STEEL PLATE FOR LINEPIPE HAVING ULTRA-HIGH STRENGTH AND EXCELLENT LOW TEMPERATURE TOUGHNESS AND MANUFACTURING METHOD OF THE SAME

• US 20100074794A1
• Filed: 11/02/2007
• Published: 03/25/2010
• Est. Priority Date: 11/02/2006
• Status: Abandoned Application

• Current Assignee: Posco Holdings Incorporated
• Original Assignee: Posco Holdings Incorporated
• Inventors: Cho, Sang Hyun, Ahn, Seong Soo, Yoo, Jang Yong
• Application Number:
  US12/447,666
• Publication Number:
  US 20100074794A1
• Time in Patent Office: Days
• US Class Current: 420/84
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C22C 38/02 containing silicon
• 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

Abstract

A steel plate for linepipes having ultra-high strength and excellent low temperature toughness, and a method for manufacturing the same are disclosed. The steel plate has a strength of 930 MPa or more and excellent toughness even with much smaller amounts of alloying elements than that of conventional steel plates, and a method for manufacturing the same. The steel includes by weight %: 0.03˜0.10% C; 0˜0.6% Si; 1.6-2.1% Mn; 0˜1.0% Cu; 0-1.0% Ni; 0.02-0.06% Nb; 0-0.1% V; 0.1-0.5% Mo; 0-1.0% Cr; 0.005-0.03% Ti; 0.01-0.06% Al; 0.0005-0.0025% B; 0.001-0.006% N; 0-0.006% Ca; 0.02% or less P; 0.005% or less S; and the balance Fe and unavoidable impurities. The microstructure includes at least about 75 area percent of a mixture of bainitic ferrite and acicular ferrite.

Claims

1-8. -8. (canceled)

9. A steel plate having ultra-high strength and excellent low temperature toughness, comprising, by weight %:

0.03˜

0.10% C;

0˜

0.6% Si;

1.6˜

2.1% Mn;

0˜

1.0% Cu;

0˜

1.0% Ni;

0.02˜

0.06% Nb;

0˜

0.1% V;

0˜

10.5% Mo;

0˜

1.0% Cr;

0.005˜

0.03% Ti;

0.01˜

0.06% Al;

0.0005˜

0.0025% B;

0.001˜

0.006% N;

0˜

0.006% Ca;

0.02% or less P;

0.005% or less S; and

the balance of Fe and unavoidable impurities, wherein the microstructure comprises at least about 75 area percent of a mixture of bainitic ferrite and acicular ferrite.

10. The steel plate according to claim 9, wherein the steel plate comprises 0.015 wt % or less Mo.

11. The steel plate according to claim 9, wherein the microstructure of the steel plate includes 5% or less granular bainite in terms of area fraction.

12. The steel plate according to claim 9, wherein the through thickness dimension of austenite grains should less than 15 μ

m.

13. A steel plate having ultra-high strength and excellent low temperature toughness, comprising, by weight %:

0.03˜

0.10% C;

0˜

0.6% Si;

1.6˜

2.1% Mn;

0˜

1.0% Cu;

0˜

1.0% Ni;

0.20˜

0.06% Nb;

0˜

0.1 V;

0.1˜

0.5% Mo;

0˜

1.0 Cr;

0.005˜

0.03% Ti;

0.01˜

0.06% Al;

0.0005˜

0.0025% B;

0.001˜

0.006% N;

0˜

0.006% Ca;

0.02% or less P;

0.005% or less S; and

the balance of Fe and unavoidable impurities, wherein the microstructure comprises at least about 75 area percent of a mixture of bainitic ferrite and acicular ferrite, yield strength is 930 MPa or more, and Charpy impact absorbed energy at −

40°

C. is 230 Joules or more.

14. The steel plate according to claim 13, wherein the steel plate comprises 0.015 wt % or less Mo.

15. The steel plate according to claim 13, wherein the microstructure of the steel plate includes 5% or less granular bainite in terms of area fraction.

16. The steel plate according to claim 13, wherein the through thickness dimension of austenite grains should less than 15 μ

m.

17. A method of manufacturing a steel plate having ultra-high strength and excellent low temperature toughness, the method comprising:

reheating a steel slab to 1,050˜

1,150°

C., the slab comprising, by weight %, 0.03˜

0.10% C, 0˜

0.6% Si, 1.6˜

2.1% Mn, 0˜

1.0% Cu, 0˜

1.0% Ni, 0.02˜

0.06% Nb, 0˜

0.1 V, 0.1˜

0.5% Mo, 0˜

1.0 Cr, 0.005˜

0.03% Ti, 0.01˜

0.06% Al, 0.0005˜

0.0025% B, 0.001˜

0.006% N, 0˜

0.006% Ca, 0.02% or less P, 0.005% or less S, and the balance of Fe and unavoidable impurities;

rolling the reheated steel slab by one or more hot rolling passes in an austenite recrystallization temperature region or more with a reduction ratio of 20˜

80%;

rolling the rolled steel slab by one or more hot rolling passes in the range from the austenite recrystallization temperature or less to Ar₃ temperature or more with a reduction ratio of 40˜

80% to provide a steel plate;

cooling the rolled steel plate at a cooling rate of 20˜

50°

C./sec; and

stopping the cooling of the steel plate at a temperature of 200˜

400°

C.

18. The method according to claim 17, wherein the steel slab comprises 0.015 wt % or less Mo.

19. The method according to claim 17, further comprising:

air cooling or room temperature-cooling the steel plate after the cooling finish step.

20. The method according to claim 18, further comprising:

air cooling or room temperature-cooling the steel plate after the cooling finish step.