METHOD FOR PRODUCING CARBON FIBER BUNDLE, AND CARBON FIBER BUNDLE

PROBLEM TO BE SOLVED: To provide a carbon fiber which has both of high strand strength and high strand elastic modulus simultaneously and excellent quality and allows even the CFRP (carbon fiber-reinforced plastic) obtained by using an extremely small amount thereof to exhibit excellent mechanical strength.SOLUTION: A carbon fiber bundle has 300-600 mm of an average splittable distance, 5,900 MPa or higher strand strength, 320 GPa or higher strand elastic modulus, and 0.5-3 pieces/m of a single fiber breaking number. A method for producing the carbon fiber bundle comprises the steps of: flame-proofing a polyacrylonitrile precursor fiber bundle to obtain a flame-proofed fiber bundle; pre-carbonizing the flame-proofed fiber bundle to obtain a pre-carbonized fiber bundle which is untwisted substantially and has 150-500 mm of the average splittable distance; and carbonizing the pre-carbonized fiber bundle in an inert gas atmosphere and in a predetermined temperature range while exerting predetermined carbonization tension thereon to obtain the substantially-untwisted carbon fiber bundle.