CA2258161C - Powder metallurgical body with compacted surface - Google Patents
Powder metallurgical body with compacted surface Download PDFInfo
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- CA2258161C CA2258161C CA002258161A CA2258161A CA2258161C CA 2258161 C CA2258161 C CA 2258161C CA 002258161 A CA002258161 A CA 002258161A CA 2258161 A CA2258161 A CA 2258161A CA 2258161 C CA2258161 C CA 2258161C
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- Prior art keywords
- iron
- process according
- powder
- compacted
- mpa
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
- B22F5/08—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of toothed articles, e.g. gear wheels; of cam discs
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/12—Both compacting and sintering
- B22F3/16—Both compacting and sintering in successive or repeated steps
-
- 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
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
- C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
-
- 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
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
- C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
- C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/12—Both compacting and sintering
- B22F3/16—Both compacting and sintering in successive or repeated steps
- B22F3/164—Partial deformation or calibration
- B22F2003/166—Surface calibration, blasting, burnishing, sizing, coining
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Powder Metallurgy (AREA)
Abstract
The present invention concerns compacted and optionally presintered bodies, which are prepared from metal powders and which have densified surfaces, obtained by shot peening or rolling.
Description
22fl55-191 POWDER METALLURGICAL BODY WITH COMPACTED SURFACE
The present invention concerns compacted bodies and more particularly compacted and optionally presintered bodies, which are prepared from metal powders and which have a densified surface.
Materials used for components subjected to a bending stress e.g. gear wheels are subjected to local stre:~s concentrations, and it is preferred that these materials have superior properties at the local stress maximum regions.
An example of such a material is disclosed in EP 552 272 which concerns sintered powder metal blanks having densified surface regions. According to this publication the densified regions are obtained by rolling.
It is also known that the surfaces of sintered powder metallurgical parts can be densified by using shot peeni.ng. The purpose of shot peening the surfaces of these sintered parts is to induce compressive stress in the surfaces, which in turn results in sintered parts having improved fatigue strength, surface hardness etc.
BRIEF SUN~lARY OF THE INVENTION
It has now been found that important advantages can be obtained if the densification of the surface is ;performed before the sintering of the compacted parts. The most interesting results have been obtained when the compacted parts are subjected to the densification process after a presintering step. Accordingly, the present invention concerns a process for preparing compacted and preferably presintered bodies having a densified surface as well as the bodies obtained by this process.
1a According to one aspect of the present invention, t=here is provided a process for the preparation of a powder metallurgical body comprising the steps of: uniaxially compacting metal powder; presintering the obtained compacted body at a temperature of at least 500°C; subjecting the obtained body to shot peening or rolling at an intensity and :Eor a period of time sufficient for establishing a densification surface layer within a deformation depth of at :Least 0.1 mm, in order to achieve a density of 90 to 100 of :Full density after sintering; and optionally subjecting the obtained body to an additional compacting step.
BRIEF DESCRIPTION OF THE DRATnIINGS
FIG. 1 is a photomicrograph at 120x of an unetched green sample compacted in a lubricated die at 700 MPa followed by shot peening at an Almen intensity of 0.13 for 1 . 5 ~;econds ;
FIG. 2 is a photomicrograph at 120x of an unetched presi.ntered sample compacted in a die at 700 MPa followed by shot peening at an Almen intensity of 0.14 for 1.5 seconds;
FIG. 3 is a photomicrograph at 120x of an unetched :presi.ntered sample compacted in a lubricated die at 700 MPa :by snot peening at an Almen intensity of 0.21 for 3 seconds;
FIG. 4 is a photomicrograph at 120x of an unetched :presi.ntered sample compacted in a lubricated die at 700 MPa followed by shot peening at an Almen intensity of 0.3 for 3 seconds ;
FIG. 5 is a photomicrograph at 120x of an unetched ~greer~ sample compacted in a die at 700 MPa followed by shot :peeni.ng at an Almen intensity of 0.08 for 1.5 seconds; and 1b FIG. 6 is a photomicrograph at 120x of an unetched ~~inte=red (1120°C.) sample compacted in a die at 700 MPa followed by shot peening at an Almen intensity of 0.3 for 3 seconds.
DETAILED DESCRIPTION OF THE INVENTION
By performing the densification of metal powder bodies in green and optionally presintered condition, a 7_arger degree of deformation can be obtained than in the case where sintered bodies are densified. When the green and optionally presintered parts are subsequently sintered, the previous pores are sintered together and a layer with full or almost full density is created. In this context the t=erm "full or almost full density" is intended to mean that a densification in the range of 90 - 100 per cent of full density is established.
By using the process according to the present inven tion not only the densification or deformation depth will be improved. Also the energy requirement will be conside rably lower than when the densification process is car-ried out after the sintering step in accordance with known methods. After sintering the bodies prepared according to the present invention can be treated with secondary operations as usual.
Suitable metal powders which can be used as starting materials for the compacting process are powders prepared from metals such as iron and nickel. In the case of iron-based powders, alloying elements, such as carbon, chro-mium, manganese, molybdenum, copper, nickel, phosphorus, sulphur, etc. can be added in order to modify the proper-ties of the final sintered products. The iron-based pow-ders can be selected from the group consisting of sub-stantially pure iron particles, pre-alloyed iron-based particles, diffusion-alloyed iron-based particles and mixtures of iron particles and alloying elements.
In order to obtain sufficient bending strength for the subsequent densification process the starting metal powder is uniaxially compacted at a pressure between 200 and 1200, preferably between 400 and 900 MPa. The compac-tion is preferably carried out in a lubricated die. Other types cf compaction are warm and cold compaction of metal powders mixed with lubricants, such as stearates, waxes, metal soaps, polymers, etc.
According to a preferred embodiment of the invention the compacted body is also presintered at a temperature above 500°C, preferably between 650 and 1000°C before the densification operation.
The green and optionally presintered bodies sub-jected to the densification process according to the pre-sent invention should be compacted and optionally pYe-sintered to a minimum bending strength of at least 15 MPa, preferably at least 20 MPa, and most preferably at least 25 MPa.
The densification process according to the invention is preferably carried out by shot peening although other densification processes such as different types of roll-ing are not excluded. In shot peening, rounded or essen-tially spherical particles ttermed "shot") made from cast or wrought steel and stainless steel, as well as from ceramic or glass beads, are propelled against a workpiece with sufficient energy and for a sufficient time to cover the surface with overlapping cold Worked dimples (see e;.g. the article by J. Mogul et al "Process controls the key to reliability of shot peening", Process Controls &
Instrumentation, November 1995).
1.5 The shot peening time according to the present in-vention normally exceeds 0.5 seconds and is preferably between 1 and 5 seconds and the Almen intensity is nor-mally in the range 0.05 - 0.5. The deformation depth depends on the final use of the product and should exceed 0.1 mm, preferably 0.2 mm and most preferably the depth should exceed 0.3 mm.
The invention is illustrated by the following rion-limiting examples.
The starting metal powder was Distaloy DC-1, which is an iron-based powder containing 2% nickel and 1.5% mo-lybdenum available from Hdganas AB, Sweden.
This powder was warm compacted at 700 MPa to a density of 7.4 g/cm3 having a bending strength of 25 MPa.
The compacted bodies were divided into the following three groups:
Group 1 The bodies were left green, i a not subjected to any additional treatment.
Group 2 The bodies were presintered at 750°C for 20 minutes in protective atmosphere.
Group 3 The bodies were sintered at 1120°C for 15 minutes in endogas.
*Trade-mark Group 1 The green bodies were shot peened. At too high in tensities, i.e. Almen intensities (cf the Mogul article referred to above) above 0.14 for 3 seconds, the partic les were torn loose and the surface was destroyed. Tt turned out that the Almen intensities should be below about 0.14 and the exposure time should be less than 2 seconds. This was true for both green bodies which had been warm compacted and for bodies which were produced in a lubricated die. As can be seen in Fig. 1, the densifi-cation was somewhat better in the bodies obtained when the compaction was performed in a lubricated die.
Group 2 The presintering of the green bodies was done in or-der to remove lubricant that could create porosity, to remove deformation hardening and to improve the strength of the material. It was essential that the graphite difu-sion was limited in order to avoid solution hardening effects in the iron powder particles. After the presin-tering, the strength of the material had improved significantly and much higher Almen intensities could be used, especially for the bodies manufactured in lubricated dies. Almen intensities up to 0.3 could be used without problems,i.e. no particles were torn loose from the surface, and deformation depths of 300 ~.m were achieved. For the warm compacted bodies the erosion started at intensities of 0.14. Due to the removal of lubricant and deformation hardening, the deformation depth had increased significantly in comparison with the green bodies of group 1.
The present invention concerns compacted bodies and more particularly compacted and optionally presintered bodies, which are prepared from metal powders and which have a densified surface.
Materials used for components subjected to a bending stress e.g. gear wheels are subjected to local stre:~s concentrations, and it is preferred that these materials have superior properties at the local stress maximum regions.
An example of such a material is disclosed in EP 552 272 which concerns sintered powder metal blanks having densified surface regions. According to this publication the densified regions are obtained by rolling.
It is also known that the surfaces of sintered powder metallurgical parts can be densified by using shot peeni.ng. The purpose of shot peening the surfaces of these sintered parts is to induce compressive stress in the surfaces, which in turn results in sintered parts having improved fatigue strength, surface hardness etc.
BRIEF SUN~lARY OF THE INVENTION
It has now been found that important advantages can be obtained if the densification of the surface is ;performed before the sintering of the compacted parts. The most interesting results have been obtained when the compacted parts are subjected to the densification process after a presintering step. Accordingly, the present invention concerns a process for preparing compacted and preferably presintered bodies having a densified surface as well as the bodies obtained by this process.
1a According to one aspect of the present invention, t=here is provided a process for the preparation of a powder metallurgical body comprising the steps of: uniaxially compacting metal powder; presintering the obtained compacted body at a temperature of at least 500°C; subjecting the obtained body to shot peening or rolling at an intensity and :Eor a period of time sufficient for establishing a densification surface layer within a deformation depth of at :Least 0.1 mm, in order to achieve a density of 90 to 100 of :Full density after sintering; and optionally subjecting the obtained body to an additional compacting step.
BRIEF DESCRIPTION OF THE DRATnIINGS
FIG. 1 is a photomicrograph at 120x of an unetched green sample compacted in a lubricated die at 700 MPa followed by shot peening at an Almen intensity of 0.13 for 1 . 5 ~;econds ;
FIG. 2 is a photomicrograph at 120x of an unetched presi.ntered sample compacted in a die at 700 MPa followed by shot peening at an Almen intensity of 0.14 for 1.5 seconds;
FIG. 3 is a photomicrograph at 120x of an unetched :presi.ntered sample compacted in a lubricated die at 700 MPa :by snot peening at an Almen intensity of 0.21 for 3 seconds;
FIG. 4 is a photomicrograph at 120x of an unetched :presi.ntered sample compacted in a lubricated die at 700 MPa followed by shot peening at an Almen intensity of 0.3 for 3 seconds ;
FIG. 5 is a photomicrograph at 120x of an unetched ~greer~ sample compacted in a die at 700 MPa followed by shot :peeni.ng at an Almen intensity of 0.08 for 1.5 seconds; and 1b FIG. 6 is a photomicrograph at 120x of an unetched ~~inte=red (1120°C.) sample compacted in a die at 700 MPa followed by shot peening at an Almen intensity of 0.3 for 3 seconds.
DETAILED DESCRIPTION OF THE INVENTION
By performing the densification of metal powder bodies in green and optionally presintered condition, a 7_arger degree of deformation can be obtained than in the case where sintered bodies are densified. When the green and optionally presintered parts are subsequently sintered, the previous pores are sintered together and a layer with full or almost full density is created. In this context the t=erm "full or almost full density" is intended to mean that a densification in the range of 90 - 100 per cent of full density is established.
By using the process according to the present inven tion not only the densification or deformation depth will be improved. Also the energy requirement will be conside rably lower than when the densification process is car-ried out after the sintering step in accordance with known methods. After sintering the bodies prepared according to the present invention can be treated with secondary operations as usual.
Suitable metal powders which can be used as starting materials for the compacting process are powders prepared from metals such as iron and nickel. In the case of iron-based powders, alloying elements, such as carbon, chro-mium, manganese, molybdenum, copper, nickel, phosphorus, sulphur, etc. can be added in order to modify the proper-ties of the final sintered products. The iron-based pow-ders can be selected from the group consisting of sub-stantially pure iron particles, pre-alloyed iron-based particles, diffusion-alloyed iron-based particles and mixtures of iron particles and alloying elements.
In order to obtain sufficient bending strength for the subsequent densification process the starting metal powder is uniaxially compacted at a pressure between 200 and 1200, preferably between 400 and 900 MPa. The compac-tion is preferably carried out in a lubricated die. Other types cf compaction are warm and cold compaction of metal powders mixed with lubricants, such as stearates, waxes, metal soaps, polymers, etc.
According to a preferred embodiment of the invention the compacted body is also presintered at a temperature above 500°C, preferably between 650 and 1000°C before the densification operation.
The green and optionally presintered bodies sub-jected to the densification process according to the pre-sent invention should be compacted and optionally pYe-sintered to a minimum bending strength of at least 15 MPa, preferably at least 20 MPa, and most preferably at least 25 MPa.
The densification process according to the invention is preferably carried out by shot peening although other densification processes such as different types of roll-ing are not excluded. In shot peening, rounded or essen-tially spherical particles ttermed "shot") made from cast or wrought steel and stainless steel, as well as from ceramic or glass beads, are propelled against a workpiece with sufficient energy and for a sufficient time to cover the surface with overlapping cold Worked dimples (see e;.g. the article by J. Mogul et al "Process controls the key to reliability of shot peening", Process Controls &
Instrumentation, November 1995).
1.5 The shot peening time according to the present in-vention normally exceeds 0.5 seconds and is preferably between 1 and 5 seconds and the Almen intensity is nor-mally in the range 0.05 - 0.5. The deformation depth depends on the final use of the product and should exceed 0.1 mm, preferably 0.2 mm and most preferably the depth should exceed 0.3 mm.
The invention is illustrated by the following rion-limiting examples.
The starting metal powder was Distaloy DC-1, which is an iron-based powder containing 2% nickel and 1.5% mo-lybdenum available from Hdganas AB, Sweden.
This powder was warm compacted at 700 MPa to a density of 7.4 g/cm3 having a bending strength of 25 MPa.
The compacted bodies were divided into the following three groups:
Group 1 The bodies were left green, i a not subjected to any additional treatment.
Group 2 The bodies were presintered at 750°C for 20 minutes in protective atmosphere.
Group 3 The bodies were sintered at 1120°C for 15 minutes in endogas.
*Trade-mark Group 1 The green bodies were shot peened. At too high in tensities, i.e. Almen intensities (cf the Mogul article referred to above) above 0.14 for 3 seconds, the partic les were torn loose and the surface was destroyed. Tt turned out that the Almen intensities should be below about 0.14 and the exposure time should be less than 2 seconds. This was true for both green bodies which had been warm compacted and for bodies which were produced in a lubricated die. As can be seen in Fig. 1, the densifi-cation was somewhat better in the bodies obtained when the compaction was performed in a lubricated die.
Group 2 The presintering of the green bodies was done in or-der to remove lubricant that could create porosity, to remove deformation hardening and to improve the strength of the material. It was essential that the graphite difu-sion was limited in order to avoid solution hardening effects in the iron powder particles. After the presin-tering, the strength of the material had improved significantly and much higher Almen intensities could be used, especially for the bodies manufactured in lubricated dies. Almen intensities up to 0.3 could be used without problems,i.e. no particles were torn loose from the surface, and deformation depths of 300 ~.m were achieved. For the warm compacted bodies the erosion started at intensities of 0.14. Due to the removal of lubricant and deformation hardening, the deformation depth had increased significantly in comparison with the green bodies of group 1.
Group 3 Only warm pressed materials were tested as no sig-nificant pore structure difference from various compac-ting methods is considered to remain after a full sinte-ring operation. The sintered body had their full strength, and therefore very high Almen intensities, up to 0.3, could be used. The effect of the shot peeving operation is, however, much less in comparison with the bodies which were shot peeved in green or presintered condition according to the present invention. It can be seen that only one third of the deformation depth was achieved at the same intensity due to the high hardness of the presintered body.
The experiments are listed in the following table.
Compaction Sintering Shot Peeving Deforma- Picture Time/ tion number Almen depth Intensity Lubricated Green 1.5 s/0.08 50 um Die Lubricated Green 1.5 s/0.13 100 ~.tn 960686 Die Warm CompactedGreen 1.5 s/0.08 30 dun 960585 Warm CompactedGreen 1.5 s/O.I3 30-50 ~m Lubricated Presintered 3 s/0.17 200 ~.m Die Lubricated Presintered 3 s/0.21 250 ~.m 960694 Die Lubricated Presintered 3 s/0.30 300 ~.m 960642 Die Warm CompactedPresintered 1.5 s/0.13 200 ~.m Warm CompactedPresintered 1.5 s/0.14 200 Eun 960640 Warm CompactedSintered 3 s /0.17 70 Eun Warm CompactedSintered 3 s/0.21 100 um Warm CompactedSintered 3 s/0.30 130 um 960645
The experiments are listed in the following table.
Compaction Sintering Shot Peeving Deforma- Picture Time/ tion number Almen depth Intensity Lubricated Green 1.5 s/0.08 50 um Die Lubricated Green 1.5 s/0.13 100 ~.tn 960686 Die Warm CompactedGreen 1.5 s/0.08 30 dun 960585 Warm CompactedGreen 1.5 s/O.I3 30-50 ~m Lubricated Presintered 3 s/0.17 200 ~.m Die Lubricated Presintered 3 s/0.21 250 ~.m 960694 Die Lubricated Presintered 3 s/0.30 300 ~.m 960642 Die Warm CompactedPresintered 1.5 s/0.13 200 ~.m Warm CompactedPresintered 1.5 s/0.14 200 Eun 960640 Warm CompactedSintered 3 s /0.17 70 Eun Warm CompactedSintered 3 s/0.21 100 um Warm CompactedSintered 3 s/0.30 130 um 960645
Claims (9)
1. A process for the preparation of a powder metallurgical body comprising the steps of:
uniaxially compacting metal powder;
presintering the obtained compacted body at a temperature of at least 500°C;
subjecting the obtained body to shot peening or rolling at an intensity and for a period of time sufficient for establishing a densification surface layer within a deformation depth of at least 0.1 mm, in order to achieve a density of 90 to 100% of full density after sintering; and optionally subjecting the obtained body to an additional compacting step.
uniaxially compacting metal powder;
presintering the obtained compacted body at a temperature of at least 500°C;
subjecting the obtained body to shot peening or rolling at an intensity and for a period of time sufficient for establishing a densification surface layer within a deformation depth of at least 0.1 mm, in order to achieve a density of 90 to 100% of full density after sintering; and optionally subjecting the obtained body to an additional compacting step.
2. The process according to claim 1, wherein the deformation depth is at least 0.2 mm.
3. The process according to claim 1, wherein the metal powder is an iron-based powder.
4. The process according to claim 3, wherein the iron-based powder includes one or more elements selected from the group consisting of C, Cr, Mn, Mo, Cu, Ni, P, V, S, B, Nb, Ta, N and inevitable impurities in addition to Fe.
5. The process according to claim 4, wherein the iron-based powder is selected from the group consisting of pre-alloyed iron-based particles, diffusion alloyed iron-based particles and mixtures of iron particles and alloying elements.
6. The process according to claim 3, wherein the iron-based powder comprises substantially pure iron particles.
7. The process according to any one of claims 1 to 6, wherein the powder is uniaxially compacted and presintered to a bending strength of at least 15 MPa.
8. The process according to claim 7, wherein the bending strength of at least 20 MPa.
9. The process according to claim 7, wherein the bending strength of at least 25 MPa.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9602376A SE9602376D0 (en) | 1996-06-14 | 1996-06-14 | Compact body |
| SE9602376-7 | 1996-06-14 | ||
| PCT/SE1997/001027 WO1997047418A1 (en) | 1996-06-14 | 1997-06-12 | Powder metallurgical body with compacted surface |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2258161A1 CA2258161A1 (en) | 1997-12-18 |
| CA2258161C true CA2258161C (en) | 2007-01-23 |
Family
ID=37684483
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002258161A Expired - Fee Related CA2258161C (en) | 1996-06-14 | 1997-06-12 | Powder metallurgical body with compacted surface |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2258161C (en) |
-
1997
- 1997-06-12 CA CA002258161A patent/CA2258161C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2258161A1 (en) | 1997-12-18 |
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