SHALLOW CASE HARDENING PROCESS

Abstract: A shallow case hardening process comprising passing selected mixtures of gases for prescribed times through sand in which workpieces are imbedded at temperatures substantially different from recommended levels in normal nitriding.

Description: SHALLOW CASE HARDENING PROCESS SPECIFICATIONS In the past » it has been a common practice in heat treating of metal workpieces to utilize fluid beds, such as those made by Procedyne Corporation of New Brunswick, New Jersey. An example of these fluidized beds is designated 18502048HT, standing respectively for: 1850 degress Fahrenheit, 20 inch diameter, 48 inch depth. These are essentially, furnaces that have a sand- like bed, where the sand is made of aluminum oxide. Diffusion plates are underneath the sand, in the sense that the top of a coffee percolator has little holes in it for diffusing water, except that the holes in this case are filled with small screws that are countersunk but not entirely screwed in, and they are oversized holes with respect to the shafts of the countersunk screws, so that a small passageway is created for flow of gasses through the diffusion plate underneath the bed of alumi¬ num oxide. These fluidized beds are utilized to facilitate carborizing, nitrocarbonizing, carboni triding, and nitro-hardening. In the case of ni tro-hardening, tem¬ peratures of approximately 1500 degrees Fahrenheit are utilized, in an Austenitizing type process, to provide core-hardening as opposed to case-hardening of parts. As to carborizing, temperatures of approximately 1750 degrees Fahrenheit are utilized to provide case-hardening at a high temperature with high carbon content. TE SHEET Nitrocarborizing refers to providing case-hardening with a relatively larger nitrogen content at temperatures of approximately 1050 degrees Fahrenheit. Carbonitriding is provided at temperatures of approximately 1600 degrees " Fahrenheit fo-r a higher carbon content of the mixture of carbon and nitrogen in providing the case-hardening for high Rockwells at surface. Nitrocarborizing is a light case process at light case process at low temperature, high surface hardnesses, and not a lot of depth; the opposite is true of carbonitriding, with a higher temperature,, and a deeper case hardening. Carborizing is 60 thousandths deep, carbonitriding is 15 to 20 thousandths deep, and nitrocarborizing is 3 to 5 thousandths deep. 5" Another process for finishing metal is the Quench-Polish-Quench (or Q.P.Q.) Process for applying corrosion resistance. The Q.P.Q. Process, is in part inadequate, because, while it provides excellent corrosion characteristics, it destroys the hardening 3 characteristics required, and this has dramatic results affecting tool life and possible failure. Past experience with the Procedyne Process in the way it has been utilized provides excellent increases in Rockwell and case-hardening, as opposed to _f core-hardening. Prior to the subject invention, it had not been considered using processes analogous to the Procedyne Process for achieving not only case-hardening but simultaneously, corrosion resistance. Accordingly, it is an object of this invention to combine the two objectives and manipulate and change parameters involving gas flow and temperature, for obtaining simultaneously the appropriate corrosion resistance and case-hardening for the particular product. Previous to this time, a blanket rule of thumb had been recommended by procedyne, and utilized throughout the industry, which was a standard half-hour saturation in the bed at fluid flows of approximately, or a least not exceeding 800 cubic feet per hour. This cookbook was a standard flow, standard diffusion at the end of the cycle, standard temperature, and standard time within the furnace prior to diffusion: two hours in a nitrocarborizing atmosphere, one half hour diffusion time, 800 cubic feet per hour total gas flows its various components are as follows: 35% ammonia, 45% natural gas, 10% nitrogen. It is another object of this invention to achieve case hardening and corrosion resistance in an integral heat-treating process in an uncomplicated, inexpensive, readily utilizable manner. These and other objects of this invention may be more readily understood from the following specifications and claims. This invention relates generally to nitrocarborizing, carborizing and the like, and more particularly, it relates to case-hardening with corrosion resistance characteristics achieved by passing gas through a bed of sand a specified rates of flow, type of gas, time prior to diffusion, and diffusion time, and temperature. For example, in making parts, specifically a chain for a front-wheel drive, the time is 3 hours in nitrogen and other gas atmosphere. 800 pounds of work¬ pieces will be dropped into the furnace. It will take about a half hour for the furnace to restore its initial temperature of 980 degrees Fahrenheit. The preferred gas atmosphere is then introduced. It comprises the following: at the rate of 250 cubic feet of nitrogen per hour, 700 cubic feet of ammonia per hour, 350 oubic feet of natural gas per hour; held at temperature at those atmospheres for 3 hours. This phase is followed by an hour and a half of humidified nitrogen. Humidified nitrogen is obtained by passing dry nitrogen through a humidifier, in a manner well known in the humdifying art. Nitrogen, being hygroscopic, absorbing moisture through a humidifier, then is passed through the bed at 300 cubic feet an hour, humidified to approximately 10 to 20 percent. This forms an oxidized SUBSTITUT layer on top of the previous nitrocarborized layer. The oxide layer is highly porous, which allows for its lubri¬ cation properities, and underneath it is the nitrocarbide layer, which is extremely non-porous. The depth of the oxide layer is approximately 5 tenths of a thousandth of an inch. White layer is between one and one-and-one-half thousandths pure nitrogen. Below that is six thousandths of diffused nitrogen zone. This contrasts with the Procedyne process described above, where there would be no oxide layer, white layer would be one to two-tenths of a thousandths of an inch, nitride layer would be two to three thousandths. This invention provides an extraordinarily deep loading of fifty to a hundred times what it would ordi¬ narily be of the case-hardened depth, which gives signi¬ ficantly greater hardening and corrosion resistant properties In an alternative embodiment of this invention, the parameters would change for a cutting-type tool, such as an end mill, in which temperature would be lowered (950 degrees Fahrenheit)-, atmosphere total flows would be the same, time in the atmosphere would be 30 minutes (a 30 minute diffuse on humidified nitrogen), it would give an oxide depth of 5 tenths or a thousandth, the white layer would be one to two tenths of a thousandth, and a nitride layer of 5 to 7 tenths of a thousandth. The oxide layer cuts down the welding effect of chips on the cutting edge *

Claims: CLAIMS 1. In a heat treating method for case hardening metal workpieces utilizing gaseous entities flowing through a fluidized sand bed at temperatures substantially above the boiling point of moisture and substantially below the freezing point of the metal workpieces, the improvements comprising: heating a fluidizable sand bed furnace to a first temperature; introducing workpieces into said furnace; allowing the combined mass of the workpieces and the furnace to recover to said first temperature; after said temperature recovery, introducing a first preferred atmosphere into said furnace; said first preferred atmosphere comprising ammonia; said first preferred atmosphere comprising nitrogen; said first preferred atmosphere comprising natural gas; * maintaining said first preferred atmosphere in said furnace at said first temperature with said mass of workpieces for a first preferred period of time; passing nitrogen through a humidifier in such a manner as to obtain a resultant mixture of nitrogen humidified; replacing said first preferred atmosphere with a second preferred atmosphere; said second preferred atmosphere comprising said humidified nitrogen mixture being introduced into said furnace; and maintaining said second preferred atmosphere in said furnace with said mass of workpieces for a second preferred period of time. 2. In the method of Claim 1, wherein said first preferred period of time is of an order of magnitude corresponding to three hours and said second preferred period of time corresponds to an order of magnitude in the range of one to one and one half hours. 3. A product obtained from a workpiece pro- cessed from the method of Claim 1, wherein said first preferred period of time is of an order of magnitude corresponding to three hours and said second preferred period of time corresponds to an order of magnitude in the range of one to one and one half hours, having: an outer layer that is substantially porous and operable to hold petroleum product in measurable amounts and having a coefficient of friction substantially lower than the outer surface of said workpiece prior subjection to said method. 4. A product obtained from a workpiece pro- cessed from them method of Claim 1, wherein said first preferred period of time is of an order of magnitude corresponding to three hours and said second preferred 5 period of time corresponds to an order of magnitude in 6 the range of one to one and one half hours, having: 7 an outer layer that is substantially porous and 8 operable to hold petroleum product in measurable amounts 9 and having a coefficient of friction substantially lower 0 that the outer surface of said workpiece prior subjection 1 to said method; and 2 a second layer adjacent said outer layer being 3 substantially nonporous and inoperable to transmit 4 further interiorly or to hold any petroleum product. 1 5. A product obtained from a workpiece processed 2 from the method of Claim 1, wherein said first preferred 3 period of time is of an order of magnitude corresponding 4 to three hours and said second preferred period of time 5 corresponds to an order of magnitude in the range of one 6 to one and one half hours, having: 7 an outer layer that is substantially porous and 8 operable to hold petroleum product in measurable amounts 9 and having a coefficient of friction substantially lower 0 that the outer surface of said workpiece prior subjection 1 to said method; - a second layer adjacent said outer layer being 3 substantially nonporous and inoperable to transmit - further interiorly or to hold any petroleum product; and ^ a third layer interior from and adjacent to said 6 second layer, and having a substantial amount of diffused 7 nitrogen throughout therein. 1 6. A product obtained from a workpiece pro- 2 cessed from the method of Claim 1, wherein said first 3 preferred period of time is of an order of magnitude 4 corresponding to three hours and said second preferred 5 period of time corresponds to an order of magnitude in 6 the range of one to one and one half hours, havings 7 an outer layer that has oxide portions substan- 8 tially uniformly distributed therein and is substantially 9 porous and operable to hold petroleum product in 10 measurable amounts and having a coefficient of friction II. substantially lower than the outer surface of said work- 12 piece prior subjection to said method; 13 a second layer adjacent said outer layer being 14 substantially nonporous and inoperable to transmit 15 further interiorly or to hold any petroleum product; 16 and a third layer interior from and adjacent to 17 said second layer, and having a substantial amount of 18 diffused nitrogen throughout therein; and 19 said outer layer having a thickness of an order 2.0 of magnitude of five tenths of a thousandths of an inch; 21 said second layer having a thickness of an order of 22 magnitude of one and one-half thousandths of an inch; and 23 said third layer having thickness of an order of magni- 24 tude of six thousandths of an inch. 1 7. A product obtained from a workpiece pro- 2- cessed from the method of Claim 1, wherein said first preferred period of time is of an order of magnitude corresponding to three hours and said second preferred period of time corresponds to an order of magnitude in the range of one to one and one half hours, having: and outer layer that has oxide portions substan- tially uniformly distributed therein and is substantially porous and operable to hold petroluem product in 0 measurable amounts and having a coefficient of friction 1 substantially lower than the outer surface of said work- 2 piece prior subjection to said method; 3 a second layer adjacent said outer layer being 4 substantially nonporous and inoperable to transmit 5 further interiorly or to hold any petroleum product; 6 and a third layer interior from and adjacent to T said second layer and having a substantial amount of 8 diffused nitrogen throughout therein; and 9 the surface of said outer layer having a 0 substantially greater hardness as measured by Rockwell -1 test than the surface of said workpiece prior to subjec- 2 tion to said method. 1 8. In apparatus for heat treating metal 2 workpieces, the improvements comprising: 3 a fluidizable sand bed furnace; 4 means holding metal workpieces within the sand 5 of said furnace; BSTITUTE SHEET means conducting gas through said sand and said workpieces; a source of gas flows means humidifying said gas flow; and means transmitting said humidified gas flow to said conducting means. 9. In the apparatus of Claim 8, said gas flow being nitrogen flow, and said humidifying means operable to humidify said gas flow with 1O per cent to 20 per cent moisture, and said metal workpieces being made of ferrous metal. 10. In the method of Claim 1, the improvements comprising: said first temperature being measurably below 1000 degrees Fahrenheit and substantially above 900 degrees Fahrenheit; said workpieces having a mass on the order of magnitude exceeding one quarter ton, when said furnace has an interior diameter of the order of magnitude of 20 inches and a depth of the order of magnitude of 48 inches; said first preferred atmosphere comprising a total flow exceeding the order of magnitude of 1200 cubic feet per hour; said first preferred atmosphere comprising nitrogen flowing at an order of magnitude corresponding to 700 cubic feet per hour; SUBS 16 said first preferred atmosphere comprising 17 nitrogen flowing at an order of magnitude corresponding 18 to 250 cubic feet per hour; ' 19 said first preferred atmosphere comprising 20 natural gas flowing at an order of magnitude corresponding 21 to 350 cubic feet per hour; 22 passing nitrogen through a humidifier in such a 23 manner as to obtain a resultant mixture of nitrogen humi- 24 dified in the range of 10 percent to 20 percent; 25 said second preferred atmosphere comprising 26 said humidified nitrogen mixture being introduced into 27 said furnace at a rate having an order of magnitude of 28 300 cubic feet per hour; and 29 maintaining said second preferred atmosphere in 30 said furnace with said mass of workpieces for a second 31 preferred period of time. 1 11. In the method of Claim 1, the improvements 2 comprising: 3 said first temperature being measurably below 4 1000 degrees Fahrenheit and substantially above 900 5 degrees Fahrenheit; 6 said workpieces having a mass on the order of 7 magnitude exceeding one quarter ton, when said furnace 8 has an interior diameter of the order of magnitude of 20 ' inches and a depth of the order of magnitude of 48 10 inches; SUBSTITUTE SHEET 14 said first preferred atmosphere comprising a total flow exceeding the order of magnitude of 1200 cubic ; feet per hour; said first preferred atmosphere comprising ammo- nia flowing at an order of magnitude corresponding to 700 cubic feet per hour; said first preferred atmosphere comprising nitrogen flowing at an order of magnitude corresponding to 250 cubic feet per hour; said first preferred atmosphere comprising natural gas flowing at an order of magnitude corresponding to 350 cubic feet per hour; passing nitrogen through a humidifier in such a manner as to obtain a resultant mixture of nitrogen humi- dified in the range of 10 percent to 20 percent; said second preferred atmosphere comprising said humidified nitrogen mixture being introduced into said furnace at a rate having an order of magnitude of 300 - cubic feet per hour; and maintaining said second preferred atmosphere in said furnace with said mass of workpieces for a second preferred period of time; said first period of time having an order of magnitude of 3 hours; said second period of time having an order of magnitude in the range of one hour to one and one half hours . 12. In a heat treating method for case har- dening metal workpieces utilizing gaseous entities flowing through a fluidized sand bed at temperatures substantially above the boiling point of moisture and substantially below the freezing point of the metal workpieces, the improvements comprising: heating a fluidizable sand bed furnace to a first temperature, said first temperature being measurably below 1000 degrees Fahrenheit and substan- tially above 900 degrees Fahrenheit; introducing workpieces into said furnace; allowing the combined mass of the workpieces and the furnace to recover to said first temperture; said workpieces having a mass on the order of magnitude exceeding one quarter ton, when said furnace has an interior diameter of the order of magnitude of 20 inches and a depth of the order of magnitude of 48 inches; after said temperature recovery, introducing a first preferred atmosphere into said furnace; said first preferred atmosphere comprising a total flow exceeding the order of magnitude of 1200 cubic feet per hour; said first preferred atmosphere comprising ammo- nia flowing at an order of magnitude corresponding to 700 cubic feet per hour; SUBSTITUTE SHEET 7 said first preferred atmosphere comprising 8 nitrogen flowing at an order of magnitude corresponding 9 to 250 cubic feet per hour; 0 said first preferred atmosphere comprising f natural gas flowing at an order of magnitude 2 corresponding to 350 cubic feet per hour; 3 maintaining said first preferred atmosphere in 4 said furnace at said first temperature with said mass of 5 workpieces for a first preferred period of time; 6 passing nitrogen through a humidifier in such a 7 manner as to obtain a resultant mixture of nitrogen humi- 8 dified in the range of 10 percent to 20 percent; 9 replacing said preferred atmosphere with a second 0 preferred atmosphere; 1 said second preferred atmosphere comprising said - humidified nitrogen, mixture being introduced into said -3 furnace at a rate having an order of magnitude of 300 -4 cubic feet per hour; and -5 maintaining said second preferred atmosphere in 6 said furnace with said mass or workpieces for a second 7 preferred period of time. SUBSTITUTE SHEET

Inventors: FOX PATRICK L, FOX, PATRICK, L.
Applicants: FOX PATRICK L, FOX, PATRICK, L.
Application year: 1985
Main classification: C21D1
IPC codes: C21D1, C23C8