Ever play with Armox 500? It's got more of everything (Cr, C, Mo, Mn and I think some Boron thrown in there just for extra measure.) in it that commonly makes steel alloys tougher. Ar is commonly used as a "cheap" armor plate and where flexibility is concerned. I've seen where Armox failed in the cyclic loading, but can't really go into detail or I'd have to shoot you... then some one else would have to shoot me just for having told you...