US2975083A - Carburizing procedure - Google Patents

Description

March 14, 1961 w. E. ENGELHARD CARBURIZING PROCEDURE Filed Nov. 5, 1959 INVEN TOR. E 5 N6 1 644R .2 BY

United States Patent w 2,975,082 CARBURIZING. PROCEDURE William E. Engelhard, Apalachin, N.Y. Temperature Processing Co. Inc., 228 River Road, North Arlington,

Filed Nov. 5, 1959, Ser. No. 851,066 1 Claim. I (Cl. iris-16.5

This invention relates to the art of carburizing metallic parts initially having a low carbon content, to increase such content at and slightly below the surface and thereby enhance the surface hardening characteristics of such parts.

The degree of case hardening desired varies according to use to be made of the parts; hence it is essential, for practical purposes, that the car-burizing procedure .be adaptable to the requirements of various, uses. Various procedures heretofore proposed to attain this objective are objectionable as they are not adapted to practical carburizing of parts to precise degrees of case depth and within precisely controlled ranges. Many .carburizing plants will not undertake to do case hardening, for example, of two to three thousandths of an inch, or to control case hardening within a thousandth of an inch. That is so because, generally, carburizing is performed concurrently with the heating of the parts to the critical carburizing temperature, some parts of the load reaching this temperature before others, making it difiicult .to control the procedure and degree of carburizing. There isthe further complication that while heating to carburizing temperature, the parts. become carburized or decarburized to a degree that is difficult to calculate for shallow cases. As a result the finished product (even if an attempt is made to compensate for'the varying degree of carbon gain) will not be carburized to precisely the depth desired. Control. of precise degrees of cartical matter, be attained. Under the previous practices, burization, under such procedures, could not, as a practical matter, be attained. Under the previous practices, where carburization occurs while work is approaching carburizing temperature, as in most standard practices, the degree of carburization cannot be accurately controlled by the operator; consistently uniform results cannot be attained, unless the case depth required (.010" or more for example) is so great that the effect of carburizing during the initial (coming to heat) part of the cycle is relatively insignificant.

1 The procedure of this invention enables the carburizing of parts to precisely the predetermined desired degree consistently commercially-for example .0002" to .010"; the parts in batches thus treated are carburized to the predetermined desired degree, uniformly and without risk of over or under-casing.

The foregoing and other advantages and objects of the invention will become apparent from the description below and from the accompanying drawings, wherein:

Fig. l is a vertical, partly fragmentary, sectional view of a carburizing procedure embodying the invention,

Fig. 2 is a fragmentary, elevational view, illustrating parts used for connection of a source of gas19 with the valve 21 and pipe 22 of Fig. l, v

Fig. 3 is a fragmentary, vertical, sectional view, showing another source (19a) of gas for connection with valve 21 to pipe 22, said source 19a in'turn originating in gas flowing through pipe 35 and bubbled through tank Fig. 4 is a partly fragmentary, elevational view of parts used for connection of another source of gas (19b) with valve 21 for pipe 22 and Fig. 5 is a partly fragmentary, elevational view, showing parts carburizedspursuant to the invention about to be rapidly quenched and cooled.

Pursuant to the method of this invention, the batch of steel parts to be case hardened is initially placed on a plate 10 or in aholder or bell 11 (which may be a perforated member such as an inverted basket or the like positioned on plate 10) or on a spacer 12, which, in turn, is positioned on plate 10. The parts are thus positioned in a chamber 13 of a furnace 14; the chamber may be closed by a suitable cover 15 and provided with electrical or other heating means 16, thereby directing heat inwardly from the side walls of the chamber 13. Thermocouples 17 may be positioned at various points in the mass of parts being treated, as shown in Fig. l and connected, as by the wires 18, with temperature reading instruments so that the operator may control the heating means 16 (or to automatic control means) to heat the parts to their critical temperature at which they becomereceptive to rapid carbon surface penetration, continuing such heating until all of the parts have reached that temperature. The procedure of the present invention enables carburization to be successfully performed commercially of batches of parts with consistently uniform results and within ranges not possible in prior procedures.

As a practical example of an application of this invention (and without limiting the invention thereto), the parts may be thus heated. to about 1,350 to 2,000 degrees F. for about one hour. While the parts are thus heated, a gas neutral to the initial carbon content of the parts is passed under pressure onto the parts, also excluding the air atmosphere. The source of gas may, as shown in Fig. 2, be a source of gas with no carburizing potential, from a source 19 connected, as by a coupling 20, to a valve 21 and thence through a pipe 22 passing through an aperture 23 of an inverted, U'-shaped imperforate shield or bell 2.4 assembled over the parts, and onto the plate 10. The lower end of pipe 22 may be welded as at 25 to the plate 10; said pipe is preferably provided I with apertures 26 spaced from the plate ,10 a lesser] distance than. the height of the shield so that said, gas will pass through the pipe 22 fromthe source 19,, through the apertures 26 and onto the parts in the shield 24 and thence between the shield and the plate 10. The

plate 10 may be of larger dimensions than the shield 24 and may be circumferentially upturned as at 27 to form, with the lower end of the shield, arestricted passage for such gases in escaping from the shield. In practice, the actual space between the upturned circumferential edge 27 of the plate-10 and the shield may be I i steel parts and avoids oxidation as the 'parts are brought up to their critical temperature. When heating of the parts has been continued sufficiently to assure that all of i the parts are brought up to their desired critical temperature and that they are uniformly at that temperature, the source 19 is cut off, as by the valve 21, and the valve 1 30 opened to admit an active carburizing gas, such as f methane, propane, or any other carbonaceous gas, from source 32, through coupling 31 and valve 30 to the p'ipe 3 22 and thence through the apertures v26 and-ontothe parts, for a much shorter period of time-for example, from one to ten minutes. The carburizing gas may thus be applied for a fraction of the time previously-required (by controlling the rateof flow of gas from source 32 through valve 30) and then the assembly is ready for quenching. By controlling the time andquantity-ofgas from source '32 thus swept over the parts in shield 124 in this carburizing stage ofthe procedure of the invention, the precise depth of caseofthe parts thus treated may be accurately controlled within ranges heretofore not practical or commercially :possible of attainment. Case hardening to precisely the desired degree is commercially consistently attainedpursuant tothe invention. It is possibletocase-harden parts from .0002 to .010" as a practical matter and to obtain uniformly consistent results in commercial practice, pursuant to the invention.

After the carburizingprocedure, the pipe 22, the plate 10 and assembly thereon abovedescribed may be lifted from the chamber 13 ofthe furnace (as by cable 28) and cooled by suitable means, as by being immersed in the tank 29 for rapid quenching.

The parts may be suitably formed to facilitate assembly or disassembly. To that end, holder 11 may be provided with an aperture at the top thereof enabling it .to be slidably disposed on the pipe 22; as above mentioned, the shield 24 is provided with aperture 23 at the top thereof (and may have a sealing gasket 23) to freely slidably dispose it on the pipe 22.

After completion of the procedure of carburization, pursuant to the invention, the pipe 22 may be separated, as at 33 (Fig. 1) from the pipe 34 and valves 21 and30, and the holder 11 and batch of parts therein removed from the pipe 22. A holder 11 and new batch of parts therein and shield 24 may be repositioned in the assem- "bly -as in Fig. 1 for repeating the procedure of themvention. The perforated holder 11, shield 24 and asso- =ciated features thereof and of the assembly shown in Fig. 1 promote the uniform heating and subsequent uniform cooling of each of the parts in the batch being treated pursuant to the invention.

This application is a continuation in part of my copending application, Serial No. 739,039, 'filed June 2,

1958, and now abandoned; Figs. 1, 2 and 5 of present application corresponding generally to Figs. 1 and2 of said application.

I have found that, for some work normally troublesome to carburize uniformly because of varying carbon content or because of contained impurities such as sulfur or lead, or to salvage work previously over-cased, excellent results may be obtained if, instead of using the gas source illustrated in Fig. 2 of this application as a source of dry neutral non carburizing hydrogen gas, a source 19b (Fig. 4) of decarburizing gas e.g. hydrogen having a high moisture content is used. Said hydrogen gas of high dew point may either be provided as such gas flowing through the pipe 1% of Fig. 4 or it may initially be dry hydrogen or mixture of nitrogen and hydrogen passed through the pipe 35 (Fig. 3) coupling 35 and valve 37, through the pipe 38 and bubbled through water in the tank 39, emerging as a gas of high moisture content which is then passed as through a suitable coupling (as 20 and valve 21 of Pig. 2) with the pipe 22 of the apparatus. I

The carburizing procedure otherwise followed pursuan to the invention in the use of the forms shown in Figs. '3 and 4 and above described follows that described in connection with Figs. 1, 2 and 5.

l have found that, with the use of hydrogen or dissociated ammonia with a high moisture content, carbon, sulfur and other impurities may be scavenged initially, where desirable, thus providing a uniform material for precise carburization and eliminating interference with the absorption of carbon in the carburizing procedure to follow.

tank 29 (water, oil-orother liquid).

temperature of the parts. cooling of the .parts, the assembly may be removed from Far greater accuracy.is..attained, pursuant tothis inven tion, than in prior attempts :to carburize parts which are at varying temperatures. As above noted, pursuant to the invention, the parts are heated, as shown in Fig. 1, in the furnace 14 and brought up to that predetermined degree of heat at whichsit isfdesired to carburize them; heating of the parts at that temperature is continued (while the parts arercontinuously .washe'dby the neutral ,gasirom source 19, 19a .or .191 ,for .sufiicient time to insure :that all of 1the;.parts will have mnifornily .attained the precise desired predetermined temperature. 'When the parts, through sufiiciently continued heating, uniformly reach the'prccise desiredpredetermined temperature, the flow of gas :from source .19 (19mm 19b) is discontinued, as by shutting valve 21, and valve 30 opened for the precise time required for carburizing said parts to case harden them to the precise desired degree; valve 30 is then shut off.

Valve 21 may be turned on again and the assembly of Fig. 1 then liftedout of the furnace and-left tolcool in air before the case is-set, where, for example, .it is .desired to perform machining or other operations before the caseis set on all surfaces of the-parts. Where, after the carburizing procedure of Fig. 1 has been completed, it is desiredto attain case setting of allsurfaces .of the parts, the-assembly'may be immersed in a liquid 35 in The liquid is preferably unheated so as to be normally at about .room

temperature (or at substantially lower than boiling temperatures') quenching liquid, shield 24 willtend to move downwardly On immersion of the assembly in such more slowly and stay above the assembly 10, 1'1, 12; additionally the parts will boil and generate gases on immersion in the'liquid quenching medium 35; gases'will thus be generatedand will flow .upwardly in the shield 24 andhold said shield away from the parts. The pipe '22 may have stop means to limit movement of shield 24 away from the parts and to keep the shield under the surface-of liquid 35. The quenching medium'thus fully immerses the parts and rapidly quences them univolume of liquid medium 35 inside the shield, which fraction is physically adjacent and therefore close to the After such .second phase .slow

tank 29.

The invention, while not limited thereto, has provento be highly useful in connection with treatment of ferrous 'parts.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

The method of treating steel parts 'to increase their surface carbon content to an accurately predetermined extent, comprising enclosing said parts while spaced from oneanother in a furnace, with heating means lining side walls thereof, while held in a perforated bell posia flow of pressurized gas, neutral to the initial carbon content of said parts, with a dew point nothigher than 40" F., to inside the top portion of said imperforate bell, through said'perforated bell, and under the bottom edge of said imperforate bell, whereby the original carbon content of the steel parts is not decreased, then while still maintaining said parts at said uniform temperature, substituting an active carburizing gas for said 5 neutral gas for an accurately predetermined period of time of fi'om one to ten minutes, to thereby case harden said parts to a desired extent between .0002" and .010" in depth and, after treatment in said carburizing gas, rapidly cooling said steel parts by immersion in a quenching liquid.

References Cited in the file of this patent UNITED STATES PATENTS Olsen July 31, 1923 6 Machlet June 4, 1935 Saives Mar. 25, 1941 Cope July 4, 1950 Besselman et al. June 25, 1956 Tauber July 8, 1958 OTHER REFERENCES Johnson: Metal Working and Heat-Treatment Manual, vol. III, pages 51 and 155. Library Call No. TS 205

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