High-strength bolt

Patent metadata

Field	Value
Publication number	US-10487372-B2
Application number	US-201615780574-A
Country	US
Kind code	B2
Filing date	Nov 15, 2016
Priority date	Dec 4, 2015
Publication date	Nov 26, 2019
Grant date	Nov 26, 2019

Abstract

A high-strength bolt is provided that has high strength and excellent hydrogen embrittlement resistance characteristics. A bolt according to this invention has a chemical composition consisting of, in mass %, C: 0.22 to 0.40%, Si: 0.10 to 1.50%, Mn: 0.20 to less than 0.40%, P: 0.020% or less, S: 0.020% or less, Cr: 0.70 to 1.45%, Al: 0.005 to 0.060%, Ti: 0.010 to 0.045%, B: 0.0003 to 0.0040%, N: 0.0015 to 0.0080% and O: 0.0020% or less, with a balance being Fe and impurities, and satisfying Formula (1) and Formula (2), and with the high-strength bolt having a tensile strength of 1000 to 1300 MPa.

0.50≤C+Si/10+Mn/5+5Cr/22≤0.85  (1)

Si/Mn>1.0  (2)

Where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1) and Formula (2).

First claim

The invention claimed is:

1. A high-strength bolt comprising a chemical composition consisting of, in mass %:
C: 0.22 to 0.40%,
Si: 0.10 to 1.50%,
P: 0.020% or less,
S: 0.020% or less,
Cr: 0.70 to 1.45%,
Al: 0.005 to 0.060%,
Ti: 0.010 to 0.045%,
B: 0.0003 to 0.0040%,
N: 0.0015 to 0.0080%,
O: 0.0020% or less,
Cu: 0 to 0.50%,
Ni: 0 to 0.30%,
Mo: 0 to 0.04%,
V: 0 to 0.05%, and
Nb: 0 to 0.050%, with a balance being Fe and impurities, and that satisfies Formula (1) and Formula (2),
wherein the high-strength bolt has a tensile strength of 1000 to 1300 MPa,
wherein a critical diffusible hydrogen content ratio HR, defined by Formula (A), is 1.20 or more:
0.50≤C+Si/10+Mn/5+5Cr/22≤0.85  (1)

Si/Mn>1.0  (2)

HR=Hc/Href,  (A)

where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1) and Formula (2), and
where, in Formula (A), a critical diffusible hydrogen content Hc is defined by a maximum hydrogen amount at which a hydrogen introduced test specimen does not rupture in a constant load test at tensile stress of nominal stress of 1080 MPa, and a critical diffusible hydrogen content Href is defined by a critical diffusible hydrogen content of a steel having a chemical composition corresponding to SCM435 of JIS G4053 (2008) as a reference.

2. The high-strength bolt according to claim 1 , wherein:
at a root of a thread of the high-strength bolt, an absolute value of a compressive residual stress of an outer layer of the root of the thread is 10 to 90% of the tensile strength of the high-strength bolt.

3. The high-strength bolt according to claim 1 , containing one or more types selected from a group consisting of, in mass %:
Cu: 0.02 to 0.50%,
Ni: 0.03 to 0.30%,
Mo: 0.01 to 0.04%, and
V: 0.005 to 0.05%.

4. The high-strength bolt according to claim 3 , containing, in mass %: Nb: 0.0015 to 0.050%.

5. The high-strength bolt according to claim 4 , wherein:
at a root of a thread of the high-strength bolt, an absolute value of a compressive residual stress of an outer layer of the root of the thread is 10 to 90% of the tensile strength of the high-strength bolt.

6. The high-strength bolt according to claim 3 , wherein:
at a root of a thread of the high-strength bolt, an absolute value of a compressive residual stress of an outer layer of the root of the thread is 10 to 90% of the tensile strength of the high-strength bolt.

7. The high-strength bolt according to claim 1 , containing, in mass %: Nb: 0.0015 to 0.050%.

8. The high-strength bolt according to claim 7 , wherein:
at a root of a thread of the high-strength bolt, an absolute value of a compressive residual stress of an outer layer of the root of the thread is 10 to 90% of the tensile strength of the high-strength bolt.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Neishi Yutaka
• Sano Naoyuki
• Matsui Naoki

Classifications

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C22C38/02

  containing silicon · CPC title

• C22C38/42

  with copper · CPC title

• C22C38/54

  with boron · CPC title

• C22C38/06

  containing aluminium · CPC title