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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 , and HY-100 of .〔〔 == 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. The strength of a submarine hull is not merely that of absolute strength, but rather yield strength.〔 As well as the obvious need for a hull strong enough not to be crushed at depth, the hundreds of dives over a submarine's lifetime mean that the fatigue life is also an important issue. To provide resistance to fatigue, the hull must be designed so that the steel always operates below its elastic limit, i.e. the stress applied by pressure is less than its yield stress. The HY- series steels were developed to provide a high yield stress, so allowing this. US submarines post-WWII, both conventional and nuclear, had improved designs compared to the earlier Fleet submarines. Their steel was also improved and was the equivalent of "HY-42".〔 Boats of this construction included and the ''Skate''-classs, the first nuclear submarines and which were of conventional hull shape. The later ''Skipjack'' class, although of the new Albacore 'teardrop' hull form also used these earlier steels. Such boats had normal operating depths of some , and a crush depth of . Although the operating depths of submarines are highly secret, their crush depth limits can be calculated approximately, solely from knowledge of the steel strength. With the stronger HY-80 steel, this depth increased to ] and with HY-100 a depth of .〔 HY-80 steel was first used for the construction of in 1953, a small diesel research submarine. ''Albacore'' tested its eponymous teardrop hull shape, which would form a pattern for the following US nuclear classes. The first production submarines to use HY-80 steel were the ''Permit'' class. These reportedly had a normal operating depth of 1,300 feet, roughly two-thirds the crush depth limit imposed by the steel.〔 , the lead boat of this class, was lost in an accident in 1963. At the time, this unexplained accident raised much controversy about its cause and the new HY-80 steel used was looked at suspiciously, especially for theories about weld cracking having been the cause of the loss.〔〔〔 HY-100 steel was introduced for the deeper diving Seawolf class, although two of the preceding HY-80 ''Los Angeles'' class, (1987) and , had trialled HY-100 construction. is officially claimed to have a normal operating depth of "greater than 800 feet". Based on the reported operating depth of ''Thresher'', it may be assumed that the normal operating depth of ''Seawolf'' is roughly double the official figure.〔 HY-100 too was dogged by problems of weld cracking. ''Seawolf's'' construction suffered setbacks in 1991 and an estimated 15% or two years' work on hull construction had to be abandoned.〔 Although later solved, these extra costs (and the post-Soviet peace dividend) were a factor in reducing the planned 29 ''Seawolf'' submarines to just three constructed. 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「HY-80」の詳細全文を読む スポンサード リンク
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