Wire rods for bolts with excellent delayed fracture resistance after pickling and quenching tempering, and bolts

摘要

Provided is a wire rod for bolts excellent in pickling resistance and delayed fracture resistance after quenching and tempering. In mass%, C: 0.3 to 0.6%, Si: 1.0 to 3.0%, Mn: 0.1 to 1.5%, P: more than 0% and 0.020% or less, S: more than 0% and 0.020% or less, Cr: 0.3 to 1.5%, Al: 0.02 to 0.10%, N: 0.001 to 0.020%, the balance is iron and inevitable impurities, the ferrite area ratio at the diameter d × 1/4 position of the wire rod is 10 to 40%, and the balance is bainite The wire rod for bolts which consists of a pearlite, an inevitable structure | tissue, and is excellent in delayed fracture resistance after pickling and quenching tempering whose C amount in the position of 0.1 mm in depth from the surface layer is 50-100% of the base material C amount.