EP0096602B1 - Verfahren zur Wärmebehandlung von metallischen Werkstücken durch Aufkohlung - Google Patents

Verfahren zur Wärmebehandlung von metallischen Werkstücken durch Aufkohlung Download PDF

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Publication number
EP0096602B1
EP0096602B1 EP83400935A EP83400935A EP0096602B1 EP 0096602 B1 EP0096602 B1 EP 0096602B1 EP 83400935 A EP83400935 A EP 83400935A EP 83400935 A EP83400935 A EP 83400935A EP 0096602 B1 EP0096602 B1 EP 0096602B1
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EP
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Prior art keywords
atmosphere
phase
nitrogen
carbon
furnace
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Expired
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EP83400935A
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English (en)
French (fr)
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EP0096602A1 (de
Inventor
Michel Kostelitz
Phillippe 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
Priority to AT83400935T priority Critical patent/ATE16118T1/de
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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 process for heat treatment of metal parts, in particular steel parts, by carburetion.
  • the atmospheres generally used contain around 20% CO, 40% H Z , 40% N 2 , and very small amounts of carbon dioxide and water vapor. These atmospheres are obtained either from so-called endothermic generators, or synthetically from a gas-gas or gas-alcohol mixture; the most common of these synthetic mixtures is nitrogen-methanol: in fact, at the treatment temperatures used, methanol decomposes according to the reaction CH 3 OH ⁇ CO + 2H 2 and it is possible to obtain a gaseous mixture having the composition given ci -above.
  • the carburetion process takes place as follows: the carbon monoxide present in the treatment atmosphere reacts according to the relationship: 2CO ⁇ CO 2 + C (1) and there is then transfer of the carbon atoms to the metal.
  • the hydrogen present in the atmosphere also participates in carburetion from the point of view of the speed of the process because it reacts with carbon monoxide according to the reaction: CO + H 2 ⁇ C + H 2 0 (2).
  • a hydrocarbon such as carbon dioxide is injected into the furnace, in addition to the mixture intended to form the species CO, H 2 , N 2.
  • methane, propane, or butane in each of said zones and the flow rate of this hydrocarbon is adjusted as a function of the CO 2 content of the atmosphere.
  • the reaction of CO consumption by the part to be treated see equation (1)
  • the air inlets in the treatment enclosure the CO 2 concentration of the atmosphere tends to increase and therefore the carbon potential to decrease. This is why the CO 2 content of the atmosphere is monitored and the injection rate of the hydrocarbon is adjusted accordingly as a function of the desired carbon potential.
  • This regulation can also be carried out by monitoring the H 2 0 or O 2 content of the atmosphere.
  • the subject of the invention is a method of heat treatment of metal parts by carburetion which makes it possible to obtain a surface hardening and a carburetted depth of the treated parts satisfactory with a shorter treatment time.
  • the process according to the invention consists in placing the parts to be treated in an oven and in maintaining them, in a carbon enrichment atmosphere comprising in particular carbon monoxide, hydrogen and nitrogen, said treatment comprising a first phase carried out at a temperature of 850 ° C to 1050 ° C followed by a second phase carried out at a temperature of 700 ° C to 950 ° C (preferably 800 ° C to 950 ° C).
  • an atmosphere containing approximately 20% to 50% by volume of CO and approximately 40% to 75% by volume of H 2 and having a high carbon potential very close to the limit value leading to soot deposits, ie a potential carbon of about 1.1% to 1.6% by weight, and, in the second phase, to have a carbon potential significantly lower than that of the first phase, a 2 to 30-fold increase in the nitrogen content of said atmosphere so that the carbon potential difference between each of said phases is at least about 0.5% by weight.
  • the concentration of nitrogen in said atmosphere is approximately at most 40% by volume, and during the second phase, said concentration is about 30% to 80% by volume.
  • the holder sought to increase the carbon potential during the first phase to accelerate the carbon enrichment of the part.
  • the potential decreases with the ratio In d i laminatent the atmosphere by nitrogen, it decreases the partial pressures of CO and C0 2 in the same proportions; however, the report decreases and therefore the carbon potential decreases.
  • Fig. 1 represents the theoretical evolution of the carbon potential in an oven at constant temperature (without taking into account the influence of the tightness of the oven and the nature of its internal wall), under an initial atmosphere based on CO , H 2 and N 2 , when high nitrogen flows are injected into this furnace.
  • two curves (I) and (II) are shown, giving the carbon potential as a function of time for respectively, a ratio D being the nitrogen flow injected into the furnace in m 3 / h and V the volume of the furnace in m 3 .
  • the treatment atmosphere is formed by introducing into the oven a mixture of nitrogen and methanol (the methanol being sprayed by the stream of nitrogen gas) in such proportions that the desired percentages of CO and H 2 are obtained.
  • the treatment atmosphere can also be formed by introducing an endothermic gas into the oven.
  • a gaseous hydrocarbon such as methane, propane or butane is also introduced in a small percentage (from 0.5% to 5%) relative to the whole of the mixture introduced.
  • gaseous ammonia in a proportion of 0.1% to 10% by volume relative to the whole of the gaseous mixture introduced; there is then carbonitriding.
  • This alternative embodiment makes it possible to obtain additional surface hardening of the treated parts.
  • the quantity of ammonia introduced into the furnace is chosen according to the steel treated and the degree of nitriding desired.
  • a treatment is carried out in accordance with the invention on steel parts of grade 18CD4 in an oven of the “batch” type shown diagrammatically in FIG. 2 attached.
  • This oven 1 consists of a metal enclosure coated internally with a refractory lining. It has a treatment zone 2 provided with a loading door 3 for the parts to be treated and an airlock 4 provided with a tank 5 for quenching in oil and an outlet door 6 for the treated parts. The treatment zone 2 and the airlock 4 are separated by an interior door 7.
  • the parts to be treated are placed in a basket 8 resting on the bottom of the treatment zone 2.
  • a turbine 9 the function of which is to continuously brew the atmosphere of the furnace is placed at a distance above the basket 8.
  • Reservoirs of nitrogen, methanol and methane, symbolized respectively in 10, 11 and 12, are connected via conduits 13, 14 and 15, fitted with valves 16, 17 and 18, to a pipe 19 which opens into the upper part of the treatment zone 2.
  • the gaseous treatment mixture is evacuated by burning a flare 20.
  • the oven is heated to a temperature of 920 ° C. and then a nitrogen-methanol mixture is introduced into it in proportions such that the atmosphere formed in the oven contains in main species approximately 10% N 2 , 30% CO and 60% H 2 .
  • the parts to be treated are placed in the treatment zone 2, we wait until the temperature rises to 920 ° C and the carbon potential of the atmosphere reaches 1.3% and we control the parts in this atmosphere for 2 h 25 min. During this phase, the CO 2 level in the atmosphere is 0.20%.
  • the second phase is then carried out at 860 ° C., increasing the quantity of nitrogen injected into the treatment zone 2 so that the atmosphere formed in the enclosure contains in main species approximately 70% N 2 , 10% CO and 20% H 2 and that the carbon potential is 0.7%, and the parts are kept in this atmosphere for 45 min.
  • the rate of C0 2 in the atmosphere is 0.095%.
  • a small percentage of methane is injected into zone 2 of the furnace (0.5 to 5% relative to the total amount of gaseous mixture introduced) and the injection rate of said methane is adjusted to adjust the carbon potential at the expected value.
  • a treatment is carried out using an atmosphere rich in fuel species having exactly the same composition as that of the first phase of the treatment according to the invention described in Example 1 above, but without modify the nitrogen injection during the second phase, that is to say at constant atmosphere; this comparative treatment is carried out in the same furnace and on 18CD4 steel parts identical to those of Example 1.
  • the first phase is therefore carried out at a temperature of 920 ° C. with an atmosphere whose concentration in main species is 10% N 2 , 30% CO and 60% H 2 , and with injection of a small amount of methane and adjustment of the injection rate of said methane to adjust the value of the carbon potential to 1%; the rate of C0 2 in the atmosphere is 0.28%; the parts are kept in this atmosphere for 3 h.
  • the second phase is then carried out at 860 ° C., with the same atmosphere as above, for 1 h, adjusting the carbon potential to 0.8%; the CO 2 level in the atmosphere is 0.72%.
  • a treatment is carried out in accordance with the invention on steel parts of grade 18CD2, in a continuous pushing oven, shown diagrammatically in FIG. 3 attached.
  • This oven 21 comprises an entry airlock 22 provided with a loading door 23 for the parts to be treated, a carburizing zone 24, a diffusion zone 25, and an exit airlock 26 provided with an exit door 27 of the parts processed.
  • the entry airlock 22, the cementation zone 24, the diffusion zone 25 and the exit airlock 26 are separated from each other by internal doors 28.
  • the parts to be treated are arranged in baskets 29 which move on the bottom of the furnace 21.
  • the carburizing zone 24 has two parts A and B: in part A, the parts to be treated are brought to temperature, and in part B the carburizing itself.
  • Turbines 30, the function of which is to permanently stir the atmosphere of the furnace, are placed at a distance above the baskets 29, in part B of the cementation zone 24 and in the diffusion zone 25.
  • Nitrogen, methanol and methane tanks are connected by means of conduits 34, 35 and 36, provided of valves 37, 38 and 39, to a pipe 40 which opens into part B of the carburizing zone 24.
  • a pipe 41 provided with a valve 42 and connected to a nitrogen tank symbolized at 43, opens into the diffusion zone 25.
  • the evacuation of the treatment gas mixture is carried out by burning using a flare 44.
  • the treated parts are then cooled in an oil bath (not shown in the figure).
  • the carburizing zone 24 is brought to a temperature of 900 ° C.
  • a nitrogen-methanol mixture is injected into this zone in proportions such that the atmosphere formed in said zone contains in main species approximately 10% N 2 , 30% CO and 60% H 2 , as well as a small amount of methane (0.5% to 5% relative to the total amount of the gaseous mixture introduced) so as to obtain a C0 2 rate of 0.27%, which corresponds at a carbon potential of 1.2%.
  • Part B of the carburizing zone 24 can contain five baskets.
  • Diffusion zone 25 is at 860 ° C. In this zone only nitrogen is injected (fuel species such as CO and H 2 coming directly from the cementation zone), in an amount such as the atmosphere in this zone diffusion contains about 10% CO, and 20% H 2 .
  • the CO 2 rate in the atmosphere is 0.115%, which corresponds to a carbon potential of 0.6%.
  • the diffusion zone 25 can contain two baskets.
  • the baskets containing the parts to be treated are introduced into the oven every 11 min 15 s; the pieces therefore remain for approximately 56 min 15 s in the cementation zone and 22 min 30 s in the diffusion zone.
  • a treatment is carried out using an atmosphere rich in fuel species, with the same composition of N 2 , CO and H 2 (10% N 2 , 30% CO and 60% H 2 ) as the atmosphere used in the carburizing zone during the treatment according to the invention in Example 2 above; but, in this comparative treatment, the atmosphere is the same as in the carburizing zone and in the diffusion zone.
  • the treated parts and the temperatures of the cementation and diffusion zones are the same as those of Example 2.
  • the CO 2 content of the atmosphere is 0.37% in the cementation zone, which corresponds to a carbon potential of 0.9%; and the CO 2 level of the atmosphere in the diffusion zone is 0.85%, which corresponds to a carbon potential of 0.7%. It is not possible to envisage a greater variation in the rate of C0 2 between the two zones, therefore a higher carbon potential in the first zone, owing to the fact that there is no modification of the global atmosphere.
  • the baskets containing the parts to be treated are introduced into the oven every 15 min; the pieces therefore remain 1 h 15 min in the cementation zone and 30 min in the diffusion zone.

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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)
  • Automobile Manufacture Line, Endless Track Vehicle, Trailer (AREA)

Claims (8)

1. Verfahren zur Wärmebehandlung von metallischen Werkstücken, insbesondere von Werkstücken aus Stahl, durch Aufkohlung, bei dem man die Werkstücke in einen Ofen gibt und in einer an Kohlenstoff angereicherten Atmosphäre, die besonders Kohlenmonoxid, Wasserstoff und Stickstoff enthält, hält, wobei diese Behandlung eine bei einer Temperatur von 850° C bis 1050° C durchgeführte erste Phase aufweist, auf die eine bei einer Temperatur von 700° C bis 950° C durchgeführte zweite Phase folgt, dadurch gekennzeichnet, dass man während der ersten Phase eine Atmosphäre verwendet, die etwa 20 bis 50 Vol.-% CO und etwa 40 bis 75 Vol.-% H2 enthält und ein Kohlenstoffpotential von etwa 1,1 bis 1,6 Gew.-% aufweist, und dass man während der zweiten Phase, um ein wesentlich geringeres Kohlenstoffpotential als das der ersten Phase zu haben, den Stickstoffgehalt dieser Atmosphäre derart auf das 2- bis 30fache steigert, dass der Unterschied des Kohlenstoffpotentials zwischen jeder dieser Phasen wenigstens etwa 0,5 Gew.-% ist.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die zweite Phase bei einer Temperatur von 800° C bis 950° C durchgeführt wird.
3. Verfahren nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, dass während der ersten Phase die Stickstoffkonzentration in der Atmosphäre höchstens etwa 40 Vol.-% und während der zweiten Phase die Stickstoffkonzentration in der Atmosphäre etwa 30 bis 80 Vol.-% ist.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass man die an Kohlenstoff angereicherte Atmosphäre durch Einführung eines Gemisches von Stickstoff und Methanol in den Ofen bildet.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass man ausserdem einen gasförmigen Kohlenwasserstoff, wie Methan, Propan oder Butan, in einem Mengenverhältnis von 0,5 bis 5 Vol.-%, bezogen auf die Gesamtheit des in den Ofen eingespritzten Gemisches, einführt.
6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass man entsprechend der Behandlung die Konzentrationen an CO und CO2 und CO und O2 oder CO und H20 und C02 und O2 der gebildeten Atmosphäre misst, was gestattet, das Kohlenstoffpotential abzuleiten, und dass man die in den Ofen eingespritzte Stickstoffmenge sich derart verändern lässt, dass man für jede der beiden Phasen die erwünschten Kohlenstoffpotentialwerte bekommt.
7. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass man zuerst in Vorversuchen die Werte der Stickstoffkonzentration bestimmt, die die Atmosphäre haben muss, um die für jede der Phasen erwünschten Kohlenstoffpotentialwerte zu erhalten, dann die eigentliche Behandlung durchführt, indem man das Gemisch von Stickstoff und Methanol während jeder der beiden Phasen in solchen Mengenverhältnissen einspritzt, dass man die so festgelegten Stickstoffkonzentrationen bekommt, und das Kohlenstoffpotential einstellt, indem man die Menge des in den Ofen eingespritzten Kohlenwasserstoffes regelt.
8. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass man im Falle einer Carbonitrierung ausserdem in den Ofen gasförmiges Ammoniak in einem Mengenverhältnis von etwa 0,1 bis 10 Vol. -%, bezogen auf die Gesamtheit des in den Ofen eingespritzten Gemisches, einführt.
EP83400935A 1982-05-28 1983-05-09 Verfahren zur Wärmebehandlung von metallischen Werkstücken durch Aufkohlung Expired EP0096602B1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT83400935T ATE16118T1 (de) 1982-05-28 1983-05-09 Verfahren zur waermebehandlung von metallischen werkstuecken durch aufkohlung.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8209328A FR2527641A1 (fr) 1982-05-28 1982-05-28 Procede de traitement thermique de pieces metalliques par carburation
FR8209328 1982-05-28

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EP0096602A1 EP0096602A1 (de) 1983-12-21
EP0096602B1 true EP0096602B1 (de) 1985-10-16

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US (1) US4519853A (de)
EP (1) EP0096602B1 (de)
JP (1) JPH064906B2 (de)
AT (1) ATE16118T1 (de)
AU (1) AU560555B2 (de)
CA (1) CA1208528A (de)
DE (1) DE3361023D1 (de)
FR (1) FR2527641A1 (de)
ZA (1) ZA833445B (de)

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JP6773411B2 (ja) * 2015-12-08 2020-10-21 日本エア・リキード合同会社 浸炭システム及び表面硬化鋼材の製造方法
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Publication number Publication date
US4519853B1 (de) 1987-12-29
ATE16118T1 (de) 1985-11-15
EP0096602A1 (de) 1983-12-21
US4519853A (en) 1985-05-28
DE3361023D1 (en) 1985-11-21
CA1208528A (fr) 1986-07-29
JPH064906B2 (ja) 1994-01-19
ZA833445B (en) 1984-02-29
FR2527641B1 (de) 1985-02-22
AU560555B2 (en) 1987-04-09
AU1489083A (en) 1983-12-01
FR2527641A1 (fr) 1983-12-02
JPS58213870A (ja) 1983-12-12

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