Probably goes back to an overheated quenching of the steel, not really something that should be unexpected for a $.50 blade. Not really a whole lot you can do as far as just looking over a blade to see if it was worked correctly, or even the alloy makeup. There are tests that can be performed, but there all a little involved; Rockwell for hardness requires a testing machine. A good magnet is handy to have when looking at stainless steel blades... the higher the carbon content, the more of a "pull" you'll get, but it's still going to be very slight with any grade of stainless. Lemon juice (Yeah, like anyone walks into a cutlery store with a squeeze bottle of lemon juice) will discolor a carbon steel blade, and of course you can always cinch a knife into a vice and give it a bend test, but I'm not about to do that of anything I own already, let alone one in a store display. Believe it or not, the best indicator of quality steel will be the price tag, caveat emptor aside.
As for knives that can take that kind of (ab)use, carbon steel is best for hard work like that. Carbon toughens up the steel by imparting a tensility, or springiness to the granular structure, and allows for the blade to spring back to true, instead of staying bent like a piece of copper pipe, say. Stick with the name brands, and spend a little. A good knife is pleasure to use.
Best of luck,
PS- Why not saw through the brisket and ribs, and avoid having to hammer anything? Just curious...