HY-80
[1] Using HY-80 steel requires careful consideration of the welding processes, filler metal selection and joint design to account for microstructure changes, distortion and stress concentration.
To avoid detection by sonar, submarines ideally operate at least 100 metres below the sonic layer depth.
[2] World War II submarines operated at a total depth of rarely more than 100 metres.
[3] As well as the obvious need for a hull strong enough not to be crushed at depth, the cyclical effect of hundreds of dives over a submarine's lifetime[i] mean that fatigue strength is also important.
[2] Boats of this construction included USS Nautilus, and the Skate-class, which were the first nuclear submarines, with the then-conventional hull shape.
Low-carbon STS became the forerunner of HY-80,[6] and was first used in 1953 for the construction of USS Albacore, a small diesel research submarine.
Albacore tested its eponymous teardrop hull shape, which would form a pattern for the following US nuclear classes.
[8] 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.
Alloying elements, weld procedures and weldment design all need to be coordinated and considered when looking to use HY-80 steel.
HY-80 and HY-100 are covered in the following US military specifications: The alloy content will vary slightly according to the thickness of the plate material.
Thicker plate will be more restrictive in its compositional alloy ranges due to the added weldability challenges created by enhanced stress concentrations in connective joints.
Manganese – Cleans impurities in steels (most commonly used to tie up sulfur) and also forms oxides that are necessary for the nucleation of acicular ferrite.
Acicular ferrite is desirable in HY-80 steels because it promotes excellent yield strength and toughness.
[16] Silicon – Oxide former that serves to clean and provide nucleation points for acicular ferrite.
Antimony, tin and arsenic are potentially dangerous elements to have in the compositional makeup due to their ability to form eutectics and suppress local melting temperatures.
The precise range of permitted alloy content varies slightly according to the thickness of the sheet.
[17] Welding of HY-130 is considered to be more restricted, as it is difficult to obtain filler materials that can provide comparable performance.
Hydrogen embrittlement is a high risk under all conditions for HY-80 and falls into zone 3 for the AWS method.
[21] Use of filler metals is required to introduce alloying materials that serve to form oxides that promote the nucleation of acicular ferrite.
[21] The HAZ is still a concern that must be addressed with proper preheat and weld procedures to control the cooling rates.
[22] Multipass welds require a minimum and maximum inter-pass temperature with the purpose to maintain yield strength and to prevent cracking.
The ER100S-1 has a lower Carbon and Nickel content to assist in the dilutive effect during welding discussed previously.
Acicular ferrite is formed with the presence of oxides and the composition of the filler metal can increase the formation of these critical nucleation sites.
The heat input can alter the microstructure in HAZ and the fusion zone alike and weld metal/HAZ toughness is a key consideration/requirement for HY-80 weldments.
[1] SAW as an example can temper previous weld passes due to its generally high heat input characteristics.
HY-80 has been found to have less in-plane weld shrinkage and less out-of-plane distortion than the common ABS Grade DH-36.
Destructive testing is not practical for inspecting completed weldments prior to being placed in service; therefore, NDE is preferred for this case.
