A ball bat includes a substantially tubular frame having a handle portion and a primary hitting portion. The handle portion is formed of a non-steel material. The hitting portion is formed separately from, and coupled to, the handle portion. The hitting portion is formed of a steel and has an inner surface...http://www.google.co.uk/patents/US7175552?utm_source=gb-gplus-sharePatent US7175552 - Ball bat formed of carburized steel
