Legend wrote:Titanic is made of a low quality steel with a high content of iron, thus all of the brown-rust stalactites on the wreck. The Bismarck is a high carbon steel. Due to the purer and homogenous state it will last much much longer, because of the low iron content. I see Bismarck lasting longer than any nation currently standing.
The construction steel of Bismarck was ST-52. The composition of ST-52 is:
Balance is FE
The carbon content is relatively low to improve weldability. By comparision the C content of D-steel is 0.30% or 0.23% for DW. Of special interest in this context is the high Cu content. Copper significantly retards corrosion in marine enviroments. It also increases strength significantly. The armour grade steels such as Wh, Ww, and KC, will have Nickel, Chromium, and Molybdenum. These will all retard corrosion to a great extent. I have seen Cr/Mo steels of much lesser alloy amounts than armour grade steel remain shiney for a long time, even exposed to the elements and chlorides. German armour grade steels for naval use also carried 0.11% Cu.
Unless your dealing with a stainless steel or a 60% nickel steel..ect..., even armour grade steel is mostly (more than 90%) Fe. The Bismarck did not use high carbon content in its materials due to weldability concerns. The carbon content of Wh was at most 0.29%.
Of interest is the high % of welding. The heat effected zone of weld seems are prone to corrosion. These areas will likely degrade much quicker if exposed to the elements (paint scaped or burnt off ...ect...). Also the weld metal of weld seems is also more prone to corrosion than the non-heat effected areas of the parent metals. The exception will be welds of armour to armour or armour to construction steel. Here austenic stainless steel was used for the weld metal.
Another interesting aspect of the Bismarck is the extensive use of structural plates 20mm thick. That is a lot of metal to rust out.
What is interesting is that Andrea Doria has basically rusted out and collapsed on itself in many places already.