Carbon fiber bundle and production method therefor

A carbon fiber bundle that satisfies:

• retaining a twist count of 2 turns/m or more when suspended with one end fixed and the other end free;
• having a single fiber diameter of 6.1 μm or more and a heat loss rate at 450° C. of 0.15% or less, and formula (1) wherein Lc is crystallite size and π002 is an orientation parameter of crystallites determined from bulk measurement of the entire fiber bundle:
• π002>4.0×Lc+73.2 (1).

A carbon fiber bundle that satisfies:

• retaining a surface layer twist angle of 0.2° or more when suspended with one end fixed and the other end free;
• having a single fiber diameter of 6.1 μm or more and a heat loss rate at 450° C. of 0.15% or less, and formula (1) wherein Lc is crystallite size and π002 is an orientation parameter of crystallites determined from bulk measurement of the entire fiber bundle:
• π002>4.0×Lc+73.2 (1).

A method of producing a carbon fiber bundle having a single fiber diameter of 6.1 μm or more and a heat loss rate at a temperature of 450° C. of 0.15% or less, comprising:

• performing stabilization of a precursor fiber bundle for polyacrylonitrile based carbon fiber, pre-carbonization thereof, and
• carbonization thereof performed in this order, a twist count and tension of the fiber bundle being 2 turns/m or more and 1.5 mN/dtex or more, respectively, in the carbonization step.

A method of producing a carbon fiber bundle retaining a surface layer twist angle of 0.2° or more when suspended with one end fixed and the other end free and having a single fiber diameter of 6.1 μm or more and a heat loss rate at a temperature of 450° C. of 0.15% or less, comprising:

• performing stabilization of a precursor fiber bundle for polyacrylonitrile based carbon fiber, pre-carbonization thereof, and
• carbonization thereof performed in this order, tension of the fiber bundle being 1.5 mN/dtex or more in the carbonization step.