Metal treatment – Stock – Ferrous
Reexamination Certificate
1998-08-31
2002-02-26
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Ferrous
C428S683000, C415S200000, C415S216100
Reexamination Certificate
active
06350325
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a turbine shaft, in particular for a steam turbine, which is oriented along an axis of rotation and has a first axially oriented region with a maximum radius R
1
and a second axially oriented region adjoining the first axially oriented region and having a maximum radius R
2
. U.S. Pat. No. 3,767,390 describes a martensitic special steel for high-temperature applications, for example for producing steam-turbine blades or bolts for connecting two halves of a steam-turbine casing. That steel preferably has a content (all of the following data are given in per cent by weight) of 12% chromium and approximately 0.3% niobium. The addition of niobium is intended to increase the creep rupture strength and largely remove &dgr;-ferrite from the steel. In a preferred embodiment, the steel described therein has, as further alloying constituents, 0.25% Co, 4% Mn, 0.35% Si, 0.75% Ni, 1.0% Mo, 1.0% W, 0.3% V, 0.75%o N, as well as a remainder of iron and impurities of sulfur, phosphorus and nitrogen.
An article entitled “Development and Production of High Purity 9Cr1MoV Steel for High Pressure—Low Pressure Rotor Shaft” by T. Azuma, Y. Tanaka, T. Ishiguro, H. Yoshita and Y. Iketa, in Conference Proceedings of Third International Turbine Conference, 25-27 April 1995, Civic Centre, Newcastle upon Tyne, Great Britain, “Materials Engineering in Turbines and Compressors”, publisher A. Strang, pages 201 to 210, describes a steel for a combined high-pressure and low-pressure steam-turbine shaft. The steel is said to be suitable for the production of such a turbine shaft from a single material. In a preferred embodiment, it has a composition of 9.8% chromium, 1.3% nickel, 0.16% carbon, less than 0.1% silicon, less than 0.1% manganese, 1.4% molybdenum, 0.21% vanadium, 0.05% niobium, 0.04% nitrogen, and a remainder of iron and impurities of phosphorus, sulfur, aluminum, arsenic, tin, antimony.
The high-pressure part of the turbine shaft has a diameter of 1200 mm and the low-pressure part has a diameter of 1750 mm. The turbine shaft as a whole is produced from a blank having a diameter of 1800 mm.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a turbine shaft, in particular for a steam turbine, and a method for producing a turbine shaft, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which the turbine shaft is suitable for high thermal stresses with a temperature profile that decreases in axial direction, with a maximum temperature of over 550° C.
With the objects of the invention in view, there is also provided a turbine shaft, in particular for a steam turbine, oriented along an axis of rotation, comprising a first axially oriented region with a first maximum radius; a second axially oriented region adjoining the first axially oriented region and having a second maximum radius greater than the first maximum radius; the first region including a first base material for use at a first temperature, the second region including a second base material for use at a second temperature lower than the first temperature; and the base materials having an alloy steel containing 8.0% by weight to 12.0% or 12.5% by weight Cr with substantially identical austenitizing temperatures. The first base material is suitable for use at a higher temperature, in particular of over 550° C. and the second base material is suitable for use at a lower temperature, in particular between 350° C. and 550° C.
In accordance with another feature of the invention, the first base material has a lower content, in percent by weight, of nickel than the second base material, in particular a nickel content which is lower by more than 0.1%. The content of nickel, in percent by weight, is between 0.1% and 1.8% for each base material, preferably 1.0% to 1.5% nickel, preferably 1.3% for the second base material, and 0.2% to 0.6% nickel for the first base material. The chromium content of the first base material, in particular for a high-pressure part of a steam turbine, is (data in percent by weight) 10% to 12% and the chromium content of the second base material, in particular for a low-pressure part of a steam turbine, is (data in percent by weight) 9.5% to 10.5%, preferably 9.8%.
In the case of a turbine shaft which has alloy steels that are different in regions but have identical austenitizing temperatures and, in the first region having a smaller cross-section, has a base material with an optionally higher chromium content and a lower nickel content than in the second region having a larger cross-section, a high hot strength, a high creep rupture strength and a sufficient fracture toughness are achieved in the first region. In the second region, high yield strength demands are fulfilled and a very good notched impact strength and fracture toughness are ensured. A required yield strength R
p02
may be, for example, around 720 MPa {square root over (m)}. The fracture toughness is, for example, about 200 MPa and, with regard to the toughness, it can be stated that the FATT is less than 25° C. Due to the high hot strength of the first region, the latter is suitable as a high-pressure part of a combined high-pressure/low-pressure steam turbine, even at steam admission temperatures of over 550° C. to about 650° C. The second region is preferably suitable for use at temperature stresses of 350° C. to about 550° C. Different choices of the chromium and nickel content in the first region and the second region permit the high heat resistance in the first region and the toughness in the second region to be set selectively, largely independently of one another, depending on the demands placed on the materials. In contrast to a turbine shaft which is produced from a single material, there is no need to compromise between creep rupture strength in the thermally higher stressed region and toughness in the second region, which is subjected to slightly less thermal stress. In addition, as a result of having base materials of similar composition, the problem of the base materials having significantly different material properties mixing in a transition zone between the first region and the second region does not arise. Along the axis of rotation, the turbine shaft has different thermomechanical properties in regions with specifically selected different chemical compositions. In this case the regions can be produced by melting down differently alloyed electrodes by the electro-slag remelting process (ESR process).
Due to the essentially identical austenitization temperature, the material properties in the transition zone between the first region and the second region change slightly, at most. They are thus largely independent of the respective chemical composition. A similar composition of the main carbide-forming elements and main nitride-forming elements, such as C, N, V, Nb, Mo, W in the base materials results in the essentially uniform austenitizing temperature for the entire turbine shaft. This means that, in contrast to turbine shafts having significantly different base materials, the first region can be austenitized at the same temperature as the second region. A different temperature treatment, in particular for a high-pressure and low-pressure part of a steam-turbine shaft, would have a negative effect on the respective austenitizing operations.
It is now possible to produce a largely ferrite-free structure of the entire turbine shaft in one operating step.
The following stabilizing and tempering temperatures only differ from one another slightly. Moreover, using different tempering temperatures for various regions in the axial direction of the turbine shaft presents no technical problems.
In accordance with a further feature of the invention, the austenitizing temperature is in a range from 950° C. to 1150° C., in particular approximately 1050° C.
In accordance with an added feature of the invention, the first base material includes (data in per cent by weight) 0 to
Ewald Jürgen
Kern Torsten-Ulf
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
Wyszomierski George
LandOfFree
Turbine shaft and method for producing a turbine shaft does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Turbine shaft and method for producing a turbine shaft, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Turbine shaft and method for producing a turbine shaft will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2982539