It was proven on one of the various Discovery shows on the Titanic, that the steel was of an inferior grade and when exposed to below freezing tempretures became brittle and as a result weakened the structure of the ship itself.
Yep, I saw that too. It was pretty conclusive that the steel used to construct the entire ship was of poor quality and became brittle when exposed to cold temperatures. I guess this would extend to the rivets too.