EP0024106B1 - Method of heat treating ferrous workpieces - Google Patents

Method of heat treating ferrous workpieces Download PDF

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Publication number
EP0024106B1
EP0024106B1 EP19800302236 EP80302236A EP0024106B1 EP 0024106 B1 EP0024106 B1 EP 0024106B1 EP 19800302236 EP19800302236 EP 19800302236 EP 80302236 A EP80302236 A EP 80302236A EP 0024106 B1 EP0024106 B1 EP 0024106B1
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EP
European Patent Office
Prior art keywords
gas
furnace
air
endothermic
atmosphere
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP19800302236
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0024106A1 (en
Inventor
Charles Arthur Stickles
Claude Melvin Mack
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Original Assignee
Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ford Werke GmbH, Ford France SA, Ford Motor Co Ltd filed Critical Ford Werke GmbH
Publication of EP0024106A1 publication Critical patent/EP0024106A1/en
Application granted granted Critical
Publication of EP0024106B1 publication Critical patent/EP0024106B1/en
Expired legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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 method of heat treating ferrous workpieces.
  • the endothermic gas is produced in a gas generator, separate from the heat treatment furnace itself.
  • the gas is produced at elevated temperatures, cooled to ambient temperatures, then reheated again in the heat treatment furnace. No provision is made for storing the generated gas, thus, if the generator output cannot be fully utilized at any time, the excess gas is simply flared. This entire mode of operation is inefficient in its use of hydrocarbon gas.
  • Endothermic gas is usually produced at 1900-2000°F (1038-1093°C), from methane or propane according to the following approximate reaction:
  • the principal constituents of endothermic gas are CO, H 2 and N 2 with minor amounts of CO 2 , H 2 0 and CH 4 .
  • the proportions of CO, H 2 and N 2 vary with the C/H ratio of the hydrocarbon used as feed stock.
  • Heat must be supplied to an endothermic gas generator to sustain the reaction of a hydrocarbon with quantities of air substantially less than that needed for complete combustion.
  • a catalyst is therefore used in the generator by the prior art.
  • the composition of endothermic gas is modulated by varying the ratio of air and hydrocarbon fed to the generator. By this means, it is possible to produce gases which are neutral to (that is, will not carburize or decarburize) steel of a certain carbon content at a particular temperature.
  • Air/Methane ratios of about 2.5 and air/propane ratios of about 7.5 are commonly used when methane or propane is fed to the gas generator.
  • endothermic gas is enriched with, typically, a 3-12% methane addition at the carburizing furnace (or an equivalent amount of other hydrocarbon gas) so that the overall air/hydrocarbon ratio used to produce carburizing atmospheres may be as low as 1.6 when methane is used, or as low as 6.0 when propane is used.
  • endothermic gas generators are inefficient from the standpoint of energy consumption because after reacting air and hydrocarbon in the generator, the reacted gas is cooled to room temperature, piped to the heat treatment furnace, then reheated again when it enters the furnace.
  • furnace atmospheres for neutral hardening, annealing and carburizing could be generated within the heat treatment furnace itself. It has been proposed by the prior art, in certain instances, that the endothermic gas be produced directly in the actual furnace used for treatment of metal parts. However, when the process was conducted, undesirable carbon black formed on the surfaces of the work pieces which rendered the surfaces of the work pieces inactive. To solve this problem one approach suggested in U.S. Patents 3,519,257 and 3,620,518, employed a catalyst on the walls of the furnace in which the gas atmosphere was to be generated in situ. Furnace temperature of 870°C (for carbonitriding) and 900°C (for carburizing) are mentioned.
  • a method of heat treating ferrous based workpieces in a furnace chamber by heating said workpieces therein to a temperature of 1500-2000°F (800-1100°C) while in the presence of gaseous carbon source, characterised in that the gaseous carbon source is an endothermic gas formed continuously in the absence of a catalyst in situ in the furnace chamber from a feedstock containing oxygen and gaseous hydrocarbon and is passed through the furnace chamber at a flow rate sufficiently low to produce amounts of C0 2 and H 2 0 in the furnace chamber substantially equal to the amounts which would be present if the gas were in thermodynamic equilibrium.
  • the gaseous carbon source is an endothermic gas formed continuously in the absence of a catalyst in situ in the furnace chamber from a feedstock containing oxygen and gaseous hydrocarbon and is passed through the furnace chamber at a flow rate sufficiently low to produce amounts of C0 2 and H 2 0 in the furnace chamber substantially equal to the amounts which would be present if the gas were in thermodynamic equilibrium.
  • the air/hydrocarbon ratio be 1.6-2.4 when methane is selected and 6.0-7.2 when propane is selected. With such air/hydrocarbon ratios, soot-free carburization can be accomplished using the in situ generated atmosphere at lower temperatures without the necessity for special catalysts.
  • the method comprises supplying air and hydrocarbon gas to a furnace chamber at a predetermined ratio where the heat of the furnace chamber (maintained at a heat treating temperature of 1500-2000°F) (800­ 1100°C)) causes the gases to react and produce in situ an endothermic type gas atmosphere.
  • the endothermic type gas atmosphere is caused to flow through the furnace chamber at a low flow rate and the generation of the atmosphere can preferably be variably controlled to overcome the sensitivity of the method to impurities at such low flow rate.
  • Carbon is transferred from the furnace atmosphere to ferrous workpiece or vice-versa, by reactions such as
  • the first two of the above reactions are known to be much faster than the third reaction.
  • the result of this behaviour is that the carburizing/decarburizing tendency of the furnace atmosphere is strongly affected by the H 2 0 and C0 2 contents of the atmosphere, and only weakly affected by the methane content. If the CO 2 , H 2 0 and CH 4 contents of the atmosphere are all much higher than the equilibrium amounts, the atmosphere will be more decarburizing than it would be if the gaseous constituents were in equilibrium.
  • the carburizing effect of the high methane content does not offset the decarburizing effect of the high C0 2 and H 2 0 contents.
  • an endothermic type gas is defined to mean one where the air and hydrocarbon gas are reacted to produce CO, H 2 , C0 2 , H 2 0, CH 4 and N 2 .
  • the proportions of CO, H 2 , C0 2 and H 2 0 are substantially the same at thermodynamic equilibrium as for an independently generated endothermic gas, but the proportion of methane is typically 2-3 times higher.
  • This invention has provided a way of obtaining soot-free carburizing without the necessity for catalyst or pre-heating of the oxygen supply, and yet save energy up to 75% over comparable energy units used by the state of the art carburizing techniques. This is based on the appreciation that if air/hydrocarbon blends similar to those used in endothermic gas-base atmospheres are permitted a long residence time in the heat treatment furnace at temperature by using very low inlet gas flow rates, a satisfactory carburizing atmosphere can be produced.
  • Low flow rate or slow flow of air/hydrocarbon gas herein shall mean a gas movement which is sufficiently long to permit the immediate reaction products of air and hydrocarbon gas at heat treating temperature to additionally react to lower the C0 2 and H 2 0 content of the gas to substantially thermodynamic equilibrium amounts.
  • Low flow rate can also be defined as that rate of gas movement which allows the mean residency time for all molecules of the gas reaction products to be in the heat treating chamber for at least 0.2 hours (12 minutes).
  • the preselected air/hydrocarbon gas ratio will control the character of the equilibrium atmosphere as to being carburizing, neutral or decarburizing for purposes of hardening, annealing or carburizing.
  • a first series of heat treat experiments were run to determine if carburization by an in situ generated endothermic gas atmosphere at low flow rates can in fact take place, and if so, can be controlled by regulating the proportions of air and hydrocarbon gas entering the furnace.
  • A/P Ratio of air flow to propane flow.
  • Figures 2 and 3 The significance of Figures 2 and 3 is that while thermodynamic equilibrium is not achieved, it is approached reasonably closely so that the process is controllable using C0 2 analysis if that is desired. At high flow rates with the same gas blends, weight gains would be low, and the C0 2 and CH 4 contents much higher, far from the equilibrium values. Furthermore, at high flow rates carburizing is not uniform. Parts near the gas inlet in the furnace chamber will carburize less than parts located at some distance from the gas inlet.
  • Figure 4 shows the gradient of carbon content measured by electron microprobe analysis for samples from several of these trials. Figure 4 demonstrates that the inventive process can obtain the same carbon increases as would the prior art at about the same air-propane ratios, except that it is accomplished without prior reaction of the air and propane in a gas generator.
  • the automatic control system is designed so that the total reacted gas flow does not change appreciably as the inlet air/hydrocarbon ratio changes. Ideally, this can be done by regulating the flows of both air and hydrocarbon gas. However, if just the hydrocarbon flow is altered, with the air flow held constant, the variation in reacted gas flow (and residence time of the gases within the furnace) is small enough so that it does not appreciably affect process control. Table 1 shows that the computed flow of reacted gas varies only 20% for air/propane ratios from 3 to 9 and a constant air flow.
  • test samples were run at 927°C and 843°C as in the previous example.
  • Figure 9 shows that the weight gain due to carburization after 2.5 hours at 927°C increases systematically as the set oxygen sensor voltage is increased.
  • the surface carbon content of samples, determined by microprobe analysis, also increases systematically as the oxygen sensor voltage increases.
  • the airflow rate employed was chosen to give approximately the same residence time for gases within the furnace as in the previous example, Figures 1-4.
  • Figure 10 shows similar results for samples carburized for 6 hours at 843°C. Again, the air flow rate was chosen to give approximately the same residence time for gases within the furnace as in the previous example, Figures 5-8.
  • Example I samples were held in the furnace vestibule for several hours while the furnace and vestibule were purged in order to minimize the entry of air into the furnace chamber when the samples were charged into the furnace. A long purging time was necessary because the flow rates employed were low.
  • Example II no special effort was made to avoid entry of air into the furnace chamber. Samples were held in the furnace vestibule for about 15 minutes before charging into the furnace; this holding time in the vestibule is typical of commercial practice with endothermic gas-base atmospheres.
  • the mean residence time can always be found by a method of graphical or numerical integration.
  • the calculation of mean residence time will be simpler if a mathematical model for the furnace is used. For example, if the furnace chamber has a volume V and the flow rate of gas into and out of the furnace occurs at a rate f, then if perfect mixing occurs in the furnace chamber, it can be shown that and the mean residence time is
  • the steep line in each graph at short times represents the influence of the volume of the main furnace chamber, and the shallow line for longer times represents the influence of the volume of the vestibule chamber. It is very difficult to theoretically calculate ahead of time the mean residence time.
  • the volumes of such chambers can be directly measured but the rate of recirculation of gases between the furnace chamber and the vestibule cannot be predicted. Therefore, an experimental measurement of mean residence time is needed to determine appropriate flow rates.
  • appropriate flow rates can be found by progressively lowering the flow rates and simultaneously monitoring furnace gas composition until the furnace gas is close to the equilibrium composition.
  • An illustrative method for carburizing ferrous based workpieces is as follows.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
EP19800302236 1979-07-09 1980-07-02 Method of heat treating ferrous workpieces Expired EP0024106B1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US5585379A 1979-07-09 1979-07-09
US55853 1979-07-09
US9943979A 1979-12-03 1979-12-03
US99439 1979-12-03

Publications (2)

Publication Number Publication Date
EP0024106A1 EP0024106A1 (en) 1981-02-25
EP0024106B1 true EP0024106B1 (en) 1986-01-02

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Family Applications (1)

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EP19800302236 Expired EP0024106B1 (en) 1979-07-09 1980-07-02 Method of heat treating ferrous workpieces

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EP (1) EP0024106B1 (es)
DE (1) DE3071318D1 (es)
ES (1) ES493253A0 (es)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19738653A1 (de) * 1997-09-04 1999-03-11 Messer Griesheim Gmbh Verfahren und Vorrichtung zur Wärmebehandlung von Teilen

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR930001008B1 (ko) * 1989-12-26 1993-02-12 동양나이론 주식회사 열처리 가열로의 분위기 조절방법
US5194228A (en) * 1990-10-12 1993-03-16 General Signal Corporation Fluidized bed apparatus for chemically treating workpieces
US5827375A (en) * 1993-07-23 1998-10-27 Barbour; George E. Process for carburizing ferrous metal parts
ATE172253T1 (de) 1995-06-30 1998-10-15 Picard Fa Carl Aug Stammblatt einer säge, wie einer kreis- oder gattersäge, einer trennscheibe, einer schneide- oder einer schabvorrichtung
DE19940370C2 (de) * 1999-08-25 2001-07-12 Messer Griesheim Gmbh Verfahren für die Nitrocarburierung metallischer Werkstücke
EP2578704A1 (en) * 2011-10-07 2013-04-10 Linde Aktiengesellschaft Method and system for carburizing or carbonitriding a component and correspondingly treated component

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1433735B1 (de) * 1963-09-21 1969-09-04 Werner Goehring Verfahren zur Erzielung einer Ofenatmosphaere,mit der eine oxydationsfreie Waermebehandlung von Werkstuecken aus Stahl unter gleichzeitiger Beeinflussung des Kohlenstoffgehalts durchfuehrbar ist
DE1533964B2 (de) * 1967-03-23 1975-11-13 Deutsche Gold- Und Silber-Scheideanstalt Vormals Roessler, 6000 Frankfurt Ofen zur Oberflächenbehandlung von Werkstücken in Schutz- oder Trägergas
US3620518A (en) * 1967-03-23 1971-11-16 Degussa Process and device for the treatment of surfaces of workpieces in an annealing furnace
DE1918923B1 (de) * 1969-04-15 1970-11-12 Indugas Ges Fuer Ind Gasverwen Verfahren zur Aufkohlung und Entkohlung von Stahlgegenstaenden
US4049472A (en) * 1975-12-22 1977-09-20 Air Products And Chemicals, Inc. Atmosphere compositions and methods of using same for surface treating ferrous metals
US4049473A (en) * 1976-03-11 1977-09-20 Airco, Inc. Methods for carburizing steel parts
CH628092A5 (de) * 1978-03-21 1982-02-15 Ipsen Ind Int Gmbh Verfahren und vorrichtung zur regelung des kohlenstoffpegels eines chemisch reagierenden gasgemisches.

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19738653A1 (de) * 1997-09-04 1999-03-11 Messer Griesheim Gmbh Verfahren und Vorrichtung zur Wärmebehandlung von Teilen

Also Published As

Publication number Publication date
ES8106559A1 (es) 1981-07-01
ES493253A0 (es) 1981-07-01
EP0024106A1 (en) 1981-02-25
DE3071318D1 (en) 1986-02-13

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