I'm not real sure about the weldability of A2 or air hardening steel.
You get to fooling around with A2 ,O2 ,4140 etc you might bite off more than you can chew .Hard is one thing but brittle is another.
If you want a tough wedge,for one reason or another,get a piece of
" yoalloy".,which is 5 percent chrome.I used a chunk of this stuff,actually a piece of 30 " pipe to make a dozer blade.Just cutting it with a torch made the edge hard enough to wear out a grinding wheel in short order.
I've seen wedges made of every thing from mild steel cut with a torch to mangenese back hoe teeth stacked .The teeth didn't work any better than the mild steel.What ever floats your boat,have at it.