U.S. patent application number 10/538414 was filed with the patent office on 2006-07-06 for method for the production of a part having improved weldability and/or mechanical processability from an alloy.
Invention is credited to Nigel-Philip Cox, Dirk Goldschmidt, Rolf Wilkenhoner, KonstantinA Yushchenko.
Application Number | 20060144477 10/538414 |
Document ID | / |
Family ID | 32319566 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060144477 |
Kind Code |
A1 |
Cox; Nigel-Philip ; et
al. |
July 6, 2006 |
Method for the production of a part having improved weldability
and/or mechanical processability from an alloy
Abstract
Alloys known in prior art cannot be processed well enough for
producing a part. According to the inventive method, the part is
subjected to a thermal treatment in an intermediate step, which
improves the processability thereof.
Inventors: |
Cox; Nigel-Philip; (Mulheim
an de Ruhr, DE) ; Goldschmidt; Dirk; (Moers, DE)
; Wilkenhoner; Rolf; (Kleinmachnow, DE) ;
Yushchenko; KonstantinA; (Kiev, UA) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
32319566 |
Appl. No.: |
10/538414 |
Filed: |
December 8, 2003 |
PCT Filed: |
December 8, 2003 |
PCT NO: |
PCT/EP03/13882 |
371 Date: |
December 21, 2005 |
Current U.S.
Class: |
148/522 ;
148/527; 148/529; 148/675 |
Current CPC
Class: |
C22F 1/10 20130101 |
Class at
Publication: |
148/522 ;
148/527; 148/529; 148/675 |
International
Class: |
C22F 1/10 20060101
C22F001/10; C21D 9/50 20060101 C21D009/50 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2002 |
EP |
02027496.5 |
Claims
1-25. (canceled)
26. A process for producing a component from an alloy that can be
hardened by precipitations, comprising: providing the component
prior to machining or welding; and carrying out, in an intermediate
step, an improvement heat treatment on the component such that the
improvement heat treatment coarsens the precipitations, thereby
improving the welding and/or machineability of the component, and
the improvement heat treatment at least in part being carried out
during slow cooling at a cooling rate of 2.degree. to 3.degree.
C./min.
27. The process as claimed in claim 26, wherein an overaging heat
treatment is carried out as the improvement heat treatment on the
component in order to coarsen the precipitations.
28. The process as claimed in claim 26, wherein a further heat
treatment is carried out after the welding and/or machining, so
that the microstructure that is set in this way for the areas of
use of the component has better properties than without this heat
treatment.
29. The process as claimed in claim 26, wherein a subsequent heat
treatment, which at least partially reverses the coarsening of the
precipitations, is carried out after the welding and/or
machining.
30. The process as claimed in claim 26, wherein to produce the
component, the component is cast from a melt of the alloy.
31. The process as claimed in claim 26, wherein the component is
re-densified.
32. The process as claimed in claim 26, wherein the component is
re-densified prior to the improvement heat treatment.
33. The process as claimed in claim 26, wherein the component is
heated up to a set temperature and the improvement heat treatment
takes place at least in part through slow cooling.
34. The process as claimed in claim 31, wherein the improvement
heat treatment takes place immediately after the
re-densification.
35. The process as claimed in claim 30, wherein the improvement
heat treatment is carried out immediately after casting.
36. The process as claimed in claim 34, wherein the
re-densification is carried out by means of hot isostatic
pressing.
37. The process as claimed in claim 26, wherein the alloy used is
an iron-base, nickel-base or cobalt-base superalloy.
38. The process as claimed in claim 37, wherein the alloy includes
the .gamma.' phase.
39. The process as claimed in claim 26, wherein a weld filler of a
similar analysis to the base metal is used for the welding.
40. The process as claimed in claim 26, wherein a weld filler which
is of the same composition as the alloy is used for the
welding.
41. The process as claimed in claim 26, wherein a weld filler which
can be hardened by a precipitation is used for the welding.
42. The process as claimed in claim 26, wherein a weld location is
formed during the welding, and in that the at least one weld
location is hammered.
43. The process as claimed in claim 26, wherein the alloy used is
the material IN 738LC or IN 939.
44. The process as claimed in claim 26, wherein for the improvement
heat treatment the component is held at a temperature and then the
component is cooled.
45. The process as claimed in claim 26, wherein the improvement
heat treatment takes place at least at a solution-annealing
temperature of the alloy.
46. The process as claimed in claim 26, wherein the averaging heat
treatment takes place at 1180.degree. C.
47. The process as claimed in claim 29, wherein the subsequent heat
treatment for at least partially reversing the coarse
precipitations is carried out at least in part at a
solution-annealing temperature.
48. The process as claimed in claim 29, wherein the subsequent heat
treatment for at least partially reversing the coarse
precipitations is carried out at least in part during cooling at a
cooling rate of from 20.degree. C. to 40.degree. C. per minute.
49. The process as claimed in claim 41, wherein the precipitations
of the weld filler form at least 35% by volume.
50. The process as claimed in claim 31, wherein the temperature for
the re-densification is below the solidus line of the material of
the component.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is the US National Stage of International
Application No. PCT/EP2003/013882, filed Dec. 8, 2003 and claims
the benefit thereof. The International Application claims the
benefits of European Patent application No. 02027496.5 EP filed
Dec. 10, 2002, both of the applications are incorporated by
reference herein in their entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a process for producing a component
with improved weldability and/or machineability from an alloy in
accordance with claim 1.
BACKGROUND OF THE INVENTION
[0003] U.S. Pat. No. 5,938,863 has disclosed a nickel-based
superalloy which contains additions of carbides in order to improve
the fatigue properties.
[0004] U.S. Pat. No. 6,120,624 has disclosed a heat treatment for a
nickel-based superalloy prior to welding, in order to avoid the
formation of cracks during heat treatments after welding. In this
case, very low cooling rates (3 F/min=1.66.degree. C./min or less)
are used during the heat treatment.
[0005] U.S. Pat. No. 4,579,602 and U.S. Pat. No. 4,574,015 have
disclosed heat treatments for cast superalloys in order to improve
the forging of these materials.
[0006] It is known from U.S. Pat. No. 5,374,319, U.S. Pat. No.
5,106,010 and EP 478374 to heat the locally delimited weld zone of
a component to temperatures above the aging temperature. This leads
to stresses in the component which is held at different
temperatures.
[0007] During production of a component from an alloy, the
component has to be machined in various intermediate production
steps. Often, the alloy does not have the desired properties to
allow it to be optimally machined.
[0008] For example, the alloy may be relatively brittle, making
machining (straightening, cutting, grinding machining) more
difficult.
[0009] It is often also necessary to weld cracks or holes, but the
welding properties of the alloy are often poor.
SUMMARY OF THE INVENTION
[0010] Therefore, it is an object of the invention to overcome the
above problems.
[0011] The object is achieved by a process for producing a
component with improved weldability and/or machineability from an
alloy in accordance with claim 1.
[0012] The subclaims list further advantageous process steps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The measures listed in the subclaims can be combined with
one another in advantageous ways. In the drawing:
[0014] FIGS. 1, 2 shows examples of time curves for the temperature
of an alloy during a production process, and
[0015] FIG. 3 shows various microstructures of an alloy.
DETAILED DESCRIPTION OF THE INVENTION
[0016] FIG. 2 shows an example of a time curve for the temperature
of an alloy during the production process.
[0017] The alloy can be hardened, for example, by precipitations,
such as for example an iron-base, nickel-base or cobalt-base
superalloy.
[0018] The alloy can be sintered from a powder to form a component
or can be directionally solidified or cast as a melt. Other forms
of production are also conceivable.
[0019] If the alloy for a casting process has melted, the
temperature is greater than the melting point T.sub.liquidus. The
melt is cast (left-hand part of the figure) and then cooled more or
less slowly, in a controlled or uncontrolled way, so that the
temperature is below the solidus line T.sub.liquidus. The component
has then solidified. The component is, for example, cooled to room
temperature (the point where the temperature axis T intersects the
time axis t).
[0020] The casting process is followed, for example, i.e. not
necessarily, by a re-densification, in particular immediately after
the casting process, i.e. without cooling of the component after
casting.
[0021] The re-densification is effected, for example, by hot
isostatic pressing (HIP), (region I, FIG. 2) or possibly also by
sintering, in order to close up defects, such as for example pores,
voids, etc.
[0022] The re-densification may also be carried out after other
production steps, for example after welding. The temperature during
the re-densification (for example HIP) is below the solidus line
T.sub.liquidus of the alloy of the component.
[0023] In this stage (with or without re-densification), the
components which consist of this alloy are machined (for example
directionally or by cutting or grinding machining), and/or welding
repairs of defects in the component are carried out, in particular
at room temperature.
[0024] Often, however, the properties of the alloy of the component
are not suitable for the mechanical processing conditions
(weldability and mechanical processability).
[0025] A subsequent improvement heat treatment according to the
invention, which leads, for example, to coarsening of the
precipitations, for example by means of an overaging heat
treatment, which leads to overaging of the structure of the allow,
alters the microstructure of the component in such a way that the
processability of the alloy is improved compared to the untreated
microstructure. The microstructure features include, inter alia,
the crystal structure, precipitations and secondary phases.
[0026] In particular, the overaging heat treatment indicated by way
of example can directly follow the re-densification process, in
particular in the same furnace, or after casting or sintering.
[0027] There is no cooling (FIG. 2, transition between regions I,
II) or only insignificant cooling of the component.
[0028] If the re-densification process is carried out by an HIP
process, the pressure can remain unchanged, be slowly lowered or
withdrawn during the improvement heat treatment.
[0029] A holding time at the temperature for the improvement heat
treatment can in this case be dispensed with or reduced, since this
time has already been partially or completely effected by the
holding time for the HIP aftertreatment.
[0030] The overaging heat treatment, if appropriate after a holding
time at a temperature, is achieved by a low cooling rate of greater
than or equal to 2.degree. C. to 5.degree. C., in particular from
2.degree. C. to 3.degree. C. per minute, in particular 2.33.degree.
C./min, immediately after the re-densification process (region II,
FIG. 2).
[0031] FIG. 1 shows the time curve when the component is being
removed from the hot isostatic press and transferred into a
different furnace.
[0032] The overaging heat treatment is achieved by heating up to a
defined temperature, if appropriate with a holding time at this
temperature (in the sequence shown in FIG. 2, the heat-up operation
is dispensed with), and, for example, by a low cooling rate of
greater than or equal to 2.degree. C. to 5.degree. C. per minute,
in particular from 2.degree. C. to 3.degree. C. per minute, in
particular 2.33.degree. C./min (region II, FIG. 1).
[0033] An overaging heat treatment for IN738LC, which also leads to
coarsening of the precipitations, has, for example, the following
parameters:
[0034] heating at 10.degree. C.-25.degree. C./min (if
necessary),
[0035] holding temperature/time 1180.degree. C.+0.degree.
C.-10.degree. C./holding time if appropriate 3 h,
[0036] cooling at 2.degree. C.-3.degree. C./min, in particular
2.33.degree. C./min, down to 950.degree. C., followed by cooling in
air.
[0037] The same parameters are used for IN939.
[0038] For Rene80, the holding temperature is 1204.degree.
C..+-.15.degree. C. The holding temperatures for the overaging heat
treatment are also, for example, the HIP temperatures.
[0039] However, they may be higher or lower.
[0040] The overaging heat treatment effects overaging of the
.gamma.' phase, with the result that the ductility of the base
material is significantly increased.
[0041] This overaging heat treatment, by way of example, improves
the weldability of the alloy, in particular at room temperature,
compared to the untreated alloy. Moreover, the improved mechanical
ductility of the alloy compared to the untreated alloy means that
the component can be more successfully straightened (mechanically
deformed) and/or more successfully machined by cutting or
grinding.
[0042] The microstructure produced in this way may have properties
which are worse than those of the microstructure prior to the heat
treatment for the subsequent application area of the component,
such as for example high-temperature use.
[0043] On account of the poor welding and straightening properties,
hitherto high-strength nickel superalloys, such as IN939, Rene80
and IN738LC, have not been used in particular for large and
thin-walled components, such as for example combustion chamber
linings. These alloys include the .gamma.' phase in order to
increase their strength and can now be machined and used without
restrictions by the process according to the invention (with
welds).
[0044] Hitherto, the material of choice was Hastelloy X. This
material can be welded better but has a limited high-temperature
strength and straightenability compared to the other classes of
materials.
[0045] After the overaging heat treatment, any defects (cracks,
holes, etc.) are repaired, for example by means of microplasma
powder surfacing or plasma powder surfacing.
[0046] In principle, it is also possible to use other welding
processes, such as manual tungsten inert gas welding.
[0047] The weld locations formed during welding can if appropriate
be beaten (hammered), which leads to cold work-hardening, since
internal compressive stresses are induced. It is also possible for
pores or other defects to be reduced or eliminated in this way.
[0048] This is followed, for example, by cold-straightening of the
component in corresponding equipment in order to correct the
geometry of the component.
[0049] Then, by way of example, solution annealing (at a
temperature of greater than or equal to 1180.degree. C. up to, for
example, 1200.degree. C. for the abovementioned materials) can be
carried out on the component, with subsequent rapid cooling (for
example 20.degree.-40.degree. C. per minute down to 800.degree. C.,
followed by cooling in air), i.e. cooling which is faster than the
cooling rate during the improvement heat treatment.
[0050] This "extinguishes" the overaged structure again, i.e. the
coarse precipitations at least partially disappear and the
component regains its good high-temperature properties of the
alloy, for example by a finely dispersed .gamma.' structure being
established (rapid cooling).
[0051] The microstructure may have better properties for the
application area of the component than the microstructure which the
component had after the heat treatment for improving the
processability.
[0052] During the overaging heat treatment of the materials with
the .gamma.' phase, this .gamma.' phase is dissolved. When the
.gamma.' phase has dissolved, slow cooling takes place, during
which the .gamma.' phase is precipitated and correspondingly
coarsened. The coarsening leads not only to a rise in the mean
diameter of the .gamma.' phase, but also, for example, to
spheroidization of the .gamma.' phase, i.e. it is less cubic and
more in platelet form. Coarsening of this type leads to an
increased ductility.
[0053] In the case of other materials which do not have a .gamma.'
phase, a corresponding heat treatment is carried out, altering the
microstructure in such a way that it improves the processability of
the component, in particular at room temperature.
[0054] The process for improving the processability of the alloy
can be used for newly produced components and for components which
have been used (refurbishment). In this case, the procedure is, for
example, as follows.
[0055] The used component is cleaned (removal of
oxidation/corrosion products) and, for example, any coatings are
removed. This is followed by assessment of the component, i.e.
cracks and pores are detected.
[0056] An overaging heat treatment is then carried out, followed
either by welding repair of the cracks and pores at room
temperature or straightening of the component.
[0057] If appropriate, this is followed by cold-forming (beating or
hammering) of the weld locations produced in this way.
[0058] This is again followed, for example, by a heat treatment
(for example solution annealing) in order to establish the desired
finely dispersed .gamma.' structure.
[0059] If appropriate, there then follows a further subsequent
treatment of the weld locations, for example a local heat
treatment. The solution annealing takes place, for example, at the
same temperature as the temperature used for the overaging heat
treatment, but with faster cooling, in order to prevent the
coarsening of the .gamma.' structures. In this case, the cooling is
carried out so quickly that the .gamma.' phase is not completely
precipitated, but rather is forced to remain at least partly
dissolved.
[0060] If appropriate, age-hardening can then be carried out in
order to precipitate the desired .gamma.' structure (fine particles
in block form).
[0061] In particular a weld filler of a similar analysis to the
base metal or a weld filler of the same composition as the
component is used during welding. The term "of a similar analysis
to the base metal" means that it has approximately the same
composition as the component or has the same high-temperature
properties as the base material. In this case, by way of example,
the constituents of the weld filler are in the same relative
proportions as in the material of the component.
[0062] If appropriate, it is possible to dispense with weld
fillers.
[0063] In particular, weld fillers which are not very resistant to
high temperatures should be avoided.
[0064] If the weld filler can be hardened, i.e. its strength
increased, by precipitations, the weld location scarcely reduces
the strength of the component, if at all.
[0065] The weld filler should include at least 35% by volume (in
microsection) of the precipitations (for example the .gamma.'
phase).
[0066] The beating of the weld location after welding suppresses
the formation of cracks during a first heat treatment after the
welding.
[0067] Only the combination of the overaging heat treatment and the
beating allows welding at least with a similar analysis to the base
metal at room temperature in order to produce good, crack-free weld
locations.
[0068] The overaging temperature of 1180.degree. C. for IN939 is
deliberately selected to be higher than what is known from the
prior art (1160.degree. C., U.S. Pat. No. 6,120,624).
[0069] An example of a subsequent heat treatment after the welding
looks like this:
[0070] heating at 10.degree. C.-25.degree. C./min to a holding
temperature for a certain time,
[0071] cooling at 20.degree. C.-40.degree. C./min, so that the
overaging structure is dissolved.
[0072] Heating at 10.degree. C.-25.degree. C./min to a holding
temperature for a certain time (solution annealing), cooling at
20.degree. C.-40.degree. C./min and if appropriate heating at
10.degree. C.-25.degree. C./min to a defined holding temperature
for a certain time, cooling (age-hardening heat treatment).
[0073] The desired finely dispersed .gamma.' phase is restored for
use of the component, in order to achieve the required mechanical
properties.
[0074] FIG. 3 shows various microstructures of a superalloy.
[0075] This example shows the microstructure of the alloy
IN738.
[0076] FIG. 3a) shows the alloy with a cubic primary .gamma.' phase
and a fine secondary .gamma.' phase, resulting in a high-strength
alloy which has a low ductility.
[0077] FIG. 3b shows an overaged microstructure which includes a
.gamma.' phase in platelet form, but no secondary .gamma.' phase.
This microstructure has a higher ductility than that shown in FIG.
3a.
* * * * *