Method for post-weld heat treatment of welded components made of gamma prime strengthened superalloys

Abstract

A method for post-weld heat treatment of a without a filler material welded high strength component made of a gamma prime () strengthened superalloy can include providing the welded component, heating the welded component by applying a rapid heating-up rate in the range of 20 C./min to 40 C./min during the entire temperature range from room temperature (RT) up to a temperature T.sub.1 of at least 1000 C., holding the welded component at T.sub.1 and then heating the component by applying a slow heating-up rate of about 5 C./min to a final temperature T.sub.f, then holding the welded component at T.sub.f for a time t.sub.f sufficient for at least partially dissolving the gamma prime phase in a weld of the welded component and also in a base material surrounding the weld, and cooling the component with a cooling rate that is greater than or equal to about 20 C./min.

Claims

1. A method for post-weld heat treatment of a without a filler material welded high strength component made of a gamma prime () strengthened superalloy comprised of Ni or Co or Fe or combinations thereof, the method consisting of the following steps: a) providing the welded component, then b) heating the welded component by applying a rapid heating-up rate in the range of about 20 C./m in to 40 C./min during the entire temperature range from room temperature (RT) up to a temperature T.sub.1 of at least 1000 C., then c) holding the welded component at T.sub.1 and then heating the component by applying a slow heating-up rate of about 5 C./min to a final temperature T.sub.f, then d) holding the welded component at T.sub.f for a time t.sub.f sufficient for at least partially dissolving the gamma prime phase in the weld and also in a base material surrounding the weld, then e) cooling the component with a cooling rate of about 20 C./min, and f) finally optionally applying a precipitation hardening treatment.

2. The method according to claim 1, wherein the rapid heating-up rate according to step b) is high enough to avoid gamma prime precipitations in a weld of the welded component.

3. The method according to claim 2, wherein the rapid heating-up rate is about 25 C./min to 40 C./min.

4. The method according to claim 3, wherein the rapid heating-up rate is about 25 C./min to 35 C./min.

5. The method according to claim 2, wherein the rapid heating-up rate is about 20 C./min to 30 C./min.

6. The method according to claim 1, wherein the cooling rate according to step e) is 20 C./min.

7. The method according to claim 1, wherein said method is used for repairing components.

8. The method according to claim 1, wherein said method is used for joined new parts/components.

9. The method according to claim 1, wherein the welded component is welded by electron beam welding.

10. The method according to claim 1, wherein the welded component is welded by laser welding.

11. The method according to claim 1, wherein the precipitation hardening treatment is applied.

12. The method according to claim 1, wherein the applying of the precipitation hardening treatment is performed such that the welded component is held at 850 C. for a precipitation hardening treatment time period.

13. The method according to claim 1, wherein the rapid heating-up rate according to step b) is high enough to minimize gamma prime precipitations in a weld of the welded component.

14. The method according to claim 1, wherein the holding of the welded component at T.sub.f for the time t.sub.f is holding the welded component for an isothermal dwell time.

15. The method according to claim 1, wherein the providing of the welded component comprises electron beam welding a component of a turbine or laser welding a component of a turbine.

16. The method according to claim 1, wherein T.sub.1 is 1100 C.

17. The method according to claim 1, wherein T.sub.f is 1140 C.

18. The method of claim 1, wherein the cooling of the component with a cooling rate of about 20 C./min is performed until the component is at a precipitation hardening treatment temperature.

19. The method of claim 18, wherein the applying of the precipitation hardening treatment is performed at the precipitation hardening treatment temperature for a precipitation hardening treatment time period.

20. A method for post-weld heat treatment of a without a filler material welded high strength component made of a gamma prime () strengthened superalloy comprised of Ni or Co or Fe or combinations thereof, the method comprising: a) providing the welded component, b) heating the welded component by applying a rapid heating-up rate in the range of 20 C./m in to 40 C./m in during the entire temperature range from room temperature (RT) up to a temperature T.sub.1 of at least 1000 C., c) holding the welded component at T.sub.1 and then heating the component by applying a slow heating-up rate of about 5 C./min to a final temperature T.sub.f, then d) holding the welded component at T.sub.f for a time t.sub.f sufficient for at least partially dissolving the gamma prime phase in a weld of the welded component and also in a base material surrounding the weld, and e) cooling the component with a cooling rate that is greater than or equal to about 20 C./min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

(2) FIG. 1 shows a metallographic cut of a IN738LC test specimen treated according to the disclosed method after the cooling step of the post-weld treatment;

(3) FIG. 2 shows a metallographic cut of the IN738LC test specimen according to FIG. 1, but after an additional subsequent precipitation hardening;

(4) FIG. 3 shows the time-temperature-diagram for the applied post-weld treatment according to the known standard heat treatment and

(5) FIG. 4 shows the time-temperature-diagram for the applied post-weld treatment according to one embodiment of the invention.

DETAILED DESCRIPTION

(6) Two IN738LC test plates in the solutioning heat treated conditions were joined by electron beam welding without using any weld filler. The two plates could be described schematically as two modular parts of a new turbine component, for example a turbine blade, which should be joined together. No special welding conditions were applied. Without any post-weld heat treatment there are cracks in the weld region (so called strain age cracking).

(7) FIG. 3 and FIG. 4 show the time-temperature-diagrams of the standard heat treatment (FIG. 3) and of the applied post-weld heat treatment to that component according to one embodiment of the present invention (FIG. 4).

(8) The following heat treatment trials with different temperatures and heating-up rates were performed for IN738LC: 1. Standard heat treatment: 1140 C./0.5 h (5 C./min)+1180 C./2 h (5 C./min) 2. Modified/optimized heat treatment according to the present invention: 1100 C./0.5 h (20-30 C./min)+1140 C./2 h (5 C./min)+optionally 850 C./17 h The last step (850 C./17 h) is not shown in FIG. 4. The average cooling rate between 1140 C. and 850 C. was 20 C./min.

(9) The welded component was subjected to a post-weld heat treatment according to the invention with a rapid heating-up rate of about 20-30 C./min in the range of RT (room temperature) to 1100 C. (see FIG. 4), an exact measure of the heating up rate was done in the temperature range of about 400 to 1100 C. Then, after a holding time of 0.5 at 1100 C. the component was heated with a lower heating-up rate of 5 C/min to 1140 C., which is slightly below the solutioning temperature of the used superalloy, and exposed to an isothermal dwell at 1140 C. for two hours, before cooling down with about 20 C./min (average cooling rate between 1140 C. and 850 C.).

(10) As can be seen from FIG. 1, in which the metallographic cut of the weld and the surrounding base material is shown after that described post-weld treatment, no cracks were observed.

(11) With the application of the rapid heating-up rate during the post-weld treatment it is achieved that the gamma prime precipitations in the weld can be minimized resp. avoided. The final heat treatment of the part is then done at a temperature and a time long enough that the gamma prime phase is at least partially dissolved also in the base material surrounding the weld. Upon cooling, gamma prime precipitations are formed in the weld and the base material as well. However, due to the partial dissolution of the gamma prime phase in the base material during the hold time, the formation rate as well as the amount of the gamma prime phase in the weld and the base material during cooling is similar, thusas an advantagecracking can be avoided.

(12) In addition, also a subsequent precipitation hardening at about 850 C. for 17 hours did not lead to the formation of cracks (see FIG. 2).

(13) In contrast, a weld joint that was processed in the same way did not exhibit cracks in the as-welded condition, but revealed cracks in the weld joint after post-weld treatment when the heating-up rate is only about 5 C./min (see FIG. 3, standard heat treatment. The cracks were already visible by Fluorescent penetrant inspection (FPI), therefore it was not necessary to prepare metallographic cuts.

(14) Even a higher heating-up rate (>30 C./min) is beneficial for alloys with a higher amount of gamma prime than IN738LC, such as CM247LC or CMSX-4. In addition, the isothermal dwell temperature can be increased as well, depending on the solution temperature of the alloys.

(15) The present invention is not limited to the described embodiments. It could be used with advantage for all gamma strengthened superalloys where no other means of crack avoidance exist (i.e. welding processes without weld filler).