DE2365045A1 - ALLOY STRENGTHENED BY PRECIPITATION - Google Patents

Description

The present invention relates to precipitation solidified or hardened alloys; In particular, the invention relates to cobalt alloys strengthened by precipitation.

There are already good cobalt alloys known for use at high temperatures (e.g. the alloys HAYNES No. and HAYNES No. 188), but these alloys are characterized by the fact that they are "solidified in solid solution" (solid solution strengthening) in contrast to such alloys, in which the strengthening by precipitation (e.g. through precipitation of the J ^ 'phase in nickel alloys) is done. With such cobalt alloys, which are caused by precipitation reactions have been hardened, aluminum and / or titanium were usually used as reactive elements, and these alloys are characterized by improved strength at about 650 ° C, while strengthening at 870 ° C or above is ineffective.

The use of beryllium, niobium, or tantalum has also been suggested. These elements lead to excretions in Cobalt alloys, but so far strengthening at 870 C and above has not been effective.

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The object of the present invention is therefore to provide cobalt alloys which wel <
have improved strength.

to provide alloys which can be used at 870 ° C and above

Another object concerns high strength, wrought cobalt alloys.

Yet another object relates to high strength cobalt alloys which are resistant to oxidation.

Yet another task is to make cobalt alloys. which are malleable and which also have good mechanical properties such as strength and toughness Maintained at temperatures up to 1090 ° C.

Further objects and features of the present invention will become apparent from the following description and claims.

It was found to be essential to the invention that cobalt alloys with improved strength at 87O ° C. and above are then obtained if the presence of tantalum and tungsten in the alloy in a ratio of 1.5 to 2.5: 1 causes a precipitation reaction is caused; A ratio of tantalum to tungsten such as 2: 1 (data in percent by weight) is preferred , whereby molybdenum may only be present in traces as an impurity and the carbon content is below 0.3% got to.

A cobalt alloy according to the invention thus essentially consists the end:

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Tantalum Tungsten Chromium Iron Carbon Nickel Silicon Yttrium Lanthanum manganese

Cobalt with incidental, manufacturing-related impurities

Weight -%

5 to 20 2 to 15 up to 0 to 10 0 to 0.3 0 to 30 0 to 1 0 to 0.2 0 to 0.2 0 to 2

rest

wherein the ratio of tantalum to tungsten, expressed in percent by weight, is between about 1.5 to 2.5: 1 and the molybdenum content is less than i % .

A preferred alloy according to the invention with a useful Strength essentially consists of:

Tantalum Tungsten Chromium Iron Carbon Nickel

Weight -%

5 to 20 2 to 15 15 to 0 to 10 0 to 0.2 8 to 30

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Wt .- ^

Silicon O to i

Yttrium. 0 to 0.2

Lanthanum O to 0.2

Manganese O to 2

Cobalt with incidental, manufacturing-related impurities rest

wherein the ratio of tantalum to tungsten, expressed in percent by weight, is between about 1.5 to 2.5: 1 and the molybdenum content is less than 1 % .

A particularly preferred alloy according to the invention is essential from:

Weight f

Tantalum 5 to 18

Tungsten 2 to 12

Chromium 15 to

Iron 0 to 10

Carbon 0 to 0.2

Nickel 8 to 30

Silicon 0 to ί

Lanthanum 0 to 0.2

Yttrium 0 to 0.2

Manganese 0 to 2

Cobalt with incidental, manufacturing-related impurities, remainder

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wherein the ratio of tantalum to tungsten, expressed in percent by weight, is between about 1.5 to 2.5 Jl and the molybdenum content is less than 1 fo .

In addition to the components specifically listed, other alloying elements can be added without deviating from the essence of the invention, namely canceling the critical tantalum-tungsten ratio and keeping the molybdenum and carbon contents as low as possible. Among such elements, but are not limited to, up to 5 wt -. ⁰ Jo hafnium, up to 2 wt .-% titanium and / or zirconium, up to k wt .-% niobium and rhenium, up to 1 wt. -% aluminum and up to 0.04 % by weight magnesium and / or boron.

It has been found as an essential aspect of the invention that all of the cobalt alloys described can then be used for cobalt - alloys have unusual strengths up to at least 930 ° C, when the tantalum content of the alloy is approximately twice the tungsten content, and when the carbon content is kept at a relatively small value. If the critical tantalum-tungsten ratio is not maintained, then the particular strength is also not achieved.

The strength observed is apparently based on a special type of precipitation reaction, which can be seen from the fact that the material in the tempered state (after heat treatment at about 1200 ° C. and subsequent rapid cooling) is relatively soft, ductile and comparatively weak. However, if there is prolonged exposure to heat at elevated temperatures between approximately 650 and 98O ⁰ C, the alloy becomes large

409829/0736

stronger or stronger, as is expected as a result of a precipitation reaction, furthermore the alloy is harder and a little less ductile.

In addition, molybdenum has been observed to be present in such alloys is a harmful element. Such alloys have significantly lower strengths when molybdenum is present. Therefore, molybdenum is considered a harmful impurity in such alloys, and it only becomes for economic reasons up to a content of 1 wt .- $ tolerated.

Also, the carbon content will affect the actual strength of the alloys disadvantageous, and therefore, the carbon content to a maximum of 0.3 percent is -. Bounded%. Carbon contents in excess of this value drastically reduce the strength achieved.

Since the alloys in question and the ones made from them Articles generally used at high temperatures are made of the alloys in balanced amounts Chromium, silicon, manganese, lanthanum and / or yttrium added to increase the oxidation resistance of such alloys. To increase the resistance to oxidation, the alloys typically contain 15 to 30% by weight of chromium, 0.1 to 0.6 Wt% silicon, 0.5 to 1.5 wt% manganese, and small, however effective proportions of yttrium and / or lanthanum, namely up to 0.15 wt .- ^.

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Nickel and Elsen are used as necessary components for stabilization The face-centered cubic crystal structure of the cobalt alloys is considered, and it is suspected what, however It has not yet been proven that iron and nickel participate at least in part as reactants in the solidification.

To explain the present invention, the following Table I gives the composition of an alloy according to the invention and other alloys used for comparison.

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Table I.

Composition according to the invention and used for comparison

Alloys,% by weight

Alloy Al £ Co ^ Cr Fg La Mn Mo Ni £ i Ta W 9 0.37 0.12 balance 20.81 1.36 0.05 0.53 0.42 23.50 0.27 10.53 4.50

** 5 0.33 0.13 remainder 21.56 1.88 0.05 0.66 0.37 23.60 0.35 7.81 9.31

2 7 0.38 0.12 remainder 21.07 1.86 0.04 0.67 0.33 23.60 0.40 16.74 **

⁰⁰ 10 0.45 0.12 remainder 20.07 1.38 0.04 0.54 4.04 22.40 0.25 10.14 4.39

<D 24 0.19 0.55 remainder 20.88 1.18 0.07 0.48 - 21.63 0.22 10.08 4.95 I.

S -

ω.

σ> * Cobalt with random, production-related impurities ** No tungsten was added to the melt

In general, the alloys listed in Table I. melted under vacuum in induction furnace (although others Methods are useful), poured into round, conical blocks weighing about 10 kg, these are in the oven at about Forged at 1180 ° C and then rolled into sheets, tempered at temperatures between 1180 and 1200 ° C and cooled down quickly.

Alloy 24 was melted under vacuum in an induction furnace and then poured into molds for the test samples.

Among the alloys listed in Table I, alloy 9 belongs to the alloys according to the invention, while alloy 10 demonstrates the harmful influence of molybdenum, alloy 7 shows that tantalum is not effective without tungsten, alloy 5 shows that approximately equal proportions of Tantalum and tungsten are also ineffective, and alloy 2h demonstrates that excessive carbon must be avoided.

The following table II shows the comparable tear strengths of the alloys from Table I.

In the figure, a typical alloy according to the invention, namely the alloy 9 »with other experimental alloys and the commercially available alloy HAYNES No. 188 by means of the compared to the usual Larson-Miller representation.

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- ίο -

Table II,,

Tensile strength (kp / mm), tear strength (kp / mm} and elongation at break {%) for the alloys from Table I at different temperatures *

alloy - temperature tensile strenght
kp / mm Tear-proof |
kp / mm * jkeit elongation at break
¹ % .. 5 Clears.
Clears. 53.0
54.3 103.3
102.4 49
49 870
870 34.2
35.5 44.7
44.5 65
60 1090
1090 6.7
7.5 12.4
12.5 49
50 7th Clears.
Clears. 59.5
56.5 107.0
107.9 32
32 870
870 53.6
50.7 72.2
69.7 8th ·
13th IO90
1090 3.0
3.0 10.5
11.5 94
71 9 Clears.
Clears. 38.6
37.2 94.5
94.3 63
60 870
870 44.3
49.9 57.5
61.0 10
12th IO9O
1090 8.1
5.1 13.0
13.1 40
40 Clears. 91.5 128.0 20th
left on
and 16 hours
at 815 C
held 650 76.9 105.7 20th
left on
and 16 hours
at 815 C
held

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alloy

10

Temperature Tensile strength Tear strength Elongation at break ⁰ C kp / mm ^z kp / mm ^z %

24

Clears.

870 870

1090 1090

Clears.

Clears.

Clears.

980

980

48.1 95.6 62 40.7 95.7 61 50.3 61.3 11 46.4 62.1 11 8.1 12.3 65 7.5 12.4 61 40.2 68.0 5 fresh poured 37.3 72.7 8th fresh ge poured and 24 hours at 980 ° C ge keep 33.5 74.6 7.9 fresh ge poured and 16 hours at 815 C ge keep 14.3 19.5 38 fresh poured 16.3 19.1 36 fresh ge poured and - * - ■ - 24 hours at 980 ° C ge keep

* left on unless otherwise noted

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The test results listed in Table II show that the alloys 7 »9 and 10 all have improved strength at medium temperatures compared to the commercial alloy HAYNES No. 188, which for comparison has a 0.2 ^ tensile strength of approximately 26.7 kp / mm ² , a hot strength of 42.9 kp / mm and an elongation at break of 69 % . The corresponding data for the tensile strengths of the alloy show that if the critical tantalum-tungsten ratio of approximately 2: 1 is not adhered to, the hardening of the alloy is minimal; the alloy contains 7.81 5 wt .- ^ tantalum and 9.31 wt -.% tungsten.

It is noteworthy here that alloys 9 and 10 have ^{a higher tensile strength at 870 °} C. than at room temperature. This is considered to be a consequence of the precipitation reaction which occurs during the 30 to 60 minute stabilization at the corresponding temperatures prior to the determination of the tensile strength. Further evidence that a precipitation reaction occurs in the alloy according to the invention is that this alloy, after aging for 9 to 16 hours at 80 ° G, has more than twice the tensile strength at room temperature than without aging treatment.

Alloys which correspond to the alloys according to the invention, however, their carbon content is above 0.3% by weight (such as the alloy 24t), will obviously not appear solidified in the same way as the alloys of the invention.

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Alloy 24, for example, was aged for 24 hours at 980 C and then examined at room temperature, no significant increase in strength compared to a similar test bar in the freshly cast state was found could be.

Another sample made from alloy 24 was aged for 16 hours at 815 ° C and then examined at room temperature. no noticeable improvement in strength was also observed (see Table II).

Although all alloys 5 »7, 9 and OK at medium temperatures showed improved tensile and tear strengths, only alloys 9 and 10 show exceptionally good ones Stable strengths for a longer period of time, as is the case with breaking-elongation stresses over a longer period of time was established. In the following Table III are the test properties of the elongation at break of the alloys listed. The test results and the graphic representation in the figure clearly demonstrate the improved Break-elongation properties.

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Table III Fatigue strength at different temperatures *

Temperature tensile stress service life total elongation alloy C kp / mm ² _._ hours "*

OO 00
H H-
VJlUl 17.5
17.5 81.8
91.7 10
8th. 930
930 9.1
9.1 12.6
13.4 27
26th 1040
1040 3.2
3.2 27.9
26.4 17th
18th 00 00 00
H-H-H-
UlUIUl 17.5
17.5
28.1 27.6
■ 28.5
4.1 12th
29
9
left on and
16 hours at
Held at 815 C. 930
930 9.1
9.1 9
15.7 32
14th 1040
1040 3.2
3.2 10.5
11.3 27
23 00 00 00
H-H-H-
UlUlUl 17.5
17.5
28.1 654.0
626.2
47.6 11
8th
28
left on and
16 hours at
Held at 815 C. 930
930 9.1
9.1 74.8
51.1 4th
6th 1040
1040 3.2
3.2 25.3
17.9 12th
9

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alloy

Temperature tensile stress service life total elongation C kp / mm ² hours %

OO 00
H- H-
VJlVJl 17.5
17.5 229.3
231.8 930
930 9.1
9.1 26.7
23.6 1040
1040 3.2
3.2 12.8
15.4

815 17.5 229.3 8

29
24

* The samples consisted of tempered, 1.27 mm thick sheets, unless otherwise stated.

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236504

A comparison of the test results found on alloys 9 and 10 provides a good example of the harmful effects of molybdenum on the strength of the alloys according to the invention. Alloys 9 and 10 were produced from the same melt, forged at the same time, rolled out at the same time and otherwise processed identically in other ways. The only noticeable difference was that after the ingots for alloy 9 had been poured out, molybdenum was added to the remaining melt in order to modify the composition. 18 g of lanthanum and 30 g of a magnesium-nickel alloy (20 % magnesium, 80 % nickel) were also added to compensate for the loss of lanthanum and magnesium that occurred when the subsequently added molybdenum was melted down.

The test results determined for alloys 9 and 10 show that alloy 10 with k, Qk wt. ^ contains.

The test results shown clearly show that the present invention is superior to cobalt alloys leads, with the mutual content of tantalum and tungsten being of particular importance, and the contents of molybdenum and Carbon must be carefully kept below certain critical limits.

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The cobalt alloys according to the invention can be used for production of objects which are excellent at high temperatures of 870 C and beyond, even up to 1090 C. Have strength, possibly also in an oxidizing environment have to. These include, for example, engine parts on jet engines or rocket engines.

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Claims (1)

- 18 claims 1. solidified by precipitation alloy, which consists essentially of 5 to 20 wt .-% of tantalum, 2 to 15 wt .-% tungsten, up to 30 Gev.-fo chromium, O to 10 wt .- $ iron, O to 0 , 3 wt .-% carbon, 0 to 30 Gev.-fo nickel, 0 to 1 wt .- # silicon, 0 to 0.2 part by weight fa yttrium, 0 to 0.2 wt .-% lanthanum, 0 to % By weight of manganese, the remainder being cobalt with incidental, production-related impurities, the ratio of tantalum to tungsten, expressed in % by weight, being between 1.5 and 2.5 1, and the molybdenum content being less than 1% . 2. Alloy according to claim 1, consisting essentially of 5 to wt .-% tantalum, 2 to 15 wt .-% tungsten, 15 to 30 wt .-% chromium, 0 to 10 wt .-% iron, 0 to 2 wt .-% manganese, 0 to 0.2 wt .- $ lanthanum, 0 to 0.2 wt .-% yttrium, 0 to i wt .-% silicon, 0 to 0.2 Gev.-fo carbon, 8 to 30 Wt .-% nickel, the remainder cobalt with incidental, production-related impurities, the ratio from tantalum to tungsten, expressed in weight percent, is approximately between 1.5 and 2.5: 1 and the molybdenum content is less than 1 % . 3. Alloy according to claim 1, which consists essentially of 5 to 18 wt .-% tantalum, 2 to 12 wt .-% tungsten, 15 to 30 wt .-% chromium, 8 to 30 wt .-% nickel, 0 to iO wt -.% iron, 0 to 0.2 wt .-% carbon, 0 to 1 wt .-% of silicon, 0 to 0.2 wt .- ^ lanthanum, 0 to 0.2 wt .- ^ yttrium, 0 to 2% by weight manganese, the remainder cobalt with incidental, production-related impurities. 409829/0736 4. Alloy according to claim 1, consisting essentially of 5 his wt .- # tantalum, 2 to 8 wt .-% tungsten, 15 to 30 wt .-% chromium, 15 to 30 wt .-% nickel, 0.005 to 0, 2 wt .- ^ lanthanum, 0 to iO wt -.% Iron, 0 to 0.2 wt -.% Carbon, 0 to 1 % by weight silicon, 0 to 2% by weight manganese, the remainder cobalt with incidental, production-related impurities, the ratio of tantalum to tungsten being between approximately 1.5 to 2.5: 1 and the molybdenum content less than i % . 5. Alloy according to claim 1, consisting essentially of 8 to Gev .- # tantalum, 3 to 6 wt .-% tungsten, 20 to 2h wt .- # chromium, 15 to 25 wt .-% nickel, 0.005 to 0, 15 wt .-% lanthanum, 0 to 2 wt _o -% iron, 0 to 0.15 wt .- # carbon, 0 to 0.5 wt .-% silicon, 0 to 1 wt -.% manganese, the balance cobalt, with incidental, production-related impurities, the ratio of tantalum to tungsten being between approximately 1.5 to 2.5: 1, and the molybdenum content being less than 0.5 % . 6. Alloy according to claim 1, characterized by a ratio of tantalum to tungsten such as approximately 2: 1, 409829/0736 Blank page