Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2001-11-26
2004-01-27
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C419S026000, C419S036000, C419S038000
Reexamination Certificate
active
06682581
ABSTRACT:
The present invention relates to a low-nickel austenitic steel, in particular a low-nickel, low-molybdenum, low-manganese and low-copper austenitic steel, and its use. The present invention furthermore relates to processes for the production of articles consisting of such steels.
Here, as usual, the term steel denotes iron-containing alloys and includes carbon-containing iron. Strictly, austenite is a high-temperature modification of iron having a face centered cubic crystal structure (&ggr;-iron), which is thermally dynamically stable between 740° C. and 1 538° C. and contains from 0 to not more than 2.1% by weight (at 1 153° C.) of carbon in the form of a solid solution. Usually, however, all steels which have a face centered cubic crystal lattice are referred to as austenitic steels or austenites. The face centered cubic austenite structure is required for many applications of steels or at least is advantageous compared with other modifications (for example ferritic or martensitic steels); austenite is, for example, nonferromagnetic, which makes it possible to use austenitic steels for electrical or electronic components or other applications where the occurrence of repulsive or attractive magnetic forces is undesirable, for example in clocks and watches. However, since austenite is a high-temperature modification and is thermodynamically unstable at lower temperatures, an austenitic steel must be stabilized to conversion into other modifications so that it retains its desired austenitic properties at normal temperature too. This can be effected, for example, by adding alloy elements which are known as stabilizers of the austenite structure. The alloy element most frequently used for this purpose is nickel, typically in an amount of from 8 to 10% by weight.
Other alloy components are used for influencing other properties of the steel (for example corrosion stability and stability to wear, hardness, strength or ductility) in a desired manner. However, the use of specific alloy components also frequently leads—generally as a function of the amount—to certain disadvantages, which can be counteracted to a certain extent by adapting the alloy composition. For example, carbon and manganese generally help to stabilize the austenite structure but, in excessive amounts, reduce the corrosion stability. Silicon is frequently an unavoidable impurity and is sometimes also deliberately added as an oxygen scavenger but promotes the formation of &dgr;-ferrite. Chromium, molybdenum and tungsten make a decisive contribution toward corrosion stability but likewise promote the formation of &dgr;-ferrite. Nitrogen in turn stabilizes the austenite structure and increases the corrosion stability but excessively high nitrogen contents reduce the ductility of the steel. One difficulty in the optimization of steel compositions is that the properties of the steel do not change linearly with the content of specific alloy components, but very large abrupt changes in the material properties can occur even with small changes in the composition. A further disadvantage of using nonferrous metals as alloy components is in general their comparatively high price.
Steels and their production have long been known. A comprehensive overview of the technology of steels can be found, for example, under the keyword steel in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed., 1999 Electronic Release, Wiley-VCH, D-69451 Weinheim, Germany.
Low-nickel austenitic steels are desirable materials for a number of applications. An increasingly important field of use for such steels is for articles which are in contact with a human or animal body during their use, since of course these steels do not give rise to a nickel allergy. Nickel allergies are frequently the cause of contact eczemas or other allergic phenomena which occur on contact with nickel-containing steels, for example during the wearing of jewelry, watches or implants or when using medical instruments made of such steels. In many countries, limits are therefore being specified, or are already in force for the nickel content of materials or for their nickel release on contact with a human or animal body. It is also for this reason that it is becoming increasingly important to have very many low-nickel austenitic steels available for very many applications.
A number of low-nickel austenitic steels, including nickel-free ones, are known. As a rule, the austenitic structure in such steels is stabilized by the element nitrogen.
Thus, AT-B-266 900 discloses the use of austenitic, nonmagnetic steels for the production of moving machine parts, in particular those subjected to vibrational stresses, the steels to be used merely being defined in extremely wide ranges of possible compositions: from 0 to 20% by weight of Mn, from 0 to 30% by weight of Cr, from 0 to 5% by weight of Mo and/or V, at least 0.5, preferably at least 1.4, % by weight of N, from 0.02 to 0.55% by weight of C, from 0 to 2% by weight of Si and from 0 to 25% by weight of Ni, the remainder being iron. Said wide ranges cover different steels having completely different properties, criteria for choosing specific steels are not given, and there is just as little information regarding measures for the production of such steels.
EP-A-875 591 describes the use of a corrosion-resistant substantially nickel-free austenitic steel substantially comprising 5 to 26% by weight of Mn, 11-24% by weight of Cr, 2.5-6% by weight of Mo, 0.2-2.0% by weight of N, 0.1-0.9% by weight of C, and up to 0.5% by weight of Ni, the remainder being Fe, as a material for the production of articles which are in contact with living beings. DE-A-195 13 407 likewise describes the use of a corrosion-resistant substantially nickel-free austenitic steel as material for the production of articles which are in contact with living beings. This steel substantially comprises 2-26% by weight of Mn, 11-24% by weight of Cr, 2.5-10% by weight of Mo, 0.55-1.2% by weight of N, less than 0.3% by weight of C and up to 0.5% by weight of Ni, the remainder being Fe. JP-A-07/150297 (Chemical Abstracts: Abstract No. 123:175994) discloses a steel composed of 10-25% by weight of Mn, 10-25% by weight of Cr, 5-10% by weight of Mo, 0.2-1% by weight of N, 0.05-0.5% by weight of C and up to 0.5% by weight of Si, the remainder being Fe, and its use in shipbuilding. DE-A-196 07 828 describes a steel composed of 8-15% by weight of Mn, 13-18% by weight of Cr, 2.5-6% by weight of Mo, 0.55-1.1% by weight of N, up to 0.1% by weight of C and up to 0.5% by weight of Ni, the remainder being Fe, and its use for various components, in particular generator cap rings. In the case of the steels disclosed in said publications, the required high corrosion resistance is achieved with a comparatively large amount of molybdenum, by far the most expensive of the conventional alloy elements.
DE-A-42 42 757 proposes the use of a steel substantially comprising 21-35% by weight of Mn, 9-20% by weight of Cr, 0-7% by weight of Mo, 0.3-0.7% by weight of N, up to 0.015% by weight of C, up to 0.1% by weight of Ni, up to 0.5% by weight of Si, up to 0.02% by weight of P, up to 0.02% by weight of S and up to 4% by weight of Cu, the remainder being Fe, as a material for the production of articles which are in contact with living beings. EP-A-422 360 discloses the use of a steel composed of 17-20% by weight of Mn, 16-24% by weight of Cr, 0-3% by weight of Mo, 0.5-1.3% by weight of N and up to 0.20% by weight of C, the remainder being Fe, for the production of components on railway vehicles. EP-A-432 434 describes a process for the production of connecting elements from a steel composed of 17.5-20% by weight of Mn, 17.5-20% by weight of Cr, 0-5% by weight of Mo, 0.8-1.2% by weight of N, up to 0.12% by weight of C, 0.2-1% by weight of Si, up to 0.05% by weight of P, up to 0.015% by weight of S and up to 3% by weight of Ni, the remainder being Fe. DE-A-25 18 452 describes a process for the production of an austenitic steel comprising 21-45% by weight of Mn, 10-30% by weight of Cr and 0.85-3% by
Keil & Weinkauf
Mai Ngoclan
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