Ductile to Brittle Transition
Metals usually have a ductile failure. However, when they are cold, they can have a sudden transition from failing in a ductile manner to a brittle one. This is what happened to the Titanic. In the frigid water, the hull of the titanic made this transition. When it hit the iceberg, instead of denting the hull it cracked it in half with the fracture propagating quickly.