SplinterGroup

........ I'll have to try it and see if case hardening can make for a really long lived tool

SplinterGroup.... the steel flat bar is cheap stuff from HD that I used for this and wouldn't be a grade that would harden and temper properly. 
However a nice piece of tool steel flat bar or 1095 would be nice to harden and temper and yield a very strong cutting edge. Worth trying if you can get it. In thinking about it, perhaps an old plane blade or saw blade would give good results.