High-strength bolt excellent in delayed fracture resistance characteristics and its steel product

Abstract

The present invention provides a high strength bolt superior in delayed fracture resistant property having a bolt tensile strength of 1200 N / mm<2> or more and a steel material for the same. <??>A high strength bolt comprised of a head portion and shaft portion formed by a steel material, wherein the relation between a bolt tensile strength TS (N / mm<2>) and tempering temperature T ( DEG C) satisfies the following expression (1), the relation between the bolt tensile strength TS (N / mm<2>) and the carbon equivalent Ceq (%) calculated from the chemical composition of the steel material used for the high strength bolt satisfies the following expression (2), and the tensile strength of the bolt is refined to a range of 1200 N / mm<2> to 1600 N / mm<2> by quenching and tempering: <DF NUM="(1)">TS≤.1T+850 < / DF> <DF NUM="(2)">TS≤550Ceq+1000 < / DF> where, <DF>Ceq=C+(Mn / 6)+(Si / 24)+(Ni / 40) +(Cr / 5)+(Mo / 4)+(V / 14) < / DF>

Description

technical field [0001] The present invention relates to high-strength bolts and their steel materials used for construction such as civil engineering, construction or various machinery and equipment structures, and in particular to bolts with 1200N / mm 2 High-strength bolts and steel products with excellent tensile strength and delayed fracture resistance of the above-mentioned bolts. Background technique [0002] As is well known, when joining steel materials used in various industrial fields, in addition to various welding joining methods, bolt joining methods are generally used. In such a bolt joint method, the high strength of steel is promoted in pursuit of economy and technological progress, and especially in the fields of civil engineering and construction, friction of high-strength bolts with high joint reliability and excellent operability are often used. Joining method. [0003] As high-strength bolts for frictional joints, for example, sets of high-strength hexag...

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Problems solved by technology

This can reduce the stress concentration acting on the threaded part 3, but even with such a shape, the stress concentration factor acting on the central part M of the thread root 4c of the threaded thread 4 is 2.54, which corresponds to 1200N / mm 2 When the standard bolt tension of the above tensile strength is stretched along the X-X direction of the bolt axis, the thread root of the thread tooth only produces plastic strain, which cannot reach 1200N / mm 2 Treatment of delayed fracture occurrence of high-strength bolts above tensile strength

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