Tigging 12L14?

I stick welded 12L14 to steel once, just for the kicks, not for any use at all, simply because I had scrap pieces of both.
The weld looked beautiful, like in your presented youtube video.
Then I hit it with a hammer, and everything fell apart instantly.
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That is the biggest problem leaded machining steels. A hairline crack can propagate in a microsecond.
309L is a pretty amazing filler for dissimilar metals, but you have to be very careful about not getting it too hot or it will crack every time.

OK, Then. This is sounding like a not-very-good idea. So, can you suggest an easy to machine steel that also can be welded reliably with a DC TIG machine?

The only time I would weld leaded steel is if I had no other option.

I could also say that TIG brazing is far better than TIG welding on leaded steels. Silicon Bronze filler and half the amps used for welding steel. Since it does not melt the base metal, there would be much less chance of cracking.

st an easy to machine steel that also can be welded reliably with a DC TIG machine? OK, that sounds like something I could live with. I'm not expecting to make anything highly loaded, or anything where failure would present a serious threat to safety. If I were to do that, I would for sure use properly rated materials and methods (or more likely, job it out).
I'm comfortable with the idea of brazing. Is it really simply a matter of " half the amps?" Would you then reduce the size of the electrode & filler ro d to match the amperage? What flux would you use?
Sorry for the newbie questions, but I *am* pretty new to this.

No flux needed.
Try a 3/32" tungsten and 1/16" filler to start. It is surprisingly easy.
Unlike gas brazing, TIG brazing leaves what looks like a weld bead.