A thorough answerer can be better provided with more info. What type of gear is it, what's it indented use etc.?
Heat treating is not "Just" hardening of metal. I suggest you read this HEAT TREATMENT

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'01 Dodge 3500 S Cummins Auto, Fresh air kit, 4" Exhaust,
'05 Dodge Magnum R/T - Too Much to list
'60 Willys CJ5
'01 International LPX - Project,DT466, Allison
'64 Plymouth Valiant, Inj 528 Hemi, 2spd