Patent Application
20060255099
The invention relates to the field of materials engineering. It concerns a method for welding a first component that is comprised of a superalloy on the basis of nickel, ferronickel or cobalt, to a second component that is comprised of a high-alloy, high-temperature steel. These components above all are discs, drums and shaft end pieces for manufacturing rotors for turbomachines. The invention also concerns a rotor manufactured based on this method.
The efficiency of thermal turbomachines can be improved by increasing the working temperature. Therefore, if operating at working temperatures above approx. 600° C., rotors of thermal turbomachines advantageously should be manufactured based on a superalloy, for example a superalloy on nickel basis. On one hand such superalloys have excellent properties at high temperatures, but on the other hand they are considerably more expensive than customary high-temperature steel. Since, however, rotors have sections that are subject to different thermal stresses, the state of the art is to only manufacture high temperature parts with superalloy for cost reasons and to manufacture parts that are subject to less thermal stress with high-temperature steel. This requires that the parts made of high-temperature steel be joined with the parts made of superalloy. This can be accomplished mechanically with screws, for example, or by welding the discs together.
U.S. Pat. No. 4,086,690, for example, describes the manufacture of a rotor comprised of individual discs that are welded together but that are made of the same type of material. The known tungsten inert-gas welding (TIG welding) and/or submerged arc welding methods are equally suitable as welding methods for welding the rotor discs.
It is known that high-temperature martensitic/ferritic steel, especially the 12% chrome steel class, is hard to weld with superalloys on nickel, ferronickel or cobalt basis. Depending on the welding method used, fractures in the base material, the heat affected zone or the welding deposit could develop (J. Tösch and E. Perteneder: Beeinflussung des Ferritgehaltes im austenitischen Schweissgut, sowie Einsatzgebiete verschiedener umhüllter, hochlegierter Stabelektroden. [Effect on the Ferrite Content in Austenitic Welding Deposit as well as Range of Application of Various Coated, High-Alloy Stick Electrodes], Presentation, Schweisstechnische Tagung Böhler Schweisstechnik Austria GmbH, Kapfenberg 1996). These fractures are undesirable since welding seams must be free of flaws. Due to the high mechanical and thermal stress this especially applies to welded rotor parts. Fusion welding between superalloy discs and discs made of high-temperature steel therefore is not used for stationary turbomachines because superalloys tend to develop fractures at high temperatures.
Buffers with superalloy materials such as disclosed in DE 101 12 062 A1 cannot easily be checked with ultrasound, which is a disadvantage, and in addition they are susceptible to fractures just like the corresponding base materials.
Buffers with ferritic/martensitic steel also are susceptible to fractures at high temperatures at the transition zone to the superalloy. It is possible to reduce the susceptibility to fractures due to heat by using weaker supplementary materials that, however, often do not meet the strength requirements of the joint and could have a negative effect on the bending deflection behavior of the rotors.
It is known to use friction welding for lower weights and/or thin wall thickness to join superalloys and high-temperature steel. However, friction welding cannot be used for stationary turbomachines with a rotor weight up to 100 tons and corresponding wall thickness at the joint (welding seam depth ≧200 mm).
The object of the invention is to develop a method for welding a first component that is made of a superalloy on nickel, ferronickel or cobalt basis, with a second component that is comprised of high-alloy, high-temperature steel, in which the above components, especially discs, drums and shaft end pieces of rotors are for thermal turbomachines and in which the weld joints meet the stringent criteria with regard to strength and testability.
According to the invention this is achieved with a method according to the preamble of claim 1 based on the following steps:
The advantages of the invention are that large and heavy components made of the above material combinations now can be welded together very well. This fulfills the stringent quality requirements that apply to welded rotors of turbomachines due to high thermal and mechanical stress, for example. The weld joints can easily be tested with ultrasound methods.
It is practicable to counterclockwise rotate the intermediate piece and the first component onto which the intermediate piece is to be attached by means of friction welding because this results in an especially good friction-welding joint. However, it is not necessary. It might be sufficient to rotate the lighter intermediate piece and to keep the heavier component still.
Furthermore, it is advantageous when the first and second components are discs and/or drums and/or shaft end pieces of rotors for thermal turbomachines and the intermediate piece is a ring.
Furthermore, it is advantageous when the fusion welding method used is known for rotor welding such as TIG and/or submerged arc welding. The applicant has successfully been using these reliable methods for decades.
Finally it is practical if corresponding rings made of high-temperature steel are applied to both sides of a superalloy intermediate disc by means of friction welding.
The drawing shows an exemplary embodiment of the invention.
The following is shown:
Identical positions have the same reference numbers in the Figures. The arrows indicate the direction of movement of the parts.
In the following paragraphs the invention is explained in more detail based on exemplary embodiments and
Components 1 and 2, i.e. the rotor discs or rotor drum respectively and the shaft end pieces are to be welded together according to the method of the invention to form a rotor 4 of a turbomachine with the rotor being pivoted around a rotor axis 3.
To this end the steps shown in
According to
The advantages of the invention are that large and heavy components made of the above material combinations (superalloy and high-temperature steel) now can be welded together well. Susceptibility to heat fractures is very low. This fulfills the stringent quality requirements for welded rotors of turbomachines due to the high thermal and mechanical stresses. The weld joints can easily be tested with ultrasound methods.
The described method in accordance with the invention is especially suitable for joining discs and other rotor parts for rotors of turbomachines, for example gas turbines or steam turbines.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004/101209 | Nov 2004 | WO | international |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP03/50164 | May 2003 | US |
| Child | 11261765 | Oct 2005 | US |
