HY-80

HY-80 is a high-tensile alloy steel. It is most notable for its use in the construction of pressure hulls for US nuclear submarines in the 1950s to 1980s.

The 'HY' steels are a series of steels with high yield strength, hence the name. Their numbers, HY-80, HY-100, HY-130 refer to their yield strength in ksi, i.e. HY-80 has a yield strength of 80,000 psi (550 MPa), and HY-100 of 100,000 psi (690 MPa).

Submarines

The need to develop improved steels was driven by a desire for deeper-diving submarines. To avoid detection by sonar, submarines ideally operate at least 100 metres below the Sonic Layer Depth. World War II submarines operated at a total depth rarely more than 100 metres. With the development of nuclear submarines, their new independence from the surface for an air supply to their diesel engines meant that they could focus more on hidden operation at depth, rather than operating largely as surface-cruising submersibles. The increased power of a nuclear reactor allowed their hulls to become larger and faster than previously. Developments in sonar also made them able to hunt effectively at depth, rather than relying on visual observations from periscope depth. All of these factors drove a need for improved steels to build stronger pressure hulls.