Will flux core tack weld on 4130 steel affect the finish weld?

by Rob

I'm new to welding, and am working on a 4130 steel engine mount for an airplane. I've elected to try and tackweld the mount while in the jig and have a professional finish-weld the mount with TIG. I've been contemplating using flux-core wire welding to do the tacks (obviously less $ investment), but I am concerned that the tacks may contaminate the joints of the finish-weld. Do I need to worry about this in 4130 steel?

Also, most of the mount is 0.75" diameter 0.049" walled tubing (see fishmouthed tube angled up and off to the left in the photo) but a few of these connect with some beefier 0.75" x 0.3125" walled pipe pieces (vertical piece with the bolt going through it, in the photo) that actually accept the bolts that attaches the mount to the firewall. It is these latter joints that have proven to be very challenging with the ox/acetylene gas apparatus I have. I was hoping a cheap ~100 watt flux-core wire apparatus would be adequate to tack the 0.049" tubing to the 0.3125" material....would this work? (n.b. I have an aluminum 'shield' under the pieces to protect the wood table).

Many thanks,



the professional tig welder will hate it if you use flux core for tack welding. it spits and ends up with porosity .

bare wire mig would be better but there are some considerations because mig cools pretty quick for tack welding 4130.

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Mar 30, 2014
Stop NEW
by: Anonymous

When you are dealing with a 4130 material it is very hard and in order to do it properly the base material has to be brought to a 400° preheat to keep it from cracking, once you are a 400° preheat you have to maintain that temperature while you are welding on it and then it has to be post-weld heat treated, I would recommend that you find a 300 series stainless or stick to mild steel.

Mar 11, 2012
response NEW
by: Anonymous

To do it correctly, tack it with tig, and find the appropriate rod to match the base metal, a stainless rod on the 300's would be acceptable for tack welding your pieces in place,

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