| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel plate excellent in ductile fracture characteristic as well as in arrest property, capable of exhibiting, even if brittle fracture crack occurs, excellent property of arresting the propagation of the crack and also exhibiting excellent ductility characteristic even against ductile fracture at collision. SOLUTION: This steel plate has a microstructure constituted practically of ferritic structure and pearlitic structure. When the steel plate is divided into three layers consisting of both surface parts of the plate and a central part, each surface part is constituted, each over a thickness of >=5% of plate thickness, of a layer having >=50% ferritic structure having ferrite grains with an area of <=5μm circle-equivalent grain size and 2-4 aspect ratio; and the central part is constituted, over the thickness of >=50% of plate thickness, of the layer having ferrite grains of 4-10μm circle-equivalent average grain size and <=2 aspect ratio.
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