Hot rolled steel plate, cold rolled steel plate and hot dip galvanized steel plate being excellent in strain aging hardening characteristics, and method for their production

• US 20030111144A1
• Filed: 12/31/2001
• Published: 06/19/2003
• Est. Priority Date: 04/07/2000
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Shimizu, Tetsuo, Sakata, Kei, Matsuoka, Saiji, Furukimi, Osamu
• Granted Patent: US 6,676,774 B2
• Time in Patent Office: Days
• US Class Current: 148/603
• CPC Class Codes: C21D 1/185 from an intercritical temperature
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0236 Cold rolling
• CPC Class Codes: C21D 8/0273 Final recrystallisation annealing
• CPC Class Codes: C21D 8/0278 involving a particular surface treatment C21D8/0294 takes precedence
• 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 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/16 containing copper
• CPC Class Codes: C23C 2/02 Pretreatment of the material to be coated, e.g. for coating on selected surface areas C23C2/30 takes precedence
• CPC Class Codes: C23C 2/0224 Two or more thermal pretreatments
• CPC Class Codes: C23C 2/024 by cleaning or etching
• CPC Class Codes: C23C 2/06 Zinc or cadmium or alloys based thereon
• CPC Class Codes: C23C 2/40 Plates; Strips
• CPC Class Codes: Y10T 428/12799 Next to Fe-base component [e.g., galvanized]

Abstract

The present invention provides a steel sheet having a chemical composition comprising 0.15% or less C, 2.0% or less Si, 3.0% or less Mn, P, S, Al and N in adjusted amounts, from 0.5 to 3.0% Cu, or one or more of Cr, Mo and W in a total amount of 2.0% or less, and having a composite structure comprising ferrite and martensite having an area ratio of 2% or more. The steel sheet is in the form of a high-strength hot-rolled steel sheet, a high-strength cold-rolled steel sheet, or a hot-dip galvanized steel sheet. There is thus available a steel sheet excellent in press-formability and in strain age hardening property as represented by a ΔTS of 80 MPa or more.

Claims

1. A steel sheet excellent in press-formability and in strain age hardening property as typically represented by a Δ

TS of 80 MPa or more, comprising a structure having ferrite phase as a main phase forming a composite structure with a secondary phase containing martensite phase in an area ratio of 2% or more.

2. A steel sheet according to claim 1, which is a hot-rolled steel sheet.

3. A steel sheet according to claim 2, comprising, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

Cu;

from 0.5 to 3.0%,

and the balance Fe and incidental impurities.

4. A steel sheet according to claim 3, containing, in weight percentage, one or more selected from the following groups A to C, in addition to the above-mentioned chemical composition:

group A;

Ni;

2.0% or less;

group B;

one or two of Cr and Mo;

2.0% or less in total;

and

group C;

one or more of Nb, Ti and V;

0.2% or less in total.

5. A steel sheet according to claim 2, having a chemical composition comprising, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02%, or less

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

one or more selected from the group consisting of from 0.05 to 2.0% Mo, from 0.05 to 2.0% Cr and from 0.05 to 2.0% W, 2.0% or less in total, and the balance Fe and incidental impurities.

6. A steel sheet according to claim 5, further comprising, in addition to the above-mentioned chemical composition, in weight percentage, one or more selected from the group consisting of Nb, Ti, and V, 2.0% or less in total.

11. A steel sheet according to claim 1, which is a cold-rolled steel sheet.

12. A steel sheet according to claim 11, comprising, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

Cu;

from 0.5 to 3.0%,

and the balance Fe and incidental impurities.

13. A steel sheet according to claim 12, containing, in weight percentage, one or more selected from the following groups A to C, in addition to the above-mentioned chemical composition:

group;

Ni;

2.0% or less;

group B;

one or two of Cr and Mo;

2.0% or less in total;

and

group C;

one or more of Nb, Ti and V;

0.2% or less in total.

14. A steel sheet according to claim 11, having a chemical composition comprising, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

one or more selected from the group consisting of from 0.05 to 2.0% Mo, from 0.05 to 2.0% Cr and from 0.05 to 2.0% W, 2.0% or less in total, and the balance Fe and incidental impurities.

15. A steel sheet according to claim 14, further comprising, in addition to the above-mentioned chemical composition, in weight percentage, one or more selected from the group consisting of Nb, Ti and V, 2.0% or less in total.

21. A hot-dip galvanized steel sheet comprising a hot-dip galvanizing layer or an alloyed hot-dip galvanizing layer formed on the surface of the steel sheet according to any one of claims 2 to 6.

22. A hot-dip galvanized steel sheet comprising a hot-dip galvanizing layer or an alloyed hot-dip galvanizing layer formed on the surface of the steel sheet according to any one of claims 11 to 15.

7. A manufacturing method of a steel sheet excellent in press-formability and in strain age hardening property as typically represented by a Δ

TS of 80 MPa or more, comprising the steps, when hot-rolling a steel slab having a chemical composition comprising, in weight percentage;

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less, and

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

Cu;

from 0.5 to 3.0%,

into a hot-rolled steel sheet having a prescribed thickness, carrying out said hot rolling with a finish rolling end temperature FDT of the Ar₃ transformation point or more, then after the completion of the finish rolling, cooling the hot-rolled steel sheet to a temperature region from the (Ar₃ transformation point) to the (Ar₃ transformation point) at a cooling rate of 5°

C./second or more, air-cooling or slowly cooling the sheet within said temperature region for a period of from 1 to 20 seconds, then cooling the sheet again at a cooling rate of 5°

C./second or more, and coiling the sheet at a temperature of 550°

C. or below.

8. A manufacturing method of a hot-rolled steel sheet according to claim 7, containing, in addition to said chemical composition in weight percentage, one or more selected from the following groups A to C:

group A;

Ni;

2.0% or less;

group B;

one or two of Cr and Mo;

2.0% or less in total;

and

group C;

one or more of Nb, Ti and V;

0.2% or less in total.

9. A manufacturing method of a hot-rolled steel sheet, according to claim 7, wherein said steel slab has a chemical composition containing, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

and further containing one or more selected from the group consisting of from 0.05 to 2.0% Mo, from 0.05 to 2.0% Cr, and from 0.05 to 2.0% W, 2.0% or less in total.

10. A manufacturing method of a hot-rolled steel sheet according to any one of claims 7 to 9, wherein all or part of said finish rolling comprises lubrication rolling.

29. A manufacturing method of a hot-dip galvanized steel sheet excellent in press-formability and in strain age hardening property as typically represented by a Δ

TS of 80 MPa or more, further comprising a step of applying a hot-dip galvanizing treatment to the hot-rolled steel sheet resulting from the manufacturing method of a hot-rolled steel sheet according to any one of claims 7 to 10 to form a hot-dip galvanizing layer on the surface of said hot-rolled steel sheet.

31. A manufacturing method of a hot-dip galvanized steel sheet according to any one of claims 29 and 30, further comprising the step of carrying out an alloying treatment after said hot-dip galvanizing treatment.

16. A manufacturing method of a cold-rolled steel sheet excellent in press-formability and in strain age hardening property typically represented by a Δ

TS of 80 MPa or more, comprising the steps of using a steel slab having a chemical composition containing, in weight percentage;

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less, and

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

Cu;

from 0.5 to 3.0%,

as a material;

a hot rolling step of applying hot rolling to said material into a hot-rolled steel sheet;

a cold rolling step of applying cold rolling to said hot-rolled steel sheet into a cold-rolled steel sheet; and

a recrystallization annealing step of applying recrystallization annealing into a cold-rolled annealed steel sheet;

these steps being sequentially applied;

wherein said recrystallization annealing is conducted in a ferrite+austenite dual phase region within a temperature range of from Ac₁ transformation point to Ac₃ transformation point.

17. A manufacturing method of a cold-rolled steel sheet according to claim 16, containing, in addition to said chemical composition in weight percentage, one or more selected from the following groups A to C:

group A;

Ni;

2.0% or less;

group B;

one or two of Cr and Mo;

2.0% or less in total;

and

group C;

one or more of Nb, Ti and V;

0.2% or less in total.

18. A manufacturing method of a cold-rolled steel sheet according to claim 16, wherein said steel slab has a chemical composition containing, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

and further containing one or more selected from the group consisting of from 0.05 to 2.0% Mo, from 0.05 to 2.0% Cr, and from 0.05 to 2.0% W.

19. A manufacturing method of a cold-rolled steel sheet according to any one of claims 16 to 18, wherein said hot rolling is conducted under conditions including a heating temperature of said material of 900°

C. or more, a finish rolling end temperature of 700°

C. or more, and a coiling temperature of 800°

C. or below.

20. A manufacturing method of a cold-rolled steel sheet according to any one of claims 16 to 19, wherein all or part of said hot rolling comprises lubrication rolling.

30. A manufacturing method of a hot-dip galvanized steel sheet excellent in press-formability and in strain age hardening property as typically represented by a Δ

TS of 80 MPa or more, further comprising a step of applying a hot-dip galvanizing treatment to the cold-rolled steel sheet resulting from the manufacturing method of a cold-rolled steel sheet according to any one of claims 16 to 20 to form a hot-dip galvanizing layer on the surface of said cold-rolled steel sheet.

23. A manufacturing method of a hot-dip galvanized steel sheet excellent in press-formability, and in strain age hardening property as typically represented by a Δ

TS of 80 MPa or more, comprising the steps of using a steel sheet having a chemical composition containing, in weight percentage;

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less, and

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less,

Cu;

from 0.5 to 3.0%,

applying annealing comprising heating to a dual phase region of ferrite+austenite within a temperature range of from Ac₃ transformation point to Ac₁ transformation point to said steel sheet on a line for conducting continuous hot-dip galvanizing, and then, performing a hot-dip galvanizing treatment, thereby forming a hot-dip galvanizing layer on the surface of said steel sheet.

24. A manufacturing method of a hot-dip galvanized steel sheet according to claim 23, further containing, in weight percentage, in addition to said chemical composition, one or more of the following groups A to C:

group A;

Ni;

2.0% or less;

group B;

one or two of Cr and Mo, 0.2% or less in total;

and

group C;

one or more of Nb, Ti and V, 0.2% or less in total.

25. A manufacturing method of a hot-dip galvanized steel sheet according to claim 23, wherein said steel sheet is replaced by a steel sheet having a chemical composition containing, in weight percentage:

C;

0.15% or less,

Mn;

3.0% or less,

S;

0.02% or less,

N;

0.02% or less,

Si;

2.0% or less,

P;

0.1% or less,

Al;

0.1% or less, and

and further comprising one or more selected from the group consisting of from 0.05 to 2.0% Mo, from 0.05 to 2.0% Cr and from 0.05 to 2.0% W, 2.0% or less in total.

26. A manufacturing method of a hot-dip galvanized steel sheet according to any one of claims 23 to 25, wherein, prior to said annealing, a preheating treatment of heating the sheet at a temperature of 700°

C. or more on a continuous annealing line, and then applying a pretreatment comprising a pickling treatment.

27. A manufacturing method of a hot-dip galvanized steel sheet according to any one of claims 23 to 26, comprising the steps of conducting said hot-dip galvanizing treatment to form a hot-dip galvanizing layer on the surface of the steel sheet, and then, performing an alloying treatment of said hot-dip galvanizing layer.

28. A manufacturing method of a hot-dip galvanized steel sheet excellent in press-formability, and in strain age hardening property as typically represented by a Δ

TS of 80 MPa or more according to any one of claims 23 to 27, wherein said steel sheet is a hot-rolled steel sheet manufactured by hot-rolling the material having said chemical composition under conditions including a heating temperature of 900°

C. or more, a finish rolling end temperature of 700°

C. or more and a coiling temperature of 800°

C. or below, or a cold-rolled steel sheet obtained by cold-rolling said hot-rolled steel sheet.