High-strength steel material having enhanced resistance to crack initiation and propagation at low temperature and method for manufacturing the same

A high-strength steel material comprising, by weight, carbon (C):

• 0.01% to 0.07%, silicon (Si):
• 0.002% to 0.2%, manganese (Mn):
• 1.7% to 2.5%, Sol. aluminum (Sol.Al):
• 0.001% to 0.035%, niobium (Nb):
• 0.03% or less (not including 0%), vanadium (V):
• 0.01% or less (not including 0%), titanium (Ti):
• 0.001% to 0.02%, copper (Cu):
• 0.01% to 1.0%, nickel (Ni):
• 0.01% to 2.0%, chromium (Cr):
• 0.01% to 0.5%, molybdenum (Mo):
• 0.001% to 0.5%, calcium (Ca):
• 0.0002% to 0.005%, nitrogen (N):
• 0.001% to 0.006%, phosphorus (P):
• 0.02% or less (not including 0%), sulfur (S):
• 0.003% or less (not including 0%), oxygen (O):
• 0.0025% or less (not including 0%), a balance of iron (Fe), and inevitable impurities, and satisfying relational expression (1),
• wherein a microstructure of the high-strength steel material comprises polygonal ferrite and acicular ferrite in a total amount of 30 area % or more, and comprises a martensite-austenite composite phase (MA phase) in an amount of 1.1 to 3.0 area %,
• wherein the MA phase has an average size of 2.5 μm or less, when measured at an equivalent circular diameter,
• wherein the steel material comprises inclusions, wherein inclusions having a size of 10 μm or more, among the inclusions, has 11/cm2 or less, and
• wherein a weld heat-affected zone has an impact energy value at −40° C. of 200 J to 405 J, and a crack-tip opening displacement (CTOD) value at −20° C. of 0.25 mm or more:
• 5*C+Si+10*sol.Al≤0.5 Relational expression (1):
• where each symbol of the element refers to a value indicating each element content in weight %.