WO1997032052A1

WO1997032052A1 - Method for heat treating a nickel superalloy

Info

Publication number: WO1997032052A1
Application number: PCT/FR1997/000344
Authority: WO
Inventors: Yves Philippe Marc Desvallees; Jean-Michel Patrick Maurice Franchet; Michel Marty; Henri Octor; Françoise Passilly; Michèle Soucail
Original assignee: Societe Nationale D'etude Et De Construction De Moteurs D'aviation 'snecma'
Priority date: 1996-02-29
Filing date: 1997-02-27
Publication date: 1997-09-04
Also published as: RU2133784C1; FR2745588A1; FR2745588B1; DE69700059T2; EP0792945A1; EP0792945B1; JP3926877B2; JPH1025557A; DE69700059D1

Abstract

A method for heat treating nickel superalloy forgings containing 11-13 wt % of Cr, 8-17 wt % of Co, 6-8 wt % of Mo, 4-5 wt % of Ti, 4-5 wt % of Al, no more than 0.5 wt % of Nb, and no more than 500 ppm of Hf, the balance to 100 wt % being Ni, is disclosed. According to the method, an intermediate heat treatment is carried out at a temperature between the η' solvus minus 95 °C and the η' solvus minus 30 °C, following hot forging at a temperature between the η' solvus minus 95 °C and the η' solvus minus 45 °C, with a strain rate of 5.10-5s-1 to 2.10-2s-1, and a deformation ratio higher than 0.1, and prior to a supersolvus heat treatment at a temperature between the η' solvus plus 5 °C and the η' solvus plus 25 °C for 1 to 4 hours.

Description

DESCRIPTION METHOD OF HEAT TREATMENT OF A SUPERALLOY BASED ON

NICKEL

The present invention relates to a process for heat treatment of a nickel-based superalloy whose chemical composition in weight percentages is in accordance with either EP-B-0 237 378 and belongs to the following field: Cr 11 to 13; Co 8 to 17; Mo 6 to 8; Nb less than or equal to 1.5; Ti 4 to 5; Al 4 to 5; Hf less than or equal to 1; C, B, Zr each less than or equal to 500 ppm; Neither complement to 100, ie at the request FR 95.09653 and belongs to the following domain: Cr 12 to 15; Co 14.5 to 15.5; Mo 2 to 4.5; W O to 4.5; Al 2.5-4; Ti 4 to 6; Hf less than or equal to 0.5; C 100 to 300 ppm; B 100 to 500 PPm; Zr 200 to 700 ppm; No complement to 100.

These alloys are used in particular for the manufacture of highly stressed parts intended for aircraft engines, for example rotor disks. In a manner known per se, parts of this type can in particular be produced using processing techniques from powders and their shaping calls for forging operations. The heat treatments applied to the parts before use commonly comprise a solution and quenching treatment followed by an aging treatment.

The invention applies in particular in cases where a supersolvus heat treatment is carried out comprising a complete dissolution of the gamma-prime precipitates at a temperature between + 5 ° C and + 25 ° C above the solvent temperature gamma-prime for a hold time of between 1 hour and 4 hours.

These treatments indeed allow an optimization of the microstructure of the alloys towards coarse-grained structures whose favorable influence has been demonstrated on the creep behavior and in propagation of cracks at high temperatures. necessitated by the search for improvement in aircraft engine performance.

The final grain size depends on a succession of industrial stages which are: the possible pretreatment of the powders, densification by spinning, isothermal forging, the final heat treatment. In addition, the metallurgical and thermomechanical parameters that can influence recrystallization are numerous and interdependent. These include: gamma-prime phase precipitation, oxycarbon distribution, strain rate, strain rate, stress, time, temperature.

The grain enlargement phenomenon caused by the heat treatment mentioned above can correspond to the following scheme: the gamma-prime precipitates which before the supersolvus heat treatment blocked the grain boundaries dissolve and the grain boundaries, released, migrate then are generally once again anchored by very fine precipitates, the oxycarbons, preferentially located at the old powder boundaries. The result sought in this case is to obtain grains of homogeneous size, in particular of 50 μm on average, corresponding to a so-called normal grain growth.

However, a so-called abnormal grain magnification leading to the growth of one or more very large grains of several hundred micrometers to the detriment of the others has been observed under the influence of the various parameters previously recalled. The very heterogeneous microstructure which results therefrom is detrimental to good performance of the parts and in particular to the fatigue behavior. One of the aims of the invention is to avoid this so-called abnormal grain growth while retaining the advantages linked to a so-called coarse-grain alloy microstructure.

These results are obtained, in accordance with the invention, by applying to forgings made of a nickel-based superalloy conforming to EP-B-0.237.378 or on request FR 95.09653 following a thermomechanical cycle comprising at least one hot forging operation, carried out at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 45 ° C, at a rational deformation speed between 5.10 ~ ⁵ s ^_1 and 2.10 ^{~ 2} s ~ ¹ and at a rational deformation rate greater than 0.1 er a supersolvus heat treatment, carried out at a temperature between the gamma-prime solvus temperature plus 5 ° C and the gamma-prime solvus temperature plus 25 ° C and for a period of between 1 and 4 hours, an intermediate heat treatment succeeding the hot forging operation which is followed by cooling of the part and carried out at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C and at a time between 1 and 24 hours.

In certain particular applications, the results referred to and previously described are also obtained, in accordance with the invention, by carrying out at the end of the hot forging operation, that is to say from the moment when the alloy is still at the forging temperature isothermal maintenance at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C for a period of between 1 and 60 minutes.

According to another variant of the invention, the heat treatment can be carried out in two distinct stages. The first step consisting of isothermal maintenance at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C is carried out at the end of the hot forging operation c '' is to say at the moment when the alloy is still at the forging temperature, for a period of between 1 and 30 minutes after which, the part is cooled. The second step then consists of a heat treatment carried out at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-solvus temperature prime minus 30 ° C of the superalloy and for a period of between 1 and 24 hours, followed by a supersolvus heat treatment.

Other characteristics and advantages of the invention will be better understood on reading the description which follows of embodiments of the invention, with reference to the appended drawings in which:

- Figure 1 shows the conditions of forging and tensile tests carried out on samples of the material studied at 1120 ° C, in deformation rates on the abscissa and in deformation on the ordinate;

- Figure 2 shows the reproduction of a microphotograph of a microstructure of test piece subjected to standard treatment under the conditions prior to the invention;

- Figures 3 and 4 show, analogously to Figure 2, a microstructure of test pieces treated under the conditions of the invention;

- Figure 5 shows, similarly to Figures 2, 3 and 4 a microstructure of a specimen treated under the conditions of a variant of the invention.

EXAMPLES OF REALIZATION

For carrying out the tests, a nickel-based superalloy M whose chemical composition conforms to the definition given by EP-B-o.237.378 was chosen. Alloy M has the following nominal chemical composition in weight percentages:

Co 15.7; Cr 11.5; MB 6.5; Al 4.35; Ti 4.35; B 0.015; C 0.015; Hf 0.45; No complement to 100.

The gamma-prime phase solution temperature or solvent temperature of the alloy is 1195 ° C. The material studied comes from powders atomized with argon and densified by spinning at 1120 ° C.

Four rollers A, B, C, D were forged by isothermal forging at 1120 ° C under the conditions of deformation, on the ordinate, and speed of deformation, on the abscissa, represented by the respective curves 1,2,3 and 4 of Figure 1, thus covering areas greater than 0.1 in deformation and I0 ~ ⁴ s ^{-: L} at 8.10 ~ ³ s ^_1 in speed of deformation. Other tests have been carried out in traction and are represented by points 5,6,7,8,9,10,11,12 and 13 in FIG. 1.

Following the standard supersolvus heat treatment defined for the material comprising either maintaining at 1205 ° C for 4 hours, or maintaining at 1200 ° C for 2 hours, structures with very large grains, of the order of mm for example , have been observed. Tests have shown the influence of the hardening state for the growth of very large grains in the material concerned. Figure 2 shows a microstructure with some very large grains obtained after a standard supersolvus heat treatment carried out at 1205 ° C for 4 hours after a tensile test at 1120 ° C corresponding to a deformation speed of 7.10 ^" ~ ³ s ~ ¹ and a deformation of 0.62 Remarkably and in accordance with the invention, a sample is subjected to a one hour heat treatment at 1120 ° C. before applying the standard supersolvus heat treatment, as above. 3 shows the microstructure obtained in this case, having smaller grains and showing the appearance of colonies of small grains.

When the intermediate heat treatment at 1120 ° C. is extended to 24 hours before carrying out the supersolvus standard heat treatment as before, the microstructure obtained, represented in FIG. 4, is then homogeneous, totally devoid of very large grains and the average size. grain is about 50μm. The heat treatment method according to the invention therefore makes it possible to obtain a state of use of the material concerned having a microstructure ensuring the compromise sought for the mechanical characteristics of use, in particular for parts intended for aeronautical use such as rotating aircraft engine parts, satisfactory creep resistance and good crack propagation resistance at high temperatures.

According to a variant of the invention, instead of carrying out the intermediate heat treatment under the conditions defined above, in another test, a tensile test piece just after having been deformed under critical conditions leading to the presence of very large grains on the final state, namely a temperature of 1120 ° C and a deformation rate of 7.10 ~ ³ s ^-1 , was maintained at 1120 ° C for 10 minutes. After standard supersolvus heat treatment, the microstructure obtained is homogeneous and does not have very large grains, as shown in Figure 5.

For part forging applications, temperature maintenance, without intermediate cooling of the part, can be achieved by keeping the part in the forging tool at the forging temperature. Alternatively and depending on the specific applications, the maintenance at the end of the forging operation can be carried out in an oven, at a temperature between the gamma-prime solvus temperature minus 95 ° C eτ. the gamma-prime solvent temperature minus 30 ° C.

Claims

1. Process for the heat treatment of a nickel-based superalloy whose chemical composition in weight percentages belongs to the following fields:

Cr 11 to 13; Co 8 to 17; Mo 6 to 8; Ti 4 to 5; Al 4 to 5, Nb less than or equal to 1.5; Hf less than or equal to 1; C, B, Zr each less than or equal to 500 ppm; No complement to 100, or Cr 12 to 15; Co 14.5 to 15.5; Mo 2 to 4.5; W 0 to 4.5; Al 2.5-4; Ti 4 to 6; Hf less than or equal to 0.5; C 100 to 300 ppm; B 100 to 500 ppm; Zr 200 to 700 ppm; No complement to 100, applied to forgings following a thermomechanical treatment including a hot forging operation, carried out at a temperature between the gamma-prime solvus temperature minus 95 ° C of the superalloy and the gamma-prime solvus temperature minus 45 ° C of the superalloy, at a rational strain rate between 5.10 ^-5 s ^-1 and 2.10 ^"2 s ^-1 and at a rational strain rate greater than 0.1 and a supersolvus heat treatment, carried out at a temperature between the gamma-prime solvus temperature plus 5 ° C of the superalloy and the gamma-prime solvus temperature plus 25 ° C of the superalloy and for a period of between 1 and 4 hours characterized in that an intermediate heat treatment, succeeding the hot forging operation which is followed by cooling of the part, is carried out at a temperature between the gamma-prime solvent temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C of the superalloy and for a period of between 1 to 24 hours.

2. Process for heat treatment of a nickel-based superalloy whose chemical composition in weight percentages belongs to the following fields:

Cr 11 to 13; Co 8 to 17; Mo 6 to 8; Ti 4 to 5; Al 4 to 5; Nb less than or equal to 1.5; Hf less than or equal to 1; C, B, Zr each less than or equal to 500 ppm; No complement to 100, or Cr 12 to 15; Co 14.5 to 15.5;

Mo 2 to 4, 5; WO 4, 5; Al 2, 5 to 4; Ti 4 to 6; Hf less than or equal to 0.5; C 100 to 300 ppm; B 100 to 500 ppm; Zr 200 to 700 ppm; No complement to 100, applied to forgings following a thermomechanical treatment including a hot forging operation, carried out at a temperature between the gamma-prime solvus temperature minus 95 ° C of the superalloy and the premium-minus solvus temperature 45 ° C of the superalloy, at a rational strain rate between 5.10 ^-5 s ^-1 and 2.10 ^-2 s ^-1 and at a rational strain rate greater than 0.1 and a supersolvus heat treatment, carried out at a temperature between the gamma-prime solvus temperature plus 5 ° C of the superalloy and the gamma-prime solvus temperature plus 25 ° C of the superalloy and at a time between 1 and 4 hours characterized in that an isothermal maintenance at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C, is carried out at the end of the hot forging operation i.e. Rtir from the moment when the alloy is still at the forging temperature, for a period of between 1 and 60 minutes.

3. Process for the heat treatment of a nickel-based superalloy whose chemical composition in weight percentages belongs to the following fields: Cr 11 to 13; Co 8 to 17; Mo 6 to 8; Ti 4 to 5; Al 4 to 5;

Nb less than or equal to 1.5; Hf less than or equal to 1; C, B, Zr each less than or equal to 500 ppm; No complement to 100, or Cr 12 to 15; Co 14.5 to 15.5; Mo 2 to 4, 5; W 0 to 4.5; Al 2.5-4; Ti 4 to 6; Hf less than or equal to 0.5; C 100 to 300 ppm; B 100 to 500 ppm; Zr 200 to 700 ppm; No complement to 100, applied to forgings following a thermo-mechanical treatment including a hot forging operation, carried out at a temperature between gamma-prime solvus temperature minus 95 ° C of the superalloy and gamma-prime solvus temperature minus 45 ° C of the superalloy, at a rational strain rate of between 5.10 ~ ⁵ s ^-1 and 2.10 ² s ^-1 and at a rational deformation rate greater than 0.1 and a supersolvus heat treatment, carried out at a temperature between the gamma-prime solvent temperature plus 5 ° C of the superalloy and the gamma-prime solvent temperature plus 25 ° C of the superalloy and at a duration of between 1 and 4 hours characterized in that an isothermal maintenance at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C is carried out at the end of the hot forging operation, that is to say from the moment the alloy is still at the forging temperature, for a period of between 1 and 60 minutes then, after the part has cooled, a heat treatment is ef made at a temperature between the gamma-prime solvus temperature minus 95 ° C and the gamma-prime solvus temperature minus 30 ° C of the superalloy and at a time between 1 and 24 hours.