US20050109161A1 - Method for deep decarburisation of steel melts - Google Patents

Method for deep decarburisation of steel melts Download PDF

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Publication number
US20050109161A1
US20050109161A1 US10/505,610 US50561004A US2005109161A1 US 20050109161 A1 US20050109161 A1 US 20050109161A1 US 50561004 A US50561004 A US 50561004A US 2005109161 A1 US2005109161 A1 US 2005109161A1
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United States
Prior art keywords
oxygen
ini
steel
blow
bath
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Abandoned
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US10/505,610
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English (en)
Inventor
Eric Perrin
Francois Stovenot
Christian Schrade
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Primetals Technologies Germany GmbH
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VAI Fuchs GmbH
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Publication date
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Assigned to VAI FUCHS GMBH reassignment VAI FUCHS GMBH ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: PERRIN, ERIC, SCHRADE, CHRISTIAN, STOVENOT, FRANCOIS
Publication of US20050109161A1 publication Critical patent/US20050109161A1/en
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
    • C21C7/10—Handling in a vacuum
    • 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
    • C21C5/42—Constructional features of converters
    • C21C5/46—Details or accessories
    • C21C5/4606—Lances or injectors

Definitions

  • the invention relates to a method for decarburizing molten steel in an RH unit in which the steel is circulated out of a container into a vacuum container that has been placed under a vacuum and is returned into the container and by which oxygen or an oxygen-containing gas is blown onto the steel bath by means of blowing lances aimed at the steel bath contained in the vacuum container, the blowing lances being at a spacing from the top surface of the bath.
  • FIG. 1 An RH unit of this type is shown in FIG. 1 and comprises a container 1 on which a vacuum container 2 is disposed for carrying out the decarburization process, the vacuum container 2 dipping into the steel retained in the container via two submersion pipes 8 extending from the floor of the vacuum container.
  • the vacuum container 2 is connected at its branch stub 3 with a not-illustrated vacuum pump so that, as a result of the vacuum thus produced in the vacuum container 2 , a circulation of the steel is set up from the container 1 into the vacuum container 2 and back again into the container 1 .
  • This circulation can be supported by the introduction of a noble or inert gas such as argon via an injection device 4 into one of the submersion tubes 8 .
  • a blow lance 5 moveable from its disposition within the vacuum container 2 blows an oxygen spray 6 onto the bath top surface 7 of the steel bath present in the vacuum container 2 .
  • This blowing in of oxygen in the context of the RH process can be expedient for a variety of reasons.
  • a first reason is that the oxygen content that is dissolved in a charge of a melt retained in the container is not sufficient to produce the required decarburization in a natural way; the hereinafter described invention proceeds from this factual understanding. Further reasons can be found in that the temperature of the charge is too low so that a “surplus freshening” of the charge with oxygen results in more oxygen than is needed for the decarburization, whereby this additionally retained oxygen is typically bound together via aluminum, leading to a temperature increase, or that the decarburization should be accelerated, even in the event, as well, that sufficient oxygen for naturally occurring decarburization is available.
  • the typical blow processes are therefore so regulated that, with respect to a predetermined, fixedly set vacuum pressure, a not further specified amount of oxygen is blown onto the bath top surface until the required decarburization grade of the charge is reached.
  • the blow process is typically executed with a surplus of oxygen.
  • the blowing in of oxygen or, respectively, an oxygen-containing gas is, in particular, via post combustion, defined by the limiting conditions (CO+CO 2 ) ⁇ 5% of the exhaust gas amount as well as CO 2 /(CO+CO 2 ) ⁇ 30%.
  • the oxygen blowing in the context of the known process is not specified as a function of the metallurgical processes and the requirements.
  • the invention provides a solution to the challenge of providing a process for decarburization of molten steel by which reduced final carbon contents in the steel are achievable and by which the requirement for the oxygen to be blown in can be regulated to a lower level.
  • the invention takes into consideration the recognition that, due to the natural decarburization, the earliest possible introduction of oxygen into the steel melt should be effected in order, in connection with still high carbon contents in the steel melt, to effect the reaction of carbon to form CO and the removal in gas form from the melt, dissolved in the steel bath, due to a sufficient offering of oxygen, as a consequence of which the efficiency of the oxygen blowing in is increased.
  • the invention exploits, in this manner, the approach that the amount of oxygen required per unit weight of the charge, which takes into consideration the oxygen delivery mediums such as casting slags or steel bars retained in the vacuum container, can be tied in a unit-specific manner into the ratio of the starting carbon content of the melt to the starting oxygen content of the melt as known parameters and this amount of oxygen required per unit weight of the charge can thereby be available as the computational background for the oxygen amount to be blown in, so that the required total amount of oxygen, which takes into account the size G Ch of the charge to be subjected to decarburization as well as the final oxygen content O End Dec that is to be set up at the end of the blow process, can be determined and blown in.
  • a final oxygen content in the charge of between 200 ppm and 400 ppm, on average 300 ppm is set up.
  • the decarburization process is unnecessarily prolonged because too little oxygen is available in order to perform an efficient further decarburization.
  • the requirement for de-oxidation means for binding the oxygen in the melt, especially aluminum sharply increases, as the oxygen that still exists at the end of the decarburization process in the melt must be bound or combined.
  • the required de-oxidation means leads to quality problems that can have a disruptive effect upon pouring of the melt.
  • the starting pressure that is to be determined for the beginning of the blow process as a function of the starting carbon content of the melt is set such that the amount of oxygen to be blown in until reaching the requested post combustion, is introduced and, thus, to this extent, the decarburization that occurs by virtue of the oxygen blowing in before the beginning of a post combustion event that itself takes place in an oxygen surplus situation, is concluded.
  • the calculation of the amount of oxygen to be blown in is determined as a function of the starting carbon content and the starting oxygen content of the melt.
  • the oxygen amount to be blown in for the decarburization of a charge depends, as well, upon unit-specific circumstances, as the oxygen requirement necessary for the decarburization is, in part, taken care of via the process-dictated oxygen sources such as, for example, the steel bars retained in the vacuum container or available casting slags.
  • the charges having a starting carbon content C ini that is to be captured and a starting oxygen content O ini that is to be captured are subjected to decarburization via the blowing in of oxygen, whereby, via a probe withdrawn shortly before the end of the decarburization process, the oxygen content of the melt and the actual amount of oxygen that has been blown in up to this time point can be captured.
  • the desired final oxygen content is established at, for example, the amount of 300 ppm, whereby, with respect to each deviation above or below from the reference metric (300 ppm) of the actually measured oxygen content measured by the probe, the measured actual blown in oxygen amount to be converted into or, respectively, to be corrected into, a blown in amount Q ist (Nm 3 ) takes into account an end oxygen amount established as a reference metric.
  • the above-noted results are transmitted or converted into a coordinate system in which the abscissa sets forth the relationship C ini /O ini and the ordinate sets forth the actual blown in oxygen amount Q ist or, as the occasion arises, the oxygen amount corrected via conversion. At least 10 attempts should be performed in order to obtain the required precision.
  • the coefficients a, b, and c of the polynomial equation thus highlight the extent to which additional oxygen delivered via unit- or, respectively, process-, dictated oxygen sources are, in connection with decarburization conducted under vacuum condition, to be taken into account in establishing the actual oxygen requirement.
  • FIG. 3 A corresponding embodiment for the computation of the polynomial equation for an RH unit is shown in FIG. 3 , whereby, in the base-conformed RH unit, 8 test charges have been subjected to a decarburization process.
  • P start a limit pressure
  • the starting pressure P start for the release of the blow process is decidedly dependent upon the starting carbon content in the melt.
  • the unit-specific influence is, in addition to the inventive determination of the starting pressure for the blow process, to be determined via the running of test series comprising the capture of measurement data and is to be captured in the form of an approximation operation based upon such captured measurement data.
  • the coefficients a, b, and c of the polynomial equation take into account as well unit-specific parameters that dictate the CO peak.
  • FIG. 4 A further example is shown in FIG. 4 of the above-noted process course, whereby, in total, 12 charges have been run.
  • time period comprises the release of the automatic process, the running in of the lances, and the switching over from the protective gas operation to the oxygen blowing in operation.
  • the time delays can comprise, for example, up to 45 seconds. To the extent that these time delays can also be expressed as the difference in pressures between the cycle beginning and the beginning of the oxygen blowing in, this pressure difference should be taken into account in determining the P start .
  • the duration of the blow process is to be controlled via a monitoring of the post combustion, as the limit value for the end of the blow process is to be maintained at a post combustion rate of 30%, above which the blowing in of oxygen is no longer efficient in view of the metallurgical properties and the decarburization rate, whereby such blowing in of oxygen would, as occurs in the state of the art process, serve only to minimize the thermal loss of the steel subjected to decarburization in the vacuum container.
  • the blowing in of oxygen during the decarburization phase even with an optimal setting of the usual operational parameters, leads to a partial post combustion of the CO released from the steel bath.
  • the post combustion rate during the blowing in of oxygen is directly tied together to the release of CO from the melt.
  • the relationship of the post combustion increases with respect to the decarburization rate more or less, whereby it is disclosed that, during blowing in of oxygen, the post combustion increases in the event that the decarburization rate and, consequently, the release of CO, drops.
  • the optimal operation range for the blowing in of oxygen begins, in this connection, with the reaching of the limit pressure P start ; in this manner, the optimal operation range is extended with a higher starting carbon content of the melt.
  • the monitoring of the vacuum pressure occurring in the vacuum container, especially at the end of the blowing in of the oxygen can serve as an indication in order to maintain an optimal introduction of the oxygen with a minimized post combustion.
  • the pressure level within the vacuum container is dependent upon a defined suction performance of the vacuum pump together with the amount of the released gasses, whereby the CO content in the exhaust gas during the treatment process is dependent upon the starting carbon content of the melt.
  • the post combustion rate at a predetermined pressure is respectively higher, the lower the vacuum pressure within the vacuum container is set. This can be understood in that the lowering of the pressure tracks the increasingly reducing CO development.
  • the efficiency of the oxygen blow in process is further dependent upon the introduction of oxygen into the steel melt as, in contrast to the state of the art, wherein the post combustion of the freely released CO is effected above the level of the bath, instead the oxygen blown into the steel melt should be dissolved in order to react with the carbon dissolved in the bath.
  • the oxygen output that is, the relation of the oxygen dissolved in the melt bath to the oxygen blown onto the bath top surface—is strongly dependent, in individual cases, upon the level of the position of the blow lance in the RH container, the free top surface of the level of the melt—that is, the diameter of the RH container—and the circulation rate of the melt through the RH container.
  • this oxygen output can be set at approximately 80 to 90% so that the oxygen amount Q o 2 that has been calculated for the practical conversion of the melt in the blow process can be increased, taking into account the noted oxygen outputs.
  • the oxygen outputs are also influenced via the configuration of the blow jets which impact the bath top surface within a small top surface area with a compact oxygen spray at a high velocity so that the oxygen can penetrate sufficiently deeply during the movement of the steel melt through its circulation.
  • the blow jets which are configured as converging-diverging jets, produce a supersonic blow stream that, ideally, remains in the shape of a thin cylinder until contact with the bath top surface and cannot be fanned out.
  • the spacing of the blow jets from the steel bath level is also to be controlled, this spacing being, in a given known context, between 2.5 meters and 5.5 meters.
  • a blow jet with a working area that is variable via displacement of a position cone is provided in accordance with the invention as is schematically illustrated in FIG. 2 .
  • the position cone 11 is disposed in the position 1 , this means that a fully open jet cross section 12 is available with which the converging-diverging jet 10 operates according to the defined construction point.
  • the jet geometry is adjusted for a substantially reduced counter-pressure; in any event, the throughput via the jet is reduced, if the predetermined pressure remains constant.

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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)
US10/505,610 2002-02-22 2003-02-21 Method for deep decarburisation of steel melts Abandoned US20050109161A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP02004014 2002-02-22
EP02004014.3 2002-02-22
PCT/EP2003/001799 WO2003070990A1 (de) 2002-02-22 2003-02-21 Verfahren zur tiefentkohlung von stahlschmelzen

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US20050109161A1 true US20050109161A1 (en) 2005-05-26

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US (1) US20050109161A1 (ko)
EP (1) EP1476584A1 (ko)
JP (1) JP2005517812A (ko)
KR (1) KR100889073B1 (ko)
CN (1) CN1650035A (ko)
AU (1) AU2003210336A1 (ko)
BR (1) BRPI0307897A2 (ko)
WO (1) WO2003070990A1 (ko)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106979452A (zh) * 2017-04-20 2017-07-25 常州汇丰粉末冶金有限公司 含油轴承真空注油机及其注油方法

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101441187B (zh) * 2008-12-22 2012-02-08 辽宁科技学院 一种rh真空精炼顶枪喷粉测试装置及方法
JP6337681B2 (ja) * 2014-08-12 2018-06-06 新日鐵住金株式会社 溶鋼の減圧精錬方法
CN105463210A (zh) * 2015-12-26 2016-04-06 杨伟燕 一种高杂质铜精矿的冶炼方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4979983A (en) * 1988-06-21 1990-12-25 Kawasaki Steel Corporation Process for vacuum degassing and decarbonization with temperature drop compensating feature
US6156263A (en) * 1996-10-08 2000-12-05 Pohang Iron & Steel Co., Ltd. Molten steel smelting apparatus for producing ultra-low carbon steel

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2859709B2 (ja) * 1990-06-29 1999-02-24 川崎製鉄株式会社 減圧下における溶融金属の酸素吹錬方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4979983A (en) * 1988-06-21 1990-12-25 Kawasaki Steel Corporation Process for vacuum degassing and decarbonization with temperature drop compensating feature
US6156263A (en) * 1996-10-08 2000-12-05 Pohang Iron & Steel Co., Ltd. Molten steel smelting apparatus for producing ultra-low carbon steel

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106979452A (zh) * 2017-04-20 2017-07-25 常州汇丰粉末冶金有限公司 含油轴承真空注油机及其注油方法

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Publication number Publication date
BRPI0307897A2 (pt) 2016-06-21
KR100889073B1 (ko) 2009-03-17
AU2003210336A1 (en) 2003-09-09
EP1476584A1 (en) 2004-11-17
JP2005517812A (ja) 2005-06-16
WO2003070990A1 (de) 2003-08-28
CN1650035A (zh) 2005-08-03
KR20040091653A (ko) 2004-10-28

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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:PERRIN, ERIC;STOVENOT, FRANCOIS;SCHRADE, CHRISTIAN;REEL/FRAME:016230/0673

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