Here in Sacramento we have a volunteer bike-biz catering to folks. A gentleman came-in tonight with a loose crank,which upon removal of BB, the fixed cup had circumferentially broken in-two such that about 3/4" of the inner portion of cup remained threaded in the shell about 1/4" deep. Every effort to remove, including un-screwing, cutting with hacksaw, notching with file, prying with screwdriver, failed to remove hardened (why do you think they call them "fixed"?) race.
I doubt a cold chisel, which we didn't have, would have cut-through. A Dremel tool may have worked if we could have gotten the cutting-wheel inside the BB shell. Needless to say, the gentleman walked his OT bike home. Any ideas short of torch or liquid nitrogen embrittlement?
Jack Romans
Sacramento, CAlifornia