Publication of US20080302210A1 publication Critical patent/US20080302210A1/en
Assigned to LAFARGE reassignment LAFARGE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GIMENEZ, MICHEL, SORRENTINO, FRANCOIS
Abandoned legal-status Critical Current

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    • 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
    • C21C7/0645—Agents used for dephosphorising or 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
    • C21C7/064—Dephosphorising; Desulfurising

Definitions

  • the invention relates to the area of metallurgy and relates particularly to an agent for desulphurating steel, comprising high concentrations of SiO 2 , C2S, and calcium aluminate, and the use thereof in the desulphuration of steel.
  • Table 1 lists in % by weight the usual mineralogical and/or chemical compositions of steelworks slag.
  • Magnesium is difficult to use because it vaporises on contact with the steel and can result in explosions, and so must be coated in tar and placed in a bell.
  • lime is advantageous, but its high melting point, about 2200° C., stops the lime reacting with the liquid metal.
  • a steel desulphurating agent comprising, compared with the total weight of the agent:
  • composition of the desulphurating agent comprising a high concentration of C2S makes it possible, apart from the advantages described above, to obtain a swelling of the desulphurating agent, and thus a powder.
  • the desulphurating agent is preferably in the form of a powder with a specific surface comprised between 1000 and 5000 cm 2 /g, preferably from 1000 to 2000 cm 2 /g.
  • Methods for measuring the specific surface of a powder are well known to those skilled in the art. Examples that can be quoted include processes based on the physical adsorption of a gas at low temperature, for example the well-known method known as BET.
  • the desulphurating agent comprises the following mineralogical phases compared with the total weight of the agent:
  • composition comprises at least 35% of calcium aluminate or a mixture of calcium aluminate and calcium silico-aluminate.
  • the desulphurating agent comprises the following mineralogical phases compared with the total weight of the agent:
  • C2S to 50% of C2S, 20 to 70% of C12A7 and 0 to 40% of C3A, preferably 10 to 40% of C3A.
  • the desulphurating agent is obtained from steelworks slag.
  • This embodiment of the invention is particularly advantageous from an economic point of view, because it makes it possible to add value to steelworks by-products.
  • the desulphurating agent of the invention can be obtained by processing a molten steelworks slag in a controlled oxidising atmosphere so as to change its mineralogical and chemical composition and remove the impurities so that it can act as a sponge instead of the mixture of lime and furnace additions usually used for refining.
  • a method for preparing the desulphurating agent can consist in making a mixture of alumina or products that generate alumina and steelworks slag, then heating the mixture to a temperature comprised between 1250° C. and 1450° C., in a partial oxygen pressure, comprised between 10 ⁇ 1 and 10 ⁇ 6 bar.
  • the alumina, or the product generating alumina can be added to the molten steelworks slag.
  • the quantity of alumina that needs to be added to obtain the desulphurating agent from steelworks slag is between 10 and 30% compared to the total weight of the slag, depending on the composition of the slag and/or the required composition of the desulphurating agent.
  • the addition of alumina or of a compound that generates alumina makes the slag easier to melt and more readily desulphurised.
  • the source of alumina is selected from among: bauxite, aluminium residues and red mud.
  • the invention also relates to a steel desulphuration method comprising the addition to the steel of the desulphurating agent as described above and lime (CaO).
  • the desulphurating agent and the lime are mixed together before being added to the steel.
  • the weight ratio of the desulphurating agent to the lime varies from 1/0.5 to 1/2, and preferably is 1/1.
  • the steel desulphuration process preferably takes place at a temperature comprised between 1500° C. and 1600° C., and most preferably at 1550° C.
  • Desulphurating agents according to the invention were prepared from raw materials the mineralogical composition of which is shown in Table 2.
  • the slag and the bauxite were mixed at a temperature comprised between 1250° C. and 1450° C., in a partial oxygen pressure, comprised between 10 ⁇ 1 et 10 ⁇ 6 bar, then mixed with lime in proportions, expressed in percent by weight, given in Table 3.
  • the mineralogical phase composition of the desulphurating agents obtained from the compositions described in Table 3 is given in Table 4 below.
  • the capacity of the desulphurating agents was laboratory tested.
  • the desulphurating agents were mixed with molten steel in a weight ratio of 1/1.
  • the concentrations (W/W) of sulphur in the molten steel and in the desulphurating agent were measured by X fluorescence, before and after treating the steel with the desulphurating agent. The results are given in Table 5.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Catalysts (AREA)

Abstract

The invention relates to a steel desulphurating agent characterised in that it comprises compared with the total weight of the agent:
    • at least 10% of SiO2,
    • at least 10% of C2S,
    • at least 35% of at least one calcium aluminate and optionally a calcium silico-aluminate.

Description

  • The present application is a divisional of co-pending application Ser. No. 10/584,214, filed Jun. 23, 2006, which is a 371 National Stage of international application no. PCT/FR2004/050754, filed Dec. 23, 2004, which claims priority to French application no, 03.51202, filed Dec. 24, 2003. The entire contents of the above-referenced applications are hereby incorporated by reference in their entirety.
  • The invention relates to the area of metallurgy and relates particularly to an agent for desulphurating steel, comprising high concentrations of SiO2, C2S, and calcium aluminate, and the use thereof in the desulphuration of steel.
  • Steel manufacture can be carried out schematically in two ways:
  • transforming iron ore into steel by means such as blast furnaces or converters, and
  • processing scrap iron in an electric furnace.
  • It is known that the presence of impurities, phosphorus and sulphur in the steel obtained after refining cast iron is particularly harmful to mechanical properties. It is a known fact that the presence of a high proportion of sulphur in steel obtained after purification of cast iron produced by blast furnaces is particularly harmful because the sulphur reduces the cold ductility, the impact resistance, and the quality of the ingot surface. The proportion of sulphur that can be tolerated in the metal must be very low, that is to say, under 0.02% or even under 0.005%.
  • One of the major steps in the current process for steel production is primary metallurgy, by converter or electric furnace, which gives steel that is then reprocessed in a ladle in order to give it specific properties. The most notable progress in the area of improving the properties of steel has been from ladle metallurgy.
  • Devices for purifying cast iron and producing steel (blast furnaces, converters) make it possible to reduce the sulphur content of the metal, however they do not lead to the total desulphuration that would be necessary to remove the aforementioned disadvantages, whence the need to refine the steel. The general principles of refining can be summarised as described in the text that follows.
  • In order to extract the impurities from the steel, it has to be put in close contact with a product that has a greater affinity for the impurities, which therefore possesses a lower free enthalpy. This is a problem of thermodynamic equilibrium which can be solved by using high temperatures.
  • In order to lower the concentration in components that are deemed to have a noxious effect on the steel, the main methods of refining are:
  • 1—exchange through a slag
    2—forming insoluble compounds
    3—decreasing the solubility of the impurities in the steel by lowering their partial pressure by applying a vacuum to the steel.
  • The chemical reaction for the desulphuration of steel is as follows:

  • [S]m+(O−)s+(S−−)s+[O]m,
  • wherein [S]m and [O]m are the components dissolved in the metal, and (O−−)s and (S−−)s are the components dissolved in the slag.
  • A usual method for lowering the concentration in components that are deemed to have a noxious effect on the steel is to use a lime-based slag: In this case, the reaction would be as follows:

  • [S]m+(CaO)s→(CaS2)s+[O]m
  • wherein [S]m and [O]m are the components dissolved in the metal, and (CaO)s and (CaS2)s are the components dissolved in the slag.
  • As an indication, Table 1 lists in % by weight the usual mineralogical and/or chemical compositions of steelworks slag.
  • TABLE 1
    Free
    C2S Ferrite CaO Wustite Periclase C TiO2 V2O5 Cr2O3 MnO
    Min 15 10 1 3 2 0.02 0.3 0.2 0.20 0.5
    Max 40 50 15 20 15 0.3 1.5 0.5 20.00 10
    ZnO CoO NiO CuO PbO BaO SrO P2O5 S Na2O
    Min 0.01 0.0001 0.01 0.005 0.0001 0.001 0.001 0.05 0.01 0.05
    Max 0.5 0.001 0.5 0.5 0.005 0.5 0.05 2 2.00 0.5
    K2O ZrO2 MoO BeO Tl Sn2O3 As2O3 CdO Cl F
    Min 0.02 0.02 0.0001 0.0001 0 0.0001 0.0001 0.0001 0.05 0.0001
    Max 0.5 0.5 0.001 0.001 0.0005 0.2 0.005 0.05 2.00 0.5
  • Among the methods currently used for desulphuration however, none is totally satisfying.
  • Thus the use of sodium carbonate results in a yield of the order of 60% maximum of desulphuration with emission of noxious smoke and the production of particularly aggressive slag.
  • The use of calcium carbide results in recarburising the metal, and also, the product must be kept dry to avoid the risk of producing acetylene thus causing an explosion.
  • The use of calcium cyanamide results in nitriding and carburising the metal, which is what is trying to be avoided.
  • Magnesium is difficult to use because it vaporises on contact with the steel and can result in explosions, and so must be coated in tar and placed in a bell.
  • The use of silico-calcium, blown into the mass to be purified results in globularisation of the inclusions, and requires the use of alkaline slag and causes the steel to regain nitrogen.
  • The use of lime is advantageous, but its high melting point, about 2200° C., stops the lime reacting with the liquid metal.
  • Much research has led to the conclusion that a product with sound desulphuration qualities could contain 53 to 55% of CaO, 43 to 45% of Al2O3 and 1% of FeO. Many products exist with this type of composition such as those described in the French patent FR2541310, filed on 18 Feb. 1983 or the products available from Wacker and also the slag from vanadium production.
  • However, these products are expensive or not readily available.
  • Thus a need exists for desulphurating agents which remedy the disadvantages described above, while remaining less expensive, more readily available than the state of the art compositions, and in particular which could be obtained from industrial waste, particularly from steelworks slag.
  • The aforementioned aims are met according to the invention, by a steel desulphurating agent comprising, compared with the total weight of the agent:
  • at least 10% of SiO2,
  • at least 10% of C2S, and
  • at least 35% of at least one calcium aluminate and optionally a calcium silico-aluminate.
  • The composition of the desulphurating agent, comprising a high concentration of C2S makes it possible, apart from the advantages described above, to obtain a swelling of the desulphurating agent, and thus a powder.
  • The desulphurating agent is preferably in the form of a powder with a specific surface comprised between 1000 and 5000 cm2/g, preferably from 1000 to 2000 cm2/g. Methods for measuring the specific surface of a powder are well known to those skilled in the art. Examples that can be quoted include processes based on the physical adsorption of a gas at low temperature, for example the well-known method known as BET.
  • Preferably, the desulphurating agent comprises the following mineralogical phases compared with the total weight of the agent:
  • to 60% of C2S,
  • 0 to 50% of C3A,
  • 0 to 50% of C2AS,
  • 0 to 70% of C12A7, and
  • 0 to 60% of CA,
  • as long as the composition comprises at least 35% of calcium aluminate or a mixture of calcium aluminate and calcium silico-aluminate.
  • Most preferably, the desulphurating agent comprises the following mineralogical phases compared with the total weight of the agent:
  • to 30% of C2S, 30 to 60% of CA, and 10 to 40% of C2AS; or
  • to 50% of C2S, 20 to 70% of C12A7 and 0 to 40% of C3A, preferably 10 to 40% of C3A.
  • Preferably, the desulphurating agent is obtained from steelworks slag. This embodiment of the invention is particularly advantageous from an economic point of view, because it makes it possible to add value to steelworks by-products.
  • The desulphurating agent of the invention can be obtained by processing a molten steelworks slag in a controlled oxidising atmosphere so as to change its mineralogical and chemical composition and remove the impurities so that it can act as a sponge instead of the mixture of lime and furnace additions usually used for refining.
  • In particular, a method for preparing the desulphurating agent can consist in making a mixture of alumina or products that generate alumina and steelworks slag, then heating the mixture to a temperature comprised between 1250° C. and 1450° C., in a partial oxygen pressure, comprised between 10−1 and 10−6 bar.
  • The alumina, or the product generating alumina, can be added to the molten steelworks slag.
  • In general, the quantity of alumina that needs to be added to obtain the desulphurating agent from steelworks slag is between 10 and 30% compared to the total weight of the slag, depending on the composition of the slag and/or the required composition of the desulphurating agent.
  • The addition of alumina or of a compound that generates alumina makes the slag easier to melt and more readily desulphurised. Preferably, the source of alumina is selected from among: bauxite, aluminium residues and red mud.
  • The invention also relates to a steel desulphuration method comprising the addition to the steel of the desulphurating agent as described above and lime (CaO).
  • Preferably the desulphurating agent and the lime are mixed together before being added to the steel.
  • Preferably the weight ratio of the desulphurating agent to the lime varies from 1/0.5 to 1/2, and preferably is 1/1.
  • The steel desulphuration process preferably takes place at a temperature comprised between 1500° C. and 1600° C., and most preferably at 1550° C.
    • EXAMPLES
  • Desulphurating agents according to the invention were prepared from raw materials the mineralogical composition of which is shown in Table 2.
  • TABLE 2
    SLAG BAUXITE
    SiO2 14.00 11.69
    CaO 45.54 4.39
    AI2O3 1.16 57.75
    Fe2O3 24.61 21.60
    MgO 5.20 0.43
    K2O 0.05 0.16275
    Na2O 0.18 0.16275
    S 0.28 0.08138
    TiO2 0.59 2.72030
    MnO 4.73 0.25575
    P2O5 0.28 0.13950
    Cr2O3 0.88 0.23250
  • The slag and the bauxite were mixed at a temperature comprised between 1250° C. and 1450° C., in a partial oxygen pressure, comprised between 10−1 et 10−6 bar, then mixed with lime in proportions, expressed in percent by weight, given in Table 3.
  • TABLE 3
    N° 1 N° 2 N° 3 N° 4 N° 5 N° 6
    Slag 32 28 15 16 45 72
    Bauxite 53 53 47 45 35 22
    Lime 14 19 38 39 20 6
  • The mineralogical phase composition of the desulphurating agents obtained from the compositions described in Table 3 is given in Table 4 below.
  • TABLE 4
    Test 1 Test 2 Test 3 Test 4 Test 5 Test 6
    C2S 14 28 31 23 37 47
    CA 38 52
    C2AS 36 10
    C12A7 59 27 39 26
    C3A 40 14 13
    Fe2O3 0.4210 0.4210 1.4883 0.9012 0.9008 4.9056
    MgO 7.8819 5.8786 5.4049 6.0905 5.0091 5.5339
    K2O 0.1811 0.1567 0.1323 0.2481 0.1465 0.1476
    Na2O 0.0453 0.0157 0.0000 0.0248 0.0293 0.0590
    S 0.2900 0.1800 0.1200 0.2200 0.1500 0.0500
    TiO2 2.6713 2.7261 2.4312 2.1588 1.9629 1.9781
    MnO 0.7093 0.6110 0.9923 0.1985 1.7725 0.8267
    P2O5 0.1000 0.0500 0.0400 0.0100 0.1500 0.1200
    Cr2O3 0.0100 0.0100 0.0200 0.0100 0.0600 0.0400
  • The capacity of the desulphurating agents was laboratory tested. The desulphurating agents were mixed with molten steel in a weight ratio of 1/1. The concentrations (W/W) of sulphur in the molten steel and in the desulphurating agent were measured by X fluorescence, before and after treating the steel with the desulphurating agent. The results are given in Table 5.
  • TABLE 5
    Before desulphuration After desulphuration
    Molten steel  0.07%  0.01%
    Desulphurating agent 0.022% 0.088%
  • The results given in Table 5 show that the sulphur concentration in the molten metal decreases by a factor of 7 after treatment with the desulphurating agent. These tests clearly confirm the advantages of the use of desulphurating agents according to the invention for decreasing the sulphur concentration of molten metal.

Claims (4)

1. A steel desulphurating agent, characterised in that it comprises, compared with the total weight of the agent:
at least 10% of SiO2,
at least 10% of C2S,
at least 35% of at least one calcium aluminate and optionally a calcium silico-aluminate, and
lime (CaO).
2. A steel desulphuration method according to claim 1 characterised in that the desulphurating agent and the lime are mixed together before being added to the steel.
3. A steel desulphuration method according to claim 1 characterised in that the weight ratio of the desulphurating agent to the lime varies from 1/0.5 to 1/2, and is preferably 1/1.
4. A steel desulphuration method according to claim 2 characterised in that the weight ratio of the desulphurating agent to the lime varies from 1/0.5 to 1/2, and is preferably 1/1.
US12/176,698 2003-12-24 2008-07-21 Steel desulphurating agent and use thereof in the desulphuration of steel Abandoned US20080302210A1 (en)

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US12/176,698 US20080302210A1 (en) 2003-12-24 2008-07-21 Steel desulphurating agent and use thereof in the desulphuration of steel

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FR0351202A FR2864551B1 (en) 2003-12-24 2003-12-24 DESULFURATION AGENT FOR STEELS AND ITS USE FOR THE DESULFURATION OF STEEL
FR03.51202 2003-12-24
PCT/FR2004/050754 WO2005064022A1 (en) 2003-12-24 2004-12-23 Steel desulphurating agent and use thereof in the desulphuration of steel
US58421406A 2006-06-23 2006-06-23
US12/176,698 US20080302210A1 (en) 2003-12-24 2008-07-21 Steel desulphurating agent and use thereof in the desulphuration of steel

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PCT/FR2004/050754 Division WO2005064022A1 (en) 2003-12-24 2004-12-23 Steel desulphurating agent and use thereof in the desulphuration of steel
US58421406A Division 2003-12-24 2006-06-23

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CN102876842A (en) * 2012-06-28 2013-01-16 辽宁天和科技股份有限公司 Premelting slugging desulfurizer taking 12 CaO*7Al2O3 and 3CaO*5Al2O3 as main phases
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CN104451032B (en) * 2015-01-06 2016-06-01 攀钢集团攀枝花钢铁研究院有限公司 Dephosphorization and desulfurization agent of a kind of half steel and its production and use
EP3670677A1 (en) * 2018-12-17 2020-06-24 S.A. Lhoist Recherche Et Developpement Process for manufacturing a slag conditioning agent for steel desulfurization
US12173376B2 (en) 2019-03-22 2024-12-24 Tata Steel Nederland Technology B.V. Method of manufacturing iron in a metallurgical vessel
CN112391510A (en) * 2020-10-29 2021-02-23 张家港宏昌钢板有限公司 Novel molten iron desulphurization process
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CN103738988B (en) * 2013-12-26 2015-07-29 张延大 Industrial waste residue resource is utilized to prepare the method for slag making sweetening agent

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US20070144306A1 (en) 2007-06-28
RU2006126687A (en) 2008-01-27
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