EP0063655B1 - Verfahren zum Aufkohlen von Eisenmetallen - Google Patents

Verfahren zum Aufkohlen von Eisenmetallen Download PDF

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Publication number
EP0063655B1
EP0063655B1 EP19810301834 EP81301834A EP0063655B1 EP 0063655 B1 EP0063655 B1 EP 0063655B1 EP 19810301834 EP19810301834 EP 19810301834 EP 81301834 A EP81301834 A EP 81301834A EP 0063655 B1 EP0063655 B1 EP 0063655B1
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EP
European Patent Office
Prior art keywords
furnace
atmosphere
carbon
oxygenated hydrocarbon
nitrogen
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Application number
EP19810301834
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English (en)
French (fr)
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EP0063655A1 (de
Inventor
Jelle Hillebrand Kaspersma
Robert J. Peartree
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Air Products and Chemicals Inc
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Air Products and Chemicals Inc
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Application filed by Air Products and Chemicals Inc filed Critical Air Products and Chemicals Inc
Priority to EP19810301834 priority Critical patent/EP0063655B1/de
Priority to DE8181301834T priority patent/DE3174840D1/de
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Classifications

    • 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 invention relates to a process for gas carburization of ferrous metals and in particular to a process wherein a furnace atmosphere is created by injecting an oxygenated hydrocarbon into said furnace during the period of rapid carburization followed by control of the atmosphere during the later stages of carburization by reducing the rate of injection of oxygenated hydrocarbon while maintaining volumetric flow through the furnace by injecting a nonreactive gas along with said oxygenated hydrocarbon.
  • Carbon potential of the furnace atmosphere is maintained during the carburizing cycle by the addition of controlled amounts of enriching or hydrocarbon carburizing agents to the mixture.
  • Carburization is the conventional process for case hardening of steel.
  • gas carburizing the steel is exposed to an atmosphere which contains components capable of transferring carbon to the surface of the metal from which it diffuses into the body of the part.
  • atmospheres A variety of atmospheres have been employed but the most commonly used one is the so-called endothermic (endo) atmosphere derived by partial combustion of natural gas in air. It is usually necessary to add a relatively small quantity of another constituent, usually natural gas, to the atmosphere to raise the carbon potential.
  • the steel objects to be carburized are exposed at an elevated temperature, usually in the range of about 1600°F (871°C), until carbon penetration to a desired depth has been achieved.
  • the metal can then be cooled to room temperature by various known methods such as furnace, air, and media quench to develop the desired physical properties and case hardness in the finished article.
  • the basic endothermic atmosphere produced by the incomplete combustion of natural gas in air consists of approximately 40% N 2 , 40% H 2 , and 20% CO.
  • the reaction by which carbon is generally believed to be deposited on the surface of the steel is represented by the following equation (1).
  • Equations (1) and (2) may be added together to yield reaction (3).
  • the ratio of H 2 to CO is 2 to 1, the same as that produced in the endothermic atmosphere by partial combustion of natural gas.
  • By choice of appropriate quantities of nitrogen and methanol it is possible to generate a synthetic atmosphere which is essentially identical in composition to that produced by the partial combustion of natural gas.
  • the advantages of using such a synthetic atmosphere are several fold. First, the need'for an expensive and elaborate endo gas system is eliminated. The endo gas generator requires continuing maintenance and attention of an operator and furthermore it cannot be turned on and off at will. Once it is running it is necessary to keep it in operation even though the demand for the endothermic atmosphere may vary from maximum load to zero, thus the endo gas, and the natural gas required to produce it are wasted during periods of low demand.
  • nitrogen and methanol require only those storage facilities adequate for liquid or gaseous nitrogen and liquid methanol until they are needed. Furthermore, the nitrogen and methanol can both be injected as such directly into the furnace without the need for a separate gas generator. The methanol is immediately cracked by the high temperatures encountered in the furnace.
  • a further advantage of the methanol- nitrogen system is that the methanol is uniform in composition while natural gas contains, in addition to methane, widely varying amounts of ethane, propane and other higher hydrocarbons which affect the stoichiometry of the partial combustion reaction and may give rise to atmospheres of substantially varying composition which in turn leads to erratic and poorly controlled behavior of the carburization process itself.
  • a pure methanol-based atmosphere is inherently more expensive both in terms of monetary value and the energy required to produce it, than is an atmosphere derived in part from methanol.
  • total energy requirement to produce 2,8 m 3 of base gas nitrogen at 1700°F (927°C) is 39,27x 10 6 J, while to produce the same volume of a base gas consisting of two-thirds H 2 and one-third CO by decomposition of methanol 65,25x 1 0 6 are required.
  • the atmosphere derived from pure methanol is advantageous in insuring that carburization proceeds uniformly and at a rapid rate, it is more expensive and consumes more energy than does an atmosphere derived from a combination of methanol and nitrogen.
  • the more rapid carburization achieved with the pure methanol atmosphere is desirable since it results in a shorter cycle time to achieve a given case depth, and thereby lowers the amount of energy lost through the furnace walls.
  • this gain in energy conservation is to some extent offset by the higher thermal conductivity of the pure methanol-derived atmosphere as compared to the synthetic endo atmosphere because of the greater hydrogen content of the former. It is estimated that this increased hydrogen concentration results in a heat loss rate ranging from about 9% to about 14% greater for the all-methanol derived atmosphere.
  • an oxygenated hydrocarbon containing carbon, hydrogen, and oxygen having from 1 to 3 carbon atoms, no more than one carbon to carbon bond and a carbon to oxygen ratio of from 1 to 2 selected from the group consisting of alcohols, aldehydes, ethers, esters and mixtures thereof, and in particular the pure methanol-derived atmosphere during the first part of a carburization cycle provides the advantage of initially high carburization rate which is manifested in a reduced total cycle time. But it has also been found that after a period of time, part of the expensive methanol is replaced by less expensive nitrogen without an accompanying increase in the time necessary to achieve a given case depth.
  • a carrier gas mixture is obtained by catalytic partial oxidation of hydrocarbons (e.g. natural gas) resulting in a mixture which consists mainly of 20% CO, 40% H 2 and 40% N 2 .
  • Hydrocarbons e.g. excess natural gas
  • the carbon potential which determines the degree of carburization, is controlled by monitoring either the CO 2 or the H 2 0 concentration in the furnace gas. Theoretically, the proper control parameters are Pco 2 /Pco Z and PcoPH 2 /PH Z o, but since Pco and PH 2 are kept virtually constant, one component control by P C02 or PH 2 0 is possible.
  • the carrier gas may also be generated by thermal cracking of mixtures of nitrogen and oxygenated hydrocarbons (e.g. methanol).
  • nitrogen and oxygenated hydrocarbons e.g. methanol
  • Methanol is the preferred oxygenated hydrocarbon for this process however ethanol, acetaldehyde dimethylether, methyl formate and methylacetate have been shown to produce high CO and H 2 levels. So far efforts have been directed to imitating the composition of the endo gas mixture only, in order to achieve comparable results at temperature. This makes it possible to use exactly the same carbon control mechanism as used with the endo system, (i.e. conventional one component carbon control).
  • the present invention is directed toward improving the results obtained by the endothermic process, but at the same time at maintaining its simple carbon control mechanism. Better results are obtained by increasing the carbon transfer rate. This is achieved by higher CO and H 2 concentrations which enhance the rate of the main carbon transfer reaction:
  • the present invention resides in maintaining CO and H 2 concentrations higher than endo composition in the first part of the cycle in order to speed up carbon transfer and to reduce CO and H 2 concentrations in the later part of the cycle to endo composition which will enable the use of conventional one component control.
  • Higher CO and H 2 levels may be obtained by reducing the nitrogen content in a nitrogen-oxygenated hydrocarbon mixture to be thermally cracked.
  • the exit line was fitted with a sampling device and analytical means which permitted measurement of the concentration of carbon monoxide and carbon dioxide in the exit stream.
  • the carbon potential of the exit gas was calculated according to well-known chemical equilibrium equations and the amount of the enriching gas admitted to the furnace was varied so as to maintain a desired carbon potential (CP) in the furnace.
  • An increase in enriching gas (e.g. natural gas) flow resulted in an increase in carbon potential while a decrease in enriching gas resulted in an corresponding decrease in carbon potential.
  • the furnace was loaded with approximately 15 Ib (6.8 kg) of 1010 steel rivets, purged with nitrogen, and brought up to a final temperature of 1700°F (927°C). Nitrogen and/or methanol was passed into the furnace at a combined rate corresponding to about 3-5 standard volume changes per hour of the furnace atmosphere.
  • the first of these was generated by the introduction of methanol alone to the furnace, and the furnace atmosphere consisted of a mixture of approximately 2/3 hydrogen and 1/3 carbon monoxide.
  • the second atmosphere known as the Endo atmosphere, was derived from a combination of two parts nitrogen and one part methanol vapor by volume, and had a finalcomposition of approximately 40% nitrogen, 40% hydrogen and 20% carbon monoxide.
  • the third atmosphere known as the 10% atmosphere, was generated by passing a mixture consisting of approximately 10% methanol and 90% nitrogen into the furnace. Its composition was approximately 75% nitrogen, 16.7% hydrogen and 8.3% carbon monoxide.
  • Each test involved a total time cycle of three hours including a heat recovery period after loading of thirty minutes. At the end of this time, the rivets were discharged from the furnace, quenched and subjected to metallurgical testing to determine the case depth and hardness. The effectiveness of carbon potential control was determined by the analysis of a shimstock sample which had been placed in the furnace along with the rivets.
  • Examples 1-1 through I-5 natural gas was introduced at an initial rate corresponding to approximately 10% of that of the total gas flow, and was adjusted so as to give a target carbon potential of 1.0% when the furnace load had come to the final temperature of 1700°F (927°C).
  • the 100% Endo, and 10% atmospheres were employed throughout the entire cycle. The decline in capability of effecting carbon transfer as the nitrogen content of the atmosphere is increased is evident from the case depth data.
  • the Endo atmosphere is only about 87% as effective overall as is the 100% atmosphere, while the 10% atmosphere is only 64% as effective as the 100% atmosphere.
  • Tests 1-6 and 1-7 indicate that under the conditions of these tests (10% natural gas during warmup) little is accomplished after the first 1.5 hours of operation with the 100% atmosphere. However, this is not the most energy efficient mode of operation.
  • Table II shows a pair of tests in which natural gas was introduced at a rate of 10% of the total flow for the first 1.5 hours of operation and then was adjusted to yield a carbon potential of 1.1%.
  • test II-1 the 100% base atmosphere was employed throughout the test while in test 11-2 the Endo atmosphere was employed throughout the test. Again the Endo atmosphere is somewhat less effective (93%) than the 100% atmosphere.
  • the final case depth in both tests is somewhat greater than in the first series of tests. This is probably due both to the longer time during which a high level of natural gas flow was maintained and the slightly higher target carbon potential employed.
  • Table III presents a series of tests according to the present invention in which an essentially 100% methanol atmosphere was maintained until the furnace temperature had reached 1600°F (871°C). At this time, natural gas was admitted at a rate such that a carbon potential of 1.1 was maintained.
  • Tests 111-3 and 111-4 indicate that the degree of carburization which can be achieved with a combination of 100% and Endo atmospheres is virtually equal to that which is achieved with the 100% atmosphere alone.
  • the degree to which the methanol is diluted by nitrogen may also be varied. In tests 111-1 thru 111-4 (Table III) dilution to about endo gas composition was found desirable. In Tests 1-4 and 1-5 Table I dilution to below endo gas composition was found desirable. In Tests 1-4 and 1-5 (Table I) dilution to below endo composition after only one hour of exposure to the 100% atmosphere lead to lower case depth, but in tests 1-6 and 1-7 (Table I) the 10% atmosphere was as effective as the endo atmosphere after 1.5 hours exposure to the 100% atmosphere.
  • the exact time and degree of dilution depends upon the carbon level desired at the surface of the workpiece, the case depth, and temperature at which carburization is carried out. In general, greater case depths and the correspondingly longer times involved, permit greater dilution of the atmosphere. With longer times and greater case depths, the rate of diffusion of carbon from the surface declines and an atmosphere capable of effecting rapid carbon transfer is not needed.
  • gaseous ammonia can be added to the atmosphere to achieve carbonitriding of ferrous metal parts.
  • Processes according to the present invention can be used in place of existing gas carburizing processes in batch type furnaces and with proper furnace control in continuous furnaces.
  • Existing furnaces can be readily adapted to the present invention without altering systems used to measure carbon potential and with only minor furnace additions to accommodate the hydrocarbon and gas sources.

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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)

Claims (9)

1. Verfahren zum Aufkohlen von eisenhaltigen Gegenständen, dadurch gekennzeichnet, daß man
a. einen Ofen, der bei einer Temperatur über 1500°F (816°C) gehalten wird, mit den zu behandelnden Gegenständen beschickt;
b. einen sauerstoffhaltigen Kohlenwasserstoff, der bis zu drei Kohlenstoffatome und nicht mehr als eine Kohlenstoff-Kohlenstoff-Verbindung enthält, sowie ein Kohlenstoff zu Sauerstoff-Verhältnis von 1 zu 2 und einen Siedepunkt von nicht höher als 100°C aufweist, in den Ofen einführt, wobei der sauerstoffhaltige Kohlenwasserstoff aus der Gruppe bestehend aus Alkoholen, Aldehyden, Ester, Ether und Mischungen davon, ausgewählt wird, um im Ofen zu reagieren und um die Aufkohlungsatmosphäre zu bilden;
c. die Einführungsgeschwindigkeit des sauerstoffhaltigen Kohlenwasserstoffes und Zufügung eines Kohlenwasserstoffgases so einstellt und aufrechterhält, daß ein Kohlenstoffpotential zwischen 0,8 und 1,1% in der Ofenatmosphäre zumindest in jenem Anteil des Aufkohlungsverfahrens aufrechterhalten wird, in dem eine rasche Aufkohlung erfolgt;
d. anschließend die Einführungsgeschwindigkeit des sauerstoffhaltigen Kohlenwasserstoffes unter Beibehaltung der Gesamt-Einführungsgeschwindigkeit durch Einführen von Stickstoff in den Ofen vermindert, um eine Aufkohlungsatmosphäre für eine bestimmte Zeit zur Vervollständigung der Aufkohlung der Gegenstände bis in die gewünschte Schichttiefe aufrecht zu erhalten; und
e. die Gegenstände aus dem Ofen entfernt und diese mit einer Geschwindigkeit, die durch die gewünschten physikalischen Eigenschaften der Gegenstände bestimmt wird, abkühlt.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man den Ofen bei einer Temperatur zwischen 1550°F (816°C) und 1900°F (1038°C) hält.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der sauerstoffhaltige Kohlenwasserstoff aus der Gruppe bestehend aus Methanol, Ethanol, Acetaldehyd, Dimethylether, Methylformiat, Methylacetat und Mischungen davon ausgewählt ist.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man vor dem Beschichten des Ofens ein flüssiges Äquivalent von drei bis fünf Volumen-Beladungen sauerstoffhaltigen Kohlenwasserstoff pro Stunde in den Ofen einsprüht, um die aus vorhergehenden Aufkohlungsabläufen entstandene Ofenatmosphäre zu konditionieren.
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man die verminderte Einführungsgeschwindigkeit des sauerstoffhaltigen Kohlenwasserstoffes dadurch erreicht, indem man Stickstoff mit einem Verhältnis von 2 zu 1 bis -10 zu 1 zu sauerstoffhaltigem Kohlenwasserstoff bis zu einem Gesamt-Volumenfluß einführt, der gleich dem Volumen des sauerstoffhaltigen Kohlenwasserstoffes ist, der im vorhergehenden Schritt eingeführt wurde.
6. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß das Verhältnis von Stickstoff zu sauerstoffhaltigem Kohlenwasserstoff 2 zu 1 beträgt.
7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man die schnelle Aufkohlung dadurch erreicht, indem man die sauerstoffhaltigen Kohlenwasserstoffe zur Aufrechterhaltung einer Ofenatmosphäre aus etwa zwei Drittel Wasserstoff zu einem Drittel Kohlenmonoxid einführt.
8. Verfahren nach Anspruch 1 oder 4, dadurch gekennzeichnet, daß das Verhältnis von Stickstoff zu sauerstoffhaltigem Kohlenwasserstoff 9 zu 1 beträgt.
9. Verfahren nach Anspruch 1 oder 4, dadurch gekennzeichnet, daß gasförmiges Ammoniak ebenfalls in den Ofen eingeführt wird, um die Teile zu carbonitrieren.
EP19810301834 1981-04-27 1981-04-27 Verfahren zum Aufkohlen von Eisenmetallen Expired EP0063655B1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP19810301834 EP0063655B1 (de) 1981-04-27 1981-04-27 Verfahren zum Aufkohlen von Eisenmetallen
DE8181301834T DE3174840D1 (en) 1981-04-27 1981-04-27 Process for carburizing ferrous metals

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP19810301834 EP0063655B1 (de) 1981-04-27 1981-04-27 Verfahren zum Aufkohlen von Eisenmetallen

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EP0063655A1 EP0063655A1 (de) 1982-11-03
EP0063655B1 true EP0063655B1 (de) 1986-06-18

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3631389A1 (de) * 1985-09-20 1987-03-26 Aichelin Ind E Com Fornos Ind Verfahren zur anreicherung der atmosphaere von oefen zur thermo-chemischen behandlung von metallteilen
DE4340060C1 (de) * 1993-11-24 1995-04-20 Linde Ag Verfahren zum Gasaufkohlen

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3460075B2 (ja) * 1995-12-28 2003-10-27 同和鉱業株式会社 金属の浸炭方法
CN112899611B (zh) * 2021-01-19 2022-09-27 潍坊丰东热处理有限公司 一种热处理方法及热处理工装

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1110675B (de) * 1954-12-18 1961-07-13 Renault Verfahren zur Herstellung von stickstoffhaltigen Gasatmosphaeren zur Aufkohlung oder zum Schutz von Staehlen
DE1167152B (de) * 1957-12-26 1964-04-02 Renault Verfahren zum Aufkohlen von Stahl unter Verwendung von Methylalkohol und enthaltenden Gasgemischen
DE1446242A1 (de) * 1960-03-02 1969-03-20 Siemens Ag Verfahren zum Aufkohlen von Eisenwerkstoffen durch organische Fluessigkeiten
NL126085C (de) * 1960-06-17
CH548457A (de) * 1969-12-04 1974-04-30 Maag Zahnraeder & Maschinen Ag Verfahren zum regelbaren aufkohlen der oberflaechenschicht von werkstuecken aus stahl.

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3631389A1 (de) * 1985-09-20 1987-03-26 Aichelin Ind E Com Fornos Ind Verfahren zur anreicherung der atmosphaere von oefen zur thermo-chemischen behandlung von metallteilen
DE4340060C1 (de) * 1993-11-24 1995-04-20 Linde Ag Verfahren zum Gasaufkohlen

Also Published As

Publication number Publication date
EP0063655A1 (de) 1982-11-03
DE3174840D1 (en) 1986-07-24

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