Hot-rolled steel strip for high strength electric resistance welding pipe and manufacturing method thereof

• US 20040187982A1
• Filed: 03/24/2004
• Published: 09/30/2004
• Est. Priority Date: 03/27/2003
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Shimizu, Tetsuo, Kami, Chikara, Nakata, Hiroshi, Iwata, Koji, Kageyama, Nobuyuki
• Granted Patent: US 7,501,030 B2
• Time in Patent Office: Days
• US Class Current: 148/653
• CPC Class Codes: B23K 35/3053 Fe as the principal constituent
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 8/0205 of ferrous alloys
• CPC Class Codes: C21D 8/105 of ferrous alloys
• CPC Class Codes: C21D 9/50 for welded joints
• CPC Class Codes: C21D 9/52 for wires; for strips ; for rods of unlimited length
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/16 containing copper

Abstract

A hot-rolled steel strip having superior low temperature toughness and weldability, which is suitably used as a starting material for high strength electric resistance welding pipe, is provided at a low cost without constructing new production facilities and increasing cost. The hot-rolled steel strip is low carbon steel containing at least one of about 0.5.% or less of Cu, about 0.5% or less of Ni, and about 0.5% or less of Mo, wherein Pcm represented by the following equation (1) is 0.17 or less:

Pcm=(% C)+(% Si)/30+((% Mn)+(% Cu))/20+(% Ni)/60+(% Mo)[7+(% V)/10   Equation (1),

(where (% M) indicates the content of element M on a mass percent basis), and the balance includes Fe and incidental impurities. In addition, in the entire microstructure, the ratio of bainitic ferrite, which is a primary phase, is controlled to be about 95 percent by volume or more.

Claims

1. A hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

on a mass percent basis,

about 0.005 to about 0.04% of C;

about 0.05 to about 0.3% of Si;

about 0.5 to about 2.0% of Mn;

about 0.001 to about 0.1% of Al;

about 0.001 to about 20.1% of Nb;

about 0.001 to about 0. 1% of V;

about 0.001 to about 0.1% of Ti;

about 0.03% or less of P;

about 0.005% or less of S;

about 0.006% or less of N;

at least one selected from the group consisting of about 0.5% or less of Cu, about 0.5% or less of Ni, and about 0.5% or less of Mo; and

the balance being Fe and incidental impurties,

wherein Pcm represented by the following equation (1) is 0.17 or less;

Pcm=(% C)+(% Si)/30+((% Mn)+(% Cu))/20+(% Ni)/60+(% Mo)/7+(% V)/10  

 

Equation (1),

in which (% M) indicates the content of element M on a mass percent basis, and

the hot-rolled steel stp is composed of bainitic ferrite as a primary phase at a content of about 95 percent by volume or more.

2. The hot-rolled steel strip according to claim 1;

wherein the ratio in percent of the amount of precipitated Nb to the total amount of Nb is from about 5 to about 80%.

3. The hot-rolled steel strip according to claim 1;

further comprising about 0.005% or less of Ca and/or REM on a mass percent basis.

4. The hot-rolled steel strip according to claim 2;

further comprising about 0.005% or less of Ca and/or REM on a mass percent basis.

5. The hot-rolled steel strip according to claim 1;

further comprising at least one component selected from the group consisting of about 0.1% or less of Cr and about 0.003% or less of B,

wherein Pcm′

represented by the following equation (2) is 0.17 or less;

Pcm′

=(% C)+(% Si)/30+((% Mn)+(% Cu)+(% Cr))/20+(% Ni)/60+(% Mo)/7+(% V)/10  

 

Equation (2),

in which (% M) indicates the content of element M on a mass percent basis.

6. The hot-rolled steel strip according to claim 2;

further comprising at least one component selected from the group consisting of about 0.1% or less of Cr and about 0.003% or less of B,

wherein Pcm′

represented by the following equation (2) is 0.17 or less;

Pcm′

=(% C)+(% Si)/30+((% Mn)+(% Cu)+(% Cr))/20+(% Ni)/60+(% Mo)/7+(% V)/10  

 

Equation (2),

in which (% M) indicates the content of element M on a mass percent basis.

7. The hot-rolled steel strip according to claim 3;

further comprising at least one component selected from the group consisting of about 0.1% or less of Cr and about 0.003% or less of B,

wherein Pcm′

represented by the following equation (2) is 0.17 or less;

Pcm′

=(% C)+(% Si)/30+((% Mn)+(% Cu)+(% Cr))/20+(% Ni)/60+(% Mo)/7+(% V)/10  

 

Equation (2),

in which (% M) indicates the content of element M on a mass percent basis.

8. The hot-rolled steel strip according to claim 4;

further comprising at least one component selected from the group consisting of about 0.1% or less of Cr and about 0.003% or less of B,

wherein Pcm′

represented by the following equation (2) is 0.17 or less;

Pcm′

=(% C)+(% Si)/30+((% Mn)+(% Cu)+(% Cr))/20+(% Ni)/60+(% Mo)/7+(% V)/10  

 

Equation (2),

in which (% M) indicates the content of element M on a mass percent basis.

9. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 1 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

10. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 2 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

11. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 3 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

12. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 4 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

13. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 5 to a temperature of about 1,000 to about. 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

14. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 6 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

15. A method for manufacturing a hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 7 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.

16. A method for manufacturing a hot-tolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising:

heating a steel slab having a composition according to claim 8 to a temperature of about 1,000 to about 1,300°

C.;

finish rolling the heated steel slab to form a steel strip;

completing finish rolling under the condition in which the steel strip has a surface temperature of about (Ar₃—

50°

C.) or more;

cooling the steel strip immediately after finish rolling; and

coiling the steel strip at a temperature of about 700°

C. or less for slow cooling.