Steel for high-strength bolts which has excellent delayed fracture resistance and bolt formability, and bolt

Patent metadata

Field	Value
Publication number	US-10060015-B2
Application number	US-201415022857-A
Country	US
Kind code	B2
Filing date	Sep 16, 2014
Priority date	Sep 25, 2013
Publication date	Aug 28, 2018
Grant date	Aug 28, 2018

Abstract

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).

First claim

The invention claimed is:

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%; and
iron,
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)

where [C], [Si] [Mn] [Ni], [Cr], [Mo], and [V] indicate contents of C, Si, Mn, Ni, Cr, Mo, and V in percentage by mass, respectively.

2. The steel according to claim 1 , further comprising:
Cu: more than 0% and 0.70% or less.

3. A high-strength bolt with delayed fracture resistance, wherein the high-strength bolt is obtained from the steel according to claim 1 , and a grain size number of a prior austenite crystal grain size of the steel is 10.0 or more.

4. A high-strength bolt with delayed fracture resistance and a tensile strength of 1,100 to 1,400 MPa, obtained from a process comprising
quenching the steel according to claim 1 from 880 to 960° C. and
then tempering the steel at 550 to 650° C.

5. The steel according to claim 1 , wherein the content of C is 0.10% or more and less than 0.25%.

6. The steel according to claim 1 , wherein the content of C ranges from 0.10% to 0.18%.

Assignees

• Kobe Steel Ltd

Inventors

• Matsumoto Yosuke
• Inada Atsushi
• Chiba Masamichi
• Ureshino Yoshimasa
• Kato Reiko

Classifications

• C22C38/50 Primary

  with titanium or zirconium · CPC title

• C22C38/02

  containing silicon · CPC title

• C21D1/18

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• C22C38/46

  with vanadium · CPC title

• C21D6/005

  containing Mn · CPC title