Seamless steel pipe and method for producing same

• US 10,131,962 B2
• Filed: 08/28/2013
• Issued: 11/20/2018
• Est. Priority Date: 08/29/2012
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel & Sumitomo Metal Corporation (Nippon Steel Corporation)
• Inventors: Arai, Yuji, Kobayashi, Kenji, Nagayama, Hiroyuki
• Primary Examiner(s): Dunn, Colleen P
• Assistant Examiner(s): Wang, Nicholas A
• Application Number:
  US14/423,480
• Publication Number:
  US 20150315685A1
• Time in Patent Office: 1,910 Days
• CPC Class Codes: C21D 1/18 Hardening C21D1/02 takes precedence; Quenching with or without subsequent tempering quenching devices C21D1/62
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 6/002 containing Cr C21D6/004 takes precedence
• CPC Class Codes: C21D 6/004 containing Cr and Ni
• CPC Class Codes: C21D 6/005 containing Mn
• CPC Class Codes: C21D 6/008 containing Si
• CPC Class Codes: C21D 8/10 during manufacturing of tubular bodies
• CPC Class Codes: C21D 8/105 of ferrous alloys
• CPC Class Codes: C21D 9/08 for tubular bodies or pipes
• CPC Class Codes: C21D 9/085 Cooling or quenching
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/20 with copper
• CPC Class Codes: C22C 38/22 with molybdenum or tungsten
• CPC Class Codes: C22C 38/24 with vanadium
• CPC Class Codes: C22C 38/26 with niobium or tantalum
• CPC Class Codes: C22C 38/28 with titanium or zirconium
• CPC Class Codes: C22C 38/38 : with more than 1.5% by weight of manganese
• CPC Class Codes: C22C 38/42 : with copper
• CPC Class Codes: C22C 38/44 : with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 : with vanadium
• CPC Class Codes: C22C 38/48 : with niobium or tantalum
• CPC Class Codes: C22C 38/50 : with titanium or zirconium
• CPC Class Codes: C22C 38/58 : with more than 1.5% by weight of manganese
• CPC Class Codes: F16L 9/02 : of metal F16L9/16 - F16L9/22 take precedence

Abstract

A seamless steel pipe has a carbon equivalent Ceq of 0.50% to 0.58%, and contains specified carbides containing Mo at a ratio of 50 mass % or more, V, and at least one selected from the group consisting of Ti and Nb, and having a size of 20 nm or more.

Claims

1. A seamless steel pipe comprising, as a chemical composition, by mass %:

C;

0.02% to 0.10%;

Si;

0.05% to 0.5%;

Mn;

1.0% to 2.0%;

Mo;

0.5% to 1.0%;

Cr;

0.1% to 1.0%;

Al;

0.01% to 0.10%;

P;

0.03% or less;

S;

0.005% or less;

Ca;

0.0005% to 0.005%;

V;

0.010% to 0.040%;

N;

0.002% to 0.007%;

at least one selected from the group consisting of Ti;

0.008% or less and Nb;

0.02% to 0.05%; and

a balance comprising Fe and impurities,

wherein a carbon equivalent Ceq defined by the following Formula (1) is 0.50% to 0.58%, and

specified carbides containing Mo at a ratio of 50 mass % or more, V, and at least one selected from the group consisting of Ti and Nb, and having a size defined by an average value of major axes of 20 nm or more are contained,

Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 

 

(1)

here, into each of the symbols of elements in the Formula (1), the amount of a unit mass % of a corresponding element is substituted, and in the case where an element corresponding to the symbol of the element is not contained, “

0”

is substituted into the corresponding symbol of the element,

wherein a yield strength is 550 MPa or more, and a Vickers hardness at a position on an inner side 1 mm away from an inner surface is 248 HV10 or less.

2. The seamless steel pipe according to claim 1, further comprising

at least one selected from the group consisting of Cu:

1.0% or less and Ni;

1.0% or less in place of some of Fe.

3. The seamless steel pipe according to claim 2,

wherein the seamless steel pipe is produced by a process including a quenching and a tempering at 660°

C. to 700°

C.

4. The seamless steel pipe according to claim 1,

wherein the seamless steel pipe is produced by a process including a quenching and a tempering at 660°

C. to 700°

C.

5. The seamless steel pipe according to claim 1, wherein the size of the specified carbides is 20 nm to 70 nm.

6. The seamless steel pipe according to claim 1, wherein a tensile strength is 653 MPa or more.