"which would be toughness wouldn't it?
because toughness is how much deformation something can take?"

Yes. Another part of toughness though is also the ability to retain it's shape. No one wants a knife that will bend to 30 degrees and stay bent. <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />

Also - If bending was all you were concerned about - just don't heat treat or anneal or anything. you will have a very tough and flexible steel pretzel. <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />