I suspect the the metal strips, if they exist, are part of the debris from the breakup as she sank. It is quite possible that there was some damage to the underside of the hull but remember the underside is the one portion of the hull that had a double bottom. All the intial reports indicate that water was entering from the side and not the bottom. It is also extremely unlikely that the impact could actually have torn off any hull plating-ice could pop rivets and bend hull plates but it would break away as it did so.
Also, the Titanic actually sank quite slowly. Two hours and forty minutes may sound quick to someone unfamiliar with maritime history, but in fact it's a long time. Some comparisons: Lusitania-18 minutes after being torpedoed in 1915, Titanic's sister ship Brittanic went \went down in less than an hour after she either struck a mine (as the Germans claimed) or was torpedoed (as the British claimed) in the Agean in 1916. The Empress of Ireland sank in 14 minutes after being rammed by the collier Storstad in the St. Lawrence River in 1914. To me the fact that it took nearly three hours for Titanic to sink is a good indication that the damage, while severe, was not beyond repair had Smith and the crew made any attempt to do so (see my article at the Steamship Historical Society of America's website: http://www.sshsa.org