US3891473A - Heat treating atmospheres - Google Patents
Heat treating atmospheres Download PDFInfo
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- US3891473A US3891473A US361082A US36108273A US3891473A US 3891473 A US3891473 A US 3891473A US 361082 A US361082 A US 361082A US 36108273 A US36108273 A US 36108273A US 3891473 A US3891473 A US 3891473A
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- United States
- Prior art keywords
- carbon
- ammonia
- methane
- atmosphere
- constituents
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/76—Adjusting the composition of the atmosphere
Definitions
- ABSTRACT A heat treating atmosphere and method for its use wherein the atmosphere provides precise control over carbon content in metal parts, such as steel, and which is particularly applicable to powder metal sintering.
- the method uses a mixture of resultant constituents from dissociated ammonia and methane combusted with air to provide an atmosphere of controlled car bon potential.
- the ammonia is dissociated, the methane is combusted with air and the resultant constituents are mixed together prior to introduction into the heat treating furnace.
- the method prevents the formation of undesirable hard and brittle phases of carbides during sintering, the resulting products being free of segregated high carbon constituents, i.e., eementite, and being easier to machine, thus providing much longer cutting tool life.
- dissociation of the ammonia in the furnace provides nascent nitrogen which nitrides the workpiece undergoing treatment whereas in the subject method dissociation prior to introduction to the furnace provides molecular N which is inert and does not affect the workpiece undergoing treatment.
- this can include any carbide forming composition.
- Precise control is obtained according to this invention by diluting a carbiding atmosphere formed from methane combusted with air and with a diluent of anhydrous ammonia which is dissociated into N; and H prior to its being mixed with the combusted or cracked methane and prior to the introduction of the blended constituents into the furnace. It is important to this invention that the ammonia be dissociated prior to its introduction into the furnace. Otherwise, when dissociation occurs in the furnace, nascent nitrogen forms and nitrides the workpiece. This is to be avoided in the subject method.
- the use of anhydrous ammonia as a diluent represents a practical and low cost approach.
- a typical ferrous metal powder contains extremely low amounts of carbon.
- a low carbon powder metal is mixed with graphite to provide about the carbon content desired. This mixture is pressed into a green compact which is subsequently sintered. Sintering is carried out in an atmosphere consisting of a certain or predetermined ratio of the products of cracked methane and dissociated ammonia.
- the proper diluted atmosphere can be selected to provide, during normal sintering times and temperatures, an equilibrium condition which provides and/or maintains a desired final amount of carbon in the workpiece. Since the cracked methane is diluted with the nitrogen and hydrogen resulting from the dissociated ammonia, low amounts of carbon, or in other words a low carbon potential, is provided in the atmosphere so that precise amounts of carbon can be obtained by this method. This low carbon potential atmosphere is lower than has been possible heretofore. Further, it prevents oxidation because each separately generated gas is dry and of low dew point.
- FIGURE shows a schematic combination endothermic gas generator and ammonia dissociator.
- this invention provides Sintering and/or heat treating atmospheres for carbon level control and oxidation prevention.
- the invention makes use of blended, low dew point atmospheres during the heating, sintering, cooling and/or subsequent heat treat ment of powder metal compacts or parts of ferrousbase or non-ferrous base compositions, which are carbide formers, so that the various levels of carbon are controlled, and at the same time the formation of metal oxides of active elemental constituents is prevented.
- Equipment is also described which simultaneously produces and controls the atmosphere in balance with the various levels of carbon desired in the resulting sintered or heat treated workpieces to provide definite ranges of composition.
- Typical compositions are listed in Table I as obtained from the various volume blends of dissociated ammonia (25% nitrogen and hydrogen) and endothermic cracked methane gas at 2.5 to one air/gas ratio (20% carbon monoxide, 38% hydrogen and 42% nitrogen).
- Table I is derived for a furnace requirement of 2,000 cubic feet per hour of gas atmosphere. It shows the flow scope readings for dissociated ammonia and for endothermic gas at the various percentages of each. It also shows the number of cubic feet of each constituent flowing into the furnace at the corresponding ratios of each type of gas.
- Table II shows the resultant analysis of the atmosphere in a furnace for the various volume percentages of dissociated ammonia gas and endothermically cracked methane gas.
- the preferred equipment for this method is a combination endothermic generator and ammonia dissociator as shown in the FIGURE.
- the equipment includes two or more retorts l and 11 within a combustion chamber heated by burning gas or electric heating elements.
- One or more retorts crack an air to gas (methane) ratio of about 2.5 to l, to produce endothermic gas, and one or more retorts dissociate ammonia.
- the input to each retort is regulated to produce desired amounts of cracked endothermic gas constituents (20% CO, 38% H and 42% N and de sired amounts of dissociated ammonia (25% H and 75% N from each of the separate retorts and 11.
- the required output is mixed or blended to form a desired composition which will be used in equilibrium with the chemistry of the parts or workpiece to be sintered. To accomplish this the desired atmosphere is piped, as shown, to a sintering furnace.
- Endothermic gas atmospheres are ordinarily both too high in carbon potential at low dew point and too Inn in decarburizing resistance at higher dew point to sintcr the full range of powder metal pressed parts to meet the A.I.S.I. carbon steel compositions. lt has therefore not been possible heretofore to control the carbon level of the lower range composition of carbon when high a1 loying element content of other elements prone to oxidation are included.
- Such principal elements may be 5 manganese and chromium and there may be others to a lesser degree.
- the low dew point endothermic atmosphere is too potent in carburizing action to be in eqilibrium with 0.7%, 0.8% and 09% carbon level compositions. Often times undesirable hard constituents such as cementite inclusions were formed. This caused brittle products and made machining difficult.
- a predetermined ratio of constituent gas composition, to be in equilibrium with the desired composition of the sintered compact, has been used with success in accordance with this invention.
- the exact carbon analysis of the steel grade was successfully controlled by using the subject invention.
- the alloying elements of high level manganese content for each of the materials was also controlled without oxidation of the manganese. This is accomplished, in accordance with this invention, by using an atmosphere for sintering in which the carbon potential is maintained in equilibrium with the desired carbon chemistry of the steel powder compact.
- the dew point is controlled at a low level by controlling the air and gas ratio, as well as the cracking temperature in the endothermic gas generator.
- the carbon potential is further controlled by adding a dry reducing gas, which does not contain significant amounts of oxygen, carbon dioxide or water vapor, to the low dew point endothermic cracked gas. Dissociated ammonia gas cracked to low dew point is used as the diluting constituent.
- the method of the invention produced the following results.
- A. ratio of 60% (by volume) of dissociated ammonia with 40% (by volume) of endothermic cracked gas at a low dew point produced an atmosphere that was in equilibrium with steel powder compacts of both A.l.S.l. 4023 and A.l.S.l. 1522, which contained 0.20 to 25% and 0.18 to 0.24% carbon, respectively.
- each steel powder with 0.70 to 0.90% manganese and 1.10 to 1.40% manganese. respectively could be sintered without oxidation in the above atmosphere at 2,050" F.
- the composition of the atmosphere at 60/40 ratio was (by volume) carbon monoxide, 59.8% hydrogen and 31.8% nitrogen. This blend gave consistent results as to composition on the surface and in the core of the parts over several runs.
- the dew point was determined to be at +20 F., which was that of the cracked endothermic gas.
- the carbon potential as determined by the steel strip method was 0.28% carbon.
- the control of low level carbon, as in carburizing grades of carbon or alloy steel compositions, is important to maintain tough core properties of densified powder metal preforms.
- the composition of the compacted and sintered preform must be held to narrow ranges of carbon content to obtain strong and duetile core properties in case-hardened parts.
- a method of controlling the carbon content of a steel alloy containing about 0.18% to 0.85% by weight carbon comprising:
- ammonia and methane in a volume ratio ranging from about 60/40 for the lower C contents to 20/80 for the higher C contents while maintaining the ammonia and methane separate from each other,
Abstract
Description
Claims (5)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US361082A US3891473A (en) | 1973-05-17 | 1973-05-17 | Heat treating atmospheres |
US05/514,352 US4028100A (en) | 1973-05-17 | 1974-10-15 | Heat treating atmospheres |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US361082A US3891473A (en) | 1973-05-17 | 1973-05-17 | Heat treating atmospheres |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US05/514,352 Division US4028100A (en) | 1973-05-17 | 1974-10-15 | Heat treating atmospheres |
Publications (1)
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US3891473A true US3891473A (en) | 1975-06-24 |
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US361082A Expired - Lifetime US3891473A (en) | 1973-05-17 | 1973-05-17 | Heat treating atmospheres |
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4042385A (en) * | 1974-11-09 | 1977-08-16 | Toyo Kogyo Co., Ltd. | Sintering method for making a high carbon ferrous sliding element |
US4049473A (en) * | 1976-03-11 | 1977-09-20 | Airco, Inc. | Methods for carburizing steel parts |
US4106931A (en) * | 1977-05-18 | 1978-08-15 | Airco, Inc. | Methods for sintering powder metallurgy parts |
US4139375A (en) * | 1978-02-06 | 1979-02-13 | Union Carbide Corporation | Process for sintering powder metal parts |
US4153485A (en) * | 1974-12-28 | 1979-05-08 | Kobe Steel, Ltd. | Process for heating steel powder compacts |
US4234337A (en) * | 1977-12-02 | 1980-11-18 | Hoerbiger & Co. | Method of producing sintered friction laminae |
US4579713A (en) * | 1985-04-25 | 1986-04-01 | Ultra-Temp Corporation | Method for carbon control of carbide preforms |
EP3042967A1 (en) * | 2015-01-08 | 2016-07-13 | Linde Aktiengesellschaft | Gas mixture and method for controlling a carbon potential of a furnace atmosphere |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2299138A (en) * | 1941-10-04 | 1942-10-20 | Westinghouse Electric & Mfg Co | Heat treating of steel |
US2489839A (en) * | 1946-04-30 | 1949-11-29 | Isthmian Metals Inc | Process for carburizing compacted iron articles |
-
1973
- 1973-05-17 US US361082A patent/US3891473A/en not_active Expired - Lifetime
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2299138A (en) * | 1941-10-04 | 1942-10-20 | Westinghouse Electric & Mfg Co | Heat treating of steel |
US2489839A (en) * | 1946-04-30 | 1949-11-29 | Isthmian Metals Inc | Process for carburizing compacted iron articles |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4042385A (en) * | 1974-11-09 | 1977-08-16 | Toyo Kogyo Co., Ltd. | Sintering method for making a high carbon ferrous sliding element |
US4153485A (en) * | 1974-12-28 | 1979-05-08 | Kobe Steel, Ltd. | Process for heating steel powder compacts |
US4049473A (en) * | 1976-03-11 | 1977-09-20 | Airco, Inc. | Methods for carburizing steel parts |
US4106931A (en) * | 1977-05-18 | 1978-08-15 | Airco, Inc. | Methods for sintering powder metallurgy parts |
US4234337A (en) * | 1977-12-02 | 1980-11-18 | Hoerbiger & Co. | Method of producing sintered friction laminae |
US4139375A (en) * | 1978-02-06 | 1979-02-13 | Union Carbide Corporation | Process for sintering powder metal parts |
FR2416075A1 (en) * | 1978-02-06 | 1979-08-31 | Union Carbide Corp | PROCESS FOR SINTING PARTS SHAPED FROM POWDER |
US4579713A (en) * | 1985-04-25 | 1986-04-01 | Ultra-Temp Corporation | Method for carbon control of carbide preforms |
EP3042967A1 (en) * | 2015-01-08 | 2016-07-13 | Linde Aktiengesellschaft | Gas mixture and method for controlling a carbon potential of a furnace atmosphere |
WO2016110450A1 (en) * | 2015-01-08 | 2016-07-14 | Linde Aktiengesellschaft | Gas mixture and method for controlling a carbon potential of a furnace atmosphere |
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Owner name: FIDELITY UNION TRUST COMPANY, 765 BROAD ST., NEWAR Free format text: MORTGAGE;ASSIGNOR:CHRYSLER CORPORATION;REEL/FRAME:003832/0358 Effective date: 19810209 Owner name: FIDELITY UNION TRUST COMPANY, TRUSTEE,NEW JERSEY Free format text: MORTGAGE;ASSIGNOR:CHRYSLER CORPORATION;REEL/FRAME:003832/0358 Effective date: 19810209 |
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Owner name: CHRYSLER CORPORATION Free format text: PARTES REASSIGN, TRANSFER AND RELINQUISH THEIR ENTIRE INTEREST UNDER SAID PATENTS ALSO RELEASE THEIR SECURITY INTEREST.;ASSIGNOR:MANUFACTURERS NATIONAL BANK OF DETROIL (CORPORATE TRUSTEE) AND BLACK DONALD E., (INDIVIDUAL TRUSTEE);REEL/FRAME:004355/0154 Effective date: 19840905 |