AUSTENITE ALLOY, BLANK AND COMPONENT, AND METHOD

Abstract

An alloy, including at least (in wt. %): carbon (C) 0.03%-0.08%, silicon (Si) 0.2%-0.4%, manganese (Mn) 1.6%-2.0%, molybdenum (Mo) 4.0%-5.0%, chromium (Cr) 20.0%-25.0%, nickel (Ni) 24.0%-27.0%, vanadium (V) 0.25%-0.35%, titanium (Ti) 2.0%-2.3%, aluminum (Al) 0.4%-0.6%, boron (B) 0.004%-0.006%, iron (Fe).

Description

FIELD OF INVENTION

The invention relates to an austenite alloy, to a blank and/or component composed of this alloy, and to a method for production.

BACKGROUND OF INVENTION

In correlation to the usage condition, forged disks for rotors have to date been produced from various forging steels.

For instance, NiCrMoV is used for compressor disks, and CrMoWVNbN for turbine disks.

The usage 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.

The iron-based material having the highest service temperature is currently a martensite.

For higher service temperatures there is currently no solution.

Considerations are being given to a transition to nickel-based disks.

With these disks, service temperatures of greater than 923 K ought theoretically to be possible.

The components comprising nickel (Ni), however, have disadvantages as follows, which is why the usage is under discussion:

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

SUMMARY OF INVENTION

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

The object is achieved by an alloy, a component or a blank, and a method as claimed.

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

The description presents only exemplary embodiments of the invention.

The validation of an austenitic steel indicated its usability in principle for higher usage temperatures.

The chemistry and the heat treatment are sufficient in principle to match the challenges of a forged component for utilization in energy production plants at temperatures greater than 873 K.

The iron-based composition in this context comprises constituents as follows (in % by weight):

carbon (C)      0.03%-0.08%
silicon (Si)    0.2%-0.4%
manganese (Mn)  1.6%-2.0%
molybdenum (Mo) 4.0%-5.0%
chromium (Cr)   20.0%-25.0%, more particularly 21.5%-23.5%,
nickel (Ni)     24.0%-27.0%, more particularly 25.0%-26.0%,
vanadium (V)    0.25%-0.35%
titanium (Ti)   2.0%-2.3%
aluminum (Al)   to 0.6%
iron (Fe), more particularly balance
iron (Fe), optionally
boron (B)
                0.004%-0.006%,
phosphorus (P)  to 0.03%, more particularly to 0.025%,
sulfur (S)      to 0.02%, more particularly to 0.015%,
tungsten (W)    to 2.5%, more particularly 1.8%-2.2%,
niobium (Nb):   to 1.5%, more particularly 1.0%-1.2%,
nitrogen (N)    to 0.005%.

More particularly, the alloy consists of these elements.

DETAILED DESCRIPTION OF INVENTION

Building up, the following composition is to be preferably used:

									Optionally
C	Si	Mn	Mo	Cr	Ni	V	Ti	Al	B
0.03-	0.2-	1.6-	4.0-	20.0-	24.0-	0.25-	2.0-	0.4-	0.004-0.006
0.08	0.4	2.0	5.0	25.0	27.0	0.35	2.3	0.6

Particular exemplary embodiments are:

C	Si	Mn	Mo	Cr	Ni	V	Ti	A1	B
0.03-	0.2-	1.6-	4.0-	20.0-	24.0-	0.25-	2.0-	0.4-	0.004-
0.08	0.4	2.0	5.0	25.0	27.0	0.35	2.3	0.6	0.006
C	Si	Mn	Mo	Cr	N	V	Ti	Al
0.03-	0.2-	1.6-	4.0-	20.0-	24.0-	0.25-	2.0-	0.01-
0.08	0.4	2.0	5.0	25.0	27.0	0.35	2.3	0.06

A PREN value (DIN 81249-2) of greater than 32 should preferably be maintained:

PREN=% Cr+3.3*% Mo.

The background is as follows:

a) Corrosion Resistance

Increasing the chromium fraction from 14% to greater than 20% by weight increases the resistance toward HTC2.

The background is the formation of a stable Cr₂O₃ layer with sufficiently high chromium reservoir (Cr).

At the same time, increasing the molybdenum (Mo) increases the corrosion resistance toward chlorine-containing media under high-temperature corrosion conditions.

The effect of molybdenum (Mo) and chromium (Cr) is not fixed to the high-temperature range alone, but would also bring about increased corrosion protection for maritime applications.

b) Notched Embrittlement

Increasing the chromium and molybdenum content results in a boost to the strength. This on the one hand is desired. On the other hand, it is appropriate to choose the tempering conditions so as to exert influence that the risk of notched embrittlement is low/the toughness is sufficient.

Against this background, the optimal quality heat treatment (QHT) is to be ascertained preferably by tempering trials. Preference is given to using a 2- or 3-stage QHT tempering treatment.

Initial parameters in this regard are represented by the following minimum temperatures.

	Solution	1st	2nd	3rd
Variant	annealing	tempering	tempering	tempering
2-stage	>=1243 K	>=1013 K	>=923 K
tempering
treatment
3-stage	>=1243 K	>=973 K	>=923 K	>=923 K
tempering
treatment

In particular, the “>=” temperatures are situated at the numerical values indicated, for example “>=1013 K” is situated in particular at “=1013 K”.

The solution annealing temperature is preferably always the maximum temperature.

The temperature of the 1st tempering is therefore in particular at least 100 K or at least 200 K below the solution annealing temperature.

The subsequent temperatures for the subsequent 2nd or 3rd tempering are situated in particular at least 20 K lower again by comparison with the solution annealing temperature.

The temperature of the 3rd tempering is below the temperature of the 2nd tempering or is the same.

Advantages in addition to the primary utilization as a forged component in energy production plants:

• • Expansion of the service range of “good-value” iron-based alloys by comparison with “expensive nickel-based materials”.
  • Faster machinability of the iron-based rotor components 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 particular in all probabilistic approaches.
  • Usage temperature can be raised and therefore enables power boosting and performance boosting of the machine without need for external cooling.

Exemplary embodiments of the iron-based (Fe) material are as follows:

	EX1	EX2	EX3	EX4	EX5
	C	0.05	0.03	0.07	0.08	0.03
	Si	0.2	0.3	0.2	0.4	0.2
	Mn	2.0	1.7	1.8	1.6	1.9
	Mo	4.2	4.8	4.2	4.1	4.9
	Cr	21.2	24.9	23.7	24.7	20.5
	Ni	24.3	24.1	26.7	24.9	25.5
	V	0.29	0.31	0.30	0.26	0.33
	Ti	2.1	2.1	2.2	2.2	2.3
	Al	0.44	0.44	0.57	0.05	0.01
	B	0.004	0.005	0.004	—	—

Claims

1. An alloy at least comprising (in % by weight):

2. The alloy as claimed in claim 1, comprising: one, more particularly two, very especially comprising all of the elements from the following group:boron (B), tungsten (W) and niobium (Nb).

3. The alloy as claimed in claim 1, comprising: 0.4% to 0.6% of aluminum (Al).

4. The alloy as claimed in claim 1, comprising: up to 0.06% of aluminum (Al),more particularly up to 0.01% of aluminum (Al),very especially 0.004%-0.006% of aluminum (Al).

5. The alloy as claimed in claim 1, having a value: % Cr+3.3% Mo≥32.

6. A blank or component, comprising: an alloy as claimed in claim 1.

7. A method for the heat treatment of an alloy, a blank or a component as claimed in claim 1, comprising: solution annealing for the heat treatment,more particularly single solution annealing and tempering at least twice,more particularly tempering only twice.

8. The method as claimed in claim 7, in which a solution annealing takes place at at least 1243 K,more particularly at 1243 K.

9. The method as claimed in claim 7, in which a first tempering takes place at a temperature of at least 100 K below the solution annealing,more particularly at at least 1013 K,very especially at 1013 K.

10. The method as claimed in claim 7, in which a first tempering takes place at a temperature of at least 100 K below the solution annealing,more particularly at at least 973 K,very especially at 973 K.

11. The method as claimed in claim 9, in which a second tempering temperature is at least 20 K lower than the first tempering temperature.

12. The method as claimed in claim 11, in which a second tempering temperature is at least 923 K,more particularly 923 K.

13. The method as claimed in claim 11, in which a third tempering temperature is not higher than the second tempering temperature.

14. The method as claimed in claim 13, in which a third tempering temperature is at least 923 K,more particularly 923 K.

15. The method as claimed in claim 7, by means of solution annealing and only triple tempering.

16. An alloy consisting of (in % by weight) elements as claimed in claim 1.