EP0532386B1 - Verfahren und Vorrichtung zum Aufkohlen von Stahl in einer Atmosphere von niedrigem Druck - Google Patents

Verfahren und Vorrichtung zum Aufkohlen von Stahl in einer Atmosphere von niedrigem Druck Download PDF

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Publication number
EP0532386B1
EP0532386B1 EP92402395A EP92402395A EP0532386B1 EP 0532386 B1 EP0532386 B1 EP 0532386B1 EP 92402395 A EP92402395 A EP 92402395A EP 92402395 A EP92402395 A EP 92402395A EP 0532386 B1 EP0532386 B1 EP 0532386B1
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EP
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Prior art keywords
injection
phase
gas
duration
gas flow
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Expired - Lifetime
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EP92402395A
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English (en)
French (fr)
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EP0532386A1 (de
Inventor
Georges Dervieux
Jean Bares
Patrick Jacquot
Sophie Dubois
Joséphine German
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Innovatique SA
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Innovatique SA
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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

  • this treatment is carried out in a charge oven (or not) inside which the parts are brought to a treatment temperature in an atmosphere based on nitrogen and methanol.
  • this oxygen reacts on the surface of the steel by phenomenon of intergranular oxidation.
  • the latter weakens the surface structure by locally reducing the hardness and above all the fatigue limit.
  • the oxygen present has the effect of limiting the transfer of carbon at the interface between the cementing gas phase and the solid to be cemented. This phenomenon therefore limits the rate of carburizing.
  • carburizing equipment is often provided with an oxygen sensor and an infrared analyzer, so as to control the carbon potential in the atmosphere.
  • the invention therefore more particularly aims to eliminate all these drawbacks.
  • a case hardening process consisting in bringing the parts to be treated to a temperature of between 800 ° C. and 1100 ° C., in a gaseous atmosphere free of oxygen maintained by pumping at low pressure, and in carrying out a plurality of successive carbon enrichment phases, each obtained by an injection of limited duration, of a treatment gas comprising one or more pure hydrocarbons, each enrichment phase having a duration less than the time of transition to saturation phase of austenite, these enrichment phases being separated by longer diffusion phases under vacuum making it possible to adjust the surface carbon content.
  • this process is characterized in that the above pressure is maintained at a value between 1 and 10 mbar with a gas flow such that the cementing atmosphere is saturated or has a high cementing potential, and in that the process gas injection phases are obtained by means of a plurality of injection nozzles implemented in a sequence making it possible to generate a moving gas flow on the parts to be treated.
  • the main cementing agent is ethylene from "cracking", propane or ethane, methane being the least effective compound.
  • Another important advantage of the process according to the invention consists in that it makes it possible to control the residence time of the gas in the furnace: As soon as the injection stops (which caused a rise in pressure), the gas is quickly found pumped until the pressure returns to its initial value at which the treatment gas content is negligible. It then becomes possible to avoid passing below the saturation threshold of austenite and the resulting drawbacks.
  • the invention also relates to a device for implementing the method described above, this device involving a heat or thermochemical vacuum treatment oven, of the type comprising, inside a sealed enclosure connected to a pumping station, a thermally insulating muffle equipped with heating means, inside which the charges to be treated are arranged, and a plurality of means making it possible to inject a treatment gas inside the oven, the pumping being designed so as to be able to obtain inside the enclosure, a pressure of the order of 1 to 10 mbar, and the heating means being designed so as to carry the load disposed inside the oven, at a temperature between 800 ° C and 1100 ° C.
  • the invention proposes a gas injection system which makes it possible to rotate the gas flow of hydrocarbon in the enclosure of the furnace whatever its geometry, and this, in order to cement any type of parts. , homogeneously, without introducing any complex mechanism in the hot part of the oven.
  • the device according to the invention is characterized in that the injection means comprise a plurality of injection nozzles connected to respective solenoid valves controlled by a computer programmed so as to carry out injection phases having each a duration calculated so as to be less than the time of transition to the saturation phase of the austenitic phase of the steel brought to high temperature, each injection phase comprising a sequence of successive openings and closings of the solenoid valves, according to a pre-established sequence, causing a displacement of treatment gas flow on the parts to be treated.
  • the above sequence may be designed so as to obtain an atmosphere of pulsating cementing gas, in permanent, circular or helical movement.
  • the pressure inside the furnace (indicated in thick lines) is maintained by pumping at a relatively low value until an instant t1 which follows a phase P6 of thermal homogenization of the parts at the temperature treatment (for example 30 minutes after the temperature has reached the treatment temperature).
  • a first carbon enrichment phase C1 is initiated, by carrying out a first injection of treatment gas, for a short duration (from 1 s to 5 min).
  • This injection has the effect of slightly increasing the pressure for a period calculated so as to avoid exceeding the saturation threshold of the austenite. Due to the pumping of the injected gas, the pressure then quickly returns to its initial value (instant t2).
  • the duration of this enrichment phase C1 is generally of the order of a few seconds to a few minutes.
  • a first diffusion phase D am (diffusion of carbon towards the core of the steel) is initiated during which the temperature is maintained at the treatment temperature, and the atmosphere at low pressure does not contains almost more process gas to allow carbon enrichment.
  • a second carbon enrichment phase C2 is triggered by carrying out a second injection of treatment gas.
  • the duration of this second enrichment phase may be different from that of the first, provided that the saturation threshold previously mentioned is not exceeded.
  • the treatment ends with the vacuum quenching using oil or pressurized gas (phase P5) which occurs (instant t5) after a diffusion phase D2 (instant t4) of a duration substantially equal to that of the diffusion phase D1.
  • the temperature suddenly changes from the treatment temperature to the ambient temperature corresponding to the quenching operation of the steel or hardening of the case-hardened steel.
  • the invention is not limited to the previously described treatment cycle:
  • the number of enrichment phases and the number of diffusion phases could be greater than two depending on the desired cemented depth.
  • FIG. 2 shows an installation capable of carrying out a cementation treatment at low pressure using a vacuum type heat treatment furnace of the bell type, that is to say comprising a sealed enclosure comprising a cylindrical body 1, oriented vertically and open in its lower part, this body being movable and mounted in a sealed and disconnectable manner on a circular base 2 forming the bottom of the oven on which the parts to be treated are placed.
  • a vacuum type heat treatment furnace of the bell type that is to say comprising a sealed enclosure comprising a cylindrical body 1, oriented vertically and open in its lower part, this body being movable and mounted in a sealed and disconnectable manner on a circular base 2 forming the bottom of the oven on which the parts to be treated are placed.
  • the body 1 contains a cylindrical muffle 3 made of refractory material, inside of which electrical heating resistors 4 are arranged making it possible to provide heating of the parts by radiation.
  • the interior volume of the oven is connected to a suction circuit comprising a vacuum pump 5 controlled by a regulation circuit at least partially housed in a control cabinet 6.
  • This control cabinet 6 also contains the usual electronic instruments such as displays or recorders as well as the device for programming and regulating the heating.
  • the interior volume of the enclosure is connected to a treatment gas injection system comprising one or more (here, a source of propane and a source of nitrogen) gas sources G1, G2 connected to nozzles injection 7 which pass through the body 1 / muffle 3 assembly, by means of a circuit successively comprising a flow meter 8 and solenoid valves (block 9) each associated with one or more injection nozzles 7.
  • a treatment gas injection system comprising one or more (here, a source of propane and a source of nitrogen) gas sources G1, G2 connected to nozzles injection 7 which pass through the body 1 / muffle 3 assembly, by means of a circuit successively comprising a flow meter 8 and solenoid valves (block 9) each associated with one or more injection nozzles 7.
  • the oven comprises six groups of three nozzles (B1 to B18) arranged vertically one above the other, these groups being angularly offset by 60 ° with respect to each other ( Figures 3 and 4).
  • FIG. 6 is an unrolled view of the cylindrical surface of the muffle 3, in which the locations of the injection nozzles B1 to B18 have been indicated, while FIG. 5 shows an embodiment of an injection circuit comprising nine solenoid valves E1 to E9, at the rate of one solenoid valve for two injection nozzles each belonging to two different groups.
  • a microcomputer 11 suitably programmed so as to obtain, during the enrichment phases, a current of pulsating cementing gas in permanent movement.
  • each solenoid valve can work for 2.77 hundredths of a second during a loop of duration of the order of 0.5 seconds.
  • the cementing gas may, as for it has a speed of 1.48 m / s at the outlet of the injection nozzles.
  • two additional solenoid valves E10 and E11 are provided at the outlet of the two sources G1, G2 so as to send into the injection circuit either the cementing gas (propane) or the neutral gas (nitrogen) used to clean the nozzles after each carburizing phase.
  • FIG. 7 shows a mode of implantation of the injection nozzles in an oven of which the muffle 12 has simply been shown diagrammatically.
  • the right and left lateral faces FD, FG of the muffle 12 are crossed by three batteries of five injection nozzles aligned horizontally on three respective levels, each nozzle being indicated by a point.
  • the upper face FS of the muffle 12 is, for its part, traversed by three batteries of five injection nozzles oriented parallel to the batteries of the side faces.
  • the nozzles of each of these faces are numbered from +1 to +18 in the order of their opening, during an injection cycle, it being understood that the solenoid valve which has the same number on each of the three faces of the oven opens at the same time and the sequence takes place in ascending order of the numbers.
  • the gas injection speed at the outlet of the nozzles can be, here, of the order of 4.71 m / s.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • On-Site Construction Work That Accompanies The Preparation And Application Of Concrete (AREA)

Claims (8)

  1. Verfahren zur Härtung von Stahlteilen, wobei dieses Verfahren darin besteht, die zu behandelnden Teile auf eine Temperatur zwischen 800 und 1100°C in einer Sauerstoff-freien Gasatmosphäre zu bringen, die durch Pumpen auf einem niedrigen Druck gehalten wird, und mehrere aufeinanderfolgende Phasen (C₁, C₂) der Anreicherung mit Kohlenstoff durchzuführen, die je durch eine zeitlich begrenzte Injektion eines Behandlungsgases erhalten werden, das einen oder mehrere reine Kohlenwasserstoffe enthält, wobei jede Anreicherungsphase (C₁, C₂) kürzer ist als die Übergangsphase der austenitischen Phase des auf hohe Temperatur gebrachten Stahls in die Sättigungsphase, wobei diese Anreicherungsphasen (C₁, C₂) durch längere Phasen (D₁, D₂) einer Vakuumdiffusion getrennt sind, die es ermöglichen, den Oberflächengehalt an Kohlenstoff einzustellen,
    dadurch gekennzeichnet, dass der Druck auf einem Wert zwischen 1 und 10 mbar mit einem solchen Gasdurchsatz gehalten wird, dass die härtende Atmosphäre gesättigt ist oder ein hohes Härtungspotential aufweist, und dass die Phasen der Injektion von Behandlungsgas mittels einer Vielzahl von Injektionsdüsen erhalten werden, die gemäss einer Folge verwendet werden, die es ermöglicht, einen Gasfluss zu erzeugen, der sich über die zu behandelnden Teile hinweg bewegt.
  2. Verfahren nach Anspruch 1,
    dadurch gekennzeichnet, dass das injizierte Gas Propangas oder Methangas ist, dessen "Cracking" oder Zerfall Äthylen und Methan sowie das Haupthärtungsmittel erzeugt, d.h. den atomaren Kohlenstoff, indem mittels eines angepassten ursprünglichen Gasdurchsatzes eine mit Kohlenstoff gesättigte Atmosphäre erzeugt wird.
  3. Verfahren nach einem der vorhergehenden Ansprüche,
    dadurch gekennzeichnet, dass die Injektion so erfolgt, dass der Gasfluss um die zu härtende Ladung gedreht wird.
  4. Verfahren nach Anspruch 1,
    dadurch gekennzeichnet, dass die Dauer jeder Injektionsphase zwischen 1 s und 5 min liegt und dass die Dauer einer Diffusionsphase immer länger ist als die Injektionszeit des härtenden Gases, die vor dieser Diffusionsphase liegt.
  5. Vorrichtung zur Anwendung des Verfahrens nach einem der vorhergehenden Ansprüche, wobei diese Vorrichtung einen Vakuumhärteofen der Art verwendet, der im Inneren eines dichten Raumes (1, 2) der mit einer Pumpstation (5) verbunden ist, einen mit Heizmitteln (4) versehenen wärmeisolierenden Muffel (3), in dessen Innerem die zu behandelnden Ladungen angeordnet sind, und eine Vielzahl von Mitteln (G₁, G₂, 7, 8, 9) aufweist, die es ermöglichen, ein Behandlungsgas ins Innere des Ofens zu injizieren, wobei die Pumpstation (5) so ausgebildet ist, dass man im Inneren des Raums einen Druck der Grössenordnung von 1 bis 10 mbar erhalten kann, und dass die Heizmittel (4) derart ausgebildet sind, dass sie die im Inneren des Ofens angeordnete Ladung auf eine Temperatur zwischen 800 und 1100°C bringen,
    dadurch gekennzeichnet, dass die Injektionsmittel (G₁, G₂, 7, 8, 9) eine Vielzahl von Injektionsdüsen (7) aufweisen, die je mit Elektroventilen (9) verbunden sind, die von einem Rechner (11) gesteuert werden, der so programmiert ist, dass Injektionsphasen durchgeführt werden, die je eine derart berechnete Dauer haben, dass sie kürzer sind als die Zeit des Übergangs der austenitischen Phase des auf hohe Temperatur gebrachten Stahls in die Sättigungsphase, wobei jede Injektonsphase eine Folge von aufeinanderfolgenden Öffnungen und Schliessungen der Elektroventile (9) gemäss einer vorbestimmten Folge aufweist, die eine Bewegung des Behandlungsgasflusses auf den zu behandelnden Teilen bewirkt.
  6. Vorrichtung nach Anspruch 5,
    dadurch gekennzeichnet, dass jede Injektionsphase mittels einer Vielzahl von Injektionsdüsen (7) erfolgt, deren Durchsatz von Elektroventilen (9) gesteuert wird, wobei die Anordnung der Düsen im Inneren des Ofens und die Steuerung der Elektroventile (9) durch den Rechner (11) so ausgelegt sind, dass der Gasfluss mit einer Drehbewegung um die Ladung bewegt wird.
  7. Vorrichtung nach Anspruch 6,
    dadurch gekennzeichnet, dass die Bewegung des Gasflusses eine ansteigende und abfallende Schraube ist.
  8. Vorrichtung nach Anspruch 6,
    dadurch gekennzeichnet, dass die Bewegung des Gasflusses eine waagerechte Schraube ist.
EP92402395A 1991-09-13 1992-09-03 Verfahren und Vorrichtung zum Aufkohlen von Stahl in einer Atmosphere von niedrigem Druck Expired - Lifetime EP0532386B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9111304 1991-09-13
FR919111304A FR2681332B1 (fr) 1991-09-13 1991-09-13 Procede et dispositif de cementation d'un acier dans une atmosphere a basse pression.

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EP0532386A1 EP0532386A1 (de) 1993-03-17
EP0532386B1 true EP0532386B1 (de) 1996-04-17

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EP (1) EP0532386B1 (de)
JP (1) JPH05195192A (de)
AT (1) ATE136946T1 (de)
DE (1) DE69209947D1 (de)
FR (1) FR2681332B1 (de)
TW (1) TW225558B (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6093303A (en) * 1998-08-12 2000-07-25 Swagelok Company Low temperature case hardening processes
US6165597A (en) * 1998-08-12 2000-12-26 Swagelok Company Selective case hardening processes at low temperature
US9212416B2 (en) 2009-08-07 2015-12-15 Swagelok Company Low temperature carburization under soft vacuum

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AT404029B (de) * 1996-09-16 1998-07-27 Ald Aichelin Ges M B H Niederdruck-aufkohlungsanlage
JP2000336469A (ja) * 1999-05-28 2000-12-05 Nachi Fujikoshi Corp 真空浸炭方法及び装置
US6547888B1 (en) 2000-01-28 2003-04-15 Swagelok Company Modified low temperature case hardening processes
FR2813892B1 (fr) * 2000-09-13 2003-09-26 Peugeot Citroen Automobiles Sa Procede de traitement thermique d'aciers d'outillages hypoeutectoides
FR2821362B1 (fr) 2001-02-23 2003-06-13 Etudes Const Mecaniques Procede de cementation basse pression
FR2832735B1 (fr) * 2001-11-24 2006-06-23 Bosch Gmbh Robert Dispositif et procede de cementation en depression
DE10209382B4 (de) * 2002-03-02 2011-04-07 Robert Bosch Gmbh Verfahren zur Aufkohlung von Bauteilen
DE10254846B4 (de) * 2002-11-25 2011-06-16 Robert Bosch Gmbh Verfahren zum Einsatzhärten von Bauteilen aus Warmarbeitsstählen mittels Unterdruckaufkohlung
JP4255815B2 (ja) * 2003-11-28 2009-04-15 光洋サーモシステム株式会社 ガス浸炭方法
JP4587719B2 (ja) * 2004-07-07 2010-11-24 中外炉工業株式会社 浸炭用ガス製造装置
JP5577573B2 (ja) * 2008-08-29 2014-08-27 株式会社Ｉｈｉ 真空浸炭処理方法および真空浸炭処理装置
DE102009008664A1 (de) * 2009-02-12 2010-08-19 Linde Aktiengesellschaft Vorrichtung und Verfahren zur Aufkohlung von Stahl
DK2804965T3 (da) 2012-01-20 2020-12-14 Swagelok Co Samtidigt flow af aktiveringsgas ved lavtemperatur-karburering
CN108350559B (zh) * 2015-10-30 2020-09-08 韩国生产技术研究院 低温渗碳处理方法及渗碳处理装置
KR101866754B1 (ko) * 2016-10-31 2018-06-18 한국생산기술연구원 저압 범위 내에서의 침탄방법

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US6093303A (en) * 1998-08-12 2000-07-25 Swagelok Company Low temperature case hardening processes
US6165597A (en) * 1998-08-12 2000-12-26 Swagelok Company Selective case hardening processes at low temperature
US9212416B2 (en) 2009-08-07 2015-12-15 Swagelok Company Low temperature carburization under soft vacuum

Also Published As

Publication number Publication date
EP0532386A1 (de) 1993-03-17
DE69209947D1 (de) 1996-05-23
TW225558B (de) 1994-06-21
JPH05195192A (ja) 1993-08-03
ATE136946T1 (de) 1996-05-15
FR2681332B1 (fr) 1994-06-10
FR2681332A1 (fr) 1993-03-19

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