Very interesting exercise. I'm just guessing, but an ammo can is probably made of AISI 1010 steel -- not known for strength or edge holding ability. Your results were most enlightening.

If it is 1010, tempering won't do much unless you get it real hot and pound it over hot coals -- to get the extra carbon from the coals to give it hardness.

As an expedient, this obviously gave the desired results. All in all, a worthwhile learning experience for us too. Thanks Taurus.