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AssigneeNippon Steel Corporation
InventorsNobuyoshi Uno, Hideo Kanisawa
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The present invention provides a high strength bolt superior in delayed fracture resistant property having a bolt tensile strength of 1200 N/mm2 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/mm2) and tempering temperature T (° C.) satisfies the following expression (1), the relation between the bolt tensile strength TS (N/mm2) 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/mm2 to 1600 N/mm2 by quenching and tempering: TS≦1.1T+850 (1) TS≦550Ceq+1000 (2) where, 1 C eq = C + ( Mn / 6 ) + ( Si / 24 ) + ( Ni / 40 ) + ( Cr / 5 ) + ( Mo / 4 ) + V / 14 )
A high strength bolt characterized in that the relation between a tensile strength TS (N/mm2) of the high strength bolt and tempering temperature T (° C.) satisfies the following expression (1), the relation between the tensile strength TS (N/mm2) of the high strength bolt 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/mm2 to 1600 N/mm2 by quenching and tempering:
A steel material for a high strength bolt, characterized in that the relation between a tensile strength TS (N/mm2) of the high strength bolt and tempering temperature T (° C.) satisfies the following expression (1), the relation between the tensile strength TS (N/mm2) of the high strength bolt 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/mm2 to 1600 N/mm2 by quenching and tempering:
Dependencies are inferred from the claim text.