DE1191587B - Heat treatment of nickel-chromium alloys - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C22f

German class: 4Od-1/10

Number: 1191587

File number: J 21302 VI a / 40 b

Filing date: February 15, 1962

Opening day: April 22, 1965

The invention relates to the heat treatment of nickel-chromium alloys, the titanium and / or aluminum and can be age-hardened.

Mainly two types of heat treatments have been known so far. Both served the purpose of achieving the highest possible separation resistance under long-term tensile stress and high temperature. A heat treatment that is often used for this purpose and is described, for example, in German Patent 836 570, consists in annealing the alloy at such a temperature and for so long that an essentially homogeneous solid solution is formed (so-called solution annealing). This is followed by aging at a sufficiently low temperature so that a coherent, extremely finely distributed precipitation of a Ni ₃ (Ti, Al) phase is formed. In general, this requires the use of an aging temperature in the range from 600 to 850 ^° C.

Another type of heat treatment is applied to carbonaceous alloys. It is based on the finding that the controlled precipitation of carbides at the grain boundaries of the alloy is of great importance for a high separation resistance. In this treatment, an intermediate annealing is inserted between the solution annealing and the aging, in which no significant precipitation of a hardening phase takes place. The intermediate annealing takes place at a temperature which is between the temperature of the solution heat treatment and that of aging. The carbide precipitation at the grain boundaries takes place during the intermediate annealing and the precipitation of the coherent Ni ₃ (Ti, Al) phase occurs almost entirely during aging. In this three-stage and also in two-stage heat treatment, the aging is carried out in a temperature range of 600 or 650 and 850 ⁰ C. Such three-stage heat treatments are described in British Patent 715 140 and in German Auslegeschrift 1,133,566. In general, they are particularly useful when they are applied to alloys whose total titanium and aluminum content is less than 6%.

In contrast, the invention is concerned with alloys, their total content of titanium and aluminum is greater than 8%> but not more than 9.5%. They contain 14.2 to 15.8% chromium, 14 to 25% cobalt, 3 to 5.5% molybdenum, 3 to 4.6% titanium, 4 to 5.4% aluminum, 0.01 to 0.2% carbon, 0.01 to 0.2% Zirconium, 0.003 to 0.1% boron, the remainder nickel in addition to impurities. The as impurities before heat treatment of nickel-chromium alloys

Applicant:

The International Nickel Company (moon)

Limited, London

Representative:

Dr.-Ing. G. Eichenberg

and Dipl.-Ing. H. Sauerland, patent attorneys,

Düsseldorf 10, Cecilienallee 76

Named as inventor:

Harold William George Hignett,

Southfields, Hereford;

Ernest James Bradbury, Solihull, Warwickshire; Ronald Alfred Smith, West Hagley, Worcester;

David Marshall Ward,

Edgbaston, Birmingham (Great Britain)

Claimed priority:
Great Britain dated February 17, 1961 (5982),
dated March 15, 1961 (9514)

lying proportions of silicon, manganese and iron should be as low as possible. The silicon and the The manganese content of the alloy should not exceed 0.5% and the iron content 1%.

It has been found that the alloys have the composition above for a solution heat treatment and annealing to precipitate the carbides on the grain boundaries of a low impact resistance at high temperatures, for example at 900 ⁰ C. However, high impact strength at high temperatures is of considerable importance if the alloys are to be used for the production of turbine blades in gas turbine engines. There is a risk here that the blade will come into contact with the turbine housing or with foreign bodies. Increased impact resistance is therefore of great advantage.

The invention is based on the knowledge that by precipitating sufficient amounts of a Ni ₃ (Ti, Al) phase at the grain boundaries, the impact

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strength can be increased significantly. According to the invention, this is achieved in that the alloy is annealed again after the solution _{heat treatment, namely in a narrow and critical temperature range immediately below the solution temperature of the Ni 3} (Ti, Al) phase. It is assumed that the Ni ₃ (Ti, Al) precipitates formed in the process contain substantial proportions of the carbon in the alloy in dissolved form, so that harmful deposition is avoided. Further proportions of the Ni ₃ (Ti, Al) phase are precipitated in coherent form in the interior of the grain when it cools to lower temperatures. However, this happens at such a rate of precipitation that prolonged aging in the temperature range from 600 to 850 ° C. does not result in any useful effect in these alloys.

According to the invention, an alloy of the above-mentioned composition is first subjected to a solution heat treatment, which consists in ^{leaving the ao alloy for at least 1} hour at a temperature above the solution temperature of the Ni, CTi, Al) phase but below the solidus temperature of the alloy is annealed. The alloy is then isothermally annealed for at least a further V ₄ hour at a ^{temperature of at most 50 °} C. below the solution temperature of the Ni ₈ (Ti, Al) phase and at least 1075 ^{° C.}

At temperatures very close to the solution temperature, the rate of precipitation of the Ni ₃ (Ti, Al) phase is very low, so that the isothermal annealing temperature is expediently at least 10 or even 25 ° C. below the solution temperature.

For alloys with 14.2 to 15.8% chromium, 14 to 16% cobalt, 3 to 4.5% molybdenum, 3 to 4.1% titanium, 4 to 5.1% aluminum, 0.01 to 0.2 % Carbon, 0.02 to 0.1% zirconium, 0.003 to 0.1% boron, the remainder nickel in addition to impurities and a total content of titanium and aluminum of more than 8% ^{or a} maximum of 9.2% Temperature from 1100 to 1125 ⁰ C used.

In order to avoid melting, the temperature of the solution heat treatment must of course not exceed the Solidus temperature of the alloy lie. In practice this is the temperature and the time required for the solution heat treatment limited by the condition that excessive grain growth is to be avoided. Even the condition of the material should be taken into account and, for example, whether the material has previously been processed hot or cold. Preferably the solution heat treatment should not be longer than Take 4 hours. The duration of the isothermal glow is largely due to practical considerations determined and will usually not exceed 24 hours. A useful glow time is between 1 and 10 hours.

The impact resistance of heat-treated alloys tends to be lower if the alloys are heated strongly during operation, as is the case with aircraft engines, for example. For verification tests these critical conditions can be simulated by the fact that the alloys are annealed at 980 ⁰ C for 16 hours. It has been found that the tendency to drop impact resistance can be reduced if it is ensured that the alloys from the solution annealing temperature cannot cool below the allowable range of isothermal annealing before the latter anneal is complete. Therefore, the alloy from the furnace used for solution annealing is immediately and quickly transferred to another furnace used for isothermal annealing. In practice, such a fast transport is often associated with difficulties. In this case, air cooling, optionally down to room temperature, is expedient. As an example, impact specimens of alloy A with the composition

C = 0.15%, Si = 0.25%, Fe = 0.4%, Cr = 15%, Ti = 3.9 · / ο, Al = 4.7ο / * Co = 15%, Mo = 3 , 5%, B = 0.01%, Zr = 0.05%> balance nickel

which has a solution temperature of 114O ⁰ C, subjected to various heat treatments. Thereafter, the impact strength (impact resistance) was determined at 900 ⁰ C the alloy. The results are compiled in the table below. The notched impact strengths mentioned in the third column are values which were determined immediately after the air cooling following the isothermal annealing, while the values in the fourth column were determined after air cooling and renewed heating to 980 ^° C. for 16 hours.

Tabel ; I. Additionally 980 ° C / 16 hours
the No. Heat treatment Notched impact strength (kgm) 0.27 1 1190 ° C / l, 5 hours WdIiIlC ^-
treated LK; 0.27 1050 ° C / 6 hours; 0.31 LK 2 1190 ° C / l, 5 hours LK; 1.16 1075 ° C / 6 hours; 0.61 LK 3 1190 ° C / 1.5 hours LK; 2.32 1100 ° C / 6 hours; 0.51 LK 4th 1190 ° C / 1.5 hours LK; 2.32 1125 ° C / 6 hours; 0.9 LK 5 1190 ° C / l, 5 hours DT in 2.13 1100 ° C / 6 hours; 0.83 LK 6th 1190 ° C / l, 5 hours DT in 2.02 1125 ° C / 6 hours; LK

LK = air cooling
DT = direct transport

Samples Nos. 3 to 6 according to the invention have good notched impact strength after the heat treatment on. In the heat treatments of the

Sample Nos. 1 and 2, on the other hand, the isothermal annealing temperatures were too low so that the Samples have significantly poorer impact properties.

A comparison of the heat treatments under Nos. 3 and 4 with those under Nos. 5 and 6 shows that an immediate and quick transport of the samples from the furnace for solution treatment to the furnace for the isothermal annealing a smaller decrease in the notched impact strength after heating to operating temperature has the consequence.

According to a further feature of the invention, a further improvement in this regard can be obtained in that the alloy, starting from the temperature of the isothermal annealing, is cooled to a temperature in the range from 950 to 1050 ° C. and is kept at this temperature for at least V ₄ hours . The temperature of this second isothermal annealing should be at least as high as the expected operating temperature and preferably be 1025 ° C. Before this annealing is complete, the temperature of the alloy must not drop below the permissible range for the second isothermal annealing. Here, too, the alloy is transported between the two furnaces that are used for the two-stage isothermal annealing, preferably quickly and immediately.

As an example, impact specimens of two alloys A and B were given two different heat treatments subjected. Alloy A had the composition already described, while ίο the alloy B was composed as follows:

C = 0.14%, Si = <0.15 »/ ο, Fe = 0.24%,
Cr = 14.6%, Ti = 3.9%, Al = 5%,
Co = 14.6%, Mo = 3.5%, B = 0.016%,

Zr = 0.035%,
Remainder nickel (solution temperature 1140 ° C).

The impact properties were determined; the results are in Table II below compiled:

Table II

alloy Heat treatment Notched impact strength (kgm) Additionally No. 980 ° C / heat treated 16 hours A. 1190 ° C / l, 5 hours 7th DTinll 25 ° C / l hour DT in 1050 ° C / 0.5 hours 1.0 A. 1190 ° C / l, 5 hours 1.72 8th DT in 1125 ° C / 0.25 hours DT in 1050 ° C / 0.5 hours 1.1 B. 1190 ° C / l, 5 hours 1.93 9 DTinll 25 ° C / 6 hours 0.76 B. 1190 ° C / l, 5 hours 1.67 10 DT in 1125 ° C / l hour DT in 1050 ° C / O, 5 hours 0.97 B. 1190 ° C / 2.5 hours 1.73 11 DT in 1125 ° C / l hour DT in 1025 ° C / 0.5 hours 1.25 B. 1190 ° C / 2.5 hours 1.8 12th LK; 1125 ° C / 1 hour DT in 1025 ° C / 0.5 hours 0.7 B. 1090 ° C / 2.5 hours 1.95 13th DT in 1125 ° C / l hour DT in 1000 ° C / 0.5 hours 1.38 B. 1190 ° C / 2.5 hours 1.67 14th DT in 1125 ° C / l hour DT in 950 ° C / 0.5 hours 1.1 B. 1190 ° C / 2.5 hours 1.67 15th DT in 1125 ° C / l hour DT in 900 ° C / 0.5 hours 0.7 B. 1190 ° C / 2.5 hours 1.67 16 DT in 1125 ° C / l hour DT in 850 ° C / 0.5 hours 0.62 B. 1190 ° C / l, 5 hours 1.73 17th DTin 100 ° C / 3 hours DTinl025 ° C / 3 hours 1.67 1.8

LK = air cooling
DT = direct transport

A comparison of the result of heat treatment No. 7 and 8 with the heat treatment according to No. 6 Table I shows the improvement in impact strength after intense heating. She's on that second isothermal annealing treatment. A similar improvement is when comparing the Heat treatments No. 10, 11, 13 and 14 can be found with No. 9. Heat treatments No. 11 and 13 to 16 show how the notched impact strength decreases progressively when the temperature increases after intense heating the second isothermal annealing is reduced. Heat treatments Nos. 15 and 16 have no improvement over heat treatment # 9. From the results of the heat treatment No. 12 it can be seen that a second isothermal annealing then does not produce any significant improvement, when the alloy is cooled in air before the first isothermal anneal.

Claims (5)

Claims: ao 1. Process for the heat treatment of an alloy of 14.2 to 15.8% chromium, 14 to 25% cobalt, 3 to 5.5% molybdenum, 3 to 4.6% titanium, 4 to 5.4% aluminum, 0, 01 to 0.2% carbon, 0.01 to 0.2% zirconium, 0.003 to 0.1% boron, the remainder nickel in addition to impurities in which the sum of the titanium and aluminum content is higher than 8% but a maximum of 9.5 % is by solution annealing, intermediate annealing and aging annealing, characterized in that the alloy is at least V for ₄ hours 30 a temperature above the solution temperature of the Ni ₃ (Ti, Al) phase but below the solidus temperature of the alloy is annealed and the alloy is then annealed for at least another V ₄ hours at a maximum of 50 ° C below the solution temperature of the Ni ₃ (Ti, Al) phase is isothermally annealed at a temperature of at least 1075 ° C. 2. The method according to claim 1, applied to an alloy with 14.2 to 15.8% chromium, 14 to 16% cobalt, 3 to 4.5% molybdenum, 3 to 4.1% titanium, 4 to 5.1% aluminum, 0.01 to 0.2% carbon, 0.02 to 0.1% zirconium, 0.003 to 0.1% B ° ^r > ^remainder nickel in addition to impurities in which the sum of the titanium and aluminum content is higher than 8% but is at most 9.2%, characterized in that the isothermal annealing is carried out at 1100 to 1125 ° C. 3. The method according to claim 1 or 2, characterized in that the alloy from which the First annealing furnace directly and quickly into the furnace provided for isothermal annealing Oven is brought. 4. The method according to claim 3, characterized in that the alloy is cooled from the temperature of the isothermal annealing to a temperature between 950 and 1050 ° C and is held for at least V ₄ hours. 5. The method according to claim 2, characterized in that the alloy between the first Annealing and isothermal annealing is air-cooled. 509 540/300 4.65 © Bundesdruckerei Berlin