ALLOY, RAW WORKPIECE, COMPONENT CONSISTING OF AUSTENITE, AND METHOD FOR HEAT-TREATING AN AUSTENITE

Abstract

An alloy, a raw workpiece, a component and a method contain or create austenites. The new alloy allows austenites to be formed or treated at higher temperatures, with new heat treatments also being used. Various heat treatments may be carried out with reference to the strength/toughness balance and notch sensitivity.

Description

The invention relates to an alloy of an austenite, to a blank which is produced in particular by forging and is suitable for components in high-temperature applications, and to a method.

According to service condition, forged disks for rotors of turbines, more particularly of gas turbines, have to date been produced from various forging steels. For instance, NiCrMoV is used for compressor disks, or CrMoWVNbN for the turbine disks.

The service conditions and the design requirements are critical to the choice of the forging material.

For the selection of the forging material, it is always necessary to ensure a balance between strength and toughness in order to meet the design requirements.

For higher usage temperatures there is currently no solution with austenite steels.

Consideration is currently being given to a transition to nickel disks. With these disks, usage temperatures>923K ought to be possible.

Such components unfortunately have the following disadvantages:

• • very high costs in comparison to the disk composed of steel;
  • relatively long machining times in manufacture.

It is therefore the object of the invention to solve the above-stated problem. 2.

The object is achieved by an alloy as claimed in claim 1, a blank as claimed in claim 2 and a component as claimed in claim 3, and a method as claimed in claim 9.

The dependent claims list further advantageous measures, which may be combined with one another as desired.

The A286 standard alloy has long been evaluated for use for blades in the context of the steam turbine. There it emerged that the A286 standard material per se has potential for usage up to 923K.

Unfortunately, however, the strength is too low.

More recent considerations show that through an adaptation to the chemistry, more particularly through an increase in the manganese fraction (Mn), the titanium content (Ti) and/or molybdenum content, and also a reduction in the silicon fraction (Si), the required strength is possible.

Various heat treatments are carried out with the blank, with reference to the strength/toughness balance and the notch sensitivity.

Heat treatments (HT) as follows are carried out in accordance with the invention:

annealing [AN] and also different agings [AG] as heat treatments for austenites in general and specifically for the subject of the alloy of the invention:

No.	AN	1ST AG	2ND AG	3RD AG
1	1253K	993K	—	—
2	1253K	993K	953K	—
3	1253K	1033K	993K	—
4	1253K	993K	1033K	953K
5	1253K	1033K	993K	953K
6	1293K	1033K	923K	—

The following heat treatment variants are available:

• • solution dissolving at 1253K and with only one aging at 993K; 8
  • in the second variant, starting from the first variant, there is additionally a second aging at 953K;
  • in the third variant, the first solution annealing is at 1253K, the first aging at 1033K and the second aging at 993K; 13
  • in the fourth variant, the first solution annealing is at 1253K, the first aging at 993K and the second aging at 1033K, and the third aging at 953KC, 16
  • in the fifth variant, the first solution annealing is at 1253K, the first aging at 1033K and the second aging at 993K, and the third aging at 953K,
  • in the sixth variant, the first solution annealing is at 1293K, the first aging at 1033K and the second aging at 923K. 22

As well as application as a forged disk in the gas turbine, further applications are conceivable, including:

• • gas turbine blades,
  • gas turbine rings,
  • steam turbine blades or
  • as a forged steam-turbine part.

The advantages are as follows:

• • expansion of the usage range of inexpensive iron-based alloys by comparison with expensive nickel-based materials
  • faster machinability of the rotor components based on iron by comparison with nickel-based materials
  • experiences from the construction, manufacture and production of the highly alloyed iron-based alloys can very largely be carried over. This helps in all probabilistic approaches
  • service temperature can be raised and therefore enables power boosting and performance boosting of the machine, without need for external cooling.

The composition of the austenitic steel is as follows:

Alloy comprising,

more particularly consisting of (in % by weight):

carbon (C)      0.03%-0.08%
silicon (Si)    0.20%-0.40%
manganese (Mn)  1.60%-2.00%
chromium (Cr)   13.5%-16.0%
molybdenum (Mo) 2.00%-2.50%
nickel (Ni)     24.0%-27.0%
vanadium (V)    0.25%-0.35%
aluminum (Al)   0.40%-0.60%
titanium (Ti)   2.00%-2.30%
niobium (Nb)    1.00%-1.20%
tungsten (W)    1.80%-2.20%
boron (B)       0.004%-0.006%
optionally:
phosphorus (P)  to 0.025%
sulfur (S)      to 0.015%
arsenic (As)    to 0.008%
tin (Sn)        to 0.008%
antimony (Sb)   to 0.002%
nitrogen (N)    to 0.005%
balance iron.

A blank is cast from such an alloy in accordance with the prior art and is forged in accordance with the prior art.

Claims

1-17. (canceled)

18. An alloy, comprising:

19. The alloy according to claim 18, wherein the carbon (C) is 0.02% by % weight.

20. The alloy according to claim 18, wherein the carbon (C) is 0.03%-0.08% by % weight.

21. The alloy according to claim 18, wherein the titanium (Ti) is 2.5% by % weight.

22. The alloy according to claim 18, wherein the titanium is 2.0%-2.3% by % weight of titanium.

23. The alloy according to claim 18, further comprising at least one of (in % by weight): arsenic (As) to 0.008%;tin (Sn) to 0.008%;antimony (Sb) to 0.002%;nitrogen (N) to 0.005%;phosphorus (P) to 0.025%; orsulfur (S) to 0.015%.

24. The alloy according to claim 18, the alloy consisting of:

25. A blank, comprising: an iron-based alloy, containing (in % by weight):

26. The blank according to claim 25, wherein the carbon (c) is 0.02% by % weight.

27. The blank according to claim 25, wherein the carbon (C) is 0.03%-0.08% by % weight.

28. The blank according to claim 25, wherein the titanium (Ti) is 2.5% by % weight.

29. The blank according to claim 25, wherein the of titanium (Ti) is 2.0%-2.3% by % weight.

30. The blank according to claim 25, further comprising at least one of (in % by weight): arsenic (As) to 0.008%;tin (Sn) to 0.008%;antimony (Sb) to 0.002%;nitrogen (N) to 0.005%;phosphorus (P) to 0.025%; orsulfur (S) to 0.015%.

31. A component, comprising: an iron-based alloy, containing (in % by weight):

32. The component according to claim 31, wherein the carbon (C) is 0.02% by % weight.

33. The component according to claim 31, wherein the carbon (C) is 0.03%-0.08% by % weight.

34. The component according to claim 31, wherein the titanium (Ti) is 2.5% by % weight.

35. The component according to claim 31, wherein the titanium (Ti) is 2.0%-2.3% by % weight.

36. The component according to claim 31, wherein: the component is selected from the group consisting of a rotor disk, turbine blade, turbine ring, a gas turbine part, a steam turbine blade and a forged steam-turbine part; andwherein the component is subjected to a heat treatment step where: a solution annealing at at least 1253K is performed;a first aging at at least 993K is performed; anda second aging at at least 953K is performed.

37. The component according to claim 31, further comprising at least one of (in % by weight): arsenic (As) to 0.008%;tin (Sn) to 0.008%;antimony (Sb) to 0.002%;nitrogen (N) to 0.005%;phosphorus (P) to 0.025%; orsulfur (S) to 0.015%.

38. A method for a heat treatment of an austenite, the method comprises the steps of: performing a solution annealing at at least 1253K;performing a first aging at at least 993K; andperforming a second aging at at least 953K.

39. The method according to claim 38, which further comprises performing a third aging.

40. The method according to claim 38, which further comprises: performing the first aging at at least 1033K; andperforming the second aging at at least 993K.

41. The method according to claim 38, which further comprises: performing the solution annealing at 1293K;performing the first aging at at least 1033K; andperforming the second aging at at least 923K.

42. The method according to claim 38, which further comprises: performing the solution annealing at at least 1253K;performing the first aging at at least 993K;performing the second aging at at least 1033K; andperforming a third aging at at least 953K.

43. The method according to claim 38, which further comprises: performing the solution annealing at at least 1253K;performing the first aging at at least 1033K;performing the second aging at at least 993K; andperforming a third aging at at least 953K.

44. The method according to claim 38, which further comprises: performing the second aging at a temperature at least 30 k below a temperature of the first aging; andperforming a third aging at a temperature at least 30 k below a temperature of the second aging.

45. The method according to claim 38, wherein the method is performed with the steps consisting of: performing the solution annealing at at least 1253K;performing the first aging at at least 993K; andperforming the second aging at at least 953K.

46. The method according to claim 38, wherein the method is performed with the steps consisting of: performing the solution annealing at at least 1253K;performing the first aging at at least 1033K; andperforming the second aging at at least 993K.

47. The method according to claim 38, wherein the method is performed with the steps consisting of: performing the solution annealing at 1293K;performing the first aging at at least 1033K; andperforming the second aging at at least 923K.

48. The method according to claim 38, wherein the method is performed with the steps consisting of: performing the solution annealing at at least 1253K;performing the first aging at at least 993K;performing the second aging at at least 1033K; andperforming a third aging at at least 953K.

49. The method according to claim 38, wherein the method is performed with the steps consisting of: performing the solution annealing at at least 1253K;performing the first aging at at least 1033K;performing the second aging at at least 993K; andperforming a third aging at at least 953K.