I’m not a metallurgical engineer by any stretch and I don’t have a clue about the steel that was and is used to build submarines other than the fact that I have a 2″ cube of HY80 submarine steel. It weighs a heavy pound and the pressure hull – we called it the “people tank” – on our boats was made out of HY80. It would creak creak creak each time we went deep and then when we would come back up for air. From what smart people tell me but also from first hand experience, the HY80 was good stuff and it kept us safe all the time that we were submerged.
During a shipyard period, the shipyard workers had to cut a big hole in the back end of the boat so – they were nice guys – they cut out a bunch of 2″ cubes of HY80 for the boat’s crew members I’ve had the square sitting out in the living room on a shelf for years. I have always been careful, however, to not let someone – especially a little kid – grab it and then accidentally drop it on themselves. It would definitely badly bruise or break a toe!
Since the Internets can tell you more than me about HY80, I copied a short article from here and reproduced it below:
HY80 steel and variants, a flexible steel alloy, has for decades been used on modern U.S. and Allied submarines. Its flexible properties are what makes it an asset – it contracts and expands as sea pressure increases/decreases with submerged operations. Internal submarine decks are not actually attached to the hull – they’re actually hanging from suspended cables [the decks on our boats sat on rollers that ran in tracks that were attached to the pressure hull] and the decks are several inches from the sides of the hull to allow for the contraction as the boat goes deep.
[Years] ago, there was a lot of controversy about the Russian ALFA class Fast-Attack and her known Titanium hull, able to reach depths near 3000′.
Titanium is extremely strong, but it is not flexible – sure, the ALFA can dive deep, but each time it puts stress on the hull when it deep-dives it becomes more brittle over time. It’s like putting increased pressure on an eggshell – eventually it’ll crack. This doesn’t happen with HY80. It remains flexible over decades and hundreds of dives and surfaces.
So that is that. Since the days of HY80, newer submarines are being built with HY100 and even HY130. The difference between these steels is that the newer steels have a higher pressure rating. Meaning – deeper dives!