4340 Shaft build up for fe-male threads

[PA2KS]

I have a 7' 4340 shaft roughly 16" in diameter. On one end it has male threads where it is screwed into a press and never removed. On the other end it has female threads roughly 12" into the shaft and is used regularly when changing dies. The threads were ruined when the press recently broke. We are going to machine out the existing threads and then weld build up the ID of the female end and machine new threads. After machining we will preheat to 600F and maintain until moving it to stress relieving. I am thinking we will put it into the furnace in the vertical position at 1200F for an hour with slow cool.

I am not very concerned with weldabilty as long as we maintain sufficient preheat but i am looking for a weld material that will provide a good base for the new threads and hold up for the "life" of the shaft.
My thoughts:
ER 80SD-2 for the GMAW?
EA3K for SAW if we can get in there?
E71T-12MJ or 81T1-K2M or for FCAW?
SMAW would only be if needed.

Any other input will not be turned away, thanks.

 

[metengr]

For bore welding of this type I would consider automatic GMAW using ER80S-D2. For the axial length you are talking about, a boretech type automatic welding machine will handle this inner bore weld build-up with no issues.

Make sure you remove at least 3/16" of material below the threat root to locate the weld HAZ deeper into the shaft wall. I would perform a surface NDT before welding and after rough machining but before threading. I would also perform UT of the weld buildup region to ensure no lack of fusion weld defects.
Your preheat requirements are correct and the PWHT heat treatment sounds acceptable as long as you are not modifying the original bulk shaft temper – I am presuming this is a quenched and tempered shaft.

 

[Guest102023]

Preheat sounds about right, just don't interrupt it. I agree with metengr's NDT recommendations. You are wise to significantly undermatch with the filler metal. Stay away from SAW and SMAW, which will leave some H in the metal.

 

[PA2KS]

We have Bortech equipment but found ourselves in short need of the shaft. We decided to us the manual FCAW process and the build up is looking good. We ended up removing 3/16" below the thread root.

I am presuming this is a quench and tempered shaft as well. Original prints do not indicate PWHT condition but did indicate 135,000 psi yield and 160,000 psi tensile.

Our surface Brinell testing equipment indicated 240. A co-worker and I also discussed a lower PWHT in the 800 range.

As for the NDT, I would like to preform the UT before PWHT. This should be possible if I wrap the shaft in k-wool for slow cooling, am I correct?

 

[metengr]

Yes, this would be acceptable.