Offshore construction generally refers to the installation of structures and facilities in the marine environment for the production and transportation of electricity, petroleum, gas, and other resources.The shipbuilding industry is growing globally owing to the increasing freight volume, and drilling rigs are also actively being constructed for the development of marine resources (Lee et al., 2011;Song et al., 2013;Kim and Kim, 2018). High-strength steels are used to construct these offshore structures as they are becoming increasingly large and the environments in which they are used are becoming increasingly harsh. However, the possibility of microcracks developing in high-strength steels is high in harsh environments (variable load action), and cracks that have formed can grow rapidly. Microcracks can develop when processing materials and when transporting and installing these structures. To ensure the safety and reliability of offshore structures, initial defects that lead to microcracking should be rendered harmless.Recently, many researchers have been actively attempting to render cracks harmless using peening. Peening effectively induces a compressive residual stress in high-strength steel (Al-Hassani, 1982;Al-Obaid, 1990;Harada et al., 2007) and increases its fatigue life and strength (Lee and Kim, 1997;Benedetti et al., 2002). As the heat-affected zone of welds is prone to cracking, studies have been conducted on improving fatigue life and rendering cracks harmless by peening the weld toe (Houjou et al., 2013a;Fueki et al., 2015;. Furthermore, studies simulating the behavior of steels with existing microcracks have been conducted to investigate the use of peening to render cracks harmless (Takahashi et al., 2012;Houjou et al., 2013b). A crack is determined to be harmless using the relationship

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In this study, the effect of hot stamping forming process on the properties change of compound layer in Al–Si coated high-strength steel sheet with different thickness was investigated. The coating layer in hot stamped high-strength steel sheet was composed of a diffusion layer and a compound layer. As the hot stamping temperature and holding time for forming increased, the thickness of the compound layer in the Al–Si coated high-strength steel sheet increased. The thickness of coating layer with the hot stamping for 500 sec at 890, 910 and 950 °C was obtained 8.9, 11.8, and 20.6 micrometer, respectively. The thickness of coating layer with hot stamping for 180, 500 and 550 sec at 910 oC was obtained 5.7, 11.8, and 17.8 micrometer, respectively. The compound layer in hot stamped high-strength steel sheet with Al–Si coating layer consists of Al5.4Fe2 and Fe2Si phases. In the compound layer, Al and Si were irregularly distributed.