FR2745588A1 - METHOD FOR THE HEAT TREATMENT OF A NICKEL-BASED SUPERALLOY - Google Patents

Abstract

A process for the heat treatment of nickel-based superalloy forgings whose weight composition belongs to the following range: Cr 11 to 13, Co 8 to 17, Mo 6 to 8, Ti 4 to 5, Al 4 to 5, lower Nb or equal to 0.5, Hf less than or equal to 500 ppm, Ni complement to 100 comprises after the hot forging operation, carried out at a temperature between the gamma-prime solvus minus 95 deg. C. and the gamma-solvus prime minus 45 deg. C, at a strain rate between 5.10 ** - 5s ** - 1 and 2.10 ** - 2s ** - 1 and at a strain rate greater than 0.1 and before a supersolvus heat treatment carried out at a temperature between the gamma-prime solvus plus 5 deg.C and the gamma-prime solvus plus 25 deg.C for 1 to 4 hours, an intermediate heat treatment carried out at a temperature between the gamma-prime solvus minus 95 deg.C and the gamma-prime solvus minus 30 deg.C.

Description

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DESCRIPTION

  METHOD FOR THE 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; 10 Ti 4 to 5; A1 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; A1 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. These alloys are used in particular for the manufacture of highly stressed parts intended for aircraft engines, for example rotor discs. 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 gamma- premium for a period of

  maintenance 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.

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  required by the search for performance improvement

aircraft engines.

  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: 10 gamma-prime phase precipitation, oxycarbon distribution, strain rate, velocity of

  deformation, 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 and then are generally20 again anchored by very fine precipitates, oxycarbons, preferentially located at the old powder boundaries. The result sought in this case is to obtain grains of homogeneous size, in particular 50 μm on average, corresponding to a so-called normal grain growth.25 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 were observed under the influence of the various parameters previously recalled. The resulting very heterogeneous microstructure is detrimental to good performance of the parts and

  especially fatigue resistance. One of the aims of the invention is to avoid this so-called abnormal growth of grain while retaining the advantages linked to an alloy microstructure called coarse grain.

  These results are obtained, in accordance with the invention, by applying to forgings made of a nickel-based superalloy conforming to EP-B0.237.378 or on request FR 95.09653

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  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 s-1 and 2.10-2s-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 plus 5 C temperature and the gamma 10 solus temperature -primes over 25 C and at a time 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 15 95 C and the gamma-prime solvus temperature minus 30 C and at a duration included 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 instant 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 between 1 and 60 minutes.

  According to another variant of the invention, the processing

  Thermal can be done in two separate stages. The first step consisting of an isothermal maintenance at a temperature between the gamma-

  prime 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. at the instant when the alloy is still at the forging temperature, for a period of between 1 and minutes after which the part is cooled. The second step then consists of a heat treatment carried out at a temperature between the solvent temperature

  gamma-prime minus 95 C and the gamma- solvent temperature

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  premium minus 300C of the superalloy and for a duration included

  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

  embodiments of the invention, with reference to the accompanying 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; FIG. 2 represents the reproduction of a microphotograph of a microstructure of test piece subjected to the 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; FIG. 5 represents, in a manner analogous to FIGS. 2,

  3 and 4 a test piece microstructure 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 EPB-0.237.378 was chosen. Alloy M has the following nominal chemical composition in weight percentages: 35 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 solution temperature of the gamma-prime phase or solvent temperature of the alloy is 1195 C.

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  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, in 5 ordinates, and speed deformation, on the abscissa, represented by the respective curves 1,2,3 and 4 of the

  Figure 1, thus covering domains greater than 0.1 in deformation and from 10-4s-1 to 8.10-3s-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 obtained20 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 7.10-3s-1 and a deformation of 0 , 62. Remarkably and in accordance with the invention, a sample is subjected to a heat treatment for one hour at 1120 ° C. before applying the standard supersolvus heat treatment, as above. Figure 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 11200C is extended to 24 hours before performing the standard supersolvus heat treatment as before, the microstructure35 obtained, represented in FIG. 4, is then homogeneous, completely devoid of very large grains and the average size.

grain is about 50m.

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  The heat treatment method in accordance with 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, outfit

  satisfactory in creep and good resistance to crack propagation 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 15 the final state, namely a temperature of 1120 C and a deformation rate of 7.10-3s-1, was maintained at 11200C

  for 10 minutes. After standard supersolvus heat treatment, the microstructure obtained is homogeneous and does not have very large grains, as shown in Figure 20 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. As a variant and depending on the particular applications, 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 and the gamma-prime solvus temperature minus 30 C.

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Claims (3)

  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; A1 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; A1 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 comprising 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 C superalloy, at a rational strain rate between 5.10-5 s-1 and 2.10-2 5-1 and at a rational strain rate greater than 0.1 and a supersolvus heat treatment, carried out at a   temperature between the gamma- solvus temperature   prime 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- solvus temperature   prime minus 95 C and the gamma-prime solvus temperature minus 30 C of the superalloy and at a time between 1 at 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; A1 4 to 5; Nb less than or equal to 1.5; Hf less than or equal to 1; C, B, Zr 8 2745588   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 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, applied to forged parts following a thermomechanical treatment comprising a hot forging operation, carried out at a temperature between the gamma-prime solvus temperature minus 95 C of the superalloy and the premium-range solvus temperature minus 450C superalloy, at a rational strain rate of 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- solvus temperature   prime 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 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 when the alloy is still at the forging temperature, for a period 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; A1 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; A1 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 thermo-mechanical treatment including a hot forging operation, carried out at a temperature between 9 2745588   between 5.10-5s-1 and 2.102s-1 and at a rate of rational deformation greater than 0.1 and a supersolvus heat treatment, carried out at a   temperature between the gamma- solvus temperature   prime plus 50C of the superalloy and the gamma-prime solvus temperature plus 25C of the superalloy and for a period between 1 and 4 hours characterized in that an isothermal maintenance at a temperature between the gamma-prime solvus temperature minus 95eC 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 when the alloy is still at the forging temperature, for a period between 1 and 60 minutes then, after cooling of the part, a heat treatment is carried out at a temperature between the temperature of gamma-prime solvus minus 950C and the temperature of gamma-prime solvus minus 300C of   superalloy and lasting between 1 and 24 hours.