So I had this metacarpal done and discovered a tiny crack eminating from the center rivet hole, propagating towards the central crease. I decided to scrap it and use it for destructive testing.
This had been heated to bright orange heat and quenched, then heated in an oven to 545F for 20-30 minutes.
I split it in half with one shot. I'm guessing this calls for a hotter temper.