HIGH STRENGTH BOLT SUPERIOR IN DELAYED FRACTURE RESISTANCE AND FATIGUE CHARACTERISTICS, AND MANUFACTURING METHOD THEREOF

摘要

PROBLEM TO BE SOLVED: To provide a high strength bolt superior in delayed fracture resistance and fatigue characteristics while securing tensile strength not less than 1500 MPa, and a manufacturing method thereof.SOLUTION: As for a high strength bolt, the tensile strength is not less than 1500 MPa, and when the compressive residual stress at 0.05 mm in depth position from the bottom of thread surface of the bolt is not less than the tensile strength×0.15 MPa and the diameter in the shank of the bolt is D, the mean diameter of the former austenite crystal grain in the D/4 position is 5-15 μm.SELECTED DRAWING: None