Welding 17-4ph HH1150?

I'm making some large parts out of 17-4ph HH1150. The HH1150 is the heat treat designation which results in the material being pretty
soft. That is, soft for 17-4. Well, a drilled hole went oversize and now it's too large for the 1/8 pipe threads that need to go in. So, I can either weld the hole and re-drill and tap, or machine oversize and thread in a plug that is already tapped for 1/8 pipe, or throw away a $400.00 part. I think I can get away with putting in a plug with 1-20 threads on the OD and 1/8-27 through and then welding the perimeter of the plug to retain and seal it. It needs to hold 15,000 psi. I would rather fill the hole with weld though and just re-machine it. What I don't know is if I weld it what the hardness of the weld and the HAZ will be. If the 17-4 is held at 950 degrees for an appreciable length of time it will reach maximum hardness. But if I use 308 filler I don't know what the resulting alloy will do. Any suggestions? Before I do anything to the part the customer will be notified and will need to give me the OK. And he will be doing the pressure testing. I have looked on line for info about welding 17-4 and it is possible but I have not found any real world examples. Thanks, Eric
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On Fri, 27 May 2011 22:56:54 +0000, etpm wrote:

The AWS welding handbook volume 4 has info on welding 17-4PH; much depends on part geometry and the intended post-weld heat treatment (if any). No preheat is required, cracking is not generally a problem, but the HAZ will be soft (low strength) without post-weld heat treatment. Distortion could be a problem. SMAw electrodes AWS E630 or bare wire ER630 recommended, however 308 or 309 can sometimes be used where reduced strength is not a problem (probably not suitable in your case). Suggest you read the entire precipitation hardening SST section of AWS handbook for more info if you can borrow a copy from someone.
I have designed parts using 17-4PH before, never welded it had it welded, but the AWS handbook is definitely based on real world experience.
You might be able to find a SAE straight thread to NPT adapter for an no- welding solution if your customer approves. Parker and others make them.
Regards, Glen
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I have welded a bit of 17-4. I would recommend welding in the pre-threaded plug. 17-4 does not like sustained heat such as puttying in a hole would do. You can weld the plug in using 309L, Inconel 625, or Hastelloy W. I would recommend 310 for the plug for greater strength.
You can use 17-4 filler as long as the plug is also made from 17-4, or at least 15-5, but that may be tricky to machine. Do NOT fusion weld 17-4 to itself. It will tend to crack. Filler metal must be added with as little dissolution into the parent metal as possible, so keep your amps down, and leave yourself a groove to lay the weld into. Make sure to back purge the weld, or you can get root cracking.

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