NO742347L - - Google Patents
Info
- Publication number
- NO742347L NO742347L NO742347A NO742347A NO742347L NO 742347 L NO742347 L NO 742347L NO 742347 A NO742347 A NO 742347A NO 742347 A NO742347 A NO 742347A NO 742347 L NO742347 L NO 742347L
- Authority
- NO
- Norway
- Prior art keywords
- decarburization
- melt
- cog
- flow rate
- blowing
- Prior art date
Links
- 238000005261 decarburization Methods 0.000 claims description 62
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 38
- 229910052799 carbon Inorganic materials 0.000 claims description 35
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 34
- 238000007664 blowing Methods 0.000 claims description 28
- 229910052760 oxygen Inorganic materials 0.000 claims description 26
- 239000001301 oxygen Substances 0.000 claims description 26
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 24
- 239000007789 gas Substances 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 24
- 229910052751 metal Inorganic materials 0.000 claims description 22
- 230000000694 effects Effects 0.000 claims description 21
- 239000002184 metal Substances 0.000 claims description 21
- 229910052786 argon Inorganic materials 0.000 claims description 19
- 239000000155 melt Substances 0.000 claims description 16
- 239000000161 steel melt Substances 0.000 claims description 16
- 239000011261 inert gas Substances 0.000 claims description 12
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 11
- 229910000831 Steel Inorganic materials 0.000 claims description 10
- 229910052804 chromium Inorganic materials 0.000 claims description 10
- 239000011651 chromium Substances 0.000 claims description 10
- 239000010959 steel Substances 0.000 claims description 10
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 9
- 238000003723 Smelting Methods 0.000 claims description 6
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 4
- 239000001569 carbon dioxide Substances 0.000 claims description 3
- 229910052743 krypton Inorganic materials 0.000 claims description 3
- 239000001307 helium Substances 0.000 claims description 2
- 229910052734 helium Inorganic materials 0.000 claims description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 2
- DNNSSWSSYDEUBZ-UHFFFAOYSA-N krypton atom Chemical compound [Kr] DNNSSWSSYDEUBZ-UHFFFAOYSA-N 0.000 claims description 2
- 229910052754 neon Inorganic materials 0.000 claims description 2
- GKAOGPIIYCISHV-UHFFFAOYSA-N neon atom Chemical compound [Ne] GKAOGPIIYCISHV-UHFFFAOYSA-N 0.000 claims description 2
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 229910052724 xenon Inorganic materials 0.000 claims description 2
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 claims description 2
- 239000000203 mixture Substances 0.000 description 19
- 238000007670 refining Methods 0.000 description 10
- 229910001220 stainless steel Inorganic materials 0.000 description 9
- 238000007254 oxidation reaction Methods 0.000 description 8
- 239000010935 stainless steel Substances 0.000 description 8
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 7
- 229910002091 carbon monoxide Inorganic materials 0.000 description 7
- 230000003647 oxidation Effects 0.000 description 7
- 241001062472 Stokellia anisodon Species 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 6
- 239000000956 alloy Substances 0.000 description 6
- 238000001816 cooling Methods 0.000 description 3
- 239000002893 slag Substances 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- MEUAVGJWGDPTLF-UHFFFAOYSA-N 4-(5-benzenesulfonylamino-1-methyl-1h-benzoimidazol-2-ylmethyl)-benzamidine Chemical compound N=1C2=CC(NS(=O)(=O)C=3C=CC=CC=3)=CC=C2N(C)C=1CC1=CC=C(C(N)=N)C=C1 MEUAVGJWGDPTLF-UHFFFAOYSA-N 0.000 description 1
- 229910001021 Ferroalloy Inorganic materials 0.000 description 1
- 229910000604 Ferrochrome Inorganic materials 0.000 description 1
- VVTSZOCINPYFDP-UHFFFAOYSA-N [O].[Ar] Chemical compound [O].[Ar] VVTSZOCINPYFDP-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- -1 aluminum metals Chemical class 0.000 description 1
- 229910002090 carbon oxide Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- FXNGWBDIVIGISM-UHFFFAOYSA-N methylidynechromium Chemical compound [Cr]#[C] FXNGWBDIVIGISM-UHFFFAOYSA-N 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910001256 stainless steel alloy Inorganic materials 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
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
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Description
Bruk av COg ved argon/oksygen-raffinering av metallsmelter. Use of COg in argon/oxygen refining of metal melts.
Oppfinnelsen angår generelt en fremgangsmåte for avkullingThe invention generally relates to a method for decarburization
av metaller og legeringer, og mer spesielt, forbedringer ved argon/ oksygen-avkulling av rustfrie stål-legeringer. of metals and alloys, and more particularly, improvements in argon/oxygen decarburization of stainless steel alloys.
Før o<p>pfinnelsen av argon/oksygen-avkullingen (i det følgende kalt,,AOD"-prosessen (argon-oxygen-decarburization)), var det vanlig praksis ved fremstilling av rustfrie ståltyper å smelte en legering inneholdende mye lavere krom-prosent enn spesifisert for sluttstålet, derpå avkulle og til slutt øke krominnholdet til ønsket nivå ved tilsetning av krom vanligvis i form av ferro-krom med lavt karbon-innhold. Denne fremgangsmåten ble fulgt fordi rustfrie stålsmelter inneholdende angitt krom-innhold ikke kunne avkulles uten kraftig Before the invention of the argon/oxygen decarburization (hereafter referred to as the "AOD" (argon-oxygen-decarburization) process), it was common practice in the manufacture of stainless steels to melt an alloy containing much lower chromium percent than specified for the final steel, then decarburize and finally increase the chromium content to the desired level by adding chromium usually in the form of low-carbon ferro-chromium This procedure was followed because stainless steel melts containing the specified chromium content could not be decarburized without heavy
oksydasjon av kromet.oxidation of the chromium.
AOD-prosessen er en duplex-prosess, særlig nyttig for raffinering av rustfritt stål- uten større tap av krom. Den grunn-leggende AOD-prosess er beskrevet i US-patent 3.252.790 og som en forbedring i forbindelse med programmert blåsing beskrevet i US-patent 3.O46.IO7. Metoden består i å smelte legeringen (i det vesentlige med ønsket sammensetning av metaller) i en bueovn, og overføre metallsmelten etter avslagging til en raffineringsbeholder hvor legeringen avkulles ved neddykket gjennomblåsing med inert-gass-oksygenblanding (i vanlig praksis oftest argon-oksygen-blanding), idet argonet foreligger for å redusere karbon-monoksydets partialtrykk i gassen i kontakt med smeiten. Derpå blir det smeltede metall redusert, sluttbehandlet og tappet i en støpeøse. En egnet raffineringsbeholder er beskrevet i US-patent 3*724»830. The AOD process is a duplex process, particularly useful for refining stainless steel - without major loss of chromium. The basic AOD process is described in US Patent 3,252,790 and as an improvement in connection with programmed blowing described in US Patent 3,046,107. The method consists of melting the alloy (essentially with the desired composition of metals) in an arc furnace, and transferring the molten metal after slag to a refining container where the alloy is decarburized by submerged blowing through with an inert-gas-oxygen mixture (in common practice most often an argon-oxygen mixture) ), as the argon is present to reduce the carbon monoxide partial pressure in the gas in contact with the smelt. The molten metal is then reduced, finished and poured into a ladle. A suitable refining vessel is described in US Patent 3,724,830.
Selv om innføringen av en blanding av inert-gasser og oksygen i den rustfrie stålsmelte befordrer avkulling i forhold til oksydasjon av metallelementene i smeiten, vil ikke fremgangsmåten helt fullstendig utelukke metallisk oksydas.ion. Det stadige nærvær av metalloksyder i slagget viser at en vesentlig del av oksygenet reagerer med andre forbindelser i smeiten enn karbon. Ved en typisk AOD-avkulling er karbonfjernings-effekten, nemlig den prosentvise mengde totalt oksygen innført i smeiten som forbinder seg med karbon, på mellom 75% til under 10%, avhengig av driftsbetingelsene. Det resulterende metalltap kan gjenvinnes bare ved å tilsette reduksjons-midler som f.eks. silisium eller aluminium-metaller til slagget etter ferdig avkulling av smeiten. Although the introduction of a mixture of inert gases and oxygen into the stainless steel melt promotes decarburization in relation to oxidation of the metal elements in the melt, the method will not completely exclude metallic oxidation. The constant presence of metal oxides in the slag shows that a significant part of the oxygen reacts with compounds in the smelting other than carbon. In a typical AOD decarburization, the carbon removal efficiency, namely the percentage amount of total oxygen introduced into the melt that combines with carbon, is between 75% to less than 10%, depending on the operating conditions. The resulting metal loss can be recovered only by adding reducing agents such as e.g. silicon or aluminum metals to the slag after complete decarburization of the smelting.
Et annet forbedrings-område i forbindelse med foreliggende AOD-praksis består i å innkorte den totale behandlingstid. De kjem-iske reaksjoner under stålraffinering er for det meste oksydasjons-reaksjoner som skaper varme, og slik at metallbadets temperatur etableres på et punkt hvor varmen som dannes i badet er lik varmen som tapes fra raffineringsbeh&lderen ved stråling og konveksjon. Another area of improvement in connection with the present AOD practice consists in shortening the total processing time. The chemical reactions during steel refining are mostly oxidation reactions that create heat, so that the temperature of the metal bath is established at a point where the heat generated in the bath is equal to the heat lost from the refining vessel by radiation and convection.
Jo hurtigere det således skapes varme i legeringen, jo høyere blir bad-températuren ved varmelikevekt. Følgelig, kan avkullingshastig-heten økes ved å øke gassens strømningshastigheter, men bare på bekostning av høyere bad-temperatur og øket slitasje av ovnenes ild-faste foring. Følgelig, er det et behov for å øke avkullingshastig-heten under AOD-prosessen uten å overstige en bestemt temperatur-grense, idet temperaturer over dette, generelt ca. 1700°C, i vesentlig The faster heat is thus created in the alloy, the higher the bath temperature will be at thermal equilibrium. Consequently, the decarburization rate can be increased by increasing the gas flow rates, but only at the expense of higher bath temperature and increased wear of the furnace's refractory lining. Consequently, there is a need to increase the decarburization rate during the AOD process without exceeding a certain temperature limit, since temperatures above this, generally approx. 1700°C, essentially
grad vil innskrenke foringens levetid.degree will reduce the life of the liner.
Periodevis tilsetning av skrapstål som kjølemiddel er en vanlig metode til å holde bad-temperaturen innenfor ønsket driftsområde. Imidlertid er forsyningsproblemene ved tilførsel av skrapstål til ovnen på det nøyaktige tidspunkt og vanskeligheten med å holde rustfritt stål separert etter type så store at dette ofte utelukker metoden. Videre, avkjøles?skrapjernet metallbadet dis-kontinuerlig, slik at tilsetning av skrap med påfølgende plutselig fall i legeringstemperaturen ofte forårsaker sterk metalloksydas.ion i den tid badet er avkjølt til under effektiv avkullingstemperatur. Periodic addition of scrap steel as a coolant is a common method of keeping the bath temperature within the desired operating range. However, the supply problems of supplying scrap steel to the furnace at the precise time and the difficulty of keeping stainless steel separated by type are so great that this often precludes the method. Furthermore, the scrap iron cools the metal bath discontinuously, so that the addition of scrap with subsequent sudden drop in the alloy temperature often causes strong metal oxidation during the time the bath is cooled below the effective decarburization temperature.
Det er derfor klart at en AOD-raffineringsprosess som ville nedkorte avkullings-tiden ved å øke gass-strømningshastigheten og avkullings-effekten samtidig som man kunne regulere bad-temperaturen til innenfor de riktige grenser, er en vesentlig forbedring ved vanlig AOD-praksis. It is therefore clear that an AOD refining process that would shorten the decarburization time by increasing the gas flow rate and the decarburization effect while at the same time being able to regulate the bath temperature to within the correct limits, is a significant improvement over normal AOD practice.
Det er følgelig en hensikt med oppfinnelsen å forbedre avkullings-eff ekt en ved argon/oksygen-avkulling av rustfritt stål. Et annet mål med oppfinnelsen er å øke hastigheten av argon/oksygen-avkullingen ved å muliggjøre høyere gass-strømningshastigheter under behandlingen uten å øke ovnsslitasjen. It is therefore a purpose of the invention to improve the decarburization effect of argon/oxygen decarburization of stainless steel. Another object of the invention is to increase the rate of argon/oxygen decarburization by enabling higher gas flow rates during treatment without increasing furnace wear.
Ennå en hensikt med oppfinnelsen er å fremlegge en fremgangsmåte for kontinuerlig avkjøling av rustfrie stål-smelter ved argon/oksygen-raffinéring, slik at metallbade'ts temperatur på enkel måte holdes innenfor ønsket driftsområde. Another purpose of the invention is to present a method for continuous cooling of stainless steel melts by argon/oxygen refining, so that the temperature of the metal bath is easily kept within the desired operating range.
Ovenstående hensikter og trekk med oppfinnelsen vil klart oppfattes av fagfolk og oppnås i hento ld til foreliggende oppfinnelse gjennom en utførelse som består i: ved en fremgangsmåte for avkulling av krom-holdig smeltet stål karakteriseres metoden ved dykk-.innblåsing av oksygen og minst In inert-gass valgt blant gruppen helium, neon, krypton, argon, xenon og nitrogen, gjennom stålsmelten, hvorved i det minste en del av nevnte oksygen reagerer med karbonet i stål-smelten og danner flyktig karbonoksyd, omfattende et første avkullings-trinn hvor temperaturen i stålsmelten økes til ønsket driftsområde; et andre avkullings-trinn hvor karboninnholdet i stål-smelten reduseres til en på forhånd bestemt verdi som omtrent svarer til karboninnholdet i smeiten som står i likevekt med CO ved et partialtrykk på 1 atmosfære og en temperatur innenfor ønsket driftsområde; samt et tredje akkullingstrinn hvor karboninnholdet i smeiten reduseres fra nevnte verdi til omtrent det ønskede karboninnhold i smeiten, hvor forbedringen karakteriseres ved at man innfører en gass som i det vesentlige består av COg i massen av smeltet stål under nevnte tredje avkullingstrinn, i en mengde som er mindre enn definert ved formelen: The above purposes and features of the invention will be clearly perceived by professionals and are achieved in accordance with the present invention through an embodiment which consists of: in a method for decarburizing chrome-containing molten steel, the method is characterized by deep-inhalation of oxygen and at least In inert - gas selected from the group helium, neon, krypton, argon, xenon and nitrogen, through the steel melt, whereby at least part of said oxygen reacts with the carbon in the steel melt and forms volatile carbon oxide, comprising a first decarburization step where the temperature in the steel melt is increased to the desired operating range; a second decarburization step where the carbon content in the steel melt is reduced to a predetermined value which roughly corresponds to the carbon content in the melt which is in equilibrium with CO at a partial pressure of 1 atmosphere and a temperature within the desired operating range; as well as a third decarburizing step where the carbon content in the forge is reduced from the aforementioned value to approximately the desired carbon content in the forge, where the improvement is characterized by introducing a gas which essentially consists of COg into the mass of molten steel during the said third decarburization step, in an amount which is less than defined by the formula:
hvor: F^q strømningshastigheten for COg, (ft-^/min) where: F^q the flow rate of COg, (ft-^/min)
Fj= strømningshastigheten for inert-gassen, (ft-^/min)Fj= the flow rate of the inert gas, (ft-^/min)
Fq = strømningshastighet for Og, (ft-^/min)Fq = flow rate of Og, (ft-^/min)
(Alle volumer måles ved 21°C og 1 atm. trykk).(All volumes are measured at 21°C and 1 atm. pressure).
P = likevekt-partialtrykket for CO for den spesielle bad-temperatur og karboninnhold i stålsmelten (atmosfærer), og X = avkullings-effekten i fravær av COg. P = the equilibrium partial pressure for CO for the particular bath temperature and carbon content in the steel melt (atmospheres), and X = the decarburization effect in the absence of COg.
Betegnelsen "avkulling" i denne forbindelse betegner en senkning av karboninnholdet i stålsmelten fra det aktuelle nivå til et annet ønsket og lavere nivå ved innblåsing av oksygen i smjfelten. Betegnelsen "krom-holdig stålsmelte" skal omfatte ferro-legeringer inneholdende ca. 3-4-0% krom. The term "decarburization" in this connection denotes a lowering of the carbon content in the steel melt from the relevant level to another desired and lower level by blowing in oxygen into the smelting field. The term "chromium-containing steel melt" shall include ferro-alloys containing approx. 3-4-0% chromium.
Oppfinnelsen er basert på den oppdragelsen at innføring (innblåsing) av COg sammen med oksygen og en inert-gass i stålsmelten øker avkullingseffekten ved avkullingen. Ved vanlig AOD-praksis vil, som kjent, avkullings-effekten synke når karboninnholdet i stålet synker. Nå vise_r det seg uventet at ved å erstatte en del av oksygenet og/eller argonet med COg vil avkullingseff ekten øke, og følgelig øker også den absolutte hastigheten for avkullingen. Primærfunksjonen for inert-gassen i inert-gass-oksygenblandingen er å senke karbon-monoksydets partialtrykk i kontakt med smeiten og derved øke avkullingen. Idet karbon-monoksydet er et av dekomponeringsproduktene for COg i smeiten, er den økning i avkullingseffekten som oppnås ved foreliggende oppfinnelse overraskende. The invention is based on the theory that introducing (blowing) COg together with oxygen and an inert gas into the steel melt increases the decarburization effect during decarburization. In normal AOD practice, the decarburization effect will, as is known, decrease when the carbon content in the steel decreases. Now it turns out unexpectedly that by replacing part of the oxygen and/or argon with COg, the decarburization effect will increase, and consequently the absolute rate of decarburization also increases. The primary function of the inert gas in the inert gas-oxygen mixture is to lower the partial pressure of the carbon monoxide in contact with the smelt and thereby increase decarburization. As the carbon monoxide is one of the decomposition products for COg in the smelting, the increase in the decarburization effect achieved by the present invention is surprising.
Strømningshastigheten for COg ifølge ovennevnte formel er definert som en øvre grense for å hindre at for mye COg innblåses i smeiten og oppkuller smeiten. Strømningshastigheten beregnes slik: The flow rate for COg according to the above formula is defined as an upper limit to prevent too much COg being blown into the smelter and charring the smelter. The flow rate is calculated as follows:
maksimal strømningshastighet for karbon-monoksyd ut av beholderen er knyttet til strømningshastigheten for argon ved følgende ligning: the maximum flow rate of carbon monoxide out of the container is linked to the flow rate of argon by the following equation:
hvor systemets trykk er 1 atmosfære. where the system pressure is 1 atmosphere.
Omordnet:Rearranged:
Verdien av P kan beregnes fra data i litteraturen (Electric Furnace Steelmaking, bind II, kapitel 16, s. 95»J«Chipman, J.I.S.I., s. 97-106, juni, 1955»H. Schenck ét al., Stahleisen Sonderberichte, Special Report No. 7>"Stahleisen Gmbh" Diisseldorf, I966). Den virkelige strømningshastighet for karbon-monoksyd<7>er The value of P can be calculated from data in the literature (Electric Furnace Steelmaking, volume II, chapter 16, p. 95»J«Chipman, J.I.S.I., p. 97-106, June, 1955»H. Schenck ét al., Stahleisen Sonderberichte, Special Report No. 7>"Stahleisen Gmbh" Diisseldorf, I966). The real flow rate of carbon monoxide<7> is
Forskjellen mellom F<013>,^ og F^q må oppta ekstra karbon-monoksyd fra forbedret avkulling og fra dissosiering av karbon-dioksyd. Strøm-ningshastigheten for karbon-dioksyd må derfor være mindre enn følgende mengde, for å forbedre avkullingseffekten: The difference between F<013>,^ and F^q must absorb extra carbon monoxide from improved decarburization and from dissociation of carbon dioxide. The flow rate for carbon dioxide must therefore be less than the following amount, in order to improve the decarburization effect:
For å oppnå dan mest effektive drift, har man regnet ut at strømningshas tighetene Sr de tre komponentene i gassblandingen og blåsetiden som medgår for å oppnå ønsket avkulling, kan oppsettes slik: In order to achieve the most efficient operation, it has been calculated that the flow rates Sr of the three components in the gas mixture and the blowing time required to achieve the desired decarburization can be set up as follows:
hvor: F^q = strømningshastigheten for CCv>, (ft^/min)' where: F^q = the flow rate of CCv>, (ft^/min)'
2 . o2. o
Fq = strømningshastigheten for C^, (ft^/min)Fq = flow rate of C^, (ft^/min)
2 o 2 etc
F-j- = strømningshastigheten for inert-gass, (ft<J>/min)F-j- = the flow rate of inert gas, (ft<J>/min)
Frj, = total gass-strømningshastighet for systemet (ft^/min)Frj, = total gas flow rate of the system (ft^/min)
t = blåsetid, (minutter)t = blowing time, (minutes)
= karboninnhold i smeiten ved blåsingens start (prosent)= carbon content in the smelt at the start of blowing (percent)
= karboninnhold i smeiten ved slutten av blåseprosessen (%) = carbon content in the smelt at the end of the blowing process (%)
T. = metallbadets temperatur ved blåsingens start (°F)T. = temperature of the metal bath at the start of the blowing (°F)
Tjr. = metallbadets temperatur ved slutten av blåsningen (°F)Tr. = metal bath temperature at end of blowing (°F)
W = totalvekt for metallsmelten (tonn)W = total weight of the molten metal (tonnes)
Kr = den målte varmetaps-koeffisient for beholderen (°F/min) Kr = the measured heat loss coefficient of the container (°F/min)
X = avkullingseffekten i fravær av.COg, ogX = the decarburization effect in the absence of COg, and
Zj= entalpien for inert-gassen ved driftstemperaturen for badet (for argon Zj= 0,06). Zj= the enthalpy of the inert gas at the operating temperature of the bath (for argon Zj= 0.06).
' I henhold til en annen utførelse av oppfinnelsen, kan en trekomponent-gassblanding inneholdende oksygen, COr, og en inert-gass (fortrinnsvis argon) eventuelt innblåses under nevnte første og/eller andre avkullings-trinn. Således kan trekomponents-gassblandingen effektivt brukes under alle tre trinn i avkullingen, under andre eller tredje trinn av avkullingsprosessen eller bare under tredje trinn. Når gassblandingen brukes under andre avkullingstrinn, er den foretrukne strømningshastighet for hver av gassene i trefase-blandingen og den tilsvarende blåsetid definert ved den identiske ligning som ovenfor er oppført for trinn 3 av avkullingen. Det vil si, ligningene (1), (2) og (3) definerer den foretrukne gass-strømnings-hastighet og strømningstid både for avkullingens andre og tredje trinn. According to another embodiment of the invention, a three-component gas mixture containing oxygen, COr, and an inert gas (preferably argon) can optionally be blown in during said first and/or second decarburization step. Thus, the three-component gas mixture can be effectively used during all three stages of the decarburization, during the second or third stage of the decarburization process or only during the third stage. When the gas mixture is used during the second decarburization step, the preferred flow rate for each of the gases in the three-phase mixture and the corresponding blowing time are defined by the identical equation listed above for step 3 of the decarburization. That is, equations (1), (2) and (3) define the preferred gas flow rate and flow time for both the second and third stages of decarburization.
For avkullingens første trinn, hvorunder metallbadets temperatur økes til driftsområdet, holdes strømningshastighetene for oksygén, argon og C02generelt på et forutbestemt innbyrdes forhold og følgelig, er de variable som skal bestemmes karboninnholdet ved slutten av blåsingen samt den nødvendige blåsetid. Det er foretrukket at CCv, benyttes under første trinn i stedet for argon, fordi det forbedrer' prosessreguleringen. Følgelig, kan blandinger av Cv, og-COg virk-ningsfullt brukes i forhold som varierer fra 4*1 "til 1:1. De rest erende variable tid,, temperatur, strømning og karboninnhold sammen-knyttes fortrinnsvis ved følgende ligninger: For the first stage of decarburization, during which the temperature of the metal bath is increased to the operating range, the flow rates of oxygen, argon and C02 are generally kept at a predetermined mutual ratio and, consequently, the variables to be determined are the carbon content at the end of blowing and the necessary blowing time. It is preferred that CCv is used during the first step instead of argon, because it improves process regulation. Consequently, mixtures of Cv, and -COg can be effectively used in ratios varying from 4*1" to 1:1. The remaining variables time, temperature, flow and carbon content are preferably related by the following equations:
Stålraffinering i henhold til vanlig AOD-praksis kan med fordel karakteriseres ved tre avkullings-faser som svarer til tre separate blåseperioder. Under første trinn eller fase blir metallsmelten blåst med en gassblanding som inneholder overveiende oksygen, slik at bad-temperaturen økes til det ønskede driftsområde (vanligvis ca. 3000-3100°F (1650-1700°C)) så raskt som mulig. Når metallsmelten har nådd denne temperatur, starter den andre blåseperioden, hvorunder forholdet mellom argon og oksygen i blåsegassblandingen økes for å hindre badet fra overoppheting, og karboninnholdet i smeiten reduseres til omtrent det punkt.hvor videre avkjøling bare kan oppnås på bekostning av vesentlig krom-oksydering i smeiten. Således bestemmes sluttpunktet for avkullingens andre trinn av krom-karbon-likevekten ved smeltens trykk og temperatur. Ytterligere,reduksjon Steel refining according to normal AOD practice can advantageously be characterized by three decarburization phases which correspond to three separate blowing periods. During the first step or phase, the molten metal is blown with a gas mixture containing predominantly oxygen, so that the bath temperature is raised to the desired operating range (typically about 3000-3100°F (1650-1700°C)) as quickly as possible. When the molten metal has reached this temperature, the second blowing period begins, during which the ratio of argon to oxygen in the blowing gas mixture is increased to prevent the bath from overheating, and the carbon content of the melt is reduced to approximately the point where further cooling can only be achieved at the expense of substantial chromium- oxidation in the smelter. Thus, the end point for the second stage of decarburization is determined by the chromium-carbon equilibrium at the pressure and temperature of the melt. Further, reduction
av karboninnholdet i smeiten til omtrent det ønskede nivå oppnås under avkullingens tredje trinn ved ytterligere økning av argon/ oksygen-forholdet i gassblandingen, for å senke partialtrykket for karbon-monoksyd i kontakt med smeiten og favorisere oksydasjonen av karbon i forhold til oksydasjonen av krom. of the carbon content in the forge to approximately the desired level is achieved during the third stage of decarburization by further increasing the argon/oxygen ratio in the gas mixture, in order to lower the partial pressure of carbon monoxide in contact with the forge and favor the oxidation of carbon in relation to the oxidation of chromium.
Den måten som strømningsligningene benyttes på i praksis under AOD-prosessen kan illustreres ved følgende eksempel. For en gitt beholder og ståltype vil W, Kr og Frj, være kjent. Verdien av X, avkullings-eff ekten,- beregnes ut fra ligningen: hvor The way in which the flow equations are used in practice during the AOD process can be illustrated by the following example. For a given container and steel type, W, Kr and Frj will be known. The value of X, the decarburization effect, is calculated from the equation: where
Siden X vil variere avhengig av smeltens karboninnhold, smeltens temperatur og beholderens data, må denne størrelse bestemmes empirisk Since X will vary depending on the carbon content of the melt, the temperature of the melt and the vessel data, this quantity must be determined empirically
under de aktuelle driftsforhold.under the relevant operating conditions.
For blåseperioden som svarer til første avkullings-trinn,For the blowing period corresponding to the first decarburization step,
er følgende variable generelt kjent: Tf (f.eks. l677°C = 3050°F),the following variables are generally known: Tf (e.g. 1677°C = 3050°F),
Fq og FCq (f.eks. i forholdet 3*1)• Den tiden (t) som kreves for op^varming^av badet under dette første trinn og karboninnholdet som blir resultatet avblåsingen (C^) beregnes ut fra ligningene(4) og (5). Fq and FCq (e.g. in the ratio 3*1)• The time (t) required for heating the bath during this first step and the carbon content resulting from the blow-off (C^) are calculated from equations (4) and (5).
Under avkullingens andre trinn er de kjente forhold for-skjellige fra forholdene under føBste trinn. Således er følgende variable kjent: CL (tidligere Cf), Cf (f.eks. 0,25%), T.^Tf (f.eks. 3050°F = 1667°C) og X (beregnet tidligere). De variable t, FCQog Fn kan deretter beregnes etter ligningene (1), (2) og (3) • During the second stage of decarburization, the known conditions are different from the conditions during the first stage. Thus, the following variables are known: CL (formerly Cf), Cf (eg 0.25%), T.^Tf (eg 3050°F = 1667°C) and X (calculated earlier). The variables t, FCQ and Fn can then be calculated according to equations (1), (2) and (3) •
u2 u2
Under avkullingens tredje trinn kan ovns-operatøren f.eks. ønske en avkulling til C = 0,05% under en temperatur på 1705°C før avkjøling. De gitte betingelser blir således forandret for å til-passes ytterligere argon som kreves for avkulling av smeiten til under 0,25% karbon.- De gitte betingelser er CL (0,25%), % (0,05%), Ti (3050°F), Tf (3100°F), FAr (1/2 FT, f.eks.) og X. Løsningen av ligningene (1), (2) og (3) gir tallene for de variable t, Fco og FQ . During the third stage of decarburization, the furnace operator can e.g. want a decarburization to C = 0.05% below a temperature of 1705°C before cooling. The given conditions are thus changed to accommodate the additional argon required for decarburizing the smelt to below 0.25% carbon. The given conditions are CL (0.25%), % (0.05%), Ti ( 3050°F), Tf (3100°F), FAr (1/2 FT, e.g.) and X. Solving equations (1), (2) and (3) gives the numbers for the variables t, Fco and FQ.
Tall-løsningene for ligningene (1) - (5) i eksemplet ovenfor er vistThe numerical solutions for equations (1) - (5) in the example above are shown
i Tabell I. De beregnede tallene er understreket. For en hundre tonns beholder og en total gass-strømningshastighet på 2000 ft^/min. er: ¥ = 100, Kr = 1.0°F/min. og FT= 2000 ft<3>/min. in Table I. The calculated numbers are underlined. For a one hundred ton container and a total gas flow rate of 2000 ft^/min. is: ¥ = 100, Kr = 1.0°F/min. and FT= 2000 ft<3>/min.
For å illustrere virkningen av smeltetemperatur-regulering To illustrate the effect of melt temperature control
med CO^i blåseblandingen foretok man tre oppvarminger av rustfritt stål i en AOD-beholder hvor COg ble gjennomblåst som en av prosess-gassene i henhold til ligning (1), (2) og (3). Raffineringsbehold-eren hadde en faktor Kr = 4°F/min. Det ønskede sluttpunkt for blåsningen og det virkelige sluttpunkt er sammenlignet i Tabell II. De with CO^ in the blowing mixture three heatings of stainless steel were carried out in an AOD container where COg was blown through as one of the process gases according to equations (1), (2) and (3). The refining tank had a factor Kr = 4°F/min. The desired end point for the blowing and the actual end point are compared in Table II. The
meget små forskjeller mellom virkelig og ønsket karboninnhold og slutt-temperatur angir den effektive temperaturregulering som kan oppnås ved hjelp av CO^som behandlingsgass i henhold til oppfinnelsen. very small differences between actual and desired carbon content and final temperature indicate the effective temperature regulation that can be achieved with the help of CO as treatment gas according to the invention.
Den ;mest overraskende virkning av å bruke CO^i blåsegassblandingen knytter seg'til avkullings-effekten. Generelt vil avkullings-eff ekten være desto lavere jo lavere smeltens karboninnhold er. Derfor er en forbedring i avkullings-effekten vanligvis mest ønsket under den perioden hvor stålet skal avkulles til et karbon-innhold som ligger lavere enn det som befinner seg i likevekt med CO ved et partialtrykk på en atmosfære, nemlig under avkullingens tredje trinn. For å illustrere forbedringen i avkullingseffekten ved lave karbon-innhold, foretok man 6 kjøringer av rustfritt stål 1 en l8 tonns AOD-beholder - 4 forsøk i henh&ld til vanlig AOD-praksis med 2-komponent-blåseblanding (argon/oksygen), de resterende The most surprising effect of using CO in the blowing gas mixture relates to the decarburization effect. In general, the lower the carbon content of the melt, the lower the decarburization effect. Therefore, an improvement in the decarburization effect is usually most desired during the period where the steel is to be decarburized to a carbon content that is lower than that which is in equilibrium with CO at a partial pressure of one atmosphere, namely during the third stage of decarburization. To illustrate the improvement in the decarburization effect at low carbon contents, 6 runs were made of stainless steel 1 an 18 ton AOD container - 4 trials in accordance with normal AOD practice with a 2-component blowing mixture (argon/oxygen), the remaining
2 forsøk med en 3-komponent-blanding inneholdende CO^i henhold til oppfinnelsen. De målte gass-strømningshastigheter, start- og slutt-karbon-innhold og metallbad-temperaturer samt resulterende avkullings-eff ekt er oppført i Tabell III. Tallene for avkullings-effekten (X) ble beregnet på basis av total mengde oksygen innført i smeiten inklusive den mengden som dannes ved dekomponering av COg. Det vil si, at den totale mengde oksygen i smeiten ble satt til FQ+ 1/2 2 tests with a 3-component mixture containing CO2 according to the invention. The measured gas flow rates, initial and final carbon content and metal bath temperatures as well as the resulting decarburization effect are listed in Table III. The figures for the decarburization effect (X) were calculated on the basis of the total amount of oxygen introduced into the smelt, including the amount formed by the decomposition of COg. That is, the total amount of oxygen in the smelting was set to FQ+ 1/2
Fqq , den samlede strømning erooppført i Tabell III som F'q . Forbedringen i avkullings-effekt under forsøk B og C hvor COg ble brukt i blåse-blandingen, er betydelig. Fqq , the total flow is listed in Table III as F'q . The improvement in decarburization effect during trials B and C where COg was used in the blowing mixture is significant.
Claims (4)
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US374635A US3861888A (en) | 1973-06-28 | 1973-06-28 | Use of CO{HD 2 {B in argon-oxygen refining of molten metal |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| NO742347L true NO742347L (en) | 1975-01-27 |
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| NO742347A NO742347L (en) | 1973-06-28 | 1974-06-27 |
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| Country | Link |
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| US (2) | US3861888A (en) |
| JP (1) | JPS5037611A (en) |
| AU (1) | AU6944374A (en) |
| BE (1) | BE816970A (en) |
| BR (1) | BR7405267A (en) |
| DD (1) | DD112468A5 (en) |
| FI (1) | FI197874A (en) |
| FR (1) | FR2235198B1 (en) |
| IL (1) | IL45137A (en) |
| NO (1) | NO742347L (en) |
| PL (1) | PL88825B1 (en) |
| SE (1) | SE7408502L (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NZ186831A (en) * | 1977-03-31 | 1981-12-15 | Union Carbide Corp | Production of metal castings refining melt by using oxygen containing gas prior to casting |
| US4174212A (en) * | 1978-03-10 | 1979-11-13 | A. Finkl & Sons Co. | Method for the refining of steel |
| DE2820555A1 (en) * | 1978-05-11 | 1979-11-15 | Basf Ag | PROCESSES FOR THE TREATMENT OF PIG IRON AND STEEL MELT RESPECTIVELY. ALLOYS |
| US4490172A (en) * | 1979-06-29 | 1984-12-25 | Moore William H | Method of melting and refining steel and other ferrous alloys |
| US4409028A (en) * | 1979-10-24 | 1983-10-11 | Moore William H | Process for producing cast iron |
| US4260415A (en) * | 1979-12-12 | 1981-04-07 | Allegheny Ludlum Steel Corporation | Decarburizing molten metal |
| US4436553A (en) | 1982-01-22 | 1984-03-13 | Union Carbide Corporation | Process to produce low hydrogen steel |
| FR2560891B1 (en) * | 1984-03-09 | 1989-10-20 | Air Liquide | CAST REFINING PROCESS |
| US4615730A (en) | 1985-04-30 | 1986-10-07 | Allegheny Ludlum Steel Corporation | Method for refining molten metal bath to control nitrogen |
| US4746361A (en) * | 1987-04-03 | 1988-05-24 | Inland Steel Company | Controlling dissolved oxygen content in molten steel |
| US5139569A (en) * | 1989-04-13 | 1992-08-18 | Messer Griesheim | Process for the production of alloy steel grades using treatment gas consisting of CO2 |
| DE3912061A1 (en) * | 1989-04-13 | 1990-10-18 | Messer Griesheim Gmbh | METHOD FOR PRODUCING ALLOY STEEL BRANDS |
| US5190577A (en) * | 1990-12-11 | 1993-03-02 | Liquid Air Corporation | Replacement of argon with carbon dioxide in a reactor containing molten metal for the purpose of refining molten metal |
| ATE123816T1 (en) * | 1991-11-28 | 1995-06-15 | Carbagas | METHOD FOR SUPPRESSING DUST AND SMOKE IN ELECTRICAL STEEL PRODUCTION. |
| 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 |
| CN102146499A (en) * | 2010-02-05 | 2011-08-10 | 鞍钢股份有限公司 | AOD blowing CO2Smelting method for producing stainless steel |
| US9045805B2 (en) | 2013-03-12 | 2015-06-02 | Ati Properties, Inc. | Alloy refining methods |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2855293A (en) * | 1955-03-21 | 1958-10-07 | Air Liquide | Method and apparatus for treating molten metal with oxygen |
| US3252790A (en) * | 1956-06-27 | 1966-05-24 | Union Carbide Corp | Preparation of metals and alloys |
| US3003865A (en) * | 1959-09-10 | 1961-10-10 | Cameron Iron Works Inc | Decarburizing process for alloy steels containing chromium |
| BE610265A (en) * | 1960-11-18 | |||
| US3397878A (en) * | 1965-11-19 | 1968-08-20 | Union Carbide Corp | Under-bath tuyere |
| GB1253581A (en) * | 1968-02-24 | 1971-11-17 | Maximilianshuette Eisenwerk | Improvements in processes and apparatus for making steel |
| BE755456A (en) * | 1969-08-29 | 1971-03-01 | Allegheny Ludlum Ind Inc | DECARBURATION OF MELT STEEL |
| US3728101A (en) * | 1970-11-09 | 1973-04-17 | Armco Steel Corp | Process for making stainless steel |
| FR2186974A5 (en) * | 1972-05-31 | 1974-01-11 | Air Liquide | Decarburisation of iron and steel alloys - contg chromium by blowing with oxygen, carbon dioxide and a rare gas |
-
1973
- 1973-06-28 US US374635A patent/US3861888A/en not_active Expired - Lifetime
-
1974
- 1974-05-28 AU AU69443/74A patent/AU6944374A/en not_active Expired
- 1974-06-27 IL IL45137A patent/IL45137A/en unknown
- 1974-06-27 BR BR5267/74A patent/BR7405267A/en unknown
- 1974-06-27 FI FI1978/74A patent/FI197874A/fi unknown
- 1974-06-27 PL PL1974172235A patent/PL88825B1/pl unknown
- 1974-06-27 DD DD179518A patent/DD112468A5/xx unknown
- 1974-06-27 BE BE145977A patent/BE816970A/en unknown
- 1974-06-27 JP JP49072891A patent/JPS5037611A/ja active Pending
- 1974-06-27 SE SE7408502A patent/SE7408502L/ unknown
- 1974-06-27 FR FR7422449A patent/FR2235198B1/fr not_active Expired
- 1974-06-27 NO NO742347A patent/NO742347L/no unknown
-
1977
- 1977-01-21 US US05/760,841 patent/USRE29584E/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| SE7408502L (en) | 1974-12-30 |
| FR2235198B1 (en) | 1978-01-20 |
| FI197874A (en) | 1974-12-29 |
| DE2430975A1 (en) | 1975-01-09 |
| BR7405267A (en) | 1976-02-24 |
| PL88825B1 (en) | 1976-09-30 |
| AU6944374A (en) | 1975-12-04 |
| JPS5037611A (en) | 1975-04-08 |
| IL45137A0 (en) | 1974-09-10 |
| BE816970A (en) | 1974-12-27 |
| DD112468A5 (en) | 1975-04-12 |
| FR2235198A1 (en) | 1975-01-24 |
| IL45137A (en) | 1976-09-30 |
| US3861888A (en) | 1975-01-21 |
| USRE29584E (en) | 1978-03-21 |
| DE2430975B2 (en) | 1975-09-04 |
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