I want to make a touch mark out of h13 on the cnc machines at the polytech I go to. my tutor told me to bring the metal as soft as possible. So can i just anneal h13 in the normal way or does the air hardening property of it mean that the longer it takes to cool the harder it gets?

H13 should be cooled as slowly as possible to get maximum softness. Best to cool it in vemiculite or if not available bury in clean DRY sand. You could also bury it in fiberglass insulation if nothing else available. Yes it is air hardening , so slowing the rate of cooling is critical.

The longer steel takes to cool the softer it gets.

The faster steel is cooled the harder it becomes.

If you cannot control the cooling rate in your forge, heat a heavy mass of steel along with the H13. Put the heavy mass in the ashes/vermiculite/kaowool or whatever you have below the H13. Cover them together and let the heavy mass keep heat in the H13 longer than just letting the H13 cool by itself.

Ideally, H13 should be heated to 1600F and held for a minimum of 1 hour per inch, then cooled to 1000F at a rate no faster than 50F per hour (12 hours). After that is can be cooled more rapidly without an increase in hardness. If you don't have access to the equipment to do this, it will probably be simpler and cheaper to buy a small section of annealed bar stock from one of the online suppliers.

Patrick

Ever see the sticky on "advanced annealing methods"? You might want to read this one.
Knives in General - Knife stickies here at IForgeIron.com

Ideally, H13 should be heated to 1600F and held for a minimum of 1 hour per inch, then cooled to 1000F at a rate no faster than 50F per hour (12 hours). After that is can be cooled more rapidly without an increase in hardness. If you don't have access to the equipment to do this, it will probably be simpler and cheaper to buy a small section of annealed bar stock from one of the online suppliers.

Patrick

Patrick,
If a person didn't have the sophisticated equipment to do this slow of an anneal, could they sister a large piece of steel with the H13 in an annealing bucket to achieve the same result?

What size should that extra piece of steel be (in a just and fair world with a large annealing bucket and no air movement etc)?

Principal Metals

Annealing Anneal at 1600 F followed by slow furnace cooling at a maximum of 40 F per hour.

thanks ApprenticeMan, looks like the answer was right under my nose in the second line of the product description. guess i was o busy marveling over the tempering diagram.
Now does any one know what causes the air hardening characteristic?

Lots of chromium, plus sizable amounts of molybdenum and vanadium. It has a lot of silicon, too; I'm not sure how much that contributes as far as air-hardening goes.