Actually, it could have come from anywhere in the Reich...
(Unless, of course, the Tirpitz was built before 1938...)
[For those who don't know, the Third Reich by January 1, 1939 {to be blunt and innacurate; I don't know when Czechosloazakia was annexed or when the Annschluss occured other than in the year Nineteen-Hundred, Thirty-Eight, A.D.} already consisted of Germany, Austria, and Czechoslovakia.... What I'm getting at is that the metal itself might not have been German...]
Just to make things more complicated...