Well funny you said that..
I am a heavy equipment mechanic and started fooling around with a massive Timken bearing race, its an inch and a half wide and when it was round was something like 8 or so inches across, I think it was a carrier bearing from a bucket loader.
Its made out of 52100 steel, not the number one choice for knifemaking but really close, took me a week hammering on it orange hot to get the curve out of it, countless hours with a belt sander, side grinder, tempering to shape it, making the handle, getting the edge just right. I learned a lot, became a member on some knifemaking forums, learned how to make the steel stronger at certain parts, oh its a knife...about the size of a small machete with a sharp point.