Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Patent
1999-06-01
2000-09-26
Mai, Ngoclan
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
75231, 75246, 419 37, 419 38, B22F 100
Patent
active
061237485
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with an iron-based powder for use in manufacturing a component by a powder metallurgy route (PM).
It is well known to manufacture components by the PM route, i.e. by preparing an iron-based powder, compacting the powder to form a "green" body, and then sintering so that the powder fuses together to form the component. In some cases, the powder is a mixture of elemental powders with iron predominating, and, in other cases, the powder comprises an alloy of iron and other elements (such alloyed powders can be produced by water atomisation). It is also known to mix alloyed powder with elemental iron, and to mix different alloyed powders. The PM route provides many advantages, particularly in reduced machining.
Indeed, due to the nature of products produced by known methods of powder metallurgy, it is desired that a minimum degree of machining be required. Products produced by known methods of powder metallurgy, since they are not full density products, can suffer from the phenomenon known as chattering, which damages both the products and the machining tool. This problem is accentuated when the mixture from which the product is formed contains a powder of a tool steel, which may result in excessive tool wear.
It has been recognised that it would be desirable to utilise the PM route for the manufacture of components which need to operate in conditions requiring hot oxidation resistance, e.g. at temperatures of up to 850.degree. C., and in the presence of corrosive gas. An example of such an application is a turbocharger wastegate valve bushing which operates in an exhaust gas environment. Such bushings are conventionally made from high chromium cast iron or austenitic steel. However, hitherto, bushings of this type manufactured by a PM route have not proved to be satisfactory, being, for example, prone to causing seizure due to swelling.
GB 2 298 869 A discloses an alloy powder having a composition consisting of, in weight percentages, 14 to 30 chromium, 1 to 5 molybdenum, 0 to 5 vanadium, 0 to 6 tungsten, the total of molybdenum, vanadium and tungsten being at least 3, a total of 0 to 5 of other strong carbide forming elements, e.g. niobium, tantalum, and titanium, 0 to 1.5 silicon, carbon with a minimum level sufficient to form carbides with the all of the molybdenum, vanadium, tungsten, and any other strong carbide forming elements present, and a balance which is iron and incidental impurities. The maximum level of carbon is expressed as one fifth of the chromium content minus 2. Examples are given comprising 20 to 28 chromium, 2 to 3 molybdenum, 1.5 to 2.5 vanadium, 2.5 to 3.5 tungsten, 0.8 to 1.5 silicon, and 0.555 to 2 carbon. The powder is produced by rapid atomisation followed by an annealing treatment and has a substantially fenitic matrix containing at least 12% of chromium in solution and a dispersion of carbides.
Components made from the alloy powders disclosed in GB 2 298 869 A do not exhibit good hot oxidation resistance. It is also proposed in GB 2 298 869 A that the wear resistance of components made from conventional stainless steel powders can be improved by blending the stainless steel powder with the powder disclosed therein. An example is given of 80% stainless steel to 20% of the disclosed alloy powder. However, blends of minor proportions of the disclosed powder with stainless steel powder do not result in components with good hot oxidation resistance.
Further, GB 2 298 869 A, in discussing manufacture of a product from a mixture of conventional stainless steel powder and the powder disclosed therein, does not disclose any unexpected advantageous physical or mechanical properties arising as a result of the combination of these powders. Rather the hardness of the disclosed powder is brought to the mixture to enhance the hardness of the softer conventional stainless steel powder, and in the absence of any indications to the contrary the properties of the products formed from the powder mixture will be largely those of the stainless steel powder used.
However, the
REFERENCES:
patent: 4770703 (1988-09-01), Tarutani et al.
Database WPI, Section Ch, Week 8622, Derwent Publciations Ltd., London, GB: Class M22, AN 86-140941 XP002054678 & JP 61 076 650 A (Nissan Motor Co Ltd) see abstract.
Database WPI, Section Ch, Week 9431 Derwent Publciations Ltd., London, GB: Class M22, AN 94-253139 XP002055635 & JP 06 184 603 A (Nippon Steel Corp) see abstract.
Perrin Carl
Whitaker Iain R
Federal Mogul Sintered Products Limited
Mai Ngoclan
LandOfFree
Iron-based powder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Iron-based powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Iron-based powder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2096339