hi larrin. i'm working with 52100 now. from large diameter round bearing stock. so i have to flatten these. i take these up to yellow with acetylene. so it i can bend/bang them straight.
tried to simply take these to unmagnetic once, then air cool. then harden. 1 shade above unmagnetic. warped like fukn crazy. and it was totally unusable.
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then tried a very high temp one shot "normalizing" with acetylene after flattening. to get all tensions out. up to maybe light yellow. almost white.
then 3 cycles to just above unmagnetic, then air cool. in open air. now, hardening these i take them to like 1-2 shades above unmagnetic. dunk in a mix of hot hydraulic oil and motor oil. comes out hard as glass. and cracking these parts shows a grain size of almost 0. i cant ever see any grain. its just dull gray.
but its 0% unrepeatable i guess. i do this all by eye. with acetylene and propane.
after tempering 2x at 180C my bacho files just skid along.
yeah thats some anecdotal data for you. i feel i did good though.