The Australian Defence Force (ADF) is seeking to markedly improve the overall capability of the surface combatant force by the acquisition of a new Air Warfare Destroyer (AWD) through Project SEA 4000. At least three ships are to be built in Australia. The AWDs must have a capability to operate in extreme cold temperatures which could be experienced in the Southern Ocean. In such extreme conditions, steel can become susceptible to brittle fracture, particularly if subjected to combat damage above the water line. As a consequence, the AWDs must be constructed of a steel grade that has adequate low-temperature toughness to provide acceptable resistance to cold-brittle fracture. The steel grade originally used in the baseline Spanish F100-class did not meet Australian requirements. Consequently, the steel for the AWD design was changed from AH36 to DH36 for the hull, and DH55 was retained for the crack-arresting strakes. In collaboration with DSTO, the AWD Alliance characterised the low-temperature-toughness properties of DH36, and DH55. The notch toughness of these steels was investigated at a range of cold temperatures by Charpy V-notch (CVN) impact testing and explosive-load testing (ELT). The ductile-to-brittle-transition temperatures of these steels were determined to assess the risk of brittle fracture in cold environments. This paper presents the process of validation and testing performed for the DH55 and DH36 grade steels used in the construction of the AWD to ensure they support the required cold weather capability and satisfy ADF requirements.
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