THICK STEEL PLATE EXCELLENT IN ULTRA LOW TEMPERATURE TOUGHNESS

摘要

PURPOSE: A thick steel plate with excellent extreme low temperature toughness is provided to implement the percentage of brittle fracture which is <=10% by having excellent extreme low temperature toughness at -196°C. CONSTITUTION: A thick steel plate with excellent extreme low temperature toughness is composed of, in wt%: C: 0.02-0.10; Si: 0.40 or less (excluding 0); Mn: 0.50-2.0 (excluding 0); P: 0.007 or less (excluding 0); S: 0.007% or less (excluding 0); Al: 0.005-0.050; Ni: 5.0-7.5; N: 0.010% or less (excluding 0); and the remainder Fe and inevitable impurities. The thick steel plate has the remainder austenite phase which exists at -196°C, and satisfies the volume percentage (V) of 2.0-12.0%. When the number density of an inclusion with the diameter of over 1.0 um per circular phase which exists on the thick steel plate is N, N is N<=200 unit/mm^2.