Annealing is to bring the stock…or piece to be worked to a heat capable of allowing the molicules in the metal to relax and line up in a row. Depending on the makeup of the metal this could be a dull red heat…to… as hot as a bright orange heat (not quite to the white heat stage of melting. remove from the heat source and bury in lime or hardwood ash 6 inches surrounding the entire piece. This will take hours to cool depending on the size of the piece.
Now you work the piece to the desired finished product.
Reheat the item to harden and cool rapidy (opposed to the annealing over hours of cooling)
This reheating allows the molicules to move freely within the metal and by cooling (quenching) quickly, you trap the molicules in a random paterm (mixed directions) within the piece.
Remember, you cooled it slowly so those molicules could stay lined up as it cooled. Now you’ve jumbled them and this makes the item harder when quickly cooled…
To harden…this can be tricky because it all depends on the makeup of the base metal, some are air hardened, some oil quenched, some water quenched. And just becuase it is called tool steel the process can still be different. As an example you may use S7 tool steel and make a cold punch and harden it by oil bath
Or if the item is to be used and you still want a little flexability (not brittle at the tip) to it, you may air harden or forced air hardened with a fan, or even oven hardening.
Water hardening would be the hardest, oil hardening will cool it a bit slower making it less hard
Forced air hardening is a little less hard, air hardening will be softer yet, and oven hardening will be the softest that you can achieve. This would be like putting that red hot item in a oven and letting it cool slowly over maybe an hours time.
(when using oil bath do NOT remove the piece until it is cool.
By raising the item too soon smoke and gassed will raise from the bucket…and the hot item can easily ignite the gasses. You didn’t need those eyebrows anyway!!!
So it all depends on the type of metal and it’s alloy that determine the type of hardening.
I use H13 tool steel for some tools, but I prefer S7 tool steel for most. Though the S7 is trickier to forge it is a harder product. I just can’t let it get above a cherry red heat in the forge, so I get a real workout whailing on that to make any tools. The S7 makes better tools like punches that will have to absorb a lot of heat from the red hot piece being worked and yet hold their shape and they are best air hardened. H13 is a little more forgiving allowing me to punch cold steel and keep it’s shape yet for my work it’s best oil hardened. S7 would be too brittle and the tips would snap off in a cold hole.
Tempering is less tricky to get it right. This is heating the item back up, but only to a blue or black heat to allow the item to soften just enough to allow some flexability as in a knife blade.
Hard… to keep a good edge, not too hard that you cannot sharpen it, yet you want the blade to flex enough so it doesn’t break at the first hard use.
Usually tempering is done with the lights off and the item is heated until just past the blue heat stage into a start of red heat. Quickly the item is pulled from the heat and the slag quickly filed away as it cools. When the item cools to the dark blue heat, it is quenched to hold that temper.
Because a knife blade edge will cool quicker than the back of the blade…the blade is rested on it’s sharpened edge on a piece of large iron heated to almost a melting heat. This keeps the edge hotter while the back cools.
You may not want to temper these machine tools to keep that hardness.
These guidelines are intended for the small shop. I don’t want to hear any "Well when I worked at the Purple Thumbnail hammer company we did XXX in a heat treating oven. I don’t think George has one!!!
Gosh I ramble on don’t I. Doesn’t that Yosemite guy ever shut up???