DE1922314A1 - Process for tempering alloys - Google Patents

Description

Dr. rer. near Horst Schuler PATENT ADVOCATE

6Frankfurt / Main 1, 30. April 1969 Niddastraße 52

Telephone (0611) 237220 Postscheck-Account: 282420 Frankfurt / M.

Bank account: 523/3168 Deutsche Bank AG, Frankfurt / M.

1043-17LL-1732

GENERAL ELECTRIC COMPANY

1 River Road Schenectady, N.Y./U.S.A.

Process for tempering alloys

The invention relates to a method for tempering alloys, and in particular the tempering of oxidation and Corrosion-resistant high-temperature nickel-based alloys, which increase their breaking strength under load and high temperatures is significantly improved.

909886/0964

19223U

The use of nickel-based alloys in equipment such as gas turbines that operate at elevated temperatures work is well known. Above all, these materials are designed to withstand extreme stresses, as well as the oxidation, sulphidation and other attacks to which their surface is exposed at elevated temperatures withstand long.

The efforts that have been made to manufacture these alloys have resulted in materials which are eminently suitable for use in corrosive environments, such as those produced in a gas turbine, and which also have a relatively long service life under such conditions before they are used fail as a result of mechanical stress. However, there is a need for machines such as gas turbines, for example, which can be operated at even higher temperatures and for longer periods of time, since such characteristics increase the efficiency and economy of a plant. For example, an increase in operating temperature is a gas turbine of about 815 ⁰ C (1500 ⁰ F) to about 871 ° C (1600 ⁰ F) to increase the power by about 14% and an increase in efficiency of about 1 to 5%. It is also advantageous if a machine can be operated for 40,000 hours instead of 20,000 hours.

From this it is immediately apparent that it is desirable that the alloys used in gas turbines be made with work at high temperatures, can withstand mechanical stress over long periods of time. The invention The main task is therefore the production of such alloys based on nickel of the type described above, which not only withstand surface destruction at elevated temperatures, but also continue to withstand such Temperatures are also characterized by a significantly improved service life under the elongation at break conditions they encounter at Operation.

909886/0964

This object is inventively achieved in that the alloys described are annealed nickel-based in that they over a period of 2 to 8 hours at about 1148 to 12O4 ° C (2100 - 22oo ° F), preferably about 4 hours to about 1162 ⁰ Heated to about 1079 ° C (1975 ° F) and then cooled rapidly, then about 12 to 48 hours, preferably about 24 hours heated to about 926 ° C (1700 ° F) and then rapidly cooled and finally heated to about 760 ° C (1400 ° F) for about 8 to 25 hours, preferably 16 hours, followed by rapid cooling. It has been found that this tempering leads to a significant increase in the hot fracture life without affecting the other properties of the alloy such as its resistance to surface deterioration, its hot yield strength, its ductility, as it is represented by expansion and reduction in area, etc. to be worsened.

Nickel-based alloys that are particularly suitable for the new heat treatment include those below in Table I listed alloys.

It has been found that the heat treatment of the invention is similar, although in some respects of the usual heat treatment is that it but differs therefrom in particular by the heat treatment at about 926 ⁰ C (1700 ° F), the detected to the, in the hardened and tempered material , improved mechanical properties. These alloys, their compositions and properties are described in various publications, for example in the Journal of Metals , October 1966, pp. 1119-1130.

In accordance with the present invention, the alloy is first heated at about 1148-1232 ° C (2100-225O ° F) for a period of about 2 to 8 hours, preferably at 5162 ° C (2125 ° F) for one

909886 / 096Λ

Table I.

co ο co

Composition (wt. %)

Alloy Ni Co Cr Al Ti Mo

A remainder 15.0 14.6 4.3 3.35 specific

B Zr C
0.016 0.04 0.07

Max.

Heat treatment according to
Stand d. technology
3. 1132 ° C (2125 ° F)

Range * ¹ ^ remainder

2.00 4.00 3.00 3.90

B specific

15.75 15.25 4.60 3.70 4.50 remainder 18.5 15.0 4.3 3.5

area

(2)

Remainder 14.00 13.00 3.75 2.75 4.50 20.00 17.00 5.00 4.00 6.00 2 h, obfl. Abbr.
to 1079 ° C (1975 ° F) 2
with 37 ° C (100 ° F)
each h; Cool down on 3rd
Air to room temperature 4
76O ° C (1400 ° F) 16 h,
Cool down to room temperature

Heat treatment according to invent. (preferred) 1. 1170 ° C (2125 ° F) 4 h; quick abbr.

1086 ⁰ C (1975 ° F) for 4 hours; rapid Abbr. 932 ° C (1700 ° F)

0.012 0.04 0.05 0.020 max.0.09

0.010 0.04 0.10 1.

max. 2.

0.01 0.15

0.05 max.

1176 ° C (2150 ° F), 4h ,. Lx
1079 ° C (1975 ° F), 4h, ^M
843 ⁰ C (1550 ° F), 24h, "
1400 ° F (76O ° C), 15h, "

24 hours; quick abbr. As 764 ° C (1400 ° F) above 16 h; quick abbr. f I. ftk.

(D (2)

Also 0.15 max Mn; 0.015 max P; 0.15 max S; 0.20 max Si; 0.50 max Fe; 0.10 max Cu; Also 4.0 max. Fe.

19223H

Subjected period of about ¹ J hours to a heat treatment and then cooled down to room temperature, preferably rapidly. This was done, for example, by means of a gas, such as by introducing cold inert gas into the furnace, or by bringing the alloy into the fresh air. The purpose of this stage of heat treatment is to homogenize the alloy, temperatures above about 1232 ° C (225O ° P) would cause the alloy to begin to melt which would defeat the purpose of this heat treatment stage. During this treatment, the phase that is primarily responsible for the strength becomes k '», [Ji ₃ (Al ₅ Ti)] and the M ^ Cg carbides (M = metal atom such as chromium or molybdenum, so that M ₃₃ Cg often the composition Cr ₂₁ Mo ₂ Cg) is brought into solution, so that only the alloy matrix y and the MC carbides (which often have a composition such as (Ti, Mo) C) remain as such. A temperature of at least 11 * 19 C (2100 P) must be used, since at lower temperatures certain phases tend to separate out in an uncontrollable manner and, as already stated above, temperatures above about 1232 C (2250 ⁰ P) cause the alloy to begin to melt. Aging times of less than 2 hours do not lead to expectation that everything will go into solution, and an aging time of more than about 8 hours at 162 ° C (2125 ° P) would be uneconomical. After this treatment, the alloy is rapidly cooled as described above.

In the second stage, the alloy is for two to eight hours, preferably about four hours, at a temperature of held about 1079 ° C (1975 ° P). The task of this treatment is to start the separation of the # 'amplification phase, which is generally present as a finely divided deposit in the form of particles. The beginning of the deposition at this one After subsequent aging, temperature leads to the formation of if '' particles of optimal size, which leads to the achievement of a maximum Solidification contributes. A treatment of less than about 2 hours within this temperature range has an un-

809886/0964

192231A

sufficient deposition result, while a treatment of more than about 8 hours is unnecessary and uneconomical were. At the end of this treatment, the alloy is quenched again in the manner described above.

The third stage of the inventive remuneration is critical; The essence of the present invention lies in it and, as such, it deviates most from the remuneration methods customary up to now. At this stage, especially those excreted in the manner described above grow / * -

approximately ο particles, to a size for maximum solidification / optimal size. Furthermore, it is of great importance that this treatment also _{precipitates the M 23} Cg carbides at the grain boundaries through a reaction in the solid state, which probably corresponds to the following equation:

_MC + y _ _{M c} + yi

As already stated above, the M ₂₃ Cg compound precipitates in the form of discrete carbide particles which are optimally sized at the grain boundaries, which reinforce these boundaries, block them off or hold them in place and thereby prevent or delay undesired sliding. An important part of this heat treatment probably lies in the fact that the l · "-degradation product forms a continuous shell around the M ₂₃ Cg carbides precipitated at the grain boundaries. This coating or coating of the M ₂₃ Cg particles by / ^% prevents this Subsequent deposition of harmful M ₂₃ Cg nuclei at the grain boundaries during use of the alloy, which, according to past experience, can lead to failure of parts during operation. This coating also acts as a strong, ductile deposit that prevents the alloy from breaking Although the above-described reaction can occur even if the alloy is exposed to this temperature range during use of the alloy, the nature of the present heat treatment is that it eliminates this reaction prior to application of the

909886/0964

Alloy leads to the end, so that the alloy is in the safest and most stable condition possible from the start. A similar Effect can be achieved by using shorter reaction times, down to about 12 to 16 hours; longer response times from 36 to 48 hours are possible; but they would be uneconomical. Response times of 24 hours seem on the other hand to be optimal.

In the fourth and final stage of the inventive tempering, which in turn was already in use for alloys of the present type, the alloy is heated to 760 ° C (1400 ° F) for 16 hours and quenched as above. This final treatment leads to a further deposition of the jf * phase and can also _{bring a small additional amount of M 00} C- out of the solution. In general, it appears to have the effect of stabilizing the alloy as a whole. Optionally, the treatment time can be varied between about 8 to 24 hours.

In Table II below are the breaking load times of various numbered lots of the specific above Alloy A listed, which were subjected to the specified temperatures and loads. These alloys are one Temper as indicated in Table I for Alloy A, with the time and temperature the treatment were chosen as they are mentioned in the table as preferred. The improvement is expressed as the ratio of the Breaking load time after the new remuneration compared to that indicated, which was achieved through the previously usual remuneration.

909886/0964

TABLE II

Batch

Temp./load

(° F / Ksi)

(° C / kg / cm ² ) service life
(Stde.)

Improvement compared to the usual remuneration (-subject)

1900/3 1037/210 3745 1800/6 982/420 7264 1700/16 926/1120 3475 1600/20 870/1400 11774 1900/5 1037/350 2466 1850/15 1010/1050 101 1600/30 870/2100 1455 1850/15 1O10 / 1050 105 1800/10 982/700 1159 1750/15 954/150 752 1850/8 1O10 / 560 1773 1750/14 954/980 1486 1850/15 IC 10/150 99 1750/25 954/1750 90

4.6 2.9 2.5 2.3

4.1 2.0 2.6

2.1 1.9

1.7

4.4 2.2

2.0 2.2

From the above values it can be seen that the inventive Compensation compared to the prior art brings a very large advance, since the service life, as the table shows is increased by 1.7 to 4.6 times.

909886/0964

Claims (6)

1. A method for tempering a nickel-based alloy, the essential main components, expressed in percent by weight, about 14 to 20% cobalt, about 13 to 17% chromium, about 3 to 5 % aluminum, about 2.5 to 4 % titanium, about Contains 3.5 to 6 % molybdenum, about 0.01 to 0.05% boron, at most about 0.04 % zirconium, about 0.03 to 0.15 % carbon and the remainder nickel, characterized in that the alloy 1. Ge for about two to eight hours at about 1148 to 1204 C hold and then cooled down quickly, about two to eight hours ι quickly cooled down afterwards, about 12 to 48 hours on < Cooled down quickly and finally 2. held at about 1079 ° C for about two to eight hours and 3. held at about 926 ° C for about 12 to 48 hours and then 4. Maintained at about 760 ° C. for about 8 to 25 hours and then rapidly cooled. 2. The method according to claim 1, characterized in that the compensation time 1. at about 1148 to 1204 ⁰ C for about 4 hours, 2. at about 1079 ⁰ C for about 4 hours, 3. at about 926 ^° C. for about 24 hours and 4. is about 16 hours at about 760 ° C. 3. The method according to claims 1 or 2, characterized in that the alloy as essential main components, expressed in percent by weight, about 14.25 to 15.75% cobalt, about 14.0 to 15.52% chromium, about 4.00 to 4.60% aluminum, about 3.00 to 3.70% titanium, about 3.90 to 4.50 % molybdenum, about 0.012 to 0.020 % boron, at most about 0.04% zirconium, about 0 .05 to 0.09% carbon and as The remainder contains nickel. 909886/0964 19223H 4. The method according to claims 1 or 2, characterized PE indicates that the lep-ation expressed as the essential main constituents in percent by weight, about 15.0 % cobalt, about 14.6 % chromium, about 3 /4% aluminum, about 3.35 % titanium, about 2.5 % molybdenum, about O ₅ OL6% boron, no greater than about _0: contains 04% zirconium, about 0.07% carbon and the balance nickel. 5. The method according to claim 4, characterized in that that the Lep-ierunp- 1. Maintained at about 1162 ° C for about 4 hours and then cooled down quickly, 2. held for about ^ hours at about 1079 ° C and then rapidly cooled, 3. Maintained at about 926 ° C for about 2k hours and then rapidly cooled and k. is held for about 16 hours at about 760 ° C and then rapidly cooled. 6. Process according to claims 1 to 5, characterized in that in each case down to room temperature is rapidly cooled. 909886/0964