DE2034608C2 - Process for increasing the ductility at high temperatures of nickel-based cast alloys - Google Patents

Description

The main patent relates to a method for increasing the üuktilltäl at temperatures in the range from 704 to 87Γ C of cast nickel-based alloys that consist of a Batch with no more than 5% return scrap, in which the y'-phase is the basic phase in of the crystalline matrix and that is for use under stress at temperatures up to 1038 ° C are suitable, consisting of 0.02 to 0.20% carbon, up to 13% chromium, up to 8% molybdenum, up to 6% tantalum, up to 14% tungsten, up to 35% cobalt. 4 to 7% aluminum. 0.5 up to 6% titanium, up to 3% niobium, up to 1.5% vanadium, 0.002 to 0.02% boron, 0.01 to 0.20% zirconium, the remainder at least 36% nickel and up to 2% of production-related customary impurities, with the molten Batch 0.5 to 4% hafnium added after deoxidation will.

The main patent deals with the solution of an essential problem. the development of "Superleglerungen" occurs, the / for use are determined under high loads and at high Temperaluren such. B. in the production of high-temperature castings that are processed into high-temperature gas turbine parts to prevent up to 871 ° C.

From US-PS 30 05 705 are nickel-chromium-iron alloys and cobalt-nickel-chromium alloys known. These are wrought alloys that are used in the manufacture of forged goods.

in US-PS 30 05 705 these alloys are referred to as high-temperature alloys, which at temperatures from about 650 to 870 ° C can be used. From the US-PS it is apparent that these alloys contain significant amounts of iron or chromium, which are considerably higher than those obtained according to the invention Alloys are acceptable quantities. When aluminum is present in the known alloys. it is present in significantly smaller amounts than in the case of the cast alloys according to the invention.

Because of these differences, those in the US-PS 30 05 705 are unsuitable for use at significantly higher temperatures, i. H. Temperatures of up to 1038 ° C. are, however, very suitable for soft alloys obtained according to the invention are. Even at low temperatures, such as B. 815 ° C, the strength values for the known alloys are substantially below those for the inventive ones Cast alloys. The limits of the ranges of the compositions as well as the requirements for the Nickel-based cast alloys according to the invention differ fundamentally from those for known wrought alloys. These differences lead to different properties and uses the known alloys compared to the invention. Because of this fundamental Differences in the compositions and the properties was - even with knowledge of US Pat. No. 3,055,705 Effect of adding hafnium to the alloys according to the invention cannot be foreseen.

From US-PS 30 05 705 information on the effect of the addition of hafnium is only for one alloy to infer what large amounts of cobalt. Chromium and Elsen and only 30% nickel, but no aluminum, contains and has no y'-phase.

On the basis of this single example, it is claimed, but neither shown nor proven, in the U.S. Patent that the addition of hafnium, the ductility of other alloys, such as. B. from In the US-PS 30 05 705 disclosed alloy C. which, however, in no WeUc meet the requirements regarding the composition of the alloys according to the invention, improve would.

From FR-PS 12 27 686 hafnium-containing cast nickel alloys are known, the ones described there Alloys have poor ductility at high temperatures. Any indication that through the addition of hafnium allows high ductility to be obtained from nickel-based cast alloys this reference does not.

The invention relates to a further development of the procedure according to the main patent and lctrlfft Alloys of an improved composition, which can be used successfully under load at very high temperatures can be used and have even better properties in the range of intermediate temperatures.

The invention comprises a method according to the main patent with the proviso that 0.7 to 5 ".. hafnium is added and that the alloy treated by the process is up to 0.5 '\, carbon, aluminum + titanium

from 6.5 to 10.5%, Tanta! + Chromium up to 16%, tungsten + Tantalum, if both are present, contains up to 13%, and the hardenability factor (HF), which is derived from the formula:

HF = I χ % Cr + 1.1 χ% (W + Mo) + 3.4x% (Nb + Ta) + 4.3 χ% Ti + 6 χ% Al

calculated, is within the range of 60 to 72.

In the present context, all percentages are based on weight.

Those obtainable by the process according to the invention Alloys with no more than 5% of the previously melted and cast alloy have compositions which are generally within the ranges given in the main patent, with the exception the content of hafnium, which - has been found - expediently within the range from 0.7 to 5%, preferably from 1 to 5%, is to be kept. The total percentage of titanium + aluminum should be at least 6%, preferably about 6.5 to about 10.5%, and the carbon content can be up to 0.5% by weight. It is advisable to adjust the content of hafnium and the content of carbon dioxide in such a way that the two Elements are present in approximately equivalent atomic quantities. If cobalt is present, it is preferred limited to an amount of about 20%, with the total percentage of tantalum + chromium being 16% does not exceed. The alloys obtainable according to the invention have a hardenability factor (HF), which is within the range of 60 to 72 and which is calculated from the following equation:

HF = I x% Cr + 1.1 χ% (W + Mo) + 3.4 χ% (Nb + Ta) + 4.3 χ% Ti + 6 χ% Al.

For reasons of convenience, the numerical value calculated by the above equation is referred to as the "hardenability factor". When the HF exceeds about 60, the cast samples made from this alloy will generally have a breaking strength of at least about 1000 hours when tested ^{at 898 ° C. under a load of 14.06 kg / cm 2.}

Most of the alloys obtainable according to the invention have breaking strength values of 1000 hours ^{under a load of 14.06 kg / cm 2 at temperatures above 926 ° C.}

The temperature at which an alloy has a breaking strength of 1000 hours under a load of 14.06 kg / cm ² is generally referred to as the "temperature performance" of the alloy in question.

Further examples of alloys obtainable according to the invention are given in Table I below.

Table I.

Alloy 1

C. 0.15 0.12 0.18 0.05 0.12 0.14 0.05 0.12 Cr 9.0 10.0 10.0 12.0 9 9 9 12.5 Co 10.0 - 15.0 - 9 9 9 - Mon - 1.5 - 4.5 2.5 2.4 4.2 - W. 10.0 2.0 - - 9.9 9.6 10 - Ti 1.5 1.0 4.7 0.6 1.5 1.5 1.5 0.8 Ai 5.5 6.5 5.5 5.9 5.5 5.5 5.5 6.1 B. 0.015 0.020 0.014 0.010 - - - - Zr 0.05 0.10 0.06 0.10 - - - - Ta 1.5 2.0 - - - - 1.5 - Hf 2.5 2.5 2.5 1.5 1.5 3.3 4.5 1.5 Ni rest rest rest rest Remainder ⁺ ) Rest + » Remainder ⁺ > Remainder +> Nb - 1.0 - 2.0 - - - 2.0 V 1.0

¹ contains small common amounts of boron and zirconium

The following table II shows the results of Tests carried out with turbine wheels cast from a known alloy F of the following composition

Carbon about 0.05%

Chromium about 12 %

Molybdenum about 4.5%

Titanium about 0.6%

Aluminum about 5.9%

Niobium about 2%

Boron about 0.010%

Zirconium about 0.1%

nickel

rest

and an alloy 4, el. h. one according to the invention modified cast alloy which contained 1.5% hafnium instead of an equivalent amount of nickel Samples related to tensile strength wedge properties were carried out at room temperature.

60

Table II

alloy

65 F
(cast)

IF

at RT
(N / mm ² )

on
at RT

(N / mm ² )

807.5

702.1

continuation

alloy

if

at RT
(N / mm ² )

"02

at RT

(N / mm ² )

4th 842.5 722.1 12th (cast) F. 800.4 716.1 2.0 (heat treated) 4th 842.5 702.1 12th (heat fog)

During the heat treatment, the cast samples were kept at 982 ° C. for 4 hours.

From Table II it can be clearly seen that the addition of hafnium to alloy F significantly improves ductility. It can also be seen from the data in Table III that the alloy modified according to the invention has a lower sensitivity to the adverse effects of a heat treatment which is often required in the production of corrosion coatings on moldings made from this alloy.

The modified by the process of the invention Nickel-based cast alloys are under very high even when exposed to very high temperatures Stress extremely resistant to loss of impact strength. It is known that in certain of hafnium-free alloys of the type in question in the context of the invention at about SPhour Heating to temperatures of about 1093 ° C without exposure to stress is a significant loss strength occurs at room temperature.

Values are given in Table III below. with the loss of strength properties Show reference to alloy A described in the main patent and the great improvement of the alloy A after modification according to the method of the invention by replacing 2.5 "» molybdenum with a Illustrate the equivalent amount of hafnium.

Table III

Alloy impact strength in mkg of sample X ⁺⁾ impact strength in mkg of sample Y ^{+ + l}

poured after 50 hours poured after 50 hours

at 1093 ⁰ C at 1 093 ⁰ C

A with Hf

4.14- 6.9
11.05-14.1

2.76-4.14
12.7

1.8-2.07
3.86-4.97

0.69

5.10-5.52

⁺⁾ The sample X was an unnotched Charpy round notch sample, which consists of a rod with a

Cross section of 0.993 cm ² .
* 'Sample Y was an unnotched Charpy round notch sample made from a round rod

with a diameter of 0.713 cm existed.

From Table III it can be seen that according to the procedure The alloy modified according to the invention, which contained hafnium, not only had a significantly higher initial impact strength than the comparison alloy, but that even when heated to high temperatures (e.g. 50 hours at 1093 "C) no noticeable reduction the impact resistance occurred

The values shown in Table III make it clear that the method according to the invention can also be applied to nickel-based alloys with a hardened '/' phase which contain molybdenum. Heretofore, molybdenum has been found to be an effective alloying element in alloys suitable for use in hot stage gas turbines. However, as engine temperatures and alloy content increase on both forged and cast alloys, operating temperatures approach temperatures at which certain harmful carbides and other phases can form in the alloy. It is assumed that the replacement of molybdenum by hafnium prevents the formation of these harmful phases during operation. It is clear from the values in Table IV that the replacement of molybdenum by hafnium has a far greater effect! rather than merely eliminating the drawbacks inherent in molybdenum-containing alloys, it can be seen that the room temperature strength properties of the hafnium-containing cast alloy are considerably higher than the impact strength of alloy A, thereby providing a significant technical advance.
The mkg values reported in Table IH for the alloy modified by the addition of hafnium in accordance with the process of the invention are essentially the same as those measured for some alloys originally used for aircraft gas turbine engines during development in the UK

so was used in the late thirties and early forties. This British alloys had a temperature performance (temperature, occurs when at a stress of 1.406 N / mm ^J within 1000 hours Eruch) of not more than about '! S3 ^o C. The alloy A and by the method according to the invention Alloy A modified by the addition of hafnium have one thing! Temperature output of about 971 ° C.
The fact that it is possible. with alloys which can be up to 97TC used to generate the same resistance to sudden forces, as it is known for alloys that can only be used up to 788 ° C, is ki \ the manufacture of gas turbine engines of utmost practical importance .

Further alloys obtainable in accordance with the present invention are given in Table IV below.

Table IV

continuation

alloy

0.10 0.13 0.10 9.0 ° .O 9.0 10.0 10.0 10.0 12.2 11.5 11.8 2.0 2.0 2.0 5.0 5.0 5.0 0.01 0.01 0.01 0.05 0.05 0.05 1.6 1.1 2.3 rest rest rest 1.0 1.1 1.0

Table V below shows a comparison of the alloys of the examples'). 10 and Il with an alloy of identical composition, but containing only 0.6% hafnium, shows that it's all important is to keep the hafnium content at around 0.7 to 0.8%, in order in alloys that did not exceed 5% previously molten and cast alloy included to achieve the desired improvements. The comparison Table V is shown versus samples which have been subjected to aging in an identical manner at about S45 C have been heat treated.

Table V

at % Hf Creep test load game (nom.) at 760 ° C 631.9 N / mm ² No. Time to creep δ (%) RA Fraction amount * ¹ Ή) - ¹ --- · (Hours.)

Hey ". '., IΪΓ / eitslandversuch Uelastuiig game (nom.) at 7 °) ° C 631. ') N / mm ² Nd. Time to creep Λ (Μ K.Λ. Itruch amount " (Hours.)

1.1
1.6
2.3

407.8 1.5
467.1 2.0
448.1 3.02

1.5
3.0
3.5

4.2 6.4 6.8

Comparative
lay

0.6

79.1

n.m.

n.m. *

n.m.

* 'Creep amount shows the creep within 2 hours fracture

** ■ 'nm = not measurable
* ** 'percentage reduction in curses

Ans tier vnrsl'hrmlftn T: ihcll? V isl orsi '.' St. Küch. '.!;! Ü

an alloy that is essentially a modification of alloy C of the main paient and 0, V \, Contains hafnium, when testing the resistance behavior at 760 C, whereby the disadvantages are emphasized should not exhibit satisfactory behavior in terms of time to / around breakage and the amount of creep. Table VT also shows that with an addition of 1.1 "., Hafnium, a noticeable improvement the l.egierur ^ occurs and with increasing hafnium content up to 2 "., gradually increasing. The values shown in Table VI support the teaching that the addition of at least 0.7% hafnium is required in order to achieve a considerable improvement in the alloys with no more than 5 ".- of previously melted and cast alloy.

In some cases it may be useful at least about 1.0%, e.g. B. about 1.5%, hafnium in the alloys to be introduced with no more than 5% of previously melted and cast alloy. However, there is llafnium is a relatively expensive item and in practice the aim is to give the best possible results At the lowest possible cost, the lower limit for the addition of hafnium to alloys became with no more than 5% previously melted and cast alloy set at 0.70% to the To take into account the fact to achieve the results according to the invention at the lowest possible cost can.

Claims (4)

Patent claims: 1. Process for increasing the ductility at temperatures in the range from 704 to 871 ° C. of cast alloys nickel-based, which are melted from a batch with no more than 50% return scrap, in which the y'-phase is present as the basic phase in the crystalline matrix and those for use under stress at temperatures up to 1038 ° C i; o are suitable, consisting of 0.02 to 0.20% carbon, 7 to 13% chromium, up to 8% molybdenum, up to 6% tantalum, up to 14% tungsten, up to 35% cobalt, 4 to 7% aluminum, 0.5 to 6% titanium, up to 3% niobium, up to 1.5% vanadium. 0.002 to 0.02% boron, 0.01 to 0.20% zirconium, over 5 The remainder at least 36% nickel and up to 2% of production-related customary impurities, with the 0.5 to 4% hafnium is added to the molten charge after deoxidation, according to patent 19 21 359, with the proviso that 0.7 to 5% hafnium is tensile; » and that they will be treated according to the procedure Alloy up to 04% carbon. Aluminum + Titanium from 6.5 to 10.5%, tantalum + chromium up to 16%, tungsten + tantalum, if both are present, up to Contains 13%, and the hardenability factor (HF). which results from the formula: HF = 1 χ% Cr + 1.1 χ% (W + Mo) + 3.4 χ% (Nb + Ta) + 4.3 χ% Ti + 6 χ% AI calculated, is within the range of 60 to 72. 2. The method according to claim 1, with the proviso : » that 1 to 5% hafnium is added to the alloy to be treated. 3. The method according to claim 1, with the proviso that the treated alloy is a maximum of 20% cobalt contains. -B 4. Use of the casting alloys produced by the process according to Claims 1 to 3 for the production of gas turbine parts.