High-strength steel plate excellent in drop weight properties

摘要

Disclosed is a high-strength steel plate having a predetermined chemical composition, in which a microstructure of the steel plate at a depth of one-fourth to one half the thickness from a surface has an area fraction of bainite of 90% or more, an average lath width of bainite of 3.5 μm or less, and a maximum equivalent circle diameter of martensite-austenite constituents in bainite of 3.0 μm or less. The steel plate exhibits high strengths and good drop weight properties and is useful as structural materials for offshore structure, ships, and bridges, as well as materials for pressure vessels in nuclear power plants.

主权项

1. A high-strength steel plate, comprising iron, and by mass percent based on a total mass of the steel plate:
from 0.03% to 0.150% of carbon (C); from 0% or more to 0.5% of silicon (Si); from 1.0% to 2.0% of manganese (Mn); from more than 0% to 0.015% of phosphorus (P); from more than 0% to 0.01% of sulfur (S); from 0.005% to 0.06% of aluminum (Al); from 0.10% to 0.5% of chromium (Cr); from 0.05% to 0.5% of molybdenum (Mo); from more than 0% to 0.10% of vanadium (V); from 0.0020% to 0.010% of nitrogen (N); and from more than 0% to 0.010% of oxygen (O), wherein a microstructure of the steel plate at a depth of one-fourth to one half the thickness from a surface of the steel plate has an area fraction of bainite of 90% or more, an average lath width of bainite of 3.5 μm or less, and a maximum equivalent circle diameter of martensite-austenite constituents in bainite of 3.0 μm or less.