High strength galvanized steel sheet having excellent deep drawability and stretch flangeability and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-9598755-B2
Application number	US-201113825236-A
Country	US
Kind code	B2
Filing date	Sep 15, 2011
Priority date	Sep 29, 2010
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

A high-strength galvanized steel sheet contains C: 0.010% or more and 0.06% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol.Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and 0.090% or less, and Ti: 0.015% or more and 0.15% or less, on a mass percent basis. The Nb and C contents of the steel satisfy the relation of (Nb/93)/(C/12)<0.20. C* satisfies 0.005≦C*≦0.025. Ferrite constitutes 70% by area ratio or more of the steel sheet. Martensite constitutes 3% by area ratio or more of the steel sheet. C*=C−(12/93)Nb−(12/48){Ti−(48/14)N}, wherein C, Nb, Ti, and N denote the C, Nb, Ti, and N contents of the steel.

First claim

The invention claimed is:

1. A high-strength galvanized steel sheet comprising: on a mass percent basis, C: 0.010% or more and 0.06% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol.Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and 0.090% or less, and Ti: 0.015% or more and 0.15% or less, the Nb and C contents % by mass of the steel satisfying the relation of (Nb/93)/(C/12)<0.20, C* given by the following formula (1) satisfying 0.005≦C*≦0.025, and the remainder being Fe and incidental impurities without addition of V, wherein ferrite constitutes 70% by area ratio or more, martensite constitutes 3% by area ratio or more, the average r-value Lankford value is 1.2 or more, and the hole expansion ratio λ is 80% or more:
C*=C−(12/93)Nb−(12/48){Ti−(48/14)N}  (1)

wherein C, Nb, Ti, and N denote the C, Nb, Ti, and N contents % by mass of the steel, respectively, provided that if Ti−(48/14)N≦0, then Ti−(48/14)N=0.

2. The high-strength galvanized steel sheet according to claim 1 , further comprising: on a mass percent basis, one or more of Mo and Cr constituting 0.5% or less of the steel sheet in total.

3. The high-strength galvanized steel sheet according to claim 1 , further comprising: on a mass percent basis, one or two of Cu: 0.3% or less and Ni: 0.3% or less.

4. The high-strength galvanized steel sheet according to claim 1 further comprising: on a mass percent basis, one or two of Sn: 0.2% or less and Sb: 0.2% or less.

5. A high-strength galvanized steel sheet comprising: on a mass percent basis, C: 0.010% or more and 0.06% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol.Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and 0.090% or less, Ta: 0.005% or more and 0.1% or less, and Ti: 0.015% or more and 0.15% or less, the Nb and C contents % by mass of the steel satisfying the relation of (Nb/93)/(C/12)<0.20, wherein C* given by the following formula (2) satisfies the relation of 0.005≦C*≦0.025, and the remainder being Fe and incidental impurities without addition of V, wherein ferrite constitutes 70% by area ratio or more, martensite constitutes 3% by area ratio or more, the average r-value Lankford value is 1.2 or more, and the hole expansion ratio λ is 80% or more:
C*=C−(12/93)Nb−(12/181)Ta−(12/48){Ti−(48/14)N}  (2)

wherein C, Nb, Ta, Ti, and N denote the C, Nb, Ta, Ti, and N contents % by mass of the steel, respectively, provided that if Ti−(48/14)N≦0, then Ti−(48/14)N=0.

6. A method for manufacturing a high-strength galvanized steel sheet comprising: hot rolling and cold rolling a steel having the composition described in claim 1 ; heating the steel in the temperature range of 700° C. to 800° C. at an average heating rate of less than 3° C./sec.; annealing the steel at a temperature in the range of 800° C. to 950° C.; cooling the steel from the annealing temperature at an average cooling rate in the range of 3° C./sec. to 15° C./sec.; immersing the steel in a galvanizing bath for hot-dip galvanizing; and cooling the steel at an average cooling rate in the range of 5° C./sec. to 100° C./sec. after the hot-dip galvanizing, or performing alloying treatment of the galvanized steel after the hot-dip galvanizing and cooling the steel at an average cooling rate in the range of 5° C./sec. to 100° C./sec. after the alloying treatment.

7. The method for manufacturing a high-strength galvanized steel sheet according to claim 6 , further comprising: starting cooling within three seconds after the hot rolling; cooling the steel to 650° C. at an average cooling rate of 40° C./sec. or more; coiling the steel at a coiling temperature in the range of 500° C. to 650° C.; and cold rolling the steel at a rolling reduction of 50% or more.

Assignees

• Kimura Hideyuki
• Okuda Kaneharu
• Sugihara Reiko
• Jfe Steel Corp

Inventors

• Kimura Hideyuki
• Okuda Kaneharu
• Sugihara Reiko

Classifications

• C21D8/04 Primary

  to produce plates or strips for drawing, e.g. for deep-drawing · CPC title

• C21D8/0405

  Chemistry & Metallurgy · mapped topic

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C21D2211/005

  Ferrite · CPC title

• C23C2/02 Primary

  Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence) · CPC title