US2575427A - Treatment of metalworking tools - Google Patents

Treatment of metalworking tools Download PDF

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US2575427A
US2575427A US682285A US68228546A US2575427A US 2575427 A US2575427 A US 2575427A US 682285 A US682285 A US 682285A US 68228546 A US68228546 A US 68228546A US 2575427 A US2575427 A US 2575427A
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tool
tools
temperature
treatment
steel
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US682285A
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Edward T Pavlock
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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
    • C23C8/28—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 more than one element being applied in one step
    • C23C8/30—Carbo-nitriding
    • C23C8/32—Carbo-nitriding of ferrous surfaces
    • 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
    • C23C8/40—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 liquids, e.g. salt baths, liquid suspensions
    • C23C8/42—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 liquids, e.g. salt baths, liquid suspensions only one element being applied
    • C23C8/48—Nitriding
    • C23C8/50—Nitriding of ferrous surfaces

Definitions

  • the present invention relates to methods of treating metal working tools, including those having cutting edges, to create a hard surface case of greater depth and having greater toughness, durability and resistance to corrosion than the cases developed by prior methods, in order to increase the useful life of such tools. It is applicable to tools of all types made from high speed steel and other compositions or alloys of steel which are suificiently hard to perform the actions on metal work pieces for which they are designed.
  • the procedure in which it is embodied follows the completion of the heat treatingprocesses heretofore employed in the manufacture of such tools. It may be, and preferably is, performed on completely finished tools, that is, those which have beenshaped to final form and, in the case of cutters, those of which the cutting edges have been sharpened.
  • the more generic aspects of the invention include employment of the treatment at earlier stages of manufacture than those indicated.
  • oil or grease adhering to the tool or other article to be treated is removed. Any degreasing treatment or substance suitable for the purpose may be used in this step.
  • the article is preheated to a temperature of 800? F. or approximately that temperature.
  • This heating step may be performed in a box type electric furnace wherein the temperature is maintained at the prescribed degree, and the work is held in the furnace until it has acquired the temperature of the furnace.
  • the work is immediately transferred to a furnace, for instance a pot furnace, in which a higher temperature is maintained and in which it is subjected to chemical reaction with nitrogen to form a nitride case on its surfaces.
  • the temperature of nitriding treatment is from 1025 F. to 1050 F. and the period of exposure to the nitriding treatment is preferably fifty minutes regardless of the dimensions and design of the tool.
  • the exposure of the tool to nitrogen may be accomplished by covering the tool with a cyanide or mixture of cyanides. Any commercially prepared so called hard casing salt may be used here, but best results have been obtained in practice with the use of a bath composed of 60% sodium cyanide and 40% potassium cyanide. However, any feasible mode of enveloping the tool in a nitriding atmosphere or bath, while maintaining the temperature within the effective range for the desired length of time may be used.
  • nickel be excluded,.wherefore the salt bath is contained in a nickel-free pot and a nickel-free thermo couple is used.
  • the work pieces are packed in sheet steel boxes with a granular packing material to exclude air during the prolonged heating which follows in the next step.
  • Granulated charcoal which will pass through a screen of A
  • mesh is a suitable packing material, although not the only one that can be successfully used.
  • the preferred mode of packing is to place a layer of charcoal about deep in the bottom of the box, then lay a number of tools to be treated on the packing material, as many as can be accommodated in the area of the box without touching each other, then to cover the articles with another layer of charcoal deep; and repeat until the last placed layer of tools comes to within about 1" of the top of the box, and to fill the remaining space with charcoal.
  • the box and the work pieces therein are subjected to prolonged heating treatment at a temperature near that at which the steel of which the work pieces are made commences to soften, and preferably in exposure to an oxidizing medium.
  • a temperature near that at which the steel of which the work pieces are made commences to soften, and preferably in exposure to an oxidizing medium.
  • the optimum temperature is 1025? F. or very near that temperature. It should be as near as possible to the drawing temperature.
  • the heat soaking treatment is continued for approximately three hours for all tools of one inch or less in thickness and for an additional three hours per additional inch of thickness.
  • a suitable mode of carrying out the step last described is to place the box containing the nitrided tools in an electrically heated furnace having conduits by which water can be conveyed into and discharged at a relatively high level in the chamber wherein the tools are contained.
  • Water is admitted to the delivery conduits and allowed to flow at a rate which causes discharge of approximately drops per minute for every two cubic feet of internal furnace space. An oxidizing effect is produced thereby.
  • the box with its contained workpieces is removed from the furnace and allowed to cool for about 30 minutes. If the packingmaterial used is charcoal or other inflammable substance, the top layer is brushed off immediately in order to prevent it from igniting. After preliminary cooling in the box, the work pieces are removed and allowed to cool in still air.
  • the packingmaterial used is charcoal or other inflammable substance
  • the tools are pickled by immersion in abath of acidlong enough to remove any fuzzy oxide which may have been formed.- on the-tools during the preceding heat treating operation. It has been found that a bath of 18 commercial muriatic acid gives very satisfactoryresults; although I am not limited to the use-of this particular acid. The pickling step seems to addmaterially to the life of the tools.
  • the acid is then washedoff with warm water; and'a thin blacksu-bstance which may have adhered to the tool is removed by brushing or the employment of any other means that will serve thepurpose without damaging the'cutting edges of sharpened edged tools.
  • the tools are dried, preferably by an air blast.
  • tools may be coated with oilor any other suitable rust preventive.
  • the treatment hereindescribed has been found toincrease the useful life of cutting tools in very large measure; up to an increase of more than 200 in many cases.
  • steps described those ofnitriding and prolonged heatingat a hightemperature, which is not high enough to soften the metal, are vitally important.
  • the pickling step also is believed to have a substantial iniiuencein giving prolonged life, vas it has beenobserved that under similar conditions tools which have undergone. this. step remain serviceable longer than those which have not.
  • Themethodof modifying-the characteristics of anitridedcaseona high speed steeltool which comprises packing the tool in granulatedcarbon, maintaining the packed tool for at least-three hours in an enclosed space at a temperature of approximately l025 :E, and continuously .admitting water to such enclosed-space at a regulated slow rate of approximately 120 drops per minute for each 2 cubic feet of the enclosed space.

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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)

Description

Patented Nov. 20, 1951 UNITED STATES PATENT OFFICE TREATMENT OF METALWORKING TOOLS Edward T. Pavlock, Detroit, Mich.
No Drawing. Application July 9, 1946, Serial No. 682,285
3 Claims. 1
The present invention relates to methods of treating metal working tools, including those having cutting edges, to create a hard surface case of greater depth and having greater toughness, durability and resistance to corrosion than the cases developed by prior methods, in order to increase the useful life of such tools. It is applicable to tools of all types made from high speed steel and other compositions or alloys of steel which are suificiently hard to perform the actions on metal work pieces for which they are designed. The procedure in which it is embodied follows the completion of the heat treatingprocesses heretofore employed in the manufacture of such tools. It may be, and preferably is, performed on completely finished tools, that is, those which have beenshaped to final form and, in the case of cutters, those of which the cutting edges have been sharpened. However, the more generic aspects of the invention include employment of the treatment at earlier stages of manufacture than those indicated.
The following steps constitute the preferred embodiment of the invention.
First, oil or grease adhering to the tool or other article to be treated is removed. Any degreasing treatment or substance suitable for the purpose may be used in this step.
Second, the article is preheated to a temperature of 800? F. or approximately that temperature. This heating step may be performed in a box type electric furnace wherein the temperature is maintained at the prescribed degree, and the work is held in the furnace until it has acquired the temperature of the furnace.
Third, the work is immediately transferred to a furnace, for instance a pot furnace, in which a higher temperature is maintained and in which it is subjected to chemical reaction with nitrogen to form a nitride case on its surfaces. The temperature of nitriding treatment is from 1025 F. to 1050 F. and the period of exposure to the nitriding treatment is preferably fifty minutes regardless of the dimensions and design of the tool. In this step the exposure of the tool to nitrogen may be accomplished by covering the tool with a cyanide or mixture of cyanides. Any commercially prepared so called hard casing salt may be used here, but best results have been obtained in practice with the use of a bath composed of 60% sodium cyanide and 40% potassium cyanide. However, any feasible mode of enveloping the tool in a nitriding atmosphere or bath, while maintaining the temperature within the effective range for the desired length of time may be used.
It is important that, in the nitriding step, nickel be excluded,.wherefore the salt bath is contained in a nickel-free pot and a nickel-free thermo couple is used.
Fourth, the work is washed thoroughly to remove salt. It is important that all, or as much as possible, of the salt adhering to the surfaces of the work be removed.
Fifth, the work pieces are packed in sheet steel boxes with a granular packing material to exclude air during the prolonged heating which follows in the next step. Granulated charcoal which will pass through a screen of A," mesh is a suitable packing material, although not the only one that can be successfully used. The preferred mode of packing is to place a layer of charcoal about deep in the bottom of the box, then lay a number of tools to be treated on the packing material, as many as can be accommodated in the area of the box without touching each other, then to cover the articles with another layer of charcoal deep; and repeat until the last placed layer of tools comes to within about 1" of the top of the box, and to fill the remaining space with charcoal.
Sixth, the box and the work pieces therein are subjected to prolonged heating treatment at a temperature near that at which the steel of which the work pieces are made commences to soften, and preferably in exposure to an oxidizing medium. In the case of tools made of high speed steel the optimum temperature is 1025? F. or very near that temperature. It should be as near as possible to the drawing temperature.
of the steel but not so high as to cause appreciable softening. With other alloy steels other specific temperatures may be employed, but always in accordance with the considerations above set forth. The heat soaking treatment is continued for approximately three hours for all tools of one inch or less in thickness and for an additional three hours per additional inch of thickness.
A suitable mode of carrying out the step last described is to place the box containing the nitrided tools in an electrically heated furnace having conduits by which water can be conveyed into and discharged at a relatively high level in the chamber wherein the tools are contained. When the tool or tools undergoing treatment have been brought to the temperature of the furnace, Water is admitted to the delivery conduits and allowed to flow at a rate which causes discharge of approximately drops per minute for every two cubic feet of internal furnace space. An oxidizing effect is produced thereby.
Similar effects may be obtained by covering the work pieces with a so called neutral salt which has oxidizing properties.
This heat treatment seems to diffuse the concentration of nitrides, thus decreasing the brittleness of the hard case, making it tougher and stronger. It also drives the nitride layer deeper into the tool. This last effect is aided and enhanced by the oxidizing reaction. The oxidized surface also resists attack by moisture and other agencies which cause rusting of steel.
Seventh, the box with its contained workpieces is removed from the furnace and allowed to cool for about 30 minutes. If the packingmaterial used is charcoal or other inflammable substance, the top layer is brushed off immediately in order to prevent it from igniting. After preliminary cooling in the box, the work pieces are removed and allowed to cool in still air.
Preferably the tools are pickled by immersion in abath of acidlong enough to remove any fuzzy oxide which may have been formed.- on the-tools during the preceding heat treating operation. It has been found that a bath of 18 commercial muriatic acid gives very satisfactoryresults; although I am not limited to the use-of this particular acid. The pickling step seems to addmaterially to the life of the tools.
The acid is then washedoff with warm water; and'a thin blacksu-bstance which may have adhered to the tool is removed by brushing or the employment of any other means that will serve thepurpose without damaging the'cutting edges of sharpened edged tools. Then the tools are dried, preferably by an air blast.
Finally the tools may be coated with oilor any other suitable rust preventive.
The treatment hereindescribed has been found toincrease the useful life of cutting tools in very large measure; up to an increase of more than 200 in many cases. Of the steps described, those ofnitriding and prolonged heatingat a hightemperature, which is not high enough to soften the metal, are vitally important. The pickling step also is believed to have a substantial iniiuencein giving prolonged life, vas it has beenobserved that under similar conditions tools which have undergone. this. step remain serviceable longer than those which have not.
While I have namedcertain specific valuesand figures in the foregoing specification, I Wish to point out that the scope of the invention which I desire to protect hereby includesall variations and departures from those specific values which obtain equivalent results.
What I claim is:
1. The method of case hardening a steel tool which comprises preheating the tool to a temperature of 800 F., holding the heated tool immersed for a period of about 50 minutes in a nitriding bath maintained at a temperature of from 1025 to 1050 F., cleaning the tool, packing the tool in granulated carbon, maintaining the packed tool for at least three hours in an enclosed space at a temperature near to, but below,
the hardness-drawing temperature of the steel,
and admitting water continuously at a regulated slow rate to such enclosed space.
' 2. The method of case hardening a tool of high speed steel which comprises preheating the tool to a temperature of 800 F., immersing the heated tool for a period of about 50 minutes in a nitridingc'yanide bath maintained at a temperature of from 1025 to 1050 F., cleaning the tool, packing the tool in-granulated'carbon, maintaining the packed tool for at least three-hours in an enclosed space at a temperatureof approximately 1025 F., and admitting Water to such enclosed space-ate rate ofapproximately drops per minute per2 cubic feet of suchenclosed space.
3. Themethodof modifying-the characteristics of anitridedcaseona high speed steeltool which comprises packing the tool in granulatedcarbon, maintaining the packed tool for at least-three hours in an enclosed space at a temperature of approximately l025 :E, and continuously .admitting water to such enclosed-space at a regulated slow rate of approximately 120 drops per minute for each 2 cubic feet of the enclosed space.
EDWARD TrPAVLO CK.
T001 Steels, Gill .et .al., .1944, Soc. for Metals, pp. 485-489.
Number Molten SaltBaths," E. I. du Pont de Nemours and 00., 1942, page 27...
Transactions of The American Society for Metals, vol. 27, .l939.,.page 1000.
The Journal of the Iron. and .Steel Institute, vol. 136, No.2, 1937 pp. 153-158.

Claims (1)

1. THE METHOF OF CASE HARDENING A STEEL TOOL WHICH COMPRISES PREHEATING THE TOOL TO A TEMPERTURE OF 800* F., HOLDING THE HEATED TOOL IMMERSED FOR A PERIOD OF ABOUT 50 MINUTES IN A NITRIDING BATH MAINTAINED AT A TEMPERATURE OF FROM 1025* TO 1050* F., CLEANING THE TOOL, PACKING THE TOOL IN GRANULATED CARBON, MAINTAINING THE PACKED TOOL FOR AT LEAST THREE HOURS IN AN ENCLOSED SPACE AT A TEMPERATURE NEAR TO, BUT BELOW, THE HARDNESS-DRAWING TEMPERATURE OF THE STEEL, AND ADMITTING WATER CONTINUOUSLY AT A REGULATED SLOW RATE TO SUCH ENCLOSED SPACE.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3141801A (en) * 1961-06-27 1964-07-21 Prutton Daniel Howard Method of hardening a case hardened steel
US3943908A (en) * 1972-11-03 1976-03-16 Maschinenfabrik Augsburg-Nurnberg Aktiengesellschaft One piece piston connected to a connecting rod for high speed four-stroke cycle internal combustion engines

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1774999A (en) * 1929-09-20 1930-09-02 Republic Steel Corp Method of heat treating nitrided articles

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1774999A (en) * 1929-09-20 1930-09-02 Republic Steel Corp Method of heat treating nitrided articles

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3141801A (en) * 1961-06-27 1964-07-21 Prutton Daniel Howard Method of hardening a case hardened steel
US3943908A (en) * 1972-11-03 1976-03-16 Maschinenfabrik Augsburg-Nurnberg Aktiengesellschaft One piece piston connected to a connecting rod for high speed four-stroke cycle internal combustion engines

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