GB2055404A - Gas nitriding steel - Google Patents
Gas nitriding steel Download PDFInfo
- Publication number
- GB2055404A GB2055404A GB8020504A GB8020504A GB2055404A GB 2055404 A GB2055404 A GB 2055404A GB 8020504 A GB8020504 A GB 8020504A GB 8020504 A GB8020504 A GB 8020504A GB 2055404 A GB2055404 A GB 2055404A
- Authority
- GB
- United Kingdom
- Prior art keywords
- component
- retort
- ammonia
- nitrogen
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- 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
- C23C8/80—After-treatment
-
- 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
- C23C8/24—Nitriding
- C23C8/26—Nitriding of ferrous surfaces
Landscapes
- 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)
Abstract
A metal treatment (nitriding) process for producing a hard surface layer on an alloy steel component comprises maintaining the component for a period of up to four hours at a temperature between 480 DEG - 600 DEG C in an atmosphere of nitrogen and ammonia and then maintaining the temperature for a further period of up to one hour in an inert atmosphere following which the component is allowed to cool in an inert atmosphere, e.g. nitrogen. During the nitriding treatment the ammonia content of the exhaust gas from the retort may be maintained at 28-32% by volume.
Description
SPECIFICATION
Metal treatment process
This invention relates to a nitriding process for producing a hard surface layer on an alloy steel component, i.e. a component formed from steel containing alloying metals such for example as chromium and molybdenum.
Two nitriding processes are known for producing a hard surface layer on such a component, these being the cyanide bath process often termed the liquid nitriding process and the other being the ammonia process often termed the gas nitriding process.
In the cyanide bath process the component is immersed in a molten cyanide salt for a period of time after which it must be cooled and washed to remove all traces of the cyanide. The process is dirty and hazardous and the quality of the end product is not consistant. Moreover, there is a problem in getting rid of the spent cyanide salt fom the bath and the problem of disposing of the liquid be it water our a special sovent, which is used to wash the cyanide from the component. The process also demands a considerable amount of energy most of this being required for the purpose of maintaining the cyanide salt in a liquid state.
In the ammonia process the component is maintained at a high temperature in a retort whilst ammonia is passed through the retort. The time during which the component is maintained in the retort may be as long as 40 hours. After the component has been removed from the retort and allowed to cool the working surfaces must be machined to at least partly remove an excessively thick surface layer of Fe N. This process also demands a large amount of energy to heat up the retort and maintain it at the desired temperature.
The object of the invention is to provide a nitriding process for producing a hard surface layer on an alloy steel component in a simple and convenient form.
According to the invention a nitriding process for producing a hard surface layer on an alloy steel component comprises maintaining the component in an atmosphere of nitrogen and ammonia at a temperature of between 480"C-600"C for a period of time up to four hours, maintaining the temperature for a further period of time up to one hour in an inert atmosphere, and allowing the component to cool in an inert atmosphere.
In carrying out the process in accordance with the invention the alloy steel components are loaded into a retort which is then purged of air using an inert gas, e.g. nitrogen. The component is brought up to temperature in the inert gas and when the required temperature has been attained, i.e. between 480"C and 600"C preferably 560"C + 10 , the first part of the process is carried out and this can be regarded as the activating stage.
A mixture of nitrogen and ammonia is passed through the retort and the atmosphere in the retort is maintained so that it comprises between 17 and 18 parts by volume of ammonia and between 28 and 29 parts by volume of nitrogen the remainder being hydrogen. The time during which the flow of the nitrogen/ammonia mixture is maintained is between 1 and 4 hours. In order to provide accurate control of the atmosphere in the retort of the exhaust gases from the retort are analysed and the ammonia content kept art between 28-32% by volume. It is important to maintain the accurate control through the activating stage. During this stage chemical reactions take place and nitrides are produced. The ammonia breaks down to produce active monatomic nitrogen and hydrogen. The time required depends upon the temperature and the thickness of the layer of nitrides required.
Next follows the diffusion stage during which an inert gas preferably diatomic nitrogen, is supplied to the retort. The temperature is maintained. Conveniently the flow rate of the nitrogen during this stage is arranged to be equal to the combined flow rates of the ammonia and nitrogen during the activating stage. This is to ensure that there is no possibility of air entering the retort.
The diffusion stage lasts for about one hour after which the retort is allowed to cool. During cooling the atmosphere within the retort is maintained inert using nitrogen until the components are cool enough to be unloaded. During the diffusion stage inward diffusion of the nitrides takes place.
The resulting components can be utilised without further machining.
A typical alloy steel capable of being subjected to the process described comprises by weight 6.0%
Molybdenum, 6.0% Tungsten, 4.0% Chromium, 2.0%
Vanadium, 0.85% Carbon and the remainder Iron.
The surface of the components is whitish grey in colour having uniform texture. An examination of the surface layer reveals that at the surface there is a thin layer of Fe N backed up by layers of Fe2N, Fe3N, and Fe4N in that order, to a total thickness of about 0.075mm. The surface hardness value is between 1000 and 1150 Vickers. The surface has a low coefficient of friction and a marked resistance to scuffing which is due to the Fe N.
In the ammonia process a thick layer of Fe N is produced which whilst being resistant to scuffing, is brittle and hence machining of the component is necessary to redude the thickness of the layer.
1. A nitriding process for producing a hard surface layer on an alloy steel component comprising maintaining the component in an atmosphere of nitrogen and ammonia at a temperature of between 480" - 600 C for a period of time up to four hours, maintaining the temperature for a further period of time up to one hour in an inert atmosphere, and allowing the component to cool in an inert atmosphere.
2. A process according to claim 1 in which the temperature is in the range 550 Cto 5700C.
3. A process according to claim 1 or claim 2 in which the exhaust gases of the retort during the first mentioned period of time contain ammonia in the range 28 - 32% by volume.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (6)
1. A nitriding process for producing a hard surface layer on an alloy steel component comprising maintaining the component in an atmosphere of nitrogen and ammonia at a temperature of between 480" - 600 C for a period of time up to four hours, maintaining the temperature for a further period of time up to one hour in an inert atmosphere, and allowing the component to cool in an inert atmosphere.
2. A process according to claim 1 in which the temperature is in the range 550 Cto 5700C.
3. A process according to claim 1 or claim 2 in which the exhaust gases of the retort during the first mentioned period of time contain ammonia in the range 28 - 32% by volume.
4. A process according to claim 1 comprising the initial step or purging the retort of air using an inert gas and raising the component to the required temperature in the inert gas.
5. A process according to claim 1 in which the inert atmosphere is composed of diatomic nitrogen.
6. A nitriding process for producing a hard surface layer on an alloy steel component substantially as hereinbefore described.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8020504A GB2055404B (en) | 1979-06-26 | 1980-06-23 | Gas nitriding steel |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB7922173 | 1979-06-26 | ||
GB8020504A GB2055404B (en) | 1979-06-26 | 1980-06-23 | Gas nitriding steel |
Publications (2)
Publication Number | Publication Date |
---|---|
GB2055404A true GB2055404A (en) | 1981-03-04 |
GB2055404B GB2055404B (en) | 1983-02-16 |
Family
ID=26271967
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB8020504A Expired GB2055404B (en) | 1979-06-26 | 1980-06-23 | Gas nitriding steel |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2055404B (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0122529A1 (en) * | 1983-04-08 | 1984-10-24 | Kabushiki Kaisha Toyota Chuo Kenkyusho | A method for surface hardening a ferrous-alloy article and the resulting product |
GB2214196A (en) * | 1988-01-14 | 1989-08-31 | Skf Gmbh | Case-hardening |
FR2649723A1 (en) * | 1989-07-18 | 1991-01-18 | Mo Avtomobilnyj Zavod Im I A L | METHOD FOR THE THERMOCHEMICAL PROCESSING OF PARTS, DIFFUSION COATINGS OBTAINED BY THIS PROCESS AND INSTALLATION FOR CARRYING OUT SAID METHOD |
EP0485686A1 (en) * | 1990-11-15 | 1992-05-20 | Degussa Aktiengesellschaft | Method of nitriding steel articles under pressure |
-
1980
- 1980-06-23 GB GB8020504A patent/GB2055404B/en not_active Expired
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0122529A1 (en) * | 1983-04-08 | 1984-10-24 | Kabushiki Kaisha Toyota Chuo Kenkyusho | A method for surface hardening a ferrous-alloy article and the resulting product |
GB2214196A (en) * | 1988-01-14 | 1989-08-31 | Skf Gmbh | Case-hardening |
GB2214196B (en) * | 1988-01-14 | 1992-06-03 | Skf Gmbh | Process for the case hardening of rolling-bearing elements of low-alloy steel containing nickel |
FR2649723A1 (en) * | 1989-07-18 | 1991-01-18 | Mo Avtomobilnyj Zavod Im I A L | METHOD FOR THE THERMOCHEMICAL PROCESSING OF PARTS, DIFFUSION COATINGS OBTAINED BY THIS PROCESS AND INSTALLATION FOR CARRYING OUT SAID METHOD |
EP0485686A1 (en) * | 1990-11-15 | 1992-05-20 | Degussa Aktiengesellschaft | Method of nitriding steel articles under pressure |
Also Published As
Publication number | Publication date |
---|---|
GB2055404B (en) | 1983-02-16 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |