US3796615A - Method of vacuum carburizing - Google Patents

Method of vacuum carburizing Download PDF

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US3796615A
US3796615A US00155950A US3796615DA US3796615A US 3796615 A US3796615 A US 3796615A US 00155950 A US00155950 A US 00155950A US 3796615D A US3796615D A US 3796615DA US 3796615 A US3796615 A US 3796615A
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carburizing
chamber
carbon
gas
furnace
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H Westeren
E Gronquist
D Taft
V Scotto
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HAYES C INC US
Hayes Inc C I
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Hayes Inc C I
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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
    • 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 method and apparatus as embodied in the present invention relates to carburizing by absorption and thermal diffusion of carbon into a metal article in a subatmospheric environment, wherein a carburized case on the metal article is inexpensively and effectively produced.
  • carburizing processes have included liquid carburizing using a salt bath, gas carburizing using a gaseous medium as a source of carbon, and pack carburizing using a powdered material as a source of carbon.
  • the present invention has particular application in gas carburizing and is an improvement over the prior known processes that subjected the metal articles to be treated to a carburizing atmosphere that was force circulated by a fan in the chamber in which the articles were located.
  • a hydrocarbon gas as found in natural gas was employed in the prior known carburizing processes, and in most gas carburizing furnaces a carrier gas such as an endothermic gas was used in combination with the hydrocarbon gas as the carburizing medium, and this medium was circulated in the furnace chamber and under prescribed time and temperature conditions.
  • the present invention has general application in the carburizing of metals, and more specifically relates to carburizing in a subatmospheric environment.
  • the method as embodied in the present invention provides for evacuating a chamber in which a metal article to be treated is placed, so as to remove the impurities therefrom and thereafter back-filling the chamber with an atmosphere containing a source of carbon for a predetermined cycle while maintaining the temperature in the chamber at a level that will provide for absorption and thermal diffusion of the carbon into the surface of the article.
  • the chamber is alternately avacuated and then backfilled with the source of carbon for a predetermined number of cycles, wherein effective circulation of the carbon source is obtained to produce the required absorption and diffusion of the carbon into the surface of the metal.
  • Another object of the invention is to teach a method of carburizing metallic articles in a vacuum, wherein a source of carbon is periodically introduced into an evacuated chamber and removed therefrom as absorption and diffusion of carbon occurs in the metal.
  • Sill another object is to provide apparatus for carburizing metal materials and includes a vacuum furnace in which the metal material is placed, the apparatus further including means for alternately evacuating the heating chamber and introducing therein a source of carbon while maintaining the heating chamber under subatmospheric conditions, wherein absorption and thermal diffusion of the carbon into the surface of the metal material at a controlled rate is effectively obtained.
  • Still another object is to teach a process of changing the surface chemistry of a metal article by thermal diffusion of carbon therein, wherein a source of carbon is introduced into an evacuated chamber and at a concentration that is controlled by the absolute pressure of the chamber, wherein the carbon is absorbed into the outer surface of the article at a controlled rate.
  • Still another object is to teach a carburizing process that provides for carburizing at relatively high temperatures.
  • Still another object is to provide carburizing apparatus that is pollution free.
  • Still another object is to teach a process for carburizing wherein the carburizing cycle is greatly reduced over that known heretofore.
  • FIG. 1 is a diagrammatic illustration of the apparatus is embodied in the present invention
  • FIG. 2 is a diagrammatic analysis of one example of in operating cycle as embodied in the present invention.
  • FIG. 3 is a graphical analysis of the treatment of a glurality of articles at different chamber pressures and ihowing the relationship of the carbon absorbed in the irticles to the number of pulses or times the carburizing gas is introduced into the chamber and evacuated there- :rom;
  • FIG. 4 is a graph illustrating the percent of carbon is diffused in a metal article as it relates to the absolute Jressure of the chamber in which the metal article is ocated during the carburizing process;
  • FIGS. 5 through 12 are photomicrographs of various netal articles as treated by the subject invention and llustrating carburized cases as obtained by the process he carburizing gas is introduced into the evacuated furnace chamber and withdrawn therefrom.
  • the apparatus for carrying out the process as em- )odied in the present invention includes l. vacuum furnace generally indicated at 10.
  • the vacuum 'urnace includes a housing 14 in which a heating chamer 16 is located, and as illustrated, the furnace also in- :ludes a cooling area under which a quench tank 18 is ocated, wherein the parts or articles carburized by the arocess to be described are moved after the carburizing :ycle is completed.
  • the arrangement and construction )f the furnace 10 is more clearly illustrated and described 11 co-pending application Ser. No. 770,779 entitled Vacuum Furnace With Elevator Oil Quench, filed Oct.
  • the heating chamber 16- is provided with graphite heating elements that are enclosed by insulated graphite cloth members indicated at 20 in FIG. 1.
  • a 'alve 22 is automatically operated to control a verticaly movable member 23 that is interconnected to a door hat controls communication between the heating chamyer 16 and the cooling area located above the quench ank 18.
  • a vacuum pump 24 communicates with the inerior of the housing 14 through a blower 26 and a conrol valve 28 and is operative to evacuate the interior of he housing 14 to the required vacuum.
  • a motor 30 nounted on the top of the housing 14 controls the aperation of a fan located within the housing, the fan )eing of usual construction and being employed for coolng the heated metal articles in the cooling area under ertain prescribed conditions.
  • Controlling the absolute pressure within the housing .4 is a critical part of the process as embodied in the )resent invention, and a pressure sensing element 32 ocated on the housing 14 and communicating with the nterior is provided for this purpose.
  • the sensing element 2 is interconnected to an amplifier 34 which is operative o produce an electrical signal that is indicated on a carurizing pressure control instrument 36 mounted on a ontrol panel 38.
  • the pressure control instrument 36 is lectrically connected to the control valve 28 for conrolling the position thereof.
  • the valve 8 can be opened to provide for evacuation of the housing 4 by the pump 24 to the required absolute pressure herein.
  • a temperature control instrument is also )cated on the panel 38 and communicates with the leans for energizing the graphite heating elements that are located within the heating chamber 16. The temperature Within the heating chamber 16 is thereby controlled by setting the temperature control instrument 40 as required. As will hereinafter be described, a counter 42 and timer 44 are also located on the panel 38 and form part of the operating equipment for carrying out the carburizing cycle.
  • nitrogen can be introduced into the exhaust manifold of the pump 24, thereby avoiding a combustible mixture during pump out, and this is provided through a line 46 that communicates with a control valve 48 and a solenoid operated valve 50.
  • the process as embodied in the present invention is designed to provide a source of carbon in a subatmospheric environment within the furnace heating chamber 16, and for this purpose any convenient carbon source may be provided.
  • city gas which includes methane (CH as the carbon source, but since methane does contain certain impurities such as mercaptan, it is necessary to direct the gas through an atmosphere drying chamber indicated at 52 in FIG. 1.
  • the atmosphere drying chamber 52 is generally of the type illustrated and disclosed in US. Pat. No. 2,979,828 and includes a desiccant material therein that removes moisture and impurities from the natural gas directed therethrough.
  • the natural gas from the city line is introduced into the dryer 52 by way of a line 54 that is controlled by a valve 56.
  • a pressure guage 58 is connected in the line 54 for indicating the pressure of the gas as introduced into the dryer 52, and a valve 60 controls a purge line 62 through which nitrogen as a purge gas may be introduced into the dryer 52.
  • the methane gas is directed from the dryer 52 into the heating chamber 16 of the furnace through a line 64 that is controlled by a cut-off valve 66.
  • a valve 68 that is normally closed communicates with a vent line 70 and may be used to vent the gas when required.
  • the line 64 further communicates with a line 72 in which a metering valve 74 is located that meters the flow of the gas to the heating chamber 16.
  • a flow control valve 76 is also located in the line 72 and is controlled by the pressure control instrument 36 for admitting the carburizing gas into the heating chamber 16 as required.
  • a pressure switch 78 and gauge 80 connected in the line 72 provides further control of the flow of the carburizing gas to the heating chamber 16, which is admitted to the chamber 16 through a plurality of jets '81 that are preferably formed of a graphite material which resists con-' tamination at elevated temperatures.
  • the pressure switch 78 functions to cut off the operation of the furnace should the pressure in the line 72 go to a negative value.
  • Purging of the line 72 at initial start up may be accomplished by admitting nitrogen through a shut-off valve 83.
  • the chamber 16 is backfilled with nitrogen after the carburizing cycle for heat treatment of the work parts and prior to the removal of the work parts from the furnace.
  • a line 84 communicates with a source of nitrogen and with the heating chamber 16 through a pressure switch 85, a solenoid valve 86, and a control valve 87.
  • the dryer 52 does not constitute apparatus that defines part of the carburizing cycle, it does perform the important funciton of purifying the carburizing gas prior to its being introduced into the heating chamber 16.
  • a purge gas such as nitrogen is introduced therein.
  • the purge exhaust is directed to a chamber 88 by way of a line 89, the purge exhaust filtering through a bed of particulate material such as iron oxide chips indicated at 90 that removes noxious materials such as mercaptan from the purge gas prior to its being directed to a vent or stack 91 by means of a line 92.
  • A. drain line 93 is located at the lower end of the tank 90 and is controlled by a valve 94.
  • the furnace heating chamber 16 includes a plurality of graphite heating elements that may either be in solid or woven graphite form, and in this connection reference is made to U.S. Pat. Nos. 3,257,492 and 3,525,795, wherein woven graphite heating elements are disclosed both in planular and in tubular form.
  • the use of graphite heating elements is desirable in the present invention since the carburizing temperatures are relatively high and above normal carburizing temperatures, and even at these high temperatures the graphite heating elements will not deteriorate or break down. Since the carburizing process herein is carried out in a subatmospheric environment, conventional heating elements cannot be used because they would be carburized at the high temperatures and eventually break down and fail.
  • the higher temperatures used in the carburizing process herein are desirable since the rate of carbon absorption into the article being carburized is increased exponentially with respect to the increase in temperature of the furnace.
  • the vacuum pressures as incorporated herein enable the article to be properly prepared for carburizing, and a prescribed carburized case can be obtained since carbon potential as absorbed in an article is proportional to the absolute pressure Within the furnace heating chamber.
  • One of the unique features embodied in the carburizing process of the subject invention is the introduction of the carburizing gas to the heating chamber 16 of the furnace at predetermined intervals. Since the carburizing cycle is accomplished entirely in a subatmospheric environment, withdrawal of the carburizing gas from the furnace chamber can be easily accomplished with the vacuum furnace as described above. Hence, it has been found that by alternately introducing the carburizing atmosphere into the heating chamber and then evacuating it for a predetermined cycle the carbon as contained in the carburizing atmosphere will be absorbed more readily into the surface of the article being treated.
  • This so called pulsing efiect tends to remove unwanted molecules of the carburizing environment from around the part being treated; and upon reintroduction of the carburizing atmosphere into the heating chamber after evacuation thereof, the carbon in the carburizing gas will be more readily absorbed into the article. Further, the pulsing eifect produces a better distribution of the carbon around the article, and in certain articles that are formed with irregular surfaces, the pulsing technique as provided for in the carburizing cycle insures that sufficient carbon will be difiused into the metal to produce the required result.
  • the carburizing cycle can be controlled so that residual absorption or diffusion is prevented and carburized cases having predetermined characteristics such as case depth, carbon potential and hardness can be obtained.
  • FIG. 2 is a diagrammatic illustration of one example of an operating cycle.
  • the center line in FIG. 2 represents atmospheric pressure and room temperature.
  • the values above the center line represent the temperature of the furnace during the process and the values below the center line represent the absolute pressure or vacuum in the furnace chamber. Both temperature and vacuum are correlated to the time of the operating cycle.
  • the heating chamber including the heating elements and parts therein and the work part be out-gassed and deoxidized so that there are no impurities remaining in the heating chamber during the carburizing cycle.
  • Outgassing is accomplished after the work part has been placed in the heating chamber 16 and the valve 28 opened and the pump 24 of the furnace 10 energized to pump out the housing interior and the heating chamber.
  • a vacuum control instrument (not shown) is preset, so that when the furnace chamber has been pumped down to a preset value the power to the furnace heating element is energized to begin the Outgassing.
  • the furnace temperature is preset, and in the normal operating cycle, 1900 F. is the furnace temperature used, since parts processed at this temperature are easily outgassed and deoxidized and the work part will absorb carbon at an accelerated rate to produce the required carburized case.
  • any temperature including relatively high temperatures can be used as the carburizing temperature for the furnace, usually depending upon the kind of material being treated.
  • molybdenum may require still a higher carburizing temperature, and this temperature could be in the range of 2700-3000 F.
  • Tungsten requires still a higher carburizing temperature, and this temperature could be in the range of 2700-3000 F. It is understood, however, that the temperature in the furnace is considerably higher than the carburizing temperatures used in the prior known carburizing processes.
  • a timer (not shown) is preset to provide for outgassing of the heating chamber at the selected temperature and vacuum for a predetermined period of time. In most instances a fifteen to thirty minute soak or outgassing time at approximately microns is sufficient to remove all oxidizing gases and other impurities from the heating chamber. When the period for outgassing ends, the carburizing cycle automatically begins.
  • the operator preselects the number of pulses that will be required to produce a selected carburized case and will also select the period of time for each pulse.
  • counter 42 is preset to control the number of pulses, or the number of times that the carburizing gas will be introduced into the chamber 16
  • the timer 44 is preset to control the length of time the carburizing atmosphere remains in the chamber and before the pump out thereof.
  • the absolute pressure or vacuum at which the carburizing cycle is performed is also preselected and this is controlled by the carburizing pressure control instrument 36.
  • the depth of the carburized case obtained can be determined by the number of pulses in a carburizing cycle, and the percent of carbon as contained in the carburized case would also be determined by the absolute pressure of the heating chamber with the carburizing gas contained therein.
  • the percent of carbon in the carburized case of the work part will vary up to 2.2% carbon saturation point. This relationship will be more fully discussed hereinafter.
  • the example of the operating cycle shows the pump out beginning at atmospheric pressure and 72 F. and in approximately fifteen minutes the furnace chamber is pumped down to 100 microns vacuum. At this point the heating elements in the heating chamber 16 are energized and in approximately fifteen minutes the operating temperature of 1900" F. is reached. Outgassing occurs for another fifteen minutes with the furnace chamber at approximately 100 microns. As indicated in FIG. 2, this thirty minute interval constitutes a cleaning or Outgassing portion of the operating cycle.
  • the carburizing cycle now begins and the carburizing pressure control instrument as controlled 'by the counter 42 and the timer 44 operates to close the pump valve 28 and to open the flow control valve 76 through which the carburizing gas containing methane (CH flows to the heating chamber 16.
  • CH carburizing gas containing methane
  • the chamber 16 is backfilled with the carburizing gas to 50 mm. Hg absolute pressure (pulse A) and this backfill time takes approximately two minutes.
  • the flow control valve 76 is then closed to prevent additional carburizing gas from entering the chamber 16.
  • the carburizing gas may be promptly pumped out of the chamber 16 by having the controls set to immediately open the pump valve 28, or as illustrated in FIG. 2, an absorption period of two minutes is provided before pump out begins.
  • the pressure control instrument 36 opens the valve 28 and pump out of the carburizing atmosphere proceeds for about two minutes until the vacuum of 100 microns is again reached, at which point the valve 28 is again closed.
  • the second pulse (B) of the operating cycle for introducing another shot of carburizing gas into the chamber 16 is accomplished by closing the valve 28 again and opening the flow control valve 76.
  • the carburizing gas is again permitted to flow into the chamber 16 for another two minutes until 50 mm. Hg backfill pressure is reached, at which time both valves 28 and 76 are again closed.
  • the carburizing gas is pumped out in two minutes until the furnace chamber reaches 100 microns and diffusion is continued for another five minutes.
  • a third pulse (C) as illustrated in FIG. 2 provides for another shot of carburizing gas, and after this pulse is completed and the diffusion period ends, the counter 42 automatically signals the vacuum control instrument to open the valves 86 and 87 for introducing a source of nitrogen from line 84 into the heating chamber to reduce the vacuum therein to 12 in. Hg. This completes the carburizing cycle.
  • the work parts will be treated in the conventional manner in the furnace and in this connection, the temperature in the furnace chamber 16 is reduced to approximately 1000 F. with the pressure at 12 in. Hg mercury vacuum. Thereafter the valve 28 is opened and the heating chamber is again pumped out to approximately 100 microns in approximately five minutes and after the temperature has been elevated to approximately 1500 F. The work part is then subjected to further heat treating for refining the grain structure of the metal. Nitrogen is again introduced into the heating chamber to reduce the vacuum to 12 in. Hg; and at this point, and with the furnace housing remaining at the subatmospheric pressure of approximately 12 in. Hg vacuum, the part is introduced into an oil quench. This hardens the metal in accordance with the usual metal treating practice.
  • the percent of carbon absorbed into a metal part treated by the carburizing process is proportional to the absolute pressure of the carburizing gas in the heating chamber. This relationship is reflected in the curves illustrated in FIG. 3 described above; but as illustrated in the graph shown in FIG. 4, an acceptable percent of carbon for a carburized case as obtained by the process can be determined by preselecting the absolute pressure of the heating chamber when backfilled with the carburizing gas. As will be described in the examples set forth hereinafter, the absolute pressure in the heating chamber will be varied to produce acceptable carburized cases, depending upon the results required.
  • Material 1010 steel Number of pulses of carburizing gas and dif- Three at five minutes fusion period.
  • FIG. 6 a photomicrograph of a carburized case obtained on 2.5% silicon iron pole piece is illustrated.
  • the results as obtained from the carburizing cycle indicated are as follows:
  • FIG. 7 a photomicrograph of a carburized case of 1524 steel is illustrated as treated by the following carburizing cycle.
  • FIG. 9 a photomicrograph of a portion of a gear tooth formed of 1524 steel is illustrated after "Material Number of pulses of carburizing gas and diffusion period.
  • a carburizing pressure of 45 mm. Hg (vac.) was maintained in the heating chamber at 1900 F. and a single shot of carburizing gas was introduced into the heating chamber and maintained therein for seventy minutes. After the carburizing gas was evacuated from the chamber and the part thereafter inspected, an effective case of .010 inch was observed. There was no appreciable increase in the percent of carbon in the case.
  • Material 1117 steel Number of pulses of carburizing gas and difiu- Six at five minutes sion period. carburizing pressure in chamber 2 mmg (v J carburizing temperature l,900 F.
  • Case depth inches Percent C 010 1. 01 020 Comparison of case depth and percent C 828 2g 050 30
  • a part of sintered stainless steel was carburized by introducing a single shot of carburizing gas into the heating chamber operated at 1900 F. A diffusion period of twenty minutes produced a case of .010 inch.
  • a part of sintered iron having 3% copper was carburized by introducing a single shot of carburizing gas into the heating chamber operated at 1900 F.
  • a diffusion period of twenty minutes also produced a case of .010 inch.
  • the process was incorporated in a brazing technique wherein a. steel part was brazed to another steel part with 1010 copper brazing by first heating the chamber to 2050 F. Thereafter the temperature in the chamber was lowered to 1900 F. and a normal carburizing cycle carried out.
  • the carburizing process as embodied in the present invention essentially relates to a method of changing the surface chemistry of the metal by addition of carbon through absorption and thermal diffusion.
  • the evacuation range may be as low as 10" mm. Hg.
  • the carburizing process has been carried out in a wide range of carburizing pressures and the pressure of the carburizing gas may vary from zero up to the saturation point thereof in the furnace chamber. Normally the pressure will vary according to each case since the carbon as absorbed into the work piece is proportional to the absolute pressure in the carburizing chamber.
  • the total pressure of the carburizing gas is used as a means of determining the partial pressure of the carbon in the heating chamber during the carburizing cycle.
  • the partial pressure of the carbon may vary in accordance with the surface area of the work parts being carburized and in order to maintain a preselected carbon potential, the backfill pressure of the carburizing gas is adjusted accordingly.
  • the temperature range as contemplated during the carburizing cycle will also vary, and this will depend upon the material that is being processed.
  • the temperature in the carburizing chamber could go up to 5000 and this of course would be compatible with the furnace equipment and the article being heat treated.
  • the present invention is particularly conducive to providing an impurity free environment, since relatively high temperatures may be used in the heating chamber during evacuation. Thus all surface contaminants on the material are removed as well as impurities resulting from oxidizing of any parts of the heating chamber.
  • Another unique feature of the subject invention is the precise control of the depth of case and of the percent of carbon in the case obtained by the carburizing process.
  • This precise control is possible by introducing a source of carbon into the evacuated chamber such as methane gas and controlling the concentration of carburization by pressure and temperature. Since relatively high temperatures are employed together with relatively high vacuums, the required result may be obtained by simply preselecting the number of pulses of the carburizing gas to be introduced into the chamber and the vacuum at which the carburizing gas is maintained in the chamber.
  • the time factor for carburizing by the present invention is greatly reduced over that experienced in the prior known processes.
  • prior known gas carburizing processes have taken as long as fourteen hours to carburize parts.
  • carburizing the same parts by the subject process requires only two and one half to three hours.
  • conventional gas carburizing requires more than double the time of the present process, and the present invention has the added advantage of precisely controlling the carburizing conditions to obtain a desired depth of case and carbon potential.
  • the process is carried out in an absolute ly clean environment exteriorly and interiorly of the furnace, and the parts as carburized when they are removed from the furnace have a bright and smooth surface and do not require any additional cleaning.
  • the vacuum carburizing process is performed in an absolutely clean environment that is possible because of the high vacuums and temperatures used. As a result there are no oxidizing problems encountered in startup or during operation, and it is seen that not as much of the carburizing atmosphere is required during the process. Precise control of the process also serves to reduce the amount of carburizing gas required in the operation of the furnace.
  • the use of the graphite heating elements and insulation members as provided in the heating chamber of the subject invention enable the high temperatures to be obtained in the furnace for the carburizing cycle. These temperatures have not been used heretofore for carburizing; and if they were used in a conventional atmosphere furnace, there would be a complete break down of the furnace heating elements and the other components that define the furnace interior. It is further emphasized that the vacuum technique as employed in the subject carburizing process not only removes impurities from the furnace interior and the surface of the metal parts being treated, but the surface of the metal is prepared so that absorption and thermal diffusion of the carbon during the process is more easily obtained.
  • the technique as developed in the subject invention for alternately introducing the carburizing gas into the furnace chamber and then evacuating it through a series of pulses produced the necessary circulation of the carbon material on the surface of the article to provide for the required diffusion into the surface.
  • This pulsing elfect is so controlled and is related to carbon potential and case depth that precise results can be predetermined by presetting the controls as required.
  • a method of carburizing a metallic article in a subatmospheric environment to produce a preselected amount of surface absorbed carbon and diffused gradient of carbon in said article comprising the steps of heating the article in a heating chamber in a subatmospheric environment having a pressure in the range of approximately 0.2 to 10- mm.
  • each of said pulses including backfilling said chamber with a carburizing gas to a pressure that is maintained at subatmospheric conditions, the carburizing gas defining the source of carbon and forming active carbon vapor and waste reactants in said chamber after being admitted therein, each pulse including the removal of the waste reactants from the chamber during the period of carbon absorption into said article and following each backfilling operation of admitting the carburizing gas into said chamber, controlling the amount of carburizing gas admitted into said heating chamber in each backfilling operation in proportion to the partial pressure of the carbon vapor in said chamber, wherein the partial pressure of the carbon vapor is maintained at a value from zero up to and including the saturation point of the carbon

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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)
  • Chemical Vapour Deposition (AREA)
US00155950A 1971-06-23 1971-06-23 Method of vacuum carburizing Expired - Lifetime US3796615A (en)

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CA (1) CA969841A (xx)
CS (1) CS168596B2 (xx)
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Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4030712A (en) * 1975-02-05 1977-06-21 Alco Standard Corporation Method and apparatus for circulating a heat treating gas
US4152177A (en) * 1977-02-03 1979-05-01 General Motors Corporation Method of gas carburizing
US4160680A (en) * 1976-11-05 1979-07-10 Sola Basic Industries, Inc. Vacuum carburizing
US4191598A (en) * 1978-08-21 1980-03-04 Midland-Ross Corporation Jet recirculation method for vacuum carburizing
US20020166607A1 (en) * 2001-04-04 2002-11-14 Herwig Altena Process and device for low-pressure carbonitriding of steel parts
US20040255598A1 (en) * 2003-06-18 2004-12-23 Haws James L. Method and apparatus for humidity control within a housing
US20080073001A1 (en) * 2006-09-27 2008-03-27 Kazuhiko Katsumata Vacuum carburization processing method and vacuum carburization processing apparatus
US20080216922A1 (en) * 2007-03-09 2008-09-11 Kazuhiko Katsumata Vacuum carburization method and vacuum carburization apparatus
US20110030849A1 (en) * 2009-08-07 2011-02-10 Swagelok Company Low temperature carburization under soft vacuum
EP2541177A3 (en) * 2005-11-23 2014-09-24 Surface Combustion, Inc. Fluid delivery system for an atmospheric furnace used for treating one or more articles
US9617632B2 (en) 2012-01-20 2017-04-11 Swagelok Company Concurrent flow of activating gas in low temperature carburization
CN111534784A (zh) * 2020-05-21 2020-08-14 湖南特科能热处理有限公司 一种低碳合金钢的真空渗碳工艺
AT524143A1 (de) * 2020-09-10 2022-03-15 Miba Sinter Austria Gmbh Verfahren zur Härtung eines Sinterbauteils

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US4113426A (en) * 1975-02-05 1978-09-12 Alco Standard Corporation Method for circulating a heat treating gas
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US4191598A (en) * 1978-08-21 1980-03-04 Midland-Ross Corporation Jet recirculation method for vacuum carburizing
US20020166607A1 (en) * 2001-04-04 2002-11-14 Herwig Altena Process and device for low-pressure carbonitriding of steel parts
US20040255598A1 (en) * 2003-06-18 2004-12-23 Haws James L. Method and apparatus for humidity control within a housing
US7195177B2 (en) * 2003-06-18 2007-03-27 Raytheon Company Method and apparatus for humidity control within a housing
EP2541176A3 (en) * 2005-11-23 2014-09-24 Surface Combustion, Inc. Fluid delivery system for an atmospheric furnace used for treating one or more articles
EP2541177A3 (en) * 2005-11-23 2014-09-24 Surface Combustion, Inc. Fluid delivery system for an atmospheric furnace used for treating one or more articles
US8465598B2 (en) 2006-09-27 2013-06-18 Ihi Corporation Vacuum carburization processing method and vacuum carburization processing apparatus
US20080073001A1 (en) * 2006-09-27 2008-03-27 Kazuhiko Katsumata Vacuum carburization processing method and vacuum carburization processing apparatus
US8741061B2 (en) 2007-03-09 2014-06-03 Ihi Corporation Vacuum carburization method and vacuum carburization apparatus
US20080216922A1 (en) * 2007-03-09 2008-09-11 Kazuhiko Katsumata Vacuum carburization method and vacuum carburization apparatus
US8152935B2 (en) 2007-03-09 2012-04-10 Ihi Corporation Vacuum carburization method and vacuum carburization apparatus
US10934611B2 (en) 2009-08-07 2021-03-02 Swagelok Company Low temperature carburization under soft vacuum
US20110030849A1 (en) * 2009-08-07 2011-02-10 Swagelok Company Low temperature carburization under soft vacuum
US9212416B2 (en) 2009-08-07 2015-12-15 Swagelok Company Low temperature carburization under soft vacuum
US10156006B2 (en) 2009-08-07 2018-12-18 Swagelok Company Low temperature carburization under soft vacuum
US9617632B2 (en) 2012-01-20 2017-04-11 Swagelok Company Concurrent flow of activating gas in low temperature carburization
US10246766B2 (en) 2012-01-20 2019-04-02 Swagelok Company Concurrent flow of activating gas in low temperature carburization
US11035032B2 (en) 2012-01-20 2021-06-15 Swagelok Company Concurrent flow of activating gas in low temperature carburization
CN111534784A (zh) * 2020-05-21 2020-08-14 湖南特科能热处理有限公司 一种低碳合金钢的真空渗碳工艺
CN111534784B (zh) * 2020-05-21 2022-05-27 湖南特科能热处理有限公司 一种低碳合金钢的真空渗碳工艺
AT524143A1 (de) * 2020-09-10 2022-03-15 Miba Sinter Austria Gmbh Verfahren zur Härtung eines Sinterbauteils
AT524143B1 (de) * 2020-09-10 2022-12-15 Miba Sinter Austria Gmbh Verfahren zur Härtung eines Sinterbauteils

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IT959314B (it) 1973-11-10
DE2216688A1 (de) 1973-01-11
IL38822A (en) 1975-07-28
IL38822A0 (en) 1972-04-27
SE383001B (sv) 1976-02-23
DE2216688C3 (de) 1984-03-22
FR2154398B1 (xx) 1975-10-24
ES404017A1 (es) 1975-11-16
GB1382075A (en) 1975-01-29
JPS5129703B1 (xx) 1976-08-27
SU663316A3 (ru) 1979-05-15
DE2216688B2 (de) 1978-04-27
CS168596B2 (xx) 1976-06-29
USRE29881E (en) 1979-01-16
FR2154398A1 (xx) 1973-05-11
CA969841A (en) 1975-06-24

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