This is what you want to get in practice of with all blade steels: allow the steel to cool to 'hand warm' (that is the drop to temperature that allows you to hold the steel in bare hand without burning); place steel in pre-heated temper immediately. Never allow the steel to drop below 'hand warm' before tempering. After primary, first, temper you can wait until tomorrow to secondary temper. Just to add even though you are not to this stag: for cryogenically treating the steel it can be 'snap tempered' before cryo. Snap tempering is a much lower temperature than primary temper, say about 300 F. to 325 F.. Snap temper will help stabilize enough for the cryo phase of heat treat and after cryo the blade should be tempered when blade achieves ambient temperature or shortly before. Cryogenics when used in this case is part of the entire heat treatment, even though it is about -325 F.. It is not separate of heat treat but rather a component of it. For your tempering oven, always use at least one oven thermometer placed in close as possible proximity of where blade will rest. For our purposes, all complex, deep hardening steels, are better cooled by forced air rather than still air (that is my experience). There are a lot of converts to plate quenching instead, of which I am one. Aluminum plates can be used to sandwich air hardening, deep hardening - high alloy, steels such as your D2 is. The plates drop the steel temperature sharply and is the preferred method of quench for many of us here.
Hand warm for my experience is a point where I can finally hold the steel in bare hand without discomfort but very close to discomfort.
rlinger
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