STEEL FOR HIGH STRENGTH BOLT EXCELLENT IN DELAYED FRACTURE RESISTANCE IN CORROSION ENVIRONMENT AND HIGH STRENGTH BOLT

摘要

PROBLEM TO BE SOLVED: To provide a steel for a high strength bolt having a tensile strength of 1270 MPa or more and capable of exhibiting efficient delayed fracture resistance even under environment exposed to atmosphere or weather or environment accompanying with corrosion due to salt water and the like, and to provide a high strength bolt obtained from the steel for the bolt.;SOLUTION: The steel for a high strength bolt of the present invention contains C:0.15 to 0.21%, Si:1.5 to 2.0%, Mn:2.0% or less (excluding 0%), Cr:2.5 to 5.0%, Ca:0.05% or less (excluding 0%), and/or Mg:0.05% or less (excluding 0%) and the balance iron with inevitable impurities, and has the total content of Ca and Mg of 0.0008% or more, and a micro structure is a mixed structure of ferrite and perlite.;COPYRIGHT: (C)2014,JPO&INPIT