Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Powder pretreatment
Patent
1997-11-13
1999-07-20
Jenkins, Daniel J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Powder pretreatment
419 38, 419 46, 419 54, 75246, B22F 312
Patent
active
059266864
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns sintered powder-metallurgically produced sintered products having improved density. More specifically the invention concerns products prepared from iron or steel powders having the alloying elements diffusion-bonded to the iron or steel particles. These products are prepared by a warm-compaction process using high temperature lubricants.
BACKGROUND OF THE INVENTION
The market for sintered structural components could be markedly extended if enhanced mechanical properties could be obtained with maintained precision of tolerance control. Higher densities than the range currently produced (6.5-7.2 g/cc) would be required for more highly stressed applications in automotive engineering as density affects the mechanical properties and fatigue strength in particular.
A number of options are available to increase sintered density. Methods such as double pressing/double sintering, copper infiltration and powder forging provide higher densities than traditional single press and sintered operations but their use is constrained by cost and geometry considerations. In order to retain competitive viability a satisfactory process route is required which will not add any extra processing step which will increase the processing cost.
SUMMARY OF THE INVENTION
The present invention concerns low alloy PM materials which after single warm pressing and sintering utilising traditional powder metallurgy processes and equipment combine high mechanical strength and high density with maintained precision of tolerance. These materials are obtained according to a process including the following steps:
mixing an iron powder, a high temperature lubricant and optionally an organic binder;
heating the mixture, preferably to a temperature of at least 120.degree. C.;
transferring the heat powder composition to a die which is preheated to a temperature of preferably at least 120.degree. C.; and compacting the composition, at an elevated temperature of preferably at least 120.degree. C.
sintering the compacted body at a temperature of at least 1120.degree. C.; alloying elements diffused into the outer surfaces of unalloyed iron particles, and whereby the lubricant is added in one step.
The U.S. Pat. No. 5,154,881 discloses metal compositions subjected to a warm compacting process. Compacted and sintered products prepared according to this patent exhibit improved densities and other strength properties and the advantages are obtained when the increased pressing temperatures are applied to iron based powders, which could be pure iron powders, mixtures of iron powders with alloying elements or pre-alloyed iron powders.
The U.S. Pat. No. 5,256,185 discloses a method for the preparation of a powder metallurgical product, wherein an iron powder, a lubricant and a binder are mixed, the mixture is compacted at an elevated temperature and the compacted body is subsequently sintered.
More specifically, this patent concerns a method of lubricant addition, which enables suitable adjustment of the apparent density, either upwards or downwards, as decided, without significant effect on the flow rate. This is accomplished by the following steps: (a) providing a dry admixture of an iron based powder, at least one alloying powder and a first amount of organic lubricant, (b) providing a liquid mixture of an organic binding agent dissolved or dispersed in a solvent, (c) wetting the dry admixture with the liquid mixture, (d) removing the solvent thereby forming a dry powder composition and (e) admixing a second amount of organic lubricant with the dry powder composition to form a metallurgical powder composition.
Contrary to the process disclosed in this US patent the present invention includes only one lubricant addition step. Furthermore, the present invention does not concern a method of manipulating the apparent density and thus the present invention concerns a quite different problem than the problem which is solved by the invention disclosed in the US patent.
Quite unexpectedly, it has now been fo
REFERENCES:
patent: 4483905 (1984-11-01), Engstrom
patent: 5108493 (1992-04-01), Causton
patent: 5154881 (1992-10-01), Rutz et al.
patent: 5256185 (1993-10-01), Semel et al.
patent: 5298055 (1994-03-01), Semel et al.
patent: 5498276 (1996-03-01), Luk
Engstrom Ulf
Johansson Bjorn
Hoganas AB
Jenkins Daniel J.
LandOfFree
Sintered products having improved density does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sintered products having improved density, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sintered products having improved density will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1330883