Welding 1/2 gaps, some questions.

[ScottD]

Well Ive spent all weekend working my little Harbor Freight MIG welder to death. Wow, some of the gaps in my receiver well exceeded 1/2 inch. In the areas that were larger than 1/2 inch I used filler plates of steel, the rest I just 'flowed' in. Now, do I have to heat treat these welds? (Somebody mentioned it to me and I was wondering....)

[waffendude]

scott---i'm not sure about heat treating --i did not heat treat anything on mine (about 500 rnds thru it)--maybe someone else will chime in ---but i did not heat treat my welds
just my .02
waffen

[js412000]

It is made from low carbon steel and does not need to be heat treated.

[88comm]

Ditto what JS said. You do not want to heat treat it, (as far as hardening it) because then it would likely break under stress, rather than stretch. Low carbon steel does not treat well for that exact reason, there is no carbon to treat. Keep an eye on your welds to see if there is any movement (stretching, fine cracks) then add metal thru welding again. Maybe build up a little more metal in that area.

Heat treating can be used to toughen a metal (somewhat harder and stiffer) but again, low carbon metal does not do this well.

If it was originally designed and built with low carbon steel, your welds should be fine as long as they are as thick as the original metal.

(opinion)
A machine gun that works well with low carbon steel (as originally designed) has got to be a great design. We use it as a semi-auto, it should last forever.

[nutsrusted]

I need to get out the book on this one but I think low carbon steel can be case hardened and that actually is good if you have impact, moving contact surfaces or pin holes that are under regular stress. The camming section on the receiver is under stress so I would imagine the receiver would last longer if a surface hardening was performed. Ideally if you could localize the surface hardening to that area that would be good.

Does anyone actually know if the mg42 was case hardened or is this speculation?

[88comm]

From my experience working the metal there is no indication that it was case hardened. It has never, in my memory on this forum, been mentioned that case hardening has been encountered.
Germans seem to be pretty good engineers. Had case hardening been worth the effort I think we would know from somewhere that it had been part of the process.

Any other word from others on the forum of it ever being used?

[weasel]

The 42 receiver is made of mild steel sheetmetal approx .100 thick. Not a good idea to try and heat treat or harden
the receiver. Try and keep the welds from getting to hot and over heating the area around the cuts.
Have fun with your builds. LOL
Weasel