Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1998-11-06
2001-01-23
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S679000, C228S262420, C148S525000, C148S529000, C246S468000, C246S471000
Reexamination Certificate
active
06177205
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for manufacture of a railroad track part, in particular of a large points part, where rail parts such as a frog point and connector rail comprise a first and a second material of differing composition.
The invention further relates to a railroad track part, in particular to a large points part, comprising rail parts of differing materials joined by welding, of which materials one is carbon steel and another austenitic manganese steel.
A frog with block-like frog point is known from DE-AS 1 284 439, where the pointed part comprises self-hardening steel and the connecting rails standard rail grade steel. The pointed part and connecting rails are oil-quenched after welding.
Also known is the joining of a frog point made of austenitic manganese steel to connecting rails of carbon steel via an intermediate layer of a low-carbon austenitic steel. After making the first welded join, homogenizing follows. Consequently, to join cast austenitic manganese steel to carbon steel, an intermediate layer made of steel is used, where during welding a specified sequence must be maintained and after the first welding operation a heat treatment must be performed, without this however assuring in the final analysis that any harmful influences are ruled out during the second welding operation on the intermediate layer made of special steel. Furthermore, the intermediate layer must have a certain length in order to attain a thermal separation between the welding points.
A process for manufacture of a frog is known from AT 401 359 B, where a frog point is, before being welded to connecting rails, subjected to a selective heat treatment in order to achieve a fine-lamellar pearlite structure.
DD 263 482 A5 relates to a process for the manufacture of points frogs. To improve the wear strength of the frog, it is provided that a wheel contact surface is provided by explosive plating or electron-beam welding on a base element comprising readily weldable steel.
The use of an austenitic manganese steel for manufacture of weldable parts, in particular in points frogs, is described in DE 28 46 930 C2.
SUMMARY OF THE INVENTION
The problem underlying the present invention is to develop either a process for manufacture of a railroad track part or the part itself such that a connection between rail parts consisting of differing materials in order to manufacture a railroad track part can be achieved without negative effects on the materials to be connected.
The problem is attained in accordance with the invention by means of the process in that carbon steel is used as the first material and high-manganese steel as the second material, the latter being joined to the carbon steel directly by electron-beam welding or indirectly by an intermediate layer comprising a nickel-based alloy, in that the railroad track part thus formed is then heated to a temperature T and held thereat for a period time t such that for high manganese steel solution annealing takes place and for carbon steel austenitizing, and in that the railroad track part is partially quenched after the holding time t at temperature T such that the high manganese steel is available in an austenitic structure and the carbon steel in a mixed structure with at least bainite and pearlite contents.
It is proposed in accordance with the invention that the rail parts consisting of differing materials, one of which is carbon steel and the other austenitic manganese steel, i.e. having a manganese content of at least 10% by weight, preferably in the range between 10 and 20% by weight, be joined either directly using electron-beam welding methods or indirectly via an intermediate layer comprising a nickel-based alloy, with the entire railroad track part then being subjected to selective heat treatment in order to obtain a targeted structure and hence achieve targeted material properties.
The type of join represents a simplification in comparison with the prior art, since in accordance with the invention there is the possibility of joining a rail consisting of austenitic manganese steel directly to the second rail part of carbon steel, in order to then treat the unit thus formed as a whole. The use of electron-beam welding has the advantage of directly joining the austenitic manganese steel to carbon steel. Alternatively, a join can be made using an intermediate layer in the form of a nickel-based alloy.
If nickel-based alloy is used as the intermediate layer, with the nickel content here being at least 60% by weight of the alloy, this has the advantage that the intermediate layer is very ductile and has favourable mechanical properties, without the intermediate layer being negatively affected at the high temperature fluctuations occurring during welding. The result is thus better material properties compared with the special steel used for the intermediate layer according to the prior art, in particular with an austenitic steel, whose properties are well known to depend heavily on the temperature.
In particular, the intermediate layer should contain 70 to 90% by weight of Ni, preferably 75 to 80% by weight of Ni. Particularly favourable material properties are achieved when the intermediate layer contains <0.05% by weight of C, approximately 1% by weight of Mn, and—as necessary—5 to 15% by weight of Cr and <8% by weight of Fe.
In order to weld in simple manner an intermediate layer to the differing materials, it is provided that the intermediate layer is joined to the one material by build-up or flash butt welding and then to the other material by flash butt welding.
Regardless of the type of application, the intermediate layer should have a length of approximately 3 to 15 mm.
In an embodiment of the invention, it is provided that the railroad track part be heated after welding together to 890° C.≦T≦1030° C., in particular to 900° C.≦T≦980° C. Furthermore, the railroad track part should be kept, over a time t of 0.5 h≦t≦5 h, preferably 1 h≦t≦4 h, at the temperature T.
To obtain a targeted structure in the differing materials, the railroad track part should be quenched in a polymer-stabilised bath. Partial quenching can take place here such that the carbon steel has a bainite content of 25% to 50%, preferably 30% to 40%, a pearlite content of at least 40%, preferably at least 50%, and martensite.
The austenitic manganese steel present in the austenitic structure should then be plastically formed by introducing a quasi-static or dynamic force. This can take place in the familiar form by hammering, explosive compaction or blasting with steel balls.
After the plastic formation of the rail part consisting of austenitic manganese steel, the entire railroad track part can be subjected to a further heat treatment such that in carbon steel the martensite and bainite structure contents are tempered and in austenitic manganese steel homogenizing with precipitation hardening takes place.
A railroad track part, in particular a large points part, comprising welded rail parts of differing materials, one of which is a carbon steel and another austenitic manganese steel, with the railroad track part as a whole being subjected to heat treatment, is characterised in that the railroad track part comprises rail parts joined directly by electron-beam welding or via an intermediate layer of nickel-based alloy, of which the carbon steel is in a mixed structure comprising at least bainite with a content B
1
, pearlite with a content P
1
and martensite with a content M
1
, with B
1
+P
1
>>M
1
, and that the austenitic manganese steel is plastically formed with an austenitic structure. A corresponding railroad track part is characterised in particular by a high strength and limit of elasticity.
In particular, it is provided that the bainite content B
1
is 30 to 40% and the pearlite content P
1
at least 50%, relative to the total volume of the carbon steel.
Furthermore, the heat treatment should be conducted such that the pearlite is in fine-lamellar form.
The carbon steel to be selected i
Kais Alfred
Kunitz Walter
Ratz Gerhard
BWG Butzbacher Weichenbau GmbH
Dennison, Scheiner Schultz & Wakeman
Jones Deborah
McNeil Jennifer
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