Thick composite-phase steel having excellent durability and manufacturing method therefor

A composite phase steel having excellent material and durability uniformity and a thickness of 5 mm or more, the composite-phase steel comprising:

• by wt %, C:
• 0.05 to 0.15%, Si:
• 0.01 to 1.0%, Mn:
• 1.0 to 2.3%, Al:
• 0.01 to 0.1%, Cr:
• 0.005 to 1.0%, P:
• 0.001 to 0.05%, S:
• 0.001 to 0.01%, N:
• 0.001 to 0.01%, Nb:
• 0.005 to 0.07%, Ti:
• 0.005 to 0.11%, and a balance of Fe and inevitable impurities;
• and
• a microstructure comprising:
• a mixed phase of ferrite and bainite as a base structure;
• a pearlite phase;
• a martensite and austenite (MA) phase;
• and a martensite phase, wherein an area fraction of each of the pearlite phase and the martensite and austenite (MA) phase is less than 5%, and an area fraction of the martensite phase is less than 10%,
• wherein, when a coil in a wound state is divided, in a lengthwise direction, into three parts:
• head, mid, and tail parts, a product of tensile strength, elongation, and fatigue strength of an outer wound portion of the coil, which is a region of the head part and the tail part, is 25×105 MPa2·% or greater, and a product of tensile strength, elongation, and fatigue strength of an inner wound portion of the coil, which is a region of the mid part, is 24×105 MPa2·% or greater.