4130 will get hard if quenched.welding in a cold (minus temps)shop could very well give a very hard(non ductile)I've already done most of the welding for the Hummelbird I'm building, so this is academic at this point, but the plans say to TIG or torch weld the 4130 parts, but then to stress relieve them (heat to cherry red and allow to cool) all the parts after welding.
If I'm stress relieving everything anyway, is there any reason I couldn't have used MIG instead of TIG?
zone,a cold windy shop might guarantee this.Bad.
This can easily be tested with a file,or any other sharp and hard edge,a file will just slide over the hard zone,no grip,just what is needed for a cold chisle,stone drill ,etc.
Sand paper will work to test as well.
As to mig,tig,torch,or any welding or brazing, its irelivant to
"stress relieving","anealing","normalizing" ,whatever you want to call it.
Test your heat afected zones and decide if its waranted,or just follow the instructions.....keeping in mind that in a cold and windy shop it could just get worse,over heat and quick quench and now its scrap.