Oil country tubular goods with dual phase structure and producing method thereof

Patent metadata

Field	Value
Publication number	US-9188253-B2
Application number	US-201113806415-A
Country	US
Kind code	B2
Filing date	Jul 13, 2011
Priority date	Jul 13, 2010
Publication date	Nov 17, 2015
Grant date	Nov 17, 2015

Abstract

A steel pipe with dual phase structure includes, as chemical composition, by mass %, C: 0.07% to 0.15%, Si: 0.1% to 0.5%, Mn: 0.8% to 1.9%, Nb: 0.020% to 0.10%, P: limited to 0.05% or less, S: limited to 0.01% or less, Al: limited to 0.1% or less, and a balance consisting of iron and unavoidable impurities, wherein, when [X] is amount of element X in mass %, carbon equivalent Ceq defined by Equation of Ceq=[C]+[Mn]/6 is 0.25 to 0.40 and [Nb]×[C]≧0.002 is satisfied, and includes, as metallographic structure, by area %, ferrite of 80% to 98% and martensite, residual austenite, or mixture thereof of 2% to 20% in total, wherein average grain size of ferrite is 1 μm to less than 8 μm and average grain size of martensite, residual austenite, or mixture thereof is 0.1 μm to 2 μm.

First claim

The invention claimed is:

1. A steel pipe with a dual phase structure, the steel pipe comprising, as a chemical composition, by mass %,
C: 0.07% to 0.15%,
Si: 0.1% to 0.5%,
Mn: 0.8% to 1.9%,
Nb: 0.020% to 0.10%,
P: limited to 0.05% or less,
S: limited to 0.01% or less,
Al: limited to 0.1% or less, and
a balance consisting of iron and unavoidable impurities,
wherein a carbon equivalent Ceq defined by an (Equation 1) is 0.25 to 0.40 and [Nb]×[C]≧0.002 is satisfied when a [X] is an amount of an element X in mass %, and
the steel pipe with the dual phase structure comprising, as a metallographic structure, a ferrite and a secondary hard phase,
wherein, by area % the ferrite is 80% to 98% and the secondary hard phase is 2% to 20%,
wherein the secondary hard phase consists of a martensite, a residual austenite, or a mixture thereof, and
wherein an average grain size of the ferrite is 1 μm to less than 8 μm and an average grain size of the secondary hard phase is 0.1 μm to 2 μm,
Ceq=[C]+[Mn]/6  (Equation 1)

where the [X] expresses the amount of the element X in mass %.

2. The steel pipe with the dual phase structure according to claim 1 , further comprising, as the chemical composition, by mass %, at least one of
V: 0.0001% to 0.02%,
Ti: 0.005% to 0.03%,
Ca: 0.001% to 0.010%, and
N: 0.001% to 0.01%,
wherein [V]/[Nb]≦1/3 is satisfied when the [X] is the amount of the element X [in mass %] and the carbon equivalent Ceq is defined as an (Equation 2) on behalf of the (Equation 1),
Ceq=[C]+[Mn]/6+[V]/5  (Equation 2)

where the [X] expresses the amount of the element X in mass %.

3. The steel pipe with the dual phase structure according to claim 2 ,
wherein the Nb content of the chemical composition is 0.040% to 0.10% and [Nb]×[C]≧0.003 is satisfied when the [X] is the amount of the element X in mass %.

4. The steel pipe with the dual phase structure according to claim 2 ,
wherein a plate thickness of the steel pipe with the dual phase structure is 5 mm to 15 mm.

5. The steel pipe with the dual phase structure according to claim 2 ,
wherein the chemical composition, by mass %, consists of
C: 0.07% to 0.15%;
Si: 0.1% to 0.5%;
Mn: 0.8% to 1.9%;
Nb: 0.020% to 0.10%;
P: limited to 0.05% or less;
S: limited to 0.01% or less;
Al: limited to 0.1% or less;
at least one selected from the group consisting of
V: 0.0001% to 0.02%,
Ti: 0.005% to 0.03%,
Ca: 0.001% to 0.010%, and
N: 0.001% to 0.01%; and

the balance consisting of iron and unavoidable impurities.

6. The steel pipe with the dual phase structure according to claim 2 , wherein the chemical composition is free of Ni, Cu, Cr and Mo.

7. The steel pipe with the dual phase structure according to claim 2 ,
wherein, by area %, the ferrite is 80% to 98% and the secondary hard phase is 2% to 7%.

8. The steel pipe with the dual phase structure according to claim 2 ,
wherein the metallographic structure, by area %, consists of the ferrite and the secondary hard phase.

9. The steel pipe with the dual phase structure according to claim 2 ,
wherein in the metallographic structure, by area %, a total amount of portions except for the ferrite and the secondary hard phase are limited to 2% or less.

10. The steel pipe with the dual phase structure according to claim 1 ,
wherein the Nb content of the chemical composition is 0.040% to 0.10% and [Nb]×[C]≧0.003 is satisfied when the [X] is the amount of the element X in mass %.

11. The steel pipe with the dual phase structure according to claim 1 ,
wherein a plate thickness of the steel pipe with the dual phase structure is 5 mm to 15 mm.

12. The steel pipe with the dual phase structure according to claim 1 ,
wherein the chemical composition, by mass %, consists of
C: 0.07% to 0.15%,
Si: 0.1% to 0.5%,
Mn: 0.8% to 1.9%,
Nb: 0.020% to 0.10%,
P: limited to 0.05% or less,
S: limited to 0.01% or less,
Al: limited to 0.1% or less, and
the balance consisting of iron and unavoidable impurities.

13. The steel pipe with the dual phase structure according to claim 1 , wherein the chemical composition is free of Ni, Cu, Cr and Mo.

14. The steel pipe with the dual phase structure according to claim 1 ,
wherein, by area %, the ferrite is 80% to 98% and the secondary hard phase is 2% to 7%.

15. The steel pipe with the dual phase structure according to claim 1 ,
wherein the metallographic structure, by area %, consists of the ferrite and the secondary hard phase.

16. The steel pipe with the dual phase structure according to claim 1 ,
wherein in the metallographic structure, by area %, a total amount of portions except for the ferrite and the secondary hard phase are limited to 2% or less.

17. A producing method of a steel pipe with a dual phase structure, the method comprising,
a hot rolling process of making a hot rolled steel plate under a condition in which an average grain size of a ferrite is controlled to be 1 μm to less than 10 μm by using a steel material which includes, as a chemical composition, by mass %,
C: 0.07% to 0.15%,
Si: 0.1% to 0.5%,
Mn: 0.8% to 1.9%,
Nb: 0.020% to 0.10%,
P: limited to 0.05% or less,
S: limited to 0.01% or less,
Al: limited to 0.1% or less, and
a balance consisting of iron and unavoidable impurities,
wherein a carbon equivalent Ceq defined by an (Equation 3) is 0.25 to 0.40 and [Nb]×[C]≧0.002 is satisfied when a [X] is an amount of an element X in mass %,
a pipe-making process of making a steel pipe of the hot rolled steel plate,
a heating and quenching process of heating the steel pipe to a temperature of more than Ac 1 at which an austenite transformation starts to less than Ac 3 at which the austenite transformation finishes and of quenching,
Ceq=[C]+[Mn]/6  (Equation 3)

where the [X] expresses the amount of the element X in mass %, and
the steel pipe with the dual phase structure comprising, as a metallographic structure, a ferrite and a a secondary hard phase,
wherein, by area %, the ferrite is 80% to 98% and the secondary hard phase is 2 to 20%, and
wherein the secondary hard phase consists of a martensite, a residual austenite, or a mixture thereof.

18. The producing method of the steel pipe with the dual phase structure according to claim 17 , wherein the steel material further includes, as the chemical composition, by mass %, at least one of
V: 0.0001% to 0.02%,
Ti: 0.005% to 0.03%,
Ca: 0.001% to 0.010%, and
N: 0.001% to 0.01%,
wherein [V]/[Nb]≦1/3 is satisfied when the [X] is the amount of the element X [in mass %] and the carbon equivalent Ceq is defined as an (Equation 4) on behalf of the (Equation 3),
Ceq=[C]+[Mn]/6+[V]/5  (Equation 4)

where the [X] expresses the amount of the element X in mass %.

19. The producing method of the steel pipe with the dual phase structure according to claim 18 ,
wherein the chemical composition, by mass %, consists of
C: 0.07% to 0.15%;
Si: 0.1% to 0.5%;
Mn: 0.8% to 1.9%;
Nb: 0.020% to 0.10%;
P: limited to 0.05% or less;
S: limited to 0.01% or less;
Al: limited to 0.1% or less;
at least one selected from the group consisting of
V: 0.0001% to 0.02%,
Ti: 0.005% to 0.03%,
Ca: 0.001% to 0.010%, and
N: 0.001% to 0.01%; and

the balance consisting of iron and unavoidable impurities.

20. The producing method of the steel pipe with the dual phase structure according to claim 17 ,
wherein the chemical composition, by mass %, consists of
C: 0.07% to 0.15%,
Si: 0.1% to 0.5%,
Mn: 0.8% to 1.9%,
Nb: 0

Assignees

• Sawamura Mitsuru
• Asahi Hitoshi
• Tsuru Eiji
• Agata Jun
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Sawamura Mitsuru
• Asahi Hitoshi
• Tsuru Eiji
• Agata Jun

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• F16L9/02 Primary

  of metal (F16L9/16 - F16L9/22 take precedence) · CPC title

• C21D8/0226 Primary

  Hot rolling · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/06

  containing aluminium · CPC title