[jimmontg]

You hit non-magnetic at 1650? Ferrous high carbon steels hit NM at 1413-16. Is this the 13% chromium wrench you were talking about? Non magnetic is still not 1650. If it was NM it doesn't have much iron in it if it went all the way to 1650 for NM. Are you counting the small amount of magnetism you get with stainless alloys like 316L? It is slightly magnetic, but not by much. I mean if you take a magnet it will slightly stick to the 300 series SS, slightly.

You are using a forge right? I'm a fair guesser at color temperature comparisons, but I am more practiced at O1, 1475 temp having heated it in an oven and not a forge, I know the color. I could only guess 1650 would be bright orangish yellow? I do mean bright. 1650 is hot and is close to forging heat for many carbon steels, but still not hot enough to forge 13% Cr stainless.

You are saying you are getting no decarb at 1650? Sorry MT, but your forge is not as hot as you think. At that temp there should be some decarb. Also what does " tripling from normalizing (which actually happens because of my back anyway) to heat treat to temper", actually mean? 5160 will have scale at 1650.
Not understanding your post. Maybe I'm missing something.