FR2517327A1 - METALLIC COMPONENT WITH REDUCED TOTAL FLOWING AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

METAL PART SHOWING REDUCED TOTAL CREEP ON THERMAL EXPOSURE. IT IS CHARACTERIZED BY A STATE OF ITS MICROSTRUCTURE IN WHICH ITS EXPANSION BY CREEP TAKES PLACE, DURING THERMAL EXPOSURE, IN ITS LOWEST SPEED AREA. APPLICATION TO GAS TURBINE ENGINES.

Description

The present invention relates to the hardening of metals and, more

  particularly, a process for hardening metals and parts having a better resistance to magnification by total creep during heat exposure produced from

of these hardened metals.

  Metal parts such as those used in turbomachines or in other high temperature and stress applications often experience magnification as a result of thermal expansion, creep deformation, or a combination of the two. Thermal expansion is defined as the growth of a metal part due to an increase in its temperature The creep deformation, however, is the dimensional increase undergone by a metal part when it is subjected to a stress at high temperature This magnification is generally not desirable For example, in a turbomachine such as a gas turbine engine the growth of a compressor housing will cause a loss of narrow tolerance sets inside.

  compressor, resulting in a loss of efficiency

  compressor and requiring more frequent repair. The thermal expansion of a metal or alloy is a physical characteristic There is little known mechanical conditioning that can be applied to a metal or alloy to alter its thermal expansion characteristics Thermal expansion will generally be recoverable during cooling because the dilation takes place in the elastic region before

  the establishment of a plastic or permanent deformation

  In any application at a given high temperature where the expansion of a metal or alloy is undesirable, the problems due to this expansion can be avoided or reduced by selecting a material having a resistance inherent to this thermal expansion for the temperature of the metal. chosen operation. The total creep deformation of metal alloys, generally called creep or total creep, has three distinct domains. Briefly, for a given temperature and stress, in a first domain, the metal part undergoes

  fast creep at a speed that decreases with time.

  In a second domain, the metal part undergoes creep at a linear velocity, slightly increasing

  over time, the area of lower speed.

  Finally, a third field of creep results in a rapid but brief creep of the metal part at a speed which increases with time until rupture. However, in each domain, the creep results in a permanent increase or not.

recoverable dimensions.

  Previous work to increase the creep resistance of metals or alloys has involved hardening the surface of the metal part by various means including rolling or shot blasting. These processes have had little or no success in reducing total creep In particular, none of the prior processes have involved the various creep domains to reduce total creep during

the service.

  The present invention therefore aims: to provide a better manufactured metal part whose expansion by creep growth will be in its range of lower speed; providing a method that expands a metal part throughout its first creep domain during its manufacture; to increase the lifespan and improve

  the performance of a gas turbine engine in application

  the method of the invention to a crankcase

compressor.

  Briefly, the present invention provides a better manufactured part, such as a compressor casing for gas turbine engines, which is characterized by the fact that its microstructure is in a state in which the expansion of the part by deformation or creep growth during the thermal exposure will be greatly in its area of lower speed Such a piece may be part of a set of elements of which at least one is designed to rotate relative to a

  other way, by maintaining a predetermined interval

mined between the elements.

  The present invention, in another form, provides a method for the production of such a piece

  to give it increased resistance to deformation

  by total creep during thermal exposure by heating the workpiece to a selected temperature below its initial melting point, however, a force of sufficient intensity is applied for a time sufficient to expand the workpiece in the first area creep; then we cool the piece After that, we can machine the piece to a shape

  which considers that virtually any plastic dilatation

  The tick will occur in the second creep domain during thermal exposure.

  The rest of the description refers to

  attached figures which respectively represent, in FIG. 1, a schematic view partially in section of an airplane gas turbine engine comprising a compressor casing to which the present invention can be associated; Figure 2 is a sectional view of the rear portion of a compressor showing the positional relationship between the housing and the rotor blades and the positional relationship between the stator vanes and the rotor; Figure 3 is a graphical representation of creep deformation in metals as a function of time for a given temperature and stress; Figure 4 is a partial sectional view of a non-machined compressor housing disposed around an expansion means; Figure 5, a graphical representation of the behavior of a metal part with and without the application of pre-creep according to the invention described herein; and Figure 6, a graphical representation of the creep behavior of an alloy useful with the present invention compared to two other behaviors of the same alloy after application of the present invention. In order to reap the full benefit of a material chosen for its resistance to thermal expansion, according to the present invention a method for increasing the total creep resistance can be preconditioned in the workpiece the initial growth associated with the first Creep The present invention of controlling the total creep of a piece of metal or alloy during the service life of the part, consists in preconditioning the part for the first creep domain and in making it work in the second creep area. o the speed of

magnification is the weakest.

  Thus, the present invention concerns the preconditioning of a metal part for the first creep area so that this creep does not appear in service. The pretreatment for this first creep area is carried out by passing the metal part, such as A turbomachine compressor casing, in the first creep area during manufacture and prior to application to the actual engine. The part will thus operate in service in the second creep range only.

  method of the present invention by pre-creep.

  Referring now to FIG. 1, a schematic view shows a gas turbine engine, indicated generally at 10, for the purpose of illustrating an application to which the present invention relates generally. generally comprises a blower portion 20, a compressor portion 30, with which the invention will be specifically described, a combustion portion 50 and a turbine portion 55 mounted in series. The operation of the gas turbine engine of Figure 1 is well known and therefore a

  description of this operation does not seem necessary.

sary.

  In the description below of the invention,

  the term "axial direction" will designate the direction parallel to the horizontal axis or central axis of the engine 10 as seen in FIG. 1. The term "radial directior" denotes a direction along a line that

  is perpendicular and cuts the same horizontal axis

  The term "tangential direction" shall mean a direction along a line generally formed by a place of points in the same axial plane and

  equidistant from the same horizontal axis.

  Referring now to FIG. 2 which is a sectional view of the compressor rear section

  30 and which shows the rear case 31 of the compressor.

  The rear casing 31 of the compressor is equipped with an outer surface 32, an inner surface 34, a front flange 36, a rear flange 38 and a rear groove 39. The front flange 36 comprises a set of equidistant holes 37 a arranged circularly to receive a series of fasteners for fixing the front portion of the rear case 31 to the rear portion of the front case, not shown for reasons of simplification Similarly, the rear flange 38 comprises

  a set of equidistant holes 37 b arranged circula-

  The rear groove 39 provides a concentric alignment between the rear case 31 and the compressor rotor 44 of the compressor. The rear groove 39 provides a concentric alignment between the rear case 31 and the compressor rotor 44. fixing holes in the front flange 31 and the rear flange 38 have close tolerances and are designed to

  cooperate with fasteners and overrides

  coupling faces to reduce tangential sliding of the housing during engine operation. Referring still to FIG. 2, the compressor portion 30 includes a plurality of axially aligned stator vanes 40 slidably mounted, circularly, in the compressor housing 31, and a set of axially aligned rotor vanes 42 mounted therein. sliding, circularly, in a

compressor rotor 44.

  The performance of a compressor and consequently the performance of the engine are directly related to the game

  radial 48 between the radially outermost ends

  rotor blade 42 and inner surface 34 of the housing, and the radial clearance 46 between the radially innermost ends of the stator vanes 40

  and the inner surface 43 of the turbine rotor 44.

  Significant improvements in performance and performance are achieved, such as, but not limited to, improvements in specific fuel consumption and avoiding the deterioration of the stall margin, by maintaining games 46 and 48 as well. as small as possible during any given operation of the engine and during the life of the engine Thus the enlargement of the compressor housing by thermal expansion or by creep is not desirable and must

to be avoided.

  The present invention, in one form, provides a piece of metal suitable for use as a compressor casing that will not flow to such a point that the sets 46 and 48 would grow to limits which will result in deterioration of

  compressor performance or engine performance.

  The invention is achieved by taking advantage of the characteristic shape of the creep curve of a metal or

  of a metal alloy Figure 3 is a representation

  graphical representation of the creep deformation observed in metal alloys as a function of time for a given temperature and stress, as indicated previously As the curve shows, a large creep appears in a short instant in the first

creep area.

  The high operating temperatures experienced by the rear casing 31 will result in a thermal expansion of the casing As indicated above, this expansion will generally be recoverable during cooling because the expansion takes place in the housing.

  elastic domain before the establishment of deformation

  The selection of a material with a low coefficient of thermal expansion will result in less thermal expansion and increased operating efficiencies. Such a low thermal expansion coefficient alloy, which has been chosen for the rear case 31, is the commercial iron-based alloy known under the name M 152 which has a nominal composition Cr: 11.9%, Ni: 2.5%, Mo: 1.8%, V: 0.3%, Mn: 0 , 7%, C: 0.5%, the balance being iron and possible impurities In the

  this description, unless otherwise indicated, all

  the percentages of composition are percentages by weight This alloy was chosen in preference to the previously used alloys having a higher coefficient of thermal expansion. However, it was found to be subject to a large total creep for efficient use of the beneficial characteristics. low thermal expansion coefficient of this iron-based alloy, it is necessary to reduce

  or eliminate the appearance of creep during service.

  The analysis showed that the majority of the defor-

  by creep during the life of a crankcase

  Such an iron-based alloy is in operation in the first creep range. By applying the process of the present invention to such a part, it will, in use, undergo creep only in the second range. the first domain has been removed by pre-creep during the production of the part, according to the invention The creep which then appears during the service will not result in the type of

  rapid increase of the compressor casing which

  derives from the deterioration of engine performance or performance. The present invention comprises the thermomechanical treatment of the part, for example, the unmachined casing can be used in the manufacture of the final casing 31 of the rear compressor. FIG. 4 is a partial sectional view of a non-machined compressor casing 61. for example in the form of a molded forged part, a rolled and welded sheet, a plate, etc. The unmachined compressor housing 61 is arranged around an expansion means 60. In this embodiment, the means Expansion 60 consists of a mandrel having a coefficient of thermal expansion greater than the compressor casing disposed around the expansion means. Expansion means

  will also have a melting temperature

  greater than the temperature chosen to expand the unmachined compressor casing in the first creep range during the application of the present invention, as will be discussed in more detail below. The mandrel of the expansion means 60 may be solid or annular The mandrel material may be of the type characterized by the nominal composition representing the commercial alloy A-286: Ni: 26%, Cr: 15%, Ti: 2.1%, Mn: 1.5%, Mo: 1 , 3%, Si 0.7%, Al: 0.3%, V: 0.3%, C 0.04%, B: 0.005%,

  the balance being iron and possible impurities.

  The unmachined casing 61 placed around the expansion means 60 is placed in an oven and heated for a time and at a temperature sufficient to cause the expansion means 60 to expand sufficiently against the unmachined casing 61.

  the casing is in alloy M 152, this expansion provoking

  the crankcase creep beyond 0.115%, which will be sufficient to cause the casing to pass through the first creep area as a result of the circular stresses induced in the casing by the expansion means. The unmachined casing 61 is then treated.

  in the manufacturing cycle in a normal way.

  The heat treatment has been highlighted.

  Pre-creep Mechanical Design on Two Compressor Sump Forgings In this evaluation of the present invention, a commercially available stainless steel AI SI 321 having a nominal composition Cr: 18%, Ni 9, was used as the expansion means. 5%, Mn 2%, Si: 0, 75%, - Cu: 0.5%, Mo: 0.5%, Ti 0.1%, C 0.08%, the remainder being iron and any impurities The physical arrangement shown in FIG. 4 was used: The compressor rear case forging 61 was disposed around an expansion means 60 Then the unit was heated uniformly in a forced air oven and maintained at 565 , 50 C 140 C for 4 hours 15 minutes At the end of heating, remove the whole oven and let it cool in air to room temperature A series of diametric measurements made at room temperature showed the forged compressor crankcase had exceeded a deformat creep ion of 0.115%,

  indicating that a secondary creep had begun.

  An evaluation of the effects of the pre-creep method of the invention on the other mechanical properties of the pre-flowed part was performed. The results were compared with those obtained for an identical compressor rear case which was not subject to the pre-creep process of the present invention The results of the creep tests are indicated in FIG.

17327

  Table I, Oligocyclic fatigue (LCF) in Table II, and tensile in Table III In the tables, DI represents the inside diameter, OD and the "PC" pre-creep state associated with this invention and "NPC" represents a state of non-pre-creep or the state "raw reception"

of the forged part.

TABLE I

RESULTS OF THE FLOWING TEST

TYPE SPEC

NPC (DI)

PC (DI)

NPC (DI)

PC (DI)

NPC (DE)

PC (DE)

NPC (DE)

PC (DE)

TEMPERATURE

TEST

  (C) 537.7 537.7 537.7 537.7 537.7 537.7 537.7 537.7

CONSTRAINT

(da N / mm 2)

13.788

13.788

17.235

17.235

13.788

13.788

17.235

17.235

RESULTS

TYPE SPEC NPC PC NPC PC NPC PC RO =

TABLE II

OF FATIGUE OI TEST

At 537.70 C Kt = 1.0

Pseudo-STRESS

ALTERNATE Ci (da N / mm)

63.424

63.424

48.258

48.258

41.364

41.364

LIGOCYCLIQUE

YCLES UNTIL

BREAKING

3.600 5.200

12,000

19,000

24,500

000 (RO) ::

out of time standard

UNTIL

A

CREEP

0.1%

  47.0 158.0 21.5 47.0 16.5 63.0 6.5 14.0 TIME

UNTIL

A

CREEP

0.2%

  221.5 519.0 131.0 221.5 106.0 314.0 81.4 106.0

TABLE III

  AVERAGE RESULTS OF THE TRACTION TEST.

LIMIT

TEMPERA LIMIT OF ELASTI-

TURE OF ELASTI CITE ALLON-

  TYPE OF TEST ISCED 2 TO 0.2% 2 GEMENT STRICTION

  SPEC (OC) (da N / mu) (da N / mm) (%) (%)

NPC 21.1 115.82 95.516 17 66

PC 21.1 110.30 90.311 16 65

NPC 537.7 72.387 63.424 24 81

PC 537.7 68.94 62.735 20 77

  Referring to Table I, the remarkable improvement in creep resistance was shown by the practice of the invention for each stress level, both for the inside diameter and the outside diameter of the treated specimens, at the same time. Similarly, Table II shows the significant improvement in the fatigue life of oligocyclic fatigue by the use of the present invention compared to untreated test pieces at each tested level. The results in Table III show that the tensile properties are not significantly affected by the implementation

of the invention.

  Referring now to FIG. 5, the results of radial creep at the position of the back flange (shown at 38 in FIG. 2) are graphically represented for a compressor rear case forging with and without application of the Pre-creep of the present invention By way of example, the results show that for a selected engine service of 3000 hours, the material which has not undergone pre-creep would undergo a radial growth of about 0.28. However, only material subjected to the pre-creep process of the present invention will only experience radial growth of about 0.114 mm. If maximum radial growth of about 0.23 mm is allowed before deterioration in the yield of the compressor or engine performance, the material not having undergone pre-creep will have an expected life of about 800 hours By comparison, the material subjected to the pre-creep process of the present inventio n will have an expected life of approximately 15,000 hours, an improvement

very marked.

  The method used and described is effective in forcing a metal part to flow in the first domain As in any process of this type, some residual stresses are introduced, which will be relaxed or recoverable during certain

  heating or relaxation of the contrain-

  for example, in subsequent manufacturing cycles such as coating, welding or heat stress relieving treatments,

  alone or in combination The alloy M 152 described above

  This was subjected to a quenching cycle of 565.50 C for 4 hours after application of the pre-creep method of the invention. The metal part was not fixed, i.e., was the free state,

  and some anelastic recovery has been observed.

  FIG. 6 is a graphical representation of creep versus time deformation for a given temperature and stress for a pre-creep base material, a material

  pre-cured and tempered and pre-cured material only.

  It will be observed that the pre-cured and quenched material has a significant improvement in the total creep resistance compared to the non-cured material.

undergone pre-creep.

  From the foregoing, it is clear that an effective way has been found to pass a metal piece into the first creep range during the manufacturing cycle. Such a process will prolong the life of the part and in the application to a crankcase. gas turbine engine compressor, will help maintain compressor efficiency and engine performance for a longer period of time The process is well suited to meet

  to the objectives mentioned above.

  The pre-creep method of the present invention is particularly useful for reducing the total creep of an iron-based compressor casing during thermal exposures. The method described in various forms can also be applied to other pieces of ring, circular or

  linear) and / or other metals or metal alloys

  The process is applicable to Co, Fe, Ni, Ti, Al and alloys containing these elements, such as nickel-based superalloys, stainless steels, low alloyed steels or others used in

  high temperature applications and high stresses.

Claims (7)

  1 Manufactured metal part suitable for use in an apparatus in which the expansion of this part is undesirable, characterized in that its microstructure is in a state for which the expansion of the part by creep growth will be essentially in its area of lower speed. 2 piece according to claim 1, characterized in that it comprises a machined surface adapted to cooperate in a close tolerance with another element. 3 piece according to claim 1, characterized   in that it is ring-shaped.   An assembly of elements intended to cooperate with a narrow tolerance range during a thermal exposure comprising: a first member (31) including at the gap a machined surface (34) arranged to cooperate in a tolerance relation with a second element (44), this first element (31) being characterized by a microstructure in a state for which the expansion of the first element by creep growth will be essentially in its lower speed range, whereby the interval between this first element and the second element will be maintained in a close tolerance relationship during the exhibition thermal.   Part according to Claim 1, characterized in that the metal of this part is based on at least   an element selected from Co, Fe, Ni, Ti and Al.   6 Set of elements comprising, in combination   sound: a first element (31); and a second element (44); at least one of the elements being adapted to rotate relative to the other; at least one of the first and second elements including at least one projecting member cooperating with a   part of the surface of the other element with an interval   the; at least one of the first and second elements and the protruding member being characterized in that its microstructure is in a state for which expansion by creep growth of the element or organ is in its range of lower speed, whereby the gap maintains a close tolerance relationship during thermal exposure. 7 Method for reducing the total creep of a   metal piece during the life of the piece increases   Thus, the life of the part during thermal exposures is characterized in that it consists in: providing a metal part capable of exhibiting creep when it is heated to a chosen temperature below its initial melting temperature in conditions of force sufficient to initiate a creep of the part;   heat the metal part to the temperature   chosen ture; apply a force to the metal piece of sufficient intensity to cause creep at the chosen temperature; maintain the metal part under these conditions of force and temperature to dilate the part in its first creep area t and then cool the metal part.   Process according to claim 7, characterized   in that, after cooling, the metal part is machined to a shape for which it is considered that any plastic magnification of the machined part will be in the second creep area during thermal exposure. Process according to claim 8 for   reduce the total creep of an annul-   re, characterized in that it consists in: providing a metal piece of annular shape; arranging the annular piece around a dilation means;   heat the annular piece to the temperature   it is chosen however that the expansion means applies a force to expand the annular piece in the first creep area; cool the annular piece; and then machining the annular piece to a shape for which it is considered that any plastic magnification of the machined part will be in the second area of   creep during thermal exposure.   Process according to claim 8, characterized   rised in that the metal of the piece is based on   at least one element selected from Co, Fe, Ni, Ti and Al.   The process according to claim 9, characterized   in that the expansion means is heated concurrently with the metal part and is composed of: (a) a metal based on at least one element selected from Co, Fe, Ni, Ti and Al, (b) of which the coefficient of thermal expansion is greater than that of the annular piece disposed around it, and   (c) whose melting temperature begins   is higher than the chosen temperature.   Process according to claim 9, characterized   risé in that it understands before the machining a step -   additional application of at least one cycle of quenching to the annular piece.   The method of claim 12, wherein   characterized in that quenching cycles of 1 to 4, each at a temperature of 537.8 to 593.30 C and 1 to 4 hours, are applied to the annular member before machining.