DE1295848B - Use of a nickel-tungsten-chromium alloy - Google Patents

Description

The invention relates to the use of a nickel alloy of 1 to 3.5% chromium, 7 to 19.5% tungsten, 0 to 7% molybdenum, 0 to 4 ⁽¹ / o niobium, 4.7 to 6 , 8% aluminum, 0 to 22% cobalt, 0 to 0.5% carbon, 0 to 1.3% zirconium, 0 to 0.05% boron, the balance nickel.

Known from British patent specification 963 521 are nickel-chromium alloys with 5 to 10% chromium, 7 to 16% tungsten, 0 to 5% molybdenum and 0 to 4% niobium with a total content of tungsten, molybdenum, niobium and ² k the chromium content of 17.5 to 10.5% and 2 to 8% aluminum, 0.03 to 0.3% carbon, 0 to 1% zirconium, 0 to 0.05% boron, the remainder nickel including impurities caused by the melting process.

Furthermore, from the German patent 740 895 an alloy with high permeability intended for magnetically stressed objects is known, which consists of 40 to 85% nickel, 1 to 12% tungsten, 0 to 3% chromium, 0.2 to 6% molybdenum and up to 10 % Aluminum. Finally, in British patent specification 821 745, nickel-chromium alloys with 4 to 30% chromium, 0 to 15% tungsten, 0 to 30% molybdenum, 0 to 6% niobium, 0 to 8% aluminum, 0 to 30% cobalt, 0 to 0.5% carbon, 0 to 0.5% zirconium, 0 to 0.05% boron and 35 to 90% nickel are known, which are said to have high heat resistance and creep resistance with good ductility. Tests on these alloys have shown, however, that the elongation is relatively low due to the chromium content exceeding 4% and the service life at temperatures between 800 and 900 ° C. and a load of 14.1 to 28.1 kg / mm ^{2 is} less than 200 hours .

The object on which the invention is based is to create an alloy of the type mentioned at the outset which has a long service life ^{at high temperatures, for example at 1100 ° C. and a load of 11 kg / mm 2.} The solution to this problem is based on the finding that the creep rupture strength of the known alloys can be significantly improved if their chromium content is reduced and the contents of molybdenum, tungsten and niobium are adjusted to the respective chromium content.

The invention consists in the proposal to use a nickel alloy of 1 to 3.5% chromium, 7 to 19.5% tungsten, 0 to 7% molybdenum, 0 to 4% niobium, 4.7 to 6.8% aluminum, 0 to 22% cobalt, 0 to 0.5% carbon, 0 to 1.3% zirconium and 0 to 0.05% boron, the remainder being nickel, with the following conditions: molybdenum, tungsten, niobium and chromium
1.2 (% Mo) + (% W) + (% Nb) + % i (% Cr) are sufficient to be used as material for objects which, like stator and rotor blades for gas turbines, have a high creep strength at high temperatures have to.

The main impurities are iron, silicon and manganese; the total content of this Elements must be kept as low as possible and must not exceed 3%. Preferably the maximum content of iron is 0.5%, silicon and manganese 0.3% each.

Since commercial niobium generally contains small amounts of tantalum, for example 10% of the Niobium content of an alloy of 40% nickel and 60% niobium, the alloys according to the invention can also have tantalum. Then the tantalum is part of the prescribed niobium content consider.

The castability of the alloys is impaired to a considerable extent by titanium. The alloys may therefore not contain titanium or only contain it as an impurity.

The effect of the different chromium contents on the creep behavior of the alloy is through Tests determined and illustrated in Table 1. Here the alloys 2 and 3 Alloys according to the invention, while the rest are not the alloys according to the invention belong. The best properties were found when the chromium content of the alloys is 1 to 3.5%. If the resistance of the alloys to oxidation is important, then the chromium content should be however, be at least 2%.

Table 1

Composition of the alloy, apart from the chromium content:
C = 0.13%, W = 18%, Nb = 1 ° / o, Al = 6%,

Zr = 0.5%, balance nickel.

alloy Cr
- ( ⁰ Z ₀ ) Time stand
at 11 kg / m
lifespan
(Hours.) behavior
m ^2/1100 ° C
strain
( ⁰ O) 1 0 20 *) 2 2 49 9.1 3 3 58 11.0 4th 4th 23 5.6 5 6th 9 6.1

= 16.5 to 22% *) Determined on samples at 1070 ° C.

The contents of tungsten, molybdenum and niobium are also critical for the creep behavior. The influence Table 2 shows the changes to these contents. Except for those marked with a cross all alloys the alloys according to the invention.

Tabel

composition Mon of the alloys except for the proportions of tungsten, molybdenum and niobium:
C = 0.13%, Cr = 3%, Al = 6%, Zr = 0.5 "/"), remainder nickel. Nb 1.2 Mo + W + Nb + _^2/3 cr Creep behavior be
lifespan
(Hours.) illkg / mm ^2/1100 ° C
strain alloy 0
0
0 W. 0
1.0
0 22nd
23
20th 7th
10
24 8.2
10.4 6 *
7 *
8th 20th
20th
18th

continuation

alloy Mon W. Nb 1.2 Mo + W + Nb + V ₃ Cr Creep behavior tx
lifespan ! illkg / mm ^2/1100 ° C
strain (%) (%) (%) (%) (Hours.) (%) 9 0 18th 0.5 20.5 52 13.4 3 0 18th 1.0 21 58 11.0 10 0 18th 1.5 21.5 23 - 11 * 0 18th 3.0 23 11 8.9 12th 0 16 0.5 18.5 69 32.2 13th 2 16 0.5 20.9 46 19.9 14th 2 14th 1.0 19.4 52 9.9 15th 2 14th 1.5 19.9 49 - 16 * 0 12th 1.0 15th 4th - 17th 4th 12th 1.5 20.3 43 19.8 18th 6th 12th 0.5 - 21.7 23 9.2 19 * 6th 12th 1.5 22.7 14th 7.7 20 * 2 10 0.5 14.9 5 - 21 * 4th 8th 0.5 15.3 5 - 22nd 6th 8th 1.5 18.7 23 6.4 23 * 6th 6th 0.5 15.7 12th 12.0 24 * 6th 6th 1.5 16.7 16 11.5

The alloys 6 and 24 show the insufficient creep behavior that results when the tungsten content of the alloy is greater than 19.5% and less than 7%, although the value

1,2 Mo + W + Nb + ² / _:! Cr

stays within the critical limits. The poor results for alloys 7, 11, 16, 19, 20, 21, and 23 similarly illustrate the need to maintain relationships between the elements molybdenum, tungsten, niobium and chromium.

A comparison of alloys 9, 12 and 13 with alloy 18 and alloys 15 and 17 with of alloy 22 illustrates the drop in properties when the tungsten of the alloy is replaced by molybdenum. To achieve the longest service life and the greatest elongation the molybdenum content of the alloy should not exceed 4% and preferably not more than 3% be. Alloys which are essentially free of molybdenum are particularly advantageous are.

A change in the niobium content of the alloys has a clear influence on the properties of the alloys. Alloy 9, for example, which contains only 0.5 "/ n niobium, has more than double that Lifetime of the niobium-free alloy, which is otherwise similar to alloy 8. But when If the niobium content is increased above 1%, then the service life falls again and the elongation also decreases decreased. This can be seen, for example, when comparing alloy 9 with alloys 10 and II, which was of the same composition, except that alloy 9 had a niobium content of 0.5'V (i, while alloy 10 had a niobium content of 1.5% and alloy 11 had a niobium content of 3%. The niobium content should therefore advantageously be 0.2 to 2% and Do not exceed 1.5%.

Tests on alloys with different aluminum contents showed that the best creep behavior in alloys with about 6 "/» aluminum and that the service life of the alloys declines when they contain either more or less aluminum. This effect will illustrated by the test results shown in Table 3. Here all correspond Alloys other than alloy 28 comply with the provisions of the invention. The aluminum content is therefore preferably 5.5 to 6.5%.

Table 3

Composition of the alloy apart from its aluminum content:

C = 0.13%, Cr = 3%, W = 18%, Nb = 1%,

Zr = 0.5%, balance nickel.

Al Creep behavior strain at 11 kg / mm ^2/1100 ° C «%) alloy ( ⁰ Io) lifespan 17.2 5.0 (Hours.) 25th 5.5 26th 11.0 26th 6.0 48 8.2 ' 3 6.5 58 13.9 27 7.5 24 28 4th

A change in the cobalt content between 0 and 16% has only a minor influence on this Creep behavior of the alloys. However, if the highest elongation values are required, then should the cobalt content must be at least 5%. If the cobalt content is increased above 16%, then the creep behavior deteriorates. The cobalt content should preferably not exceed 16%. These relationships are illustrated in Table 4 for alloys with different niobium contents, in which all alloys except the ticked ones (39 to 41) comply with the provisions of Invention correspond.

Table 5

Composition of the alloy apart from its carbon and niobium contents:

Cr = 3%, Co = 10%, W = 18%, Al = 6%,

Zr = 0.50 / o, B = 0.02%, balance nickel.

Table 4

Composition of the alloy apart from its cobalt and niobium content:

C = 0.13%, Cr = 3%, W = 18%, Al = 6%,

Zr = 0.5%, balance nickel.

Alloy
10 _rU ng C. Nb Blow
strength
at 850 ° C
in m kg Time stanc
beillkg / i
Life
duration !behavior
nm ^2/1100 ° C
strain (%) / 0, ι
(<o) (Hours.) CVo) 42 0.13 1 7.6 44 13.6 15 43 0.005 1 11.3 21 10.2 44 0.13- 1.5 4.3 56 10.1 45 0.005 1.5 9.8 24 2.6

Co Nb Creep behavior strain beillkg / mm ^2/1100 ° C (%) alloy 13.4 (%) (%) lifespan ir, o 0 0.5 (Hours.) - 9 0 1.0 52 17.7 3 0 1.5 58 14.2 10 5 0.5 23 14.9 29 5 1.0 58 18.9 30th 10 0.5 52 9.5 31 10 1.0 45 23.3 32 10 1.5 62 20.9 33 15th 0.5 54 19.3 .34 15th 1.0 46 12.9 35 20th 0.5 60 10.4 36 20th 1.0 19th - 37 20th 1.5 23 24.3 38 30th 0.5 26th 18.0 39 * 30th 1.0 12th 40 * 30th 1.5 9 41 * 12th

Zirconium and boron improve the creep behavior of the alloys. They should therefore be beneficial Contains 0.1 to 1.0% zirconium. In the presence of boron, the contents of zirconium and boron are advantageously adjusted to one another so that the value

% Zr + 10 χ (% B)

0.1 to 1.2%. If the boron content is increased above 0.035%, it worsens Creep behavior again, so that the boron content of the alloy is expediently kept below this value will.

The properties of some alloys with different zirconium content are shown in Table 6 indicated in which all alloys except alloy 49 meet the requirements of the invention.

Table 6

Composition of the alloy in addition to its zirconium content:

C = 0.13%, Cr = 3%, W = 18%, Nb = 1.0%,

Al = 6%, remainder nickel.

A change in the carbon content of the alloys in the range from 0.05 to 0.3% has only little influence on the creep behavior of the alloys. Above and below this Limits it worsens, and if the carbon content is below 0.03% then it should the alloys contain at least 0.01% boron.

On the other hand, the impact resistance values of the alloys at high temperatures become with a decrease the carbon content of the alloy is better. To achieve high impact strength values the carbon content should not exceed 0.05% or even be below 0.03%. The influence the carbon content on the impact strength and the creep behavior of the alloys shown in Table 5. The impact strength values were determined on unnotched bars of a diameter of 11.4 mm was determined.

Zr Creep behavior strain at 11 kg / mm ² / H00 ° C. '(%) 45 alloy 6.5 (° / o) lifespan 9.4 0.2 (Hours.) 11.0 46 0.4 32 9.7 50 47 0.5 43 11.9 3 1.0 58 48 1.5 24 49 10

The alloys can be melted in air; however, the melting is preferably done in a vacuum. Regardless of whether the alloys have been melted in a vacuum or not, they should be subjected to a refining treatment in a vacuum. It consists in that the melted Alloy is held under high vacuum for a period of time prior to casting. Preferably the alloys should be subjected to a vacuum at a temperature of 1400 to 1700 C and a pressure of not more than 0.1 torr for at least 15 and preferably 60 minutes or more. The duration of treatment also depends on the purity

the constituents of the melt, which must be refined the longer, the more impure the used Alloy components are.

Small-piece castings, for example. Turbine blades or samples for determining the time-stability behavior are advantageously cast in a vacuum. However, when large castings are made from a melt that has been melted or refined in a vacuum, the properties of the alloys differ only slightly when cast in a vacuum, inert gas, or air. All of the experiments discussed above have been carried out on samples which have been produced from a material which has been melted in vacuo, refined in vacuo at 150 ° C. and a pressure of less than 10 ³ Torr for at least 15 minutes and cast at 1600 ° C. in vacuo became.

Castings made from the alloys of the invention can be used as cast at high temperatures. If necessary, the alloys can be homogenized by heat treatment in the temperature range from 850 to 1250 ^° C. before they are used.

For use in a temperature range above 100 ° C, i.e. under conditions as described in Gas turbines exist where the parts consisting of the alloys both oxidize as well are exposed to attack by sulfur, the parts are advantageously covered with a protective coating, for example made of aluminum.

Claims (6)

Patent claims: 1. Use of a nickel alloy consisting of 1 to 3.5% chromium 7 to 19.5% tungsten, 0 to 7 ^(l / ₀ molybdenum, 0 to 4 "/" niobium, 4.7 to 6.8% Aluminum, 0 to 22% cobalt, 0 to 0.5% carbon, 0 to 1.3% zirconium, 0 to 0.05% boron, the remainder nickel, with the following conditions: molybdenum, tungsten, niobium and chromium 1.2 (% Mo) + ( ¹ VoW) + (% Nb) +% (% Cr) = 16.5 to 22% suffice as a material for objects that, such as stator and rotor blades for gas turbines, a must have high creep strength at high temperatures. 2. Use of an alloy according to claim 1, but whose molybdenum content is at most 4% for the purpose according to claim 1. 3. Use of an alloy according to claims 1 and 2, but containing 0.2 to 2% niobium contains, for the purpose of claim 1. 4. Use of an alloy according to claims 1 to 3, but containing 5.5 to 6.5% aluminum contains, for the purpose of claim 1. 5. Use of an alloy according to claims 1 to 4, but containing 5 to 16% cobalt contains, for the purpose of claim 1. 6. Use of an alloy according to claims 1 to 5, but containing 0.1 to 1.0% zirconium and contains not more than 0.035% boron, and their contents of zirconium and boron of the condition (% Zr) + 10 (% B) = 0.1 to 1.2%
suffice for the purpose according to claim 1. 909 521/415