WIRE MATERIAL FOR USE IN BOLTS THAT HAS EXCELLENT ACID PICKLING PROPERTIES AND RESISTANCE TO DELAYED FRACTURE AFTER QUENCHING AND TEMPERING, AND BOLT

摘要

A wire material for use in bolts that has excellent acid pickling properties and resistance to delayed fracture after quenching and tempering is provided. This wire material, for use in bolts and having excellent acid pickling properties and resistance to delayed fracture after quenching and tempering, contains, in mass%, C: 0.3-0.6%, Si: 1.0-3.0%, Mn: 0.1-1.5%, P: more than 0% and less than or equal to 0.020%, S: more than 0% and less than or equal to 0.020%, Cr: 0.3-1.5%, Al: 0.02-0.10%, and N: 0.001-0.020%, the remainder being iron and unavoidable impurities, wherein the ferrite area ratio in the position d×1/4 in the wire material, d being the diameter of the wire material, is 10-40%, the remainder being bainite, pearlite, and unavoidably occurring structures, and the amount of C in the position at a depth of 0.1 mm from the surface is 50-100% of the amount of C in the base material.