Zero in forge

[RUJOCO]

I just spent this morning zeroing in my new burner (venturi). The forge is behaving well. I can maintain 1700 degrees at 3# no problem and at 10# well over 2000 degrees. Pyrometer makes everything so much easier. I welded up some 1/2" cable(test) at 1850 degrees and it seemed to take.
IN the intrest of saving fuel; What would be the minimum degrees to start welding any of the 10x steels at? I recall seeing a nice simple chart on this but don't remember where.