Help Needed - Filler selection for In 718??

Date 03-24-2008 18:11

Hello. I want to thank everyone that has posted on this forum because I have learned a great deal just from reading posts.

I have a problem TIG welding some 718 material and need some help selecting the proper filler wire.

The joint is basically a plug weld. The top plate is roughly 0.040" and is in the annealed condition. The bottom plate is roughly 0.100" and is in the aged condition. Holes were drilled through the 2 plates in the wrong locations and I have to figure out how to fill them without getting cracking problems. The holes are about 0.080" in diameter. The entire part is circumferential, so if we did fill these holes we would stagger the repairs to reduce the distortion.

I want to be able to repair these holes without having to go through a heat treat cycle again because the inner plate has already been through one.

I was assuming that 625 would be the best filler due to it's crack resistant properties, but I'm not sure. If anyone could offer any advice, I would greatly appreciate it. Thanks.

In 718 forged material
Top Plate - 0.040" Annealed
Bot. Plate - 0.100" Aged

By Lawrence (*****)

Date 03-24-2008 19:43

Hey Zeek,

I looked but could find nothing to justify welding your inco 718 in the aged condition in the first place. Just not sure an EVA to change the filler choice is the best solution. It's not something I would be willing to sign off on.

Very few repairs of green inco 718 occur at all, nor would be found acceptable by GE or Pratt standard practices. When emergency on wing repairs on un annealed or un relieved Inco 718 do occur, there are often maximum time limits imposed on the repairs and scheduled inspection intervals of the weld until the thing can be properly repaired.

In an off wing manufacturing or refurbishment operation I just don't see a justification for not bringing the Inco back to a weldable condition.

So my advice......Not that you should put much weight on internet chatroom advice.... would be to separate the rings and bring the thicker one back to annealed condition, repair weld and stress relieve. Of course this is prolly the last thing you wanted to hear.

I just don't think you are going to find many folks (other than production managers) to encourage you weld inco 718 of that thickness in the aged condition and call it good without further processing.

Also.
If those holes your filling are close to the OD or on a flange, like on a TMF or LPT connection or seal, it's going to be pretty hard to keep the edge round with holes that wide and deep. It might be best to put an argon backup behind the thing and weld the top,,,, flip and finish the weld from the other side in order to reduce the heat input it's going to take to make those plug welds from one side only.

By Zeek

Date 03-24-2008 22:11

Lawrence -

Thanks for the reply. I spoke with an engineer from INCONEL and he claims that welding it with 718 wire should not be a problem. This part is basically an exhaust component, but this unit is just for test. During service it will see temperatures upwards of 1200degF. So, from my understanding this part will basically age in service anyways. So, the weld and the outer ring (which is annealed) will eventually age. In addition, the inner ring cannot be sent back to heat treat because it is already welded to another part of this exhaust.

Another interesting point is that we used to repair IN 718 parts that came back with cracks, etc. We repaired them with 718 and they kept forming cracks. Once we switched to 625, we didn't have a problem.

My understanding from this INCONEL guy is that 718 has a good amount of Niobium which is large atom and moves slowly. This makes the alloy less suseptible to strain age cracking. He mentioned that the 625 does not age favorbly and that during service that repair will form a delta phase which has low ductility.

I'm not really sure what direction to go.