EP0213991B1 - Beschleunigtes Karburierungsverfahren in einem kontinuierlichen Ofen - Google Patents

Beschleunigtes Karburierungsverfahren in einem kontinuierlichen Ofen Download PDF

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Publication number
EP0213991B1
EP0213991B1 EP86401584A EP86401584A EP0213991B1 EP 0213991 B1 EP0213991 B1 EP 0213991B1 EP 86401584 A EP86401584 A EP 86401584A EP 86401584 A EP86401584 A EP 86401584A EP 0213991 B1 EP0213991 B1 EP 0213991B1
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Prior art keywords
atmosphere
carbon monoxide
concentration
rapid
casehardening
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EP86401584A
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English (en)
French (fr)
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EP0213991A1 (de
Inventor
Philippe Queille
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Application filed by LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces

Definitions

  • the present invention relates to a rapid case-hardening process in a continuous closed furnace into which a carrier gas and optionally a hydrocarbon are injected capable of generating, at the usual case-hardening temperatures, an atmosphere of predetermined composition, having a nominal concentration of carbon monoxide, an oven door being opened with a determined periodicity to allow the passage of a charge to be cemented, the opening of this door generating in particular an increase in the concentration of oxidizing species in the atmosphere of said oven.
  • a continuous closed furnace is a furnace into which are introduced at regular time intervals the charges to be treated which advance at low speed therein, successively passing through a zone of temperature rise of the charges, a zone of case-hardening of the pieces of the charge and a diffusion zone of said coins.
  • a continuous closed oven may have entry and exit airlocks which partially decrease the increase in the concentration of oxidizing species in the atmosphere and may also have non-watertight separation doors between each zone.
  • This atmosphere consists of:
  • the method according to the invention makes it possible to avoid these drawbacks. It is characterized in that the carbon monoxide concentration of the atmosphere injected into the furnace is increased with the same periodicity, so as to compensate for the increase in the concentration of oxidizing species in the furnace and thus maintain substantially constant the carbon potential of the furnace carburizing atmosphere throughout the carburizing duration of said parts. If carbon monoxide is formed in the furnace after cracking of one of the source elements of the carrier gas, the increase in concentration of carbon monoxide is understood as the correlative increase in the element. generator.
  • the carrier gas comprises nitrogen and an alcohol, preferably methanol (or ethanol).
  • the increase in concentration of carbon monoxide signifies in this case a corresponding increase in the concentration of methanol in the carrier gas.
  • the concentration of carbon monoxide in the atmosphere is increased, so as to compensate for the increase in carbon dioxide in order to maintain a substantially constant carbon potential.
  • this increase in carbon monoxide concentration will preferably be accompanied by an increase in the flow rate of the carrier gas.
  • a carrier gas flow rate of 1.5 to 4 times the "nominal" carrier gas flow rate, corresponding to the charge treatment phase (case hardening and / or diffusion), will preferably be used.
  • the oven door will be closed before the injection of carrier gas with a high concentration of carbon monoxide begins. In this way, a carrier gas saving is achieved since when the door is opened, the increase in concentration oxidizing species cannot be avoided.
  • the opening of the oven door will be preceded for a few moments by an injection of carrier gas with a high concentration of carbon monoxide, this injection continuing at least until the door is closed. and possibly after closing thereof, under conditions of duration specified below.
  • the carbon monoxide boost can be timed when the cycle is programmed. Thus it is easy to provide a time delay after closing the door, before returning to the "nominal" carbon monoxide flow. Likewise, provision may be made for a pre-triggering of the carbon monoxide supercharging synchronized with the opening of the door.
  • the injection of carrier gas with a high concentration of carbon monoxide may or may not be accompanied by an increase in the flow rate of carrier gas, preferably within the limits mentioned above.
  • the duration of the injection of carrier gas having a concentration of carbon monoxide greater than the nominal value will be between 5% and 50% of the total duration of the treatment.
  • the carrier gas with a carbon monoxide concentration greater than the nominal value will preferably be obtained from a nitrogen-methanol mixture, with a volume ratio
  • the carrier gas with a carbon monoxide concentration equal to the nominal value will also be obtained from a nitrogen-methanol mixture in a volume ratio preferably having the value
  • a load consisting of steel parts to be cemented is introduced every few minutes (generally from 4 to 20 minutes).
  • This oven generally comprises successively an entry door, an entry airlock, a carburizing zone and a diffusion zone, possibly separated by doors, an exit airlock with quenching tank.
  • the atmosphere generated in the furnace is of the "endothermic" type, that is to say rich mainly in hydrogen, carbon monoxide and nitrogen species, obtained from a generator, or nitrogen and bodies intended for create in the oven the CO and H 2 species which may be methanol alone (preferred solution), ethanol-oxidant mixtures (H 2 0, Air, C0 2, etc.) or equivalents, to which up to 10% may be added of hydrocarbon (CH 4 , C 3 H 8 ...) to control the carbon potential and sometimes up to 5% of ammonia for specific treatments such as carbonitriding (cementation activated with ammonia).
  • the entry door is opened, which causes large uncontrolled entries of oxidizing species (0 2 or C0 2 , H 2 0, resulting from the combustion of the atmosphere of the oven with the outside air).
  • the concentration of carbon monoxide can be considered constant throughout the process. Consequently, the carbon potential varies very strongly in the carburizing zone of the furnace, according to curve C, illustrated in FIG. 5. It can decrease up to a PC M value of the order of 0.1 to 0.3 % for a case-hardening temperature of 920 ° C for example. (The setpoint for carbon potential at this temperature is often in the range of 0.8 to 1.0%.) Reconditioning the oven to the setpoint takes practically the entire time interval to to t , separating two successive introductions.
  • FIG. 2 by way of indication represents the flow rate of carrier gas injected into the furnace according to the known solution of the American patent cited above, this flow rate normally having the value DL when the door is closed, and a value DH when the door of the furnace is open, substantially equal to 2 times DL or more.
  • the concentration of carbon monoxide in the atmosphere injected into the oven is increased during the charging of a new charge (or during the charging, if the latter causes a disturbance similar) or shortly before in order to anticipate the increase in concentration of oxidizing species, without reaching an atmospheric carbon activity equal to 1, which would generate soot on the parts.
  • This increase in concentration is generally carried out during the entire duration of the opening of the oven door. It generally continues after the closing of this door in order to return more quickly to the set carbon potential.
  • This measure is doubly favorable because it allows, on the one hand, to maintain the carbon potential of the atmosphere at a sufficient value for there to be carbon transfer from the atmosphere in the room but it also allows other part to accelerate this transfer to the part, since the carbon transfer speed depends, in the carburizing phase, on the product pH 2 x pCo, which are the respective partial pressures of H 2 and CO in the furnace (here equal to concentrations).
  • This increase in carbon monoxide concentration is effected by injection into the furnace of carbon monoxide or, preferably, of a product liable to decompose, in the atmosphere of the furnace to generate this carbon monoxide.
  • the atmosphere injected into the oven is either that of an endo generator at constant flow rate, or preferably, a nitrogen / methanol mixture or equivalent as described above.
  • the injection is increased, during the time at t ′, of carbon monoxide whose concentration changes from [CO], (which is generally of the order of 20% by volume) to [CO] 2 (which is around 27% by volume).
  • the simplest method for implementing the invention is to use a nitrogen-methanol mixture to generate the atmosphere of the oven, and to vary the relative proportions of nitrogen and methanol.
  • the proportion of methanol in the mixture is increased, this increase being able to go as far as the introduction of pure methnol during or during this brief period.
  • the flow rate of the mixture and the proportions thereof can be varied simultaneously, so as to keep the nitrogen flow rate substantially constant.
  • This variant is that shown in FIG. 4 with a flow rate D ' H from to to to + At', etc. of a mixture comprising 20% nitrogen and 80% methanol and a flow rate D ' L , lower to D ' H of a mixture containing 40% nitrogen and 60% methanol.
  • This example represents the prior art typically used to date.
  • cementing of steel transmission parts of grade 16NC6 is carried out, for which the cementation depth sought at 550 HV1 is from 0.7 to 0.9 mm.
  • the oven temperature is 920 ° C, the charges, introduced every 7 minutes, being 150 kg.
  • the carbon potential that we are trying to maintain, in the cementation zone, is 0.8%.
  • the duration of the opening of the loading door, at the entrance of the oven, is 27 seconds.
  • the atmosphere injected into the oven is obtained using a nitrogen-methanol mixture, in the 40/60 ratio (so-called "endothermic" atmosphere).
  • the flow rate of the injected atmosphere is 19 m 3 / hour.
  • the consumption of atmosphere per cycle (of 7 minutes) is therefore 2.22 m 3).
  • Example 7 In the same oven, all other things being equal, the same parts are treated to obtain the same final conditions as in Example 1.
  • the atmosphere injected into the oven in the previous example is replaced by an atmosphere of variable composition, for variable durations, shown in FIG. 7.
  • the atmosphere Atm (2) is injected with a nitrogen / methanol ratio equal to 20/80 at a flow rate of 24 m 3 / h. Then the atmosphere Atm (1) is injected at a flow rate of 12 m 3 / h, for 3 minutes and 50 seconds.
  • the gas consumption during a cycle is 1.57 m 3 .
  • the variations in carbon potential are shown in Figure 8 to scale. (Note that on the time scale ( Figures 6, 7 and 8), F represents the instant of closing of the oven door).
  • the depth cemented at 550 HV1 of the parts in the batch is between 0.7 and 0.9 mm.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Tunnel Furnaces (AREA)
  • Superconductors And Manufacturing Methods Therefor (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Carbon And Carbon Compounds (AREA)
  • Multiple-Way Valves (AREA)

Claims (12)

1. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen, in welchen man ein Trägergas und einen Kohlenwasserstoff einspritzt, die bei üblichen Aufkohlungstemperaturen eine Atmosphäre vorbestimmter Zusammensetzung mit einer Nennkonzentration an Kohlenmonoxid erzeugen können, wobei eine Tür des Ofens mit einer Periodizität geöffnet wird, die so bestimmt ist, daß der Durchgang einer aufzukohlenden Charge gestattet wird, und die Öffnung dieser Tür insbesondere einen Anstieg der Konzentration oxidierender Verbindungen in der Atmosphäre des Ofens bewirkt, dadurch gekennzeichnet, daß man mit der gleichen Periodizität die Kohlenmonoxidkonzentration der in den Ofen eingespritzten Atmosphäre derart steigert, daß der Anstieg der Konzentration an oxidierenden Verbindungen des Ofens kompensiert wird und so das Kohlenstoffpotential der Aufkohlungsatmosphäre des Ofens während der gesamten Dauer der Aufkohlung der Stücke im wesentlichen konstant gehalten wird.
2. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach Anspruch 1, dadurch gekennzeichnet, daß der Anstieg der Kohlenmonoxidkonzentration von der Öffnung der Tür an erfolgt.
3. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach Anspruch 2, dadurch gekennzeichnet, daß man vom Verschließen der Ofentür an die Kohlenmonoxidkonzentration der eingespritzten Atmosphäre auf ihren Nennwert in der vorbestimmten Zusammensetzung zurückbringt.
4. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach Anspruch 2, dadurch gekennzeichnet, daß man von dem Verschließen der Ofentür an, aber mit einer regulierbaren Verzögerung die Kohlenmonoxidkonzentration der eingespritzten Atmosphäre auf ihren Nennwert in der vorbestimmten Zusammensetzung zurückbringt.
5. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach den Ansprüchen 1 bis 4, dadurch gekennzeichnet, daß die Kohlenmonoxideinspritzung einige Augenblicke der Öffnung der Tür vorausgeht.
6. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach Anspruch 1, dadurch gekennzeichnet, daß der Anstieg der Kohlenmonoxidkonzentration während eines vorbestimmten Zeitintervalls vor einer Rückkehr zu der Nennkonzentration von dem Verschließen der Tür an erfolgt oder diesem einige Augenblicke vorausgeht, wenn die Dauer der Öffnung der Tür vorbestimmt ist.
7. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach den Ansprüchen 1 bis 6, dadurch gekennzeichnet, daß die Rückkehr zu dem Nennwert der Kohlenmonoxidkonzentration der eingespritzten Atmosphäre erfolgt, wenn das in der Einfassung gemessene Kohlenstoffpotential im wesentlichen auf einen vorbestimmten Einstellwert zurückgekommen ist.
8. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach den Ansprüchen 1 bis 7, dadurch gekennzeichnet, daß der Durchsatz der in den Ofen eingespritzten Atmosphäre wenigstens während eines Teiles der Dauer des Einspritzens der Atmosphäre auf eine Kohlenmonoxidkonzentration oberhalb des Nennwertes gesteigert wird.
9. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach Anspruch 8, dadurch gekennzeichnet, daß der Anstieg des Trägergasdurchsatzes dem 1,5- bis 4fachen des Nennwertes des Durchsatzes entspricht.
10. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach Anpruch 9, dadurch gekennzeichnet, daß die Dauer der Einspritzung des Trägergases mit einer Kohlenmonoxidkonzentration oberhalb des Nennwertes zwischen 5 und 50 % der Gesamtdauer der Behandlung umfaßt.
11. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach den Ansprüchen 1 bis 10, dadurch gekennzeichnet, daß das Trägergas mit einer Konzentration an CO oberhalb des Nennwertes wenigstens teilweise aus einem Stickstoff-Methanol-Gemisch mit einem Volumenverhältnis
Figure imgb0007
erhalten wird, wobei N2 und MeOH jeweils die Konzentrationen an Stickstoff und Methanol bedeuten.
12. Verfahren zur schnellen Aufkohlung in einem kontinuierlichen geschlossenen Ofen nach den Ansprüchen 1 bis 11, in welchem man ein Gemisch von Stickstoff und Methanol benutzt, um das Trägergas zu erzeugen, dadurch gekennzeichnet, daß der Stickstoffdurchsatz während der gesamten Dauer des Verfahrens konstant bleibt, wobei der Methanoldurchsatz gemäß den Veränderungen der Kohlenmonoxidkonzentration der Atmosphäre variiert.
EP86401584A 1985-08-14 1986-07-16 Beschleunigtes Karburierungsverfahren in einem kontinuierlichen Ofen Expired EP0213991B1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86401584T ATE40416T1 (de) 1985-08-14 1986-07-16 Beschleunigtes karburierungsverfahren in einem kontinuierlichen ofen.

Applications Claiming Priority (2)

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FR8512380A FR2586259B1 (fr) 1985-08-14 1985-08-14 Procede de cementation rapide dans un four continu
FR8512380 1985-08-14

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EP0213991B1 true EP0213991B1 (de) 1989-01-25

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EP (1) EP0213991B1 (de)
JP (1) JPS6240359A (de)
AT (1) ATE40416T1 (de)
AU (1) AU587045B2 (de)
BR (1) BR8603865A (de)
CA (1) CA1259550A (de)
DE (1) DE3661943D1 (de)
ES (1) ES8706850A1 (de)
FR (1) FR2586259B1 (de)
ZA (1) ZA865392B (de)

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FR2586258B1 (fr) * 1985-08-14 1987-10-30 Air Liquide Procede pour la cementation rapide et homogene d'une charge dans un four
FR2623209B1 (fr) * 1987-11-17 1993-09-03 Air Liquide Procede de traitement thermique sous atmosphere gazeuse a base d'azote et d'hydrocarbure
FR2626292A1 (fr) * 1988-01-26 1989-07-28 Paturle Aciers Procede de traitement thermochimique superficiel de bandes d'acier et en particulier de bandes de faibles epaisseurs et installation pour sa mise en oeuvre
IT1229078B (it) * 1988-03-16 1991-07-18 Air Liquide Procedimento e dispositivo di trattamento di ricottura di articoli metallici.
FR2639250B1 (de) * 1988-11-24 1990-12-28 Air Liquide
US5133813A (en) * 1990-07-03 1992-07-28 Tokyo Heat Treating Company Ltd. Gas-carburizing process and apparatus
DE4400391A1 (de) * 1994-01-08 1995-07-13 Messer Griesheim Gmbh Verfahren zur Vermeidung von Randoxidation beim Aufkohlen von Stählen
US5934871A (en) * 1997-07-24 1999-08-10 Murphy; Donald G. Method and apparatus for supplying a anti-oxidizing gas to and simultaneously cooling a shaft and a fan in a heat treatment chamber
CN102828143A (zh) * 2012-08-30 2012-12-19 天津创真金属科技有限公司 工件高温渗碳工艺
CN113215519B (zh) * 2021-04-19 2023-08-15 常州天山重工机械有限公司 一种无马弗罐碳饱和控制工艺

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FR2586258B1 (fr) * 1985-08-14 1987-10-30 Air Liquide Procede pour la cementation rapide et homogene d'une charge dans un four

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EP0213991A1 (de) 1987-03-11
FR2586259A1 (fr) 1987-02-20
ATE40416T1 (de) 1989-02-15
JPS6240359A (ja) 1987-02-21
AU587045B2 (en) 1989-08-03
FR2586259B1 (fr) 1987-10-30
CA1259550A (fr) 1989-09-19
ZA865392B (en) 1987-03-25
AU6022586A (en) 1987-02-19
ES556249A0 (es) 1987-07-01
BR8603865A (pt) 1987-03-24
ES8706850A1 (es) 1987-07-01
DE3661943D1 (en) 1989-03-02
US4769090A (en) 1988-09-06
JPS6356304B2 (de) 1988-11-08

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