Bolt

A bolt having a chemical composition comprising, in mass %,

• C:
• 0.18 to 0.80%,
• Si:
• 0.01 to 1.50%,
• Mn:
• 0.50 to 2.00%,
• Al:
• 0.005 to 0.080%,
• P:
• 0.030% or less,
• S:
• 0.030% or less,
• Ti:
• 0.005 to 0.100%,
• B:
• 0.0003 to 0.0050%,
• N:
• 0.0150% or less, and
• O:
• 0.0100% or less,
• the composition further comprising
• one or two or more elements selected from the group consisting of group A, group B, and group C below,
• with a balance consisting of Fe and impurities, wherein
• when a diameter of a shaft portion is D, 95% or more of a metallographic structure at a D/4 position is a hard structure;
• when βC is a full width at half maximum of a X-ray diffraction peak corresponding to a (211) plane of ferrite at a center of the shaft portion of a connection portion between a bolt head portion and the shaft portion and βMAX is a maximum value of the full width at half maximum of the X-ray diffraction peak corresponding to the (211) plane of the ferrite in a region from a surface of the connection portion to a depth of 500 μm toward a central axis of the shaft portion, a ratio βMAX/βC is 1.50 or less;
• and
• a tensile strength is from 800 to 1700 MPa:
• [group A] one or two or more elements selected from the group consisting of Cr:
• 1.50% or less, Mo:
• 0.50% or less, Nb:
• 0.050% or less, V:
• 0.20% or less, and W:
• 0.20% or less;
• [group B] one or two elements selected from the group consisting of Cu:
• 0.50% or less and Ni:
• 0.50% or less;
• and
• [group C] one or two or more elements selected from the group consisting of Ca:
• 0.0100% or less, Mg:
• 0.0100% or less, Ce:
• 0.020% or less, and Sn:
• 0.0400% or less.