EP2031080B1 - High temperature alloy - Google Patents

Description

Technical area

The invention relates to the field of materials technology. It relates to a high-temperature iron-based alloy containing about 20% by weight of Cr and several parts by weight of Al and minor amounts of other constituents, and which have good mechanical properties and very good oxidation resistance at service temperatures of up to 1000 ° C.

State of the art

For some time ODS (oxide-dispersion-strengthened, oxide dispersion strengthened) materials based on iron, z. B. ferritic ODS FeCrAI alloys, known. They are due to their excellent mechanical properties at high temperatures preferred for thermally and mechanically highly stressed components, eg. B. for gas turbine blades used.

The Applicant employs such materials for thermocouple protection tubes used, for example, in temperature control gas turbine sequential combustion gas turbines where they are exposed to extremely high temperatures and oxidizing atmospheres.

For known iron-based ferritic ODS alloys, Table 1 sets forth the nominal chemical compositions (in weight%): Table 1: Nominal composition of known ODS-FeCrAlTi alloys component Fe Cr al Ti Si Addition of reactive elements (in the form of an oxide dispersion) alloy designation Kanthal APM rest 20.0 5.5 12:03 12:23 ZrO ₂ -Al ₂ O ₃ MA 956 rest 20.0 4.5 0.5 - Y ₂ O ₃ -Al ₂ O ₃ PM 2000 rest 20.0 5.5 0.5 - Y ₂ O ₃ -Al ₂ O ₃

The operating temperatures of these metallic materials reach up to 1350 ° C. They have a property potential which is more typical for ceramic materials.

The materials mentioned have very high creep ruptures at very high temperatures and also excellent high-temperature oxidation resistance by forming an Al ₂ O ₃ protective film, as well as a high resistance to sulfidation and steam oxidation. They have strong directional characteristics. For example, in pipes, the creep strength in the transverse direction is only about 50% of the creep strength in the longitudinal direction.

The production of such ODS alloys by powder metallurgy using mechanically alloyed powder mixtures, the known manner, for. B. by extrusion or by hot isostatic pressing, compacted. Subsequently, the compact is strongly plastically deformed, usually by hot rolling, and subjected to recrystallization annealing. This type of production, but also the material compositions described mean, inter alia, that these alloys are very expensive.

document W02004104257 A1 discloses an iron-base alloy consisting of 10 to 25 wt% Cr, 1 to 10 wt% Al, 1.5 to 5 wt% Mo and balance Fe, for a jet pipe in cracking furnaces. This jet tube has a creep rupture strength over 100,000 hours at a temperature of 1100 ° C and a relinquishment of 2.2 MPa.

Presentation of the invention

The aim of the invention is to avoid the mentioned disadvantages of the prior art. The invention is based on the object to develop a suitable material for the above applications, which is less expensive than the known from the prior art material PM 2000, but has at least as good oxidation resistance. In addition, the material according to the invention should be readily thermoformable and should have better mechanical properties than z. As the well-known alloy KANTHAL APM, which is used for heating elements.

• 20 Cr,
• 4-8 Al,
• mindestens eines der Elemente aus der Gruppe Ta und Mo mit insgesamt 4-8,
• 0-0.2 Zr,
• 0.02-0.05 B,
• 0.1-0.2 Y,
• 0.25 oder 0.5 Si,
• Rest Fe.

According to the invention, this is achieved by the fact that the high-temperature alloy of the FeCrAl alloy type consists of the following chemical composition (in% by weight):

• 20 Cr,
• 4-8 Al,
• at least one of the elements from the group Ta and Mo with a total of 4-8,
• 0-0.2 Zr,
• 0.02-0.05 B,
• 0.1-0.2 Y,
• 0.25 or 0.5 Si,
• Rest Fe.

The alloy preferably contains 5 to 6% by weight of Al, particularly preferably 5.5 to 6% by weight of Al. This forms a good Al ₂ O ₃ protective film on the material surface which enhances the high temperature oxidation resistance.

Further preferred ranges are 0-8% by weight of Mo and 0-4% by weight of Ta, with the proviso that the sum (Mo + Ta) = 4-8% by weight, and where, for example, the maximum value of 8 % Mo according to the independent claim 1 only applies if no Ta is present. The material according to the invention particularly preferably comprises 2-4% by weight of Mo and / or 2-4% by weight of Ta.

If the contents of (Ta + Mo) are lower than the specified values, the high-temperature strength is excessively reduced, if they are higher, the oxidation resistance is undesirably reduced, and the material becomes too expensive.

Also advantageous is the addition of 0.25 or. 0.5% by weight of Si, because this further enhances the oxidation resistance.

Furthermore, 0.2% by weight of Zr and 0.1% by weight of Y are preferably present in the material according to the invention.

Surprisingly, it has been found that it is not necessary, as is the case with the alloys known from the prior art and described above, to add titanium. Ti and Cr act as solid solution hardeners. Mo has a similar effect in the range of 2-8% by weight, but is considerably cheaper than Ti. In addition, Mo, when added together with Zr, as in the present invention in preferred embodiments, is the case. leads to improved tensile strength and creep strength.

Ta, Zr and B are elements which act as precipitation strengthening agents. The interaction of these constituents with the other constituents, in particular the Cr and the Mo, if present, leads to good strength values, while Al, Y and also Zr increase the oxidation resistance. Cr positively influences ductility.

Brief description of the drawings

In the drawings, embodiments of the invention are shown.

Fig. 1

das Oxidationsverhalten bei 1100°C/12h für PM 2000 und für ausgewählte Materialien;

Fig. 2

das Oxidationsverhalten bei 1000°C an Luft über einen Zeitraum von 1000 Stunden für PM 2000 und für ausgewählte Materialien;

Fig. 3

die Zugfestigkeit im Bereich von Raumtemperatur bis 1000°C für PM 2000 und Kanthal APM und für ausgewählte Materialien;

Fig. 4

die Streckgrenze im Bereich von Raumtemperatur bis 1000°C für PM 2000 und für ausgewählte Materialien und

Fig. 5

die Bruchdehnung im Bereich von Raumtemperatur bis 1000°C für PM 2000 und für ausgewählte Materialien.

Show it:

Fig. 1

the oxidation behavior at 1100 ° C / 12h for PM 2000 and for selected materials;

Fig. 2

the oxidation behavior at 1000 ° C in air over a period of 1000 hours for PM 2000 and for selected materials;

Fig. 3

the tensile strength ranges from room temperature to 1000 ° C for PM 2000 and Kanthal APM and for selected materials;

Fig. 4

the yield strength in the range of room temperature to 1000 ° C for PM 2000 and for selected materials and

Fig. 5

the elongation at break in the range of room temperature to 1000 ° C for PM 2000 and for selected materials.

Ways to carry out the invention

The invention will be explained in more detail with reference to embodiments and the drawings.

There have been known from the prior art ODS FeCrAl comparative alloys PM 2000 and Kanthal APM (composition see Table 1), and the alloys listed in Table 2 with respect to the oxidation behavior as well as with respect to the mechanical properties at room temperature (RT) to examined at 1000 ° C. The alloy components are given in% by weight: Table 2: Compositions of the investigated alloys according to the invention and comparative alloys. component Fe Cr al Ta Not a word Zr B Y Si alloy designation 2007 * rest 20 5.5 4 - 0.2 12:05 0.1 - 2008 * rest 20 5.5 - 4 0.2 12:05 0.1 - 2009 * rest 20 8th - 4 0.2 12:05 0.1 - 2010 * rest 20 6 - 8th 0.2 12:05 0.1 - 2011 rest 20 5.5 - 4 0.2 12:05 0.1 0.5 2012 * rest 20 6 2 2 0.2 12:05 0.1 - 2013 * rest 20 6 4 4 0.2 12:05 0.1 - 2014 rest 20 6 - 4 0.2 12:05 0.1 0.5 2015 * rest 20 5.5 4 4 0.2 12:05 0.1 - 2016 rest 20 5.5 - 4 0.2 12:05 0.1 12:25 * Comparative alloys

These alloys were prepared by arc melting the specified elements and then rolled at temperatures of 900-800 ° C before, among other things, the tensile specimens were prepared.

In Fig. 1 For the alloys listed, the weight change at 1100 ° C over time over a period of 12 hours is shown. The alloy 2008 (eg with 4% Mo and 5.5% Al) shows a comparable oxidation behavior as the comparison alloy PM 2000 and is even better with the long removal times (lower weight change), while the alloy 2009 (among others with 4% Mo and 8% Al) is the worst in this respect and can not reach the values of PM 2000 at these temperatures. This is due to the comparatively high aluminum content, the 8% by weight of Al being the maximum value, the optimum being 5 to 6% by weight of Al.

In Fig. 2 For the specified alloys, the weight change at 1000 ° C in air over time over a period of 1000 hours is shown. It can be seen that the alloys 2014 and 2013 have a significantly improved oxidation behavior. After 1,000 hours of aging in air at 1000 ° C, the weight changes in the two alloys only one-third (alloy 2013) to less than half (alloy 2014) of the weight change compared to the well-known alloy PM 2000. Apparently affects a combination of Mo and Ta in equal proportions particularly good on the oxidation behavior at 1000 ° C from. In particular, Ta increases the activity of Al in the given range and improves the oxidation resistance.

In the FIGS. 3 to 5 the results of tensile tests in the temperature range from room temperature to 1000 ° C are shown.

Fig. 3 shows the dependence of the tensile strength on the temperature of the specified materials. At room temperature, the values of the investigated materials are relatively close to each other. Some materials (eg alloys 2007 and 2013) are stronger at room temperature than those known from the prior art Materials), in others there are hardly any differences to the well-known alloys PM 2000 and Kanthal APM.

Up to about 400 ° C, the tensile strength values remain approximately constant as a function of the temperature, then they drop markedly as expected. In the temperature range from 900 to 1000 ° C, the investigated alloys invariably have higher tensile strengths than Kanthal APM and somewhat lower tensile strengths than PM 2000. However, this is associated with the excellent oxidation behavior of these alloys at 1000 ° C (see Fig. 2 ), then these are very good property combinations.

In Fig. 4 the dependence of the yield strength on the temperature is shown. The tendency corresponds approximately to the course of the tensile strength according to Fig. 3 ,

Fig. 5 finally shows the dependence of the elongation at break of the temperature in the range from room temperature to 1000 ° C. For PM 2000, the elongation at break values in the range from RT to 400 ° C. are approximately constant, at 600 ° C. the maximum value is twice the value compared with RT, then the elongation at break values decrease with increasing temperature until at 1000 ° C. approx. half of the value is reached at RT. The increase in ductility of PM 2000 at about 600 ° C is due to the softening of the material.

While at room temperature the elongations at break of the alloys according to the invention are below the values for PM 2000, they are invariably higher starting at about 600 ° C. This positive effect is due to the interaction of the material components in the given areas.

The novel materials can also be hot rolled well, they have a good plastic deformability.

They are very useful as a thermocouple thermowell, the latter being used, for example, in gas turbines with sequential combustion for temperature control where they are exposed to oxidizing atmospheres.

In summary, it should be noted that the alloys according to the invention have a very high oxidation resistance at 1000 ° C. They have better mechanical properties than the Kanthal APM alloy known from the prior art. Although the strength values of the alloys according to the invention are slightly lower than those of the alloy PM 2000 at high temperatures, the ductility is considerably better for this purpose. Moreover, at 1000 ° C., the oxidation resistance is more than twice as high as in PM 2000. Since the alloys according to the invention are also cheaper than PM 2000 (cheaper components, easier production), they are outstandingly suitable as a replacement for PM 2000 for the fields of application described above.

Claims (11)

1. Iron-based high-temperature alloy, consisting of, values given being in % by weight:

   20 Cr,

   4 to 8 Al,

   at least one of the elements Ta and Mo, where the sum (Ta + Mo) = 4 to 8,

   0-0.2 Zr,

   0.02-0.05 B,

   0.1-0.2 Y,

   0.25 or 0.5 Si,

   remainder Fe.
2. High-temperature alloy according to Claim 1, characterized by 5 to 6% by weight Al.
3. High-temperature alloy according to Claim 2, characterized by 5.5 to 6% by weight Al.
4. High-temperature alloy according to one of Claims 1 to 3, characterized by 0 to 8% by weight Mo and/or 0 to 4% by weight Ta, where the sum (Mo + Ta) is in each case in the range from 4 to 8% by weight.
5. High-temperature alloy according to Claim 4, characterized by 2% by weight Mo and 2% by weight Ta.
6. High-temperature alloy according to Claim 5, characterized by 4% by weight Mo and/or 4% by weight Ta.
7. High-temperature alloy according to one of Claims 1 to 6, characterized by 0.2% by weight Zr.
8. High-temperature alloy according to one of Claims 1 to 7, characterized by 0.05% by weight B.
9. High-temperature alloy according to one of Claims 1 to 8, characterized by 0.1% by weight Y.
10. Method for producing a high-temperature alloy according to one of Claims 1 to 9, characterized in that the elements corresponding to the alloy composition are melted by means of an arc and subsequently rolled at about 900-800°C.
11. Use of the high-temperature alloy according to one of Claims 1 to 9 for protective thermocouple tubes.

Images