I'm making a gift, the item is a frost-pin/bull-prick, its blunt, and you hammer it into the ground to create a hole. The receiver told me 'The top must take hard blows and not mushroom. The bottom must penetrate small rocks but not be brittle.' Any suggestions for how to heat treat this? Its 18" long, about 3/4" thick, blunt at the bottom. I can make a few. I have a lot of O1, so one will definitely be O1. I also have some motorcycle axles, and some D2. Its been a while since I've heat treated anything... I do have quenching oil and a bucket of ash for annealing...

Thanks,
-Tod

It is better the struck end be left soft and dressed when it mushrooms. Otherwise there is a risk of chips flying off at high speed when struck. Or at least softer than the striking utensil and soft enough to mushroom instead of chipping.

As for the working end, if I had the equipment, I'd try to harden it to lower bainite. It is tougher than martensite for the same hardness. If I didn't have the equipment then I'd harden and temper to 450˚ to 500˚F. Then I'd test it out and adjust as necessary.

ron

The geometry of the struck end can affect mushrooming. Since this tool is not left in the ground I wonder if the end can be left fat (or would that be too heavy to want to carry) However it is shaped, having the struck end a conical section with a gently rounded narrow top will help direct force nicely and resist mushrooming. It will mushroom eventually, there is no way about that. Using a good quality spring steel may be a good choice.

Phil