STEEL FOR HIGH-STRENGTH BOLTS WHICH HAS EXCELLENT DELAYED FRACTURE RESISTANCE AND BOLT FORMABILITY, AND BOLT

摘要

To provide a steel for high-strength bolts, which can exhibit the sufficient delayed fracture resistance under the severe environment, and also has excellent bolt formability. The steel for high-strength bolts of the present invention includes C: 0.10 to 0.30%; and Ni: 0.4 to 0.7%, with the chemical composition being appropriately adjust, and satisfies the following formulas (1) and (2):;0.85≦[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2≦1.3  (1);[C]−(0.07×[Mo]+0.20×[V])≦0.20  (2)

主权项

1. A steel for high-strength bolts, comprising, in percentage by mass:
C: 0.10 to 0.30%; Ni: 0.4 to 0.7%; Si: 0% or more and 0.2% or less; Mn: 0.3 to 0.8%; P: more than 0% and 0.03% or less; S: more than 0% and 0.03% or less; Cr: 0.8 to 1.2%; Mo: 0.8 to 1.5%; V: 0.05 to 0.13%; Ti: 0.02 to 0.08%; Al: 0.01 to 0.1%; N: 0.001 to 0.01%, iron; and inevitable impurities, wherein: the steel satisfies formulas (1) and (2):
0.85≦[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2≦1.3  (1)[C]−(0.07×[Mo]+0.20×[V])≦0.20  (2); and [C], [Si], [Mn], [Ni], [Cr], [Mo], and [V] indicate contents of C, Si, Mn, Ni, Cr, Mo, and V in percentage by mass, respectively.