Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2001-05-31
2003-11-04
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S252000, C419S026000, C419S037000, C419S038000
Reexamination Certificate
active
06641640
ABSTRACT:
The present invention relates to hard sintered moldings and feedstocks and processes for their preparation.
For the purposes of this invention, hard sintered moldings are defined as sintered materials which consist of a hard phase and a metallic phase as a binder of the hard phase. Hard sintered moldings, feedstocks and processes for their preparation are well known. Hard sintered moldings are generally very hard and have a high melting point but are also resistant to thermal shocks and therefore constitute a valuable group of materials. They are processed, for example, to combustion chamber linings or nozzle linings, cutting, drilling, milling, grinding, breaking, digging or press tools, sealing rings or bearing rings, welding electrodes, thread guides or the like. Among the known hard sintered moldings, particularly desirable materials are those whose hard fraction consists of hard ceramic materials, for example oxides, nitrides or carbides. Most frequently used hard materials are tantalum carbide and tungsten carbide. The metallic binder to be chosen is a metal which can be readily processed to give the hard sintered molding, does not impair the required properties of the material and binds the hard phase in a suitable manner. By far the most frequently used metals industrially are nickel and cobalt, but occasionally other metals which fulfill the required properties are also used. For example, JP-A 63-317 601 discloses the use of a cobalt-nickel alloy as a metallic binder. U.S. Pat. No. 3,964,878 describes hard sintered moldings with metal carbides whose metallic binder consists of the metal also contained in the carbide and additionally from 0.5 to 1.5% by weight of iron, copper or nickel. EP-A 169 292 and FR-A 1 475 069 describe hard sintered moldings having a metallic binder comprising iron, nickel and/or cobalt, the metallic binder of the hard sintered moldings disclosed in EP-A 365 506 additionally contains a special high-speed steel, and the metallic binder of the hard sintered moldings disclosed in JP-A 58-031 059 contains iron, nickel, cobalt and/or molybdenum. U.S. Pat. No. 4,308,059 describes a hard sintered molding bound by means of ruthenium. EP-A 46 209 discloses a hard sintered molding having steel as metallic binder. U.S. Pat. No. 3,368,882 discloses hard sintered moldings comprising 25-80% by volume of hard carbide such as WC or TaC and a binder matrix comprising a nitratable steel which is nitrated 45 on the surface of the sintered molding during preparation of the latter. FR-A-2 058 845 describes a hard sintered molding comprising 15-85% by volume of hard carbide which is dispersed in an austenitic steel matrix.
Hard sintered moldings additionally often have color properties which lead to an attractive external appearance of the workpieces produced therefrom and are therefore used not only as material for purely functional components but also as material in decorative applications, for example in watch cases, jewelry, writing implements or the like. An example of a known hard sintered molding is given, for example, in JP-A 48-018 109, which discloses hard sintered moldings consisting of TaC and a nickel-, molybdenum- and chromium-containing metallic binder and having a gold-like surface and their use in watch cases.
Usually, hard sintered moldings are produced by a powder metallurgical method. For this purpose, a mixture of the hard material powder and a metallic powder is introduced into a mold, generally compressed and then sintered, the metal powder and hard material powder combining to give the hard sintered molding. The sintered molding as such can then be further processed, for example aftertreated by a shaping procedure, or used, but it may also be milled and applied in the form of powdered hard sintered molding as surface layer on a workpiece. For example, DE-A 40 37 480 describes the production of a sintered body comprising tungsten carbide, titanium carbide, tantalum carbide or niobium carbide and cobalt as metallic binder.
A substantial disadvantage of simple powder metallurgical shaping processes, for example pressing in a mold, is that only moldings having a comparatively simple external shape can be produced thereby. Another known powder metallurgical process, which is particularly suitable for the production of sintered moldings having a complex geometry, is powder injection molding. For this purpose, a sinterable powder is mixed with a thermoplastic, which in powder injection molding technology is usually also referred to as a binder (but must not be confused with the metallic phase referred to in the technology of hard sintered moldings as the binder of the hard material), and, if required, further assistants, so that overall a thermoplastic injection molding material (feedstock) is formed. This is injection molded in a mold by the injection molding technology known from the processing of thermoplastics, the thermoplastic powder injection molding binder is then removed from the injection molded body (green compact), and the body (brown compact) freed from this binder is sintered to give the finished sintered molding. The main problem in this process is the binder removal, which is usually carried out thermally by pyrolysis of the thermoplastic, cracks frequently forming in the workpiece. A thermoplastic which is catalytically removable at low temperatures is therefore advantageously used. EP-A 413 231 describes such a catalytic binder removal process, EP-A 465 940 and EP-A 446 708 disclose feedstocks for the production of metallic moldings, and EP-A 444 475 discloses a feedstock for the production of ceramic moldings. Furthermore, EP-A 443 048 discloses the production of hard sintered moldings by a powder metallurgical method, and EP-A 800 882 describes an improved process for the preparation of feedstocks for hard sintered moldings.
U.S. Pat. No. 5,714,115 discloses a special nickel-free austenitic steel alloy comprising not more than 0.3% by weight of carbon, from 2 to 26% by weight of manganese, from 11 to 24% by weight of chromium, from 2.5 to 10% by weight of molybdenum and not more than 8% by weight of tungsten, whose austenitic structure is stabilized by from 0.55 to 1.2% by weight of nitrogen. This alloy is used for workpieces which are in contact, or can come into contact, with the human body, in order to avoid the allergic reactions to nickel or cobalt, which have recently increasingly given rise to concerns. W.-F. Bahre, P. J. Uggowitzer and M. O. Speidel: “Competitive Advantages by Near-Net-Shape-Manufacturing” (Editor H.-D. Kunze), Deutsche Gesellschaft für Metallurgie, Frankfurt, 1997 (ISBN 3-88355-246-1) and H. Wohlfromm, M. Blömacher, D. Weinand, E.-M. Langer and M. Schwarz: “Novel Materials in Metal Injection Molding”, Proceedings of PIM-97 - 1st European Symposium on Powder Injection Moulding, Munich Trade Fair Centre, Munich, Germany, Oct. 15-16, 1997, European Powder Metallurgy Association 1997, (ISBN 1-899072-05-5), describe powder injection molding processes for the production of nickel-free nitrogen-containing steels with nitriding during the sintering process.
In spite of the well developed prior art, it is an object of the present invention to provide novel hard sintered moldings having improved or novel properties and broader or novel fields of use, in view of the importance of the class of materials.
We have found that this object is achieved by hard sintered moldings having a nickel- and cobalt-free, nitrogen-containing steel as a binder of the hard phase. We have also found a process and feedstocks for the production of the novel hard sintered moldings.
The novel sintered moldings have excellent mechanical, thermal and magnetic properties. They are hard, have a high melting point, are highly resistant to thermal shocks, are non-magnetic in preferred embodiments and also cause no nickel or cobalt allergies. Moreover, they exhibit no giant grain growth during the sintering and can be very readily polished. They can be produced by the novel process in a simple manner; in particular, in the production of the nove
Hesse Werner
Speidel Markus
Uggowitzer Peter
Wohlfromm Hans
BASF - Aktiengesellschaft
Keil & Weinkauf
Mai Ngoclan
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