Welding on Inconel 1

[cmboneman]

Hello,
I'm wondering if anyone out there knows anything about repair welding of inconel. We've been repairing several inconel jet engine parts, that may be fatigued, and are having little success repair welding. Usually, the repair welding results in more cracks, often in other areas of the component far from the repair area (thermal stresses?). Any ideas as to what the failure mode, or possible repair procedures could be?

 

[CWIC]

There are several recent threads on this subject. Check out the Welding, Bonding & Fastener forum:
thread725-65418

What process are you using?

I used to work at an FAA repair station which refurbished Pratt and Whitney engines. As noted by others, these repairs are typically limited to static parts. GMAW-P was the process we used and this had to be performed by an experienced/skilled welder in this process. It sounds to me like there is too much heat input from the welding. Have seen cracking if the welder did not know what he/she was doing (too much heat input...) The cracks usually occur outside the HAZ from residual stress induced to the part.

BTW, we did not repair cracked or damgaged parts but we did restore the leading edges of vanes and such. Lot's of NDT was performed (after machining and heat treatment if required) before a part went back into service.

 

[JimMetalsCeramics]

I've seen this sort of problem. In addition to CWIC's comments, I would add that you may have to cut out the damaged area and the immediate periphery and weld a fresh piece back in.

 

[cmboneman]

The idea of too much heat input has been my gut instinct on this issue as well. Our welders are good, but are "jack of all trades" type people, so that's been the focus of my investigation. Thank's for the link to the additional thread, I wasn't able to find that yesterday.

 

[CWIC]

cmb:
Pulsed GTAW is usually the process of choice for these applications. This minimizes heat input compared to non-pulsed power supplies.

Another issue is the welders arc travel speed and amperage (peak & background amperage for pulsing) which is also critical to heat input. This means compliance with a WPS is paramount. A welder with slow travel speeds typically overheats the part making it a very expensive paper weight.

 

[mantill]

What type of Inconel material is it.

The BRITE EURAM project BE4314 considered welding of IN625 (solid solution nickel base superalloy) and IN738LC (Precipitation hardened). IN625 is considered weldable, In738LC is not. Techniques included TIG, laser and EBW. As discussed above heat input is very important and low heat input techniques (laser and EBW) offer the best options.

Also important will be geometric considerations, thickness of material and local constraints, both of which can give rise to distortions or thermal cracking.

Filler is very important and a subqsequent PWHT maybe required to improve the strength of the weld and HAZ.

After welding HIPing can greatly improve the life of the material, assuming only subsurface defects exist.

Let me know more about your problem and I will try to advise.

Marc

 

[weldengineer]

Simllarly, can anyone recommend a set of proven GTAW-P parameters for welding I-718 alloy castings? I am experiencing hot cracking prior to PWHT. The castings are in the homonegized condition prior to weld assureing the most favorible condition. I have tried lower amperage and lower interpass temps but the results are normally the same. Any recommendations?

 

[CWIC]

weldengineer:
A list parameters may not be my primary concern.

Without knowing specifics:
1.) Part geometry: Castings with thick to thin sections are problamatic, particularly if the transition areas are brief (abrubt changes in part geometry, fillets with a relatively "minimal" radius, etc.) I've seen lots of hot cracking on heavy castings on a wide variety of materials with thick/thin sections. While the welding may not be performed in these areas, they do induce significant internal stresses.

2.) Preheat/Interpass Temp.: Is the entire part being preheated and interpass temp. being applied and maintained uniformly throughout the entire part? I've had parts crack before I ever hit the pedal due to the method and manner in which it was preheated by a welders helper.

3.) Technique: Try adding more filler metal for the same weld area. "Starving the weld" during welding is a common source of hot cracking. Inconel, aluminum, magnesium, etc. are very susceptable to hot cracking if filler metal deposition rates are minimal.

Without knowing part thickness, a brief description of the part geometry, preheat/interpass temps., current welding parameters, etc., I personally would not throw any numbers out there unless more info could be obtained. I would review the above attributes first, then consider the welding parameters. I'm sure your lower-amps modification of parameters included pulse width, frequency, background and peak amperage. An increase in arc travel speed would also be inclusive to my considerations.

 

[stanweld]

To weldengineer: Is hot cracking in the weld metal or casting HAZ? I have had 2-occasions when Inconel castings could not be welded due to the deoxidizing melt practices of the foundry resulting in low melting eutectics at the grain boundary. Intergrannular hot cracks in the HAZ was the result. Only recasting using approriate melting/deox practices resulted in acceptable welds.

 

[weldengineer]

CWIC / Stanweld,
Thanks,I appreciate your replies. In reference to your comments, I do suspect that part geometry does contribute signifigantly. As noted, we are welding in areas of transition from thick to thin. In some cases, .750" to .080". We have also experienced some hot cracking in uniform thickness areas of both thick (up to 1&quot and thin (.070&quot areas. Mostly the cracking is in the filler for heavier sections and in the HAZ for thinner sections.

As for preheat, we currently do not preheat any of the thickness ranges. Ambient temperature runs around 75-80°F. The interpass temperature is held to below 250°F.

While trying to keep heat input low, we have limited the amperage to 85 amps while using pulsed current. Peak is at 65%, background between 5-10 and freq.is 500Hz. At this low amperage, it is difficult to maintain a higher rate of travel speed even while using .045" diameter wire. I suspect we may be dwelling too long in order for the puddle to achieve flow.

Stanweld, I have verified the heats for compliance and everything appears in line. Levels are nominal and the heat looks clean.

Does this offer any more improvement oppertunities?

Thanks!

 

[stanweld]

Excessive Magnesium as deoxidzer is the most common problem. The only way to really check for this problem is by microprobe analysis. This may not be your problem though based on only occuring in thin sections. Opening up the included bevel angle between 100 and 120 degrees may prove useful. Good luck.

By the way, how is the alloy melted. Vacuum furnace? Argon shielded?