US3594155A - Method for dynamically controlling decarburization of steel - Google Patents

Method for dynamically controlling decarburization of steel Download PDF

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Publication number
US3594155A
US3594155A US771752A US3594155DA US3594155A US 3594155 A US3594155 A US 3594155A US 771752 A US771752 A US 771752A US 3594155D A US3594155D A US 3594155DA US 3594155 A US3594155 A US 3594155A
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oxygen
carbon
gas
rate
input
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Sundaresan Ramachandran
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Pittsburgh National Bank
Allegheny Ludlum Steel Corp
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Allegheny Ludlum Steel Corp
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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
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/30—Regulating or controlling the blowing
    • 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

Definitions

  • This invention relates to decarburizing steel. More particularly, the invention relates to an improvement in the method of decarburizing molten steel wherein oxidizing material is introduced to the steel to react with carbon contained therein. Still more particularly the improvement in accordance with the invention comprises a dynamic method of controlling decarburization of molten steel by measuring the rates of carbon removal from the molten steel, oxidizer input rate, continuously maintaining a balance between the two rates by adjusting the carbonoxygen reaction rate and/ or oxidizer input rate in response to the measured rates.
  • the term balance as used herein means adjusting the relationship between the rates of carbon removal from the steel and oxidizer input to achieve any desired result. For example, avoidance of oxidation of expensive alloying elements is achieved by maintaining a balance such that the rate of oxidizer input is never greater than the rate of carbon removal.
  • Decarburizing is an essential part of present day steel making practices and more and more commonly is performed by blowing pure oxygen into the melt contained in a vessel or furnace, e.g. electric furnace, open hearth, basic oxygen furnace (BOF), etc.
  • a vessel or furnace e.g. electric furnace, open hearth, basic oxygen furnace (BOF), etc.
  • This so called oxygen steel making now is practiced in both the manufacture of plain carbon steel and alloy steel.
  • the oxygen efficiency for decarburization processes of the type described can be defined as:
  • Percent oxygen efliciency (oxygen to the decarburization reaction+net oxygen to the system) 100 This efficiency figure can be used to check how effectively the oxygen is used to remove carbon. Although the prime purpose of oxygen is the removal of carbon, it will also oxidize silicon, phosphorus and, if not properly controlled, other metallic values. It is apparent that to make best use of oxygen, control of the factors affecting oxygen eiiciency is necessary.
  • the present invention which is useful in both vacuum and atmospheric pressure decarburization and for alloy steel as well as plain carbon steel, involves dynamically balancing the rate of oxygen input and the rate of carbon removal and adjustment of the carbon removal rate and/ or oxygen input rate to achieve any particular maximum oxygen eliciency or any other desired result.
  • the carbon removal rate can be determined by any of several ways.
  • the composition of the bath can be continuously sampled and analyzed for carbon to determine the quantity of carbon removed per unit of time.
  • Another, and presently preferred method is to monitor the exhaust gases from the reaction vessel and measure the total ow and the amounts of carbon monoxide and carbon dioxide in the off-gas stream such as by the techniques described below. Analyses of off-gas composition and measurement of flow can be used to determine the rate of carbon removal almost instantaneously.
  • This rate of carbon removal which can be expressed conveniently as pounds per minute, is equal to the volume of carbon monoxide and carbon dioxide leaving the furnace at any given moment multiplied by a conversion factor. Set forth in an equation, this relationship is expressed as follows:
  • X atomic weight of carbon
  • 859 conversion factor based on fact 359 cubic feet of a gas contains a mole of gas
  • the volume of equivalent oxygen that has reacted with this carbon at any time during the process may be obtained by the following equation which gives the rate at which oxygen is consumed by the carbon. For practical purposes this consumption rate is expressed as cubic feet per minute to correspond to the ilow rate of the off-gases.
  • Whether the oxygen supplied to the vessel for decarburization is being consumed by the carbon in the melt or whether metallic elements are being oxodized can be determined by noting whether the rate of oxygen consumed by the carbon is greater, equal to or less than the rate of oxygen input. Adjustment of the oxygen input can be made in response to the measured rates of carbon removal and oxygen consumption. By continuously adjusting the variables responsible for the carbon-oxygen reaction and/or the flow rate of oxygen into the reaction vessel the decarburization reaction may be continuously, i.e. dynamically, balanced.
  • the oxygen input rate and/or the carbon removal rate can be varied in accordance with the measured rates of carbon removal and oxygen consumption by varying the oxygen etliciency which amounts to altering the nate of the carbon-oxygen reaction. This can be varied by several means, such as:
  • Change in the oxygen input rate may be accomplished by simply reducing the flow rate of oxygen when pure oxygen is used. In this way, the mixing caused by the input of the gas is reduced and the oxygen consumption rate is also reduced. However, if the total gas ow rate is maintained and a nonreactive gas, e.g. a diluent, is substituted for oxygen, the rate of oxygen reaction with carbon is not lowered.
  • the oxygen input rate can be varied by including a diluent gas with oxygen, but maintaining the same total gas flow rate, ⁇ without reducing the rate of oxygen reaction with carbon.
  • Diluent gases 3 which may be used other than inert gases are, for example, hydrogen and carbon monoxide as well as steam or carbon dioxide. Carbon dioxide and carbon monoxide do not displace the equilibrium of the carbon-oxygen reaction in any way.
  • the amount of oxidizing material required for carbon removal in an input gas stream can be calculated using the gaseous composition, the mass flow rate and the stoichiometry of the reactions within the steel melt.
  • the reaction of these oxidizing gases with carbon in the melt can be written as:
  • the rate of carbon removal must be corrected for the carbon input to the system. This correction can be obtained by measuring the volumetric rate at which carbon is fed into the system as carbon monoxide or carbon dioxide.
  • the carbon input can be expressed in terms of oxygen equivalent as follows:
  • Carbon input volumetric rate in equivalent oxygen units
  • ⁇ volumetric flow rate of carbon monoxide and carbon dioxide in input gas
  • the products of reaction specically the amount of oxidizing material combined with carbon in the melt.
  • One technique of the many that may be used, is to determine the composition of the exhaust gases and the exhaust gas ow rate. It may be assumed that the exhaust gases contain all of the inert or diluent gases and the gaseous products of reaction with the melt. In addition, the exhaust gases will also include the unreacted portions of the input gas and other gases entering the system.
  • the reaction products can be viewed as:
  • the amount of oxygen needed for decarburization can be calculated from the composition and oW rate of the exhaust gas.
  • the flow rate from the exhaust gas can either be estimated by means of a calibrated orifice plate or can be calculated using a tracer gas technique. In the latter, a tracer gas at a known flow rate can be mixed completely with the exhaust gas and the flow rate of the exhaust gas can be calculated.
  • an inert gas such as argon
  • the inert gas e.g. argon
  • the volumetric ow rate obtained as follows:
  • volumetric'ow rate of exhaust gas lOOXvolurnetric flow rate of input argon Volume percent argon in output str earn The presence of air leaks will affect the determination of volume flow rate when argon is used since air contains on the order of 0.94% argon by volume. A correction can be made where argon concentrations added by the air is discounted.
  • -volumetric exhaust gas ow rate (1/2 volume percent H2O-l-1/z volume per cent COz-i-volume percent O2 in exhaust gases)
  • the dynamic balance between the actual total oxygen input rate and the corrected rate of oxygen required for carbon removal can be performed Iby comparing the input and output rates.
  • the input rate can be determined according to the following expression:
  • the oxygen input rate should account for both the deliberate input oxygen as well as accidental and incidental sources of oxygen such as air or water leaks. Only the two variables, the total oxidizer input rate and the corrected rate of oxygen required for carbon removal are determined. These values can be compared to determine whether the desired balance is maintained.
  • the rate at which silicon, aluminum, etc., are being oxidized can be measured and included in determining the oxygen input so that sufficient oxygen is provided to accomplish decarburization at the desired rate as well as oxidation of the elements, e.g. silicon, aluminum, also intended to lbe removed.
  • the silicon loss rate can be estimated by noting the difference between the rate of input of the oxidizing material and the corrected oxygen rate required Ifor carbon removal.
  • the total input rate of oxidizing material may be compared with the estimated oxygen required for carbon removal. 1f the oxygen input rate is greater than that required for the carbon removal, it can b e concluded that metallic oxidation is occurring.
  • one or a combination of the following practices may be used.
  • the diluent could be one or more of the inert gases such as argon, steam, carbon monoxide or carbon dioxide).
  • the essential difference between decarburizing alloy steels and decarburizing low carbon steels is that the iron oxide buildup in the slag in plain carbon steel is desirable for phosphorus removal.
  • the efliciency of carbon removal may lbe desirably low at the start and then improved as the carbon content is lowered. It is only near the end of the process that elimination of iron loss would be particularly desirable.
  • the efliciency of carbon removal can be controlled by varying lance height or by controlling the rate of additions of lime, ore, etc. Near the end of decarburization the use of carbon monoxide and oxygen or even carbon dioxide and oxygen may be preferred.
  • Another technique for determining the occurence of metallic oxidation is lby the ratio f inert gases to Carbon-containing gases in the exhaust stream. For example, where mixtures of argon and oxygen are used for decarburization, it may be assumed that all of the input oxygen will react with the carbon and the expected ratio of argon to carbon-bearing gases will be as follows:
  • the embodiments of the present invention based on the maintenance of a dynamic balance between the input oxygen and the off-gases from the decarburization process, provide techniques for the accomplishment of decarburization without chromium loss.
  • the application of the invention requires close regulation of, among others, the following parameters:
  • Input gas flow rates can be determined by such means as flow-meters, orifice plates, etc.
  • the composition of the input gases can be generally obtained with gas-analyzing devices such as a mass spectrometer.
  • gas-analyzing devices such as a mass spectrometer.
  • techniques are available for the determination of olf-gas compositions.
  • One such technique, which generates a continuous analysis, is the subject of several French patents [Nos 1,309,212 (Oct. 8, 1962); 1,325,024 (Mar. 18, 1963)]. The method has been published in the Journal of Metals, June 1964, p. 508, and is generally familiar to steel making artisans. It involves continuous determination of the carbon monoxide and carbon dioxide contents of the effluent gases from the rening vessel.
  • the process of the present invention employs continuous inputand off-gas analysis for the purpose of indicating the eiciency of oxygen consumption by melt carbon.
  • the carbon-oxygen reaction occurs in preference to metallic oxidation if the bath carbon is equal to or above the equilibrium level for the system in question, and if the carbon available for oxidation is at least stoichiometrically balanced by the injected oxidizers.
  • the oxygen equivalent of the effluent gases is compared with the injected and entrained gaseous oxygen.
  • a lower value in the effluent stream implies that a proportion of the supplied oxidizers is consumed for metallic oxidation, with only a fraction reacting with melt carbon to yield the analyzed carbon oxides.
  • any imbalance is immediately detected and can be corrected by altering one or more of the factors listed previously in a manner to be elaborated upon in the following discussion.
  • the process of dynamically-controlled mixed gas decarburization of steels can be suitably performed in a reactor such as a BOF or other container equipped with a means for input-gas and off-gas measurements.
  • a reactor such as a BOF or other container equipped with a means for input-gas and off-gas measurements.
  • the molten steel is tapped into this vessel and held at a known temperature.
  • FIG. I is an illustration of a typical process employing mixed gases. Prior to its entry into the vessel, the
  • the example illustrated in FIG. I is a process involving stepwise reductions in the oxygen content of the injected gas stream.
  • a continuous curve is obtained.
  • Such a curve is adaptable to suitable control devices to supply mixed gases according to the specified schedule.
  • the process according to this schedule is the most efficient since it involves the use of the minimum quantity of inert gases for the amount of carbon removed, and also results in the minimum process time.
  • FIG. l1 A pressure reduction sequence along with the decarburization bath at 3000 F. is illustrated in FIG. l1 for a one ton bath of 18% chromium steel employing 30 s.c.f.m. of oxygen.
  • the scheme illustrated assumes that the gas pumping capacity of the evacuation equipment is unlimited at all pressure ranges. If the pumping capacity of the system involved decreases as the pressure within the vacuum chamber decreases, a continuous reduction of the decarburizing gas flow rate in accordance with the capacity of the pumps is required.
  • the bath temperature can be continuously monitored with the aid of such devices as thermocouples or optical pyrometers.
  • the olf-gas analysis includes the additional carbon oxides due to the heat source. The proportion of this component in the off-gases is computed from a knowledge of the combustion rate on the bath.
  • FIG. III illustrates a decarburization process, for a one ton 18% chromium heat, decarburized with oxygen at 30 s.c.f.m., and which employs the concept of dynamic control via temperature variations.
  • an imbalance between input and output oxygen is indicated by the gas analyzing devices.
  • Such irnbalance denoted by an oxygen utilization efliciency of less than 100%, is then off-set by an increase in melt temperature accomplished by one or more of the means previously indicated.
  • means for varying gas-metal contact area include (1) sub-surface gas injection resulting in the generation of small gas bubbles which furnish a large surface area, (2) mechanical or (3) induction stirring to continuously expose fresh metal surface to the decarburizing gases, etc.
  • Percent carbon removal efiieieney Rate of oxygen consumption by carbon 100 Rate of total input oxygen To avoid any metallic loss, the carbon removal efiiciency must be equal to or greater than 100%. If some metal loss is tolerable, then this factor can be some predetermined lower value, such as -85%.
  • oxidizing material consisting essentially of oxygen and oxygen-containing gas is introduced to steel to react with carbon contained therein
  • controlling decarburization to substantially preclude undesirable loss of metal values resulting from fluctuating thermodynamic conditions by supplying said oxidizing material, measuring the rate of carbon removal from the molten metal, measuring the rate of oxidizing input, and continuously maintaining a kinetic balance between the aforementioned rates by at least one of the following: (l) supplying said oxidizing material in admixture with diluent gas and substantially continuously monitoring and adjusting as necessary the proportions of oxidizing material and diluent gas and (2) substantially continuously monitoring and adjusting as necessary the ambient pressure under which decarburization is occurring.
  • diluent gas is at least one from the group consisting of inert gases, hydrogen, carbon monoxide, carbon dioxide and steam.

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  • 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)
US771752A 1968-10-30 1968-10-30 Method for dynamically controlling decarburization of steel Expired - Lifetime US3594155A (en)

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AT (1) AT315883B (de)
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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3751242A (en) * 1969-04-02 1973-08-07 Eisenwerk Gmbh Sulzbach Rosenb Process for making chrimium alloys
US3773496A (en) * 1970-02-18 1973-11-20 Maximilianshuette Eisenwerk Process for producing chrome steels and a converter for carrying out the process
US3798025A (en) * 1971-12-29 1974-03-19 Allegheny Ludlum Ind Inc Vacuum decarburization in rh and dh type degassing systems
US3816720A (en) * 1971-11-01 1974-06-11 Union Carbide Corp Process for the decarburization of molten metal
US3847593A (en) * 1971-07-13 1974-11-12 Centro Speriment Metallurg Process for refining metals, in particular liquid pig iron, in oxygen converters with continuous control of the operative procedure
US3920447A (en) * 1972-02-28 1975-11-18 Pennsylvania Engineering Corp Steel production method
US4113469A (en) * 1976-04-30 1978-09-12 British Steel Corporation Refining molten metal
US4148629A (en) * 1976-08-04 1979-04-10 Vereinigte Osterreichische Eisen- Und Stahlwerk-Alpine Montan Aktiengesellschaft Process for controlling a steel refining process for steels having a carbon content within the range of 0.1 to 0.8 % by weight
US4427443A (en) 1979-11-28 1984-01-24 Etude Et Developpement En Metallurgie Process and apparatus for automating a vacuum degasification cycle for metal alloys
US5417739A (en) * 1993-12-30 1995-05-23 Ltv Steel Company, Inc. Method of making high nitrogen content steel
US5830259A (en) * 1996-06-25 1998-11-03 Ltv Steel Company, Inc. Preventing skull accumulation on a steelmaking lance
US5865876A (en) * 1995-06-07 1999-02-02 Ltv Steel Company, Inc. Multipurpose lance
US5885323A (en) * 1997-04-25 1999-03-23 Ltv Steel Company, Inc. Foamy slag process using multi-circuit lance
WO2002075003A2 (en) * 2001-03-21 2002-09-26 Thyssenkrupp Acciai Speciali Terni S.P.A. Argon oxygen decarburisation converter control method and system
US6923843B1 (en) 2001-11-13 2005-08-02 Nupro Corporation Method for oxygen injection in metallurgical process requiring variable oxygen feed rate

Families Citing this family (12)

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Publication number Priority date Publication date Assignee Title
US3754895A (en) * 1971-01-27 1973-08-28 Allegheny Ludlum Ind Inc Process for decarburization of steels
DE2310240C2 (de) * 1973-03-01 1988-03-03 Fried. Krupp Gmbh, 4300 Essen Verfahren zur Überwachung und Regelung der Entkohlung beim Roheisen- Frischen und Vorrichtung zur Durchführung des Verfahrens
US4149877A (en) * 1974-06-27 1979-04-17 Centre De Recherches Metallurgiques, Centrum Voor Research In De Metallurgie Controlling pig iron refining
US4130419A (en) * 1977-03-11 1978-12-19 Linde Ag Process for the purification, modification and heating of a cast-iron melt
JPS5442324A (en) * 1977-09-10 1979-04-04 Nisshin Steel Co Ltd Control procedure of steel making process using mass spectrometer
JPS5442323A (en) * 1977-09-10 1979-04-04 Nisshin Steel Co Ltd Control procedure of steel making process using mass spectormeter
JPS569319A (en) * 1979-07-05 1981-01-30 Nippon Steel Corp Vacuum treatment controller for molten steel
US4260415A (en) * 1979-12-12 1981-04-07 Allegheny Ludlum Steel Corporation Decarburizing molten metal
DE3601337A1 (de) * 1986-01-16 1987-07-23 Mannesmann Ag Verfahren zur herstellung hochlegierter staehle im sauerstoffblaskonverter
DE3706742A1 (de) * 1987-02-28 1988-09-08 Salzgitter Peine Stahlwerke Verfahren und vorrichtung zur entgasungsbehandlung einer stahlschmelze in einer vakuumanlage
EP0328677B1 (de) * 1987-08-13 1994-06-22 Nkk Corporation Ofen und verfahren zur reduktion eines chromvorproduktes durch schmelzen
WO1989002478A1 (en) * 1987-09-10 1989-03-23 Nkk Corporation Process for producing molten stainless steel

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US3252790A (en) * 1956-06-27 1966-05-24 Union Carbide Corp Preparation of metals and alloys
BE610265A (de) * 1960-11-18
BE609880A (de) * 1960-11-18
FR1444050A (fr) * 1964-05-13 1966-07-01 Beteiligungs & Patentverw Gmbh Procédé de réglage automatique du processus de soufflage d'oxygène
FR1466041A (fr) * 1965-02-03 1967-01-13 Dynamit Nobel Ag Procédé de préparation d'acétals de copolymères renfermant des groupes polyhydroxyméthylène ou hydroxyméthylène
FR1486820A (fr) * 1966-07-15 1967-06-30 Leeds & Northrup Co Procédé et appareil pour la commande d'un four basique à oxygène pour la production de l'acier
LU52976A1 (de) * 1967-02-13 1968-10-09

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3751242A (en) * 1969-04-02 1973-08-07 Eisenwerk Gmbh Sulzbach Rosenb Process for making chrimium alloys
US3773496A (en) * 1970-02-18 1973-11-20 Maximilianshuette Eisenwerk Process for producing chrome steels and a converter for carrying out the process
US3847593A (en) * 1971-07-13 1974-11-12 Centro Speriment Metallurg Process for refining metals, in particular liquid pig iron, in oxygen converters with continuous control of the operative procedure
US3816720A (en) * 1971-11-01 1974-06-11 Union Carbide Corp Process for the decarburization of molten metal
US3798025A (en) * 1971-12-29 1974-03-19 Allegheny Ludlum Ind Inc Vacuum decarburization in rh and dh type degassing systems
US3920447A (en) * 1972-02-28 1975-11-18 Pennsylvania Engineering Corp Steel production method
US4113469A (en) * 1976-04-30 1978-09-12 British Steel Corporation Refining molten metal
US4148629A (en) * 1976-08-04 1979-04-10 Vereinigte Osterreichische Eisen- Und Stahlwerk-Alpine Montan Aktiengesellschaft Process for controlling a steel refining process for steels having a carbon content within the range of 0.1 to 0.8 % by weight
US4427443A (en) 1979-11-28 1984-01-24 Etude Et Developpement En Metallurgie Process and apparatus for automating a vacuum degasification cycle for metal alloys
US5417739A (en) * 1993-12-30 1995-05-23 Ltv Steel Company, Inc. Method of making high nitrogen content steel
US5865876A (en) * 1995-06-07 1999-02-02 Ltv Steel Company, Inc. Multipurpose lance
US5830259A (en) * 1996-06-25 1998-11-03 Ltv Steel Company, Inc. Preventing skull accumulation on a steelmaking lance
US5885323A (en) * 1997-04-25 1999-03-23 Ltv Steel Company, Inc. Foamy slag process using multi-circuit lance
WO2002075003A2 (en) * 2001-03-21 2002-09-26 Thyssenkrupp Acciai Speciali Terni S.P.A. Argon oxygen decarburisation converter control method and system
WO2002075003A3 (en) * 2001-03-21 2003-02-13 Thyssenkrupp Acciai Speciali Argon oxygen decarburisation converter control method and system
US6923843B1 (en) 2001-11-13 2005-08-02 Nupro Corporation Method for oxygen injection in metallurgical process requiring variable oxygen feed rate

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AT315883B (de) 1974-06-10
FR2021885B1 (de) 1974-08-09
DE1953888C3 (de) 1981-04-16
DE1953888A1 (de) 1970-05-06
DE1953888B2 (de) 1980-09-04
GB1283086A (en) 1972-07-26
FR2021885A1 (de) 1970-07-24
BE741027A (de) 1970-04-30
US3748122A (en) 1973-07-24

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