Brittle Fracture Avoidance Technology in Large Structures with Thick Steel Plates.

The 460-MPa-class steel was developed by thermomechanical control process for shipbuilding, and the maximum plate thickness was 100 mm, which has the fine grain size as 5-20 m. The surfaces were studied in terms of micro and nano structures, surface roughness, and surface energy to evaluate the effect of fracture toughness in large steel structure. The thick steel plate has possibility to occur unstable fracture because the fracture toughness will be decrease with increase of thickness. The increase in the temperature in thermomechanical control process accelerated the surface energy and created both micro and nano structures on the surfaces more effectively. It was effective to avoid brittle fracture in the base metal when the brittle crack was deviated into base metal. The developed 460-MPa-class steel plate improves the brittle fracture safety despite being a thick steel plate through the fine grain size. They had to be designed in such a manner as to avoid crack initiation, especially in welded joints. In this study, brittle crack arrest designs were developed for large weld construction using arrest design concept and micro and nano structures in high strength steel plate.