Weld repair 4340

[stillcrazy]

I'm trying to formulate a repair procedure for a part that has been EB welded. This isn't a weld integrity issue as much as it is cosmetic. Post machining of the weld area occasionally doesn't clean up the weld completely. I would like to fill in the pitts with a GTAW process and wonder about a preheat - postheat cycle to affect hydrogen embrittlement issues. Thanks for your time.

 

[metengr]

stillcrazy;
My expierence has been that filling in local pits or low spots with weld metal is difficult at best from a cosmetic standpoint because after welding, the surrounding area that was welded will pull in and create other low spots or crevices. One way around this problem is to first locally undercut the affected surface to allow for a weld build-up. The key after undercutting the surface is to raise the edge of the undercut region with a peening hammer or cold chisel to compensate for weld metal shrinkage. I would use the repair method below to weld build-up this undercut region with the GTAW process and ER80S-Ni2 filler metal.

The preheat should be 350 deg F and held for at minutes before welding. Use stringer beads with a 50% overlap to butter the area first, followed by a second weld pass while remaining on top of the first weld pass using a higher heat input (10-15%). After welding, allow the weld to sit at 500-550 deg F for 30 minutes. This should eliminate any delayed cracking issues.

The reason for the two passes is to use a technique known as temper bead to avoid post weld heat treatment of the base metal. I have used this technique on low alloy steels with success and with an experienced welder.

 

[Goahead]

A procedure used sometimes while EB welding in vacuum, before repair is needed, is to preplace a titanium shim in the joint. It may help.

http://www.welding-advisers.com/