I've never read anything regarding cast cranks not being hardened, BUT it makes sense, because I've torn down literally thousands of engines in my lifetime. I can tell you that unless there was some kinda failure, the steel crank engines had much less crank wear, so that could certainly explain it. I must assume then that the steel crank is actually softer so that it can flex and therefore must be hardened as opposed to the cast, more brittle crank. Would that be correct?