The steel you get in an investment casting may not be what you ordered. Can depend upon just what alloy was melted in the pot before they melted the 4140 or whatever.
Anyway, you might have what is essentially a tool steel, that requires either hotter anneal temp than that wood stove, or slower cooling.
I'd build me a hot fire in whatever place you have, blowing a little air in would help. That metal has to get hot enough to glow, red would be good, bright red maybe better.
Then cool it by just letting the fire die down slowly, maybe bank it.
After it is cool enough to touch - like the next day -dig it out of the ashes.
Or ask Anson what he would do with it.
Jim Kelly the P-I-T-A metallurgist