High-steel galvanized steel sheet and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-9255318-B2
Application number	US-201013380371-A
Country	US
Kind code	B2
Filing date	Jun 25, 2010
Priority date	Jun 26, 2009
Publication date	Feb 9, 2016
Grant date	Feb 9, 2016

Abstract

A high-strength galvanized steel sheet has a low YP, good stretch flangeability, and excellent corrosion resistance and contains, on a percent by mass basis, more than 0.015% to less than 0.10% of C, 0.5% or less of Si, 1.0% to 1.9% of Mn, 0.015% to 0.050% of P, 0.03% or less of S, 0.01% to 0.5% of sol. Al, 0.005% or less of N, less than 0.40% of Cr, 0.005% or less of B, less than 0.15% of Mo, 0.4% or less of V, and less than 0.020% of Ti, in which 2.2≦[Mneq]≦3.1 and [% Mn]+3.3[% Mo]≦1.9, and [% Mn]+3.3[% Mo])/(1.3[% Cr]+8[% P]+150B*)<3.5 are satisfied.

First claim

The invention claimed is:

1. A galvanized steel sheet comprising: as a chemical composition of steel, on a percent by mass basis, more than 0.015% to less than 0.10% of C, 0.5% or less of Si, 1.0% to 1.9% of Mn, 0.015% to 0.050% of P, 0.03% or less of S, 0.01% to 0.5% of sol. Al, 0.005% or less of N, less than 0.30% of Cr, 0.005% or less of B, less than 0.15% of Mo, 0.4% or less of V, less than 0.020% of Ti, and the balance being iron and inevitable impurities, in which 2.2≦[Mneq]≦3.1, [% Mn]+3.3[% Mo]≦1.9, and ([% Mn]+3.3[% Mo])/(1.3[% Cr]+8[% P]+150B*)<3.5 are satisfied, wherein as a microstructure of the steel comprises ferrite and a second phase, with a volume fraction of the second phase of 2% to 12% and the second phase includes martensite having a volume fraction of 1% to 10% and retained γ having a volume fraction of 0% to 5%, wherein a ratio of total volume fraction of martensite and retained γ to that of the second phase is 70% or more, and a ratio of the volume fraction of the second phase present at grain boundary triple points to that of the second phase is 50% or more,
where [Mneq] indicates [% Mn]+1.3[% Cr]+8[% P]+150B*+2[% V]+3.3[% Mo], B* indicates [% B]+[% Ti]/48×10.8×0.9+[% Al]/27×10.8×0.025, [% Mn], [% Cr], [% P], [% B], [Ti], [% Al], [% V], and [% Mo] indicate the contents of Mn, Cr, P, B, Ti, sol. Al, V, and Mo, respectively, [% B]=0 is represented by B*=0, and B*≧0.0022 is represented by B*=0.0022.

2. The galvanized steel sheet according to claim 1 , wherein ([% Mn]+3.3[% Mo])/(1.3[% Cr]+8[% P]+150B*) is less than 2.8.

3. The galvanized steel sheet according to claim 1 , further comprising, on a percent by mass basis, at least one of less than 0.02% of Nb, 0.15% or less of W, and 0.1% or less of Zr.

4. The galvanized steel sheet according to claim 1 , further comprising, on a percent by mass basis, at least one of 0.5% or less of Cu, 0.5% or less of Ni, 0.01% or less of Ca, 0.01% or less of Ce, 0.01% or less of La, and 0.01% or less of Mg.

5. The galvanized steel sheet according to claim 1 , further comprising, on a percent by mass basis, at least one of 0.2% or less of Sn and 0.2% or less of Sb.

6. The galvanized steel sheet according to claim 2 , further comprising, on a percent by mass basis, at least one of less than 0.02% of Nb, 0.15% or less of W, and 0.1% or less of Zr.

7. The galvanized steel sheet according to claim 2 , further comprising, on a percent by mass basis, at least one of 0.5% or less of Cu, 0.5% or less of Ni, 0.01% or less of Ca, 0.01% or less of Ce, 0.01% or less of La, and 0.01% or less of Mg.

8. The galvanized steel sheet according to claim 3 , further comprising, on a percent by mass basis, at least one of 0.5% or less of Cu, 0.5% or less of Ni, 0.01% or less of Ca, 0.01% or less of Ce, 0.01% or less of La, and 0.01% or less of Mg.

9. The galvanized steel sheet according to claim 2 , further comprising, on a percent by mass basis, at least one of 0.2% or less of Sn and 0.2% or less of Sb.

10. The galvanized steel sheet according to claim 3 , further comprising, on a percent by mass basis, at least one of 0.2% or less of Sn and 0.2% or less of Sb.

11. The galvanized steel sheet according to claim 4 , further comprising, on a percent by mass basis, at least one of 0.2% or less of Sn and 0.2% or less of Sb.

12. A method for manufacturing a galvanized steel sheet comprising:
performing hot rolling and cold rolling of a steel slab having the chemical composition of claim 1 ;
then in a continuous galvanizing line (CGL), performing heating in a range of 680° C. to 750° C. at an average heating rate of less than 5.0° C./sec;
subsequently performing annealing at an annealing temperature of 750° C. to 830° C.;
performing cooling to set an average cooling rate from the annealing temperature to immersion in a galvanizing bath to 2° C. to 30° C./sec and to set a holding time in a temperature region of 480° C. or less during cooling to 30 seconds or less;
then performing galvanizing by immersion in a galvanizing bath; and
performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the galvanizing, or further performing an alloying treatment after the galvanizing, and performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the alloying treatment.

13. A method for manufacturing a galvanized steel sheet comprising:
performing hot rolling and cold rolling of a steel slab having the chemical composition of claim 2 ;
then in a continuous galvanizing line (CGL), performing heating in a range of 680° C. to 750° C. at an average heating rate of less than 5.0° C./sec;
subsequently performing annealing at an annealing temperature of 750° C. to 830° C.;
performing cooling to set an average cooling rate from the annealing temperature to immersion in a galvanizing bath to 2° C. to 30° C./sec and to set a holding time in a temperature region of 480° C. or less during cooling to 30 seconds or less;
then performing galvanizing by immersion in a galvanizing bath; and
performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the galvanizing, or further performing an alloying treatment after the galvanizing, and performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the alloying treatment.

14. A method for manufacturing a galvanized steel sheet comprising:
performing hot rolling and cold rolling of a steel slab having the chemical composition of claim 3 ;
then in a continuous galvanizing line (CGL), performing heating in a range of 680° C. to 750° C. at an average heating rate of less than 5.0° C./sec;
subsequently performing annealing at an annealing temperature of 750° C. to 830° C.;
performing cooling to set an average cooling rate from the annealing temperature to immersion in a galvanizing bath to 2° C. to 30° C./sec and to set a holding time in a temperature region of 480° C. or less during cooling to 30 seconds or less;
then performing galvanizing by immersion in a galvanizing bath; and
performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the galvanizing, or further performing an alloying treatment after the galvanizing, and performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the alloying treatment.

15. A method for manufacturing a galvanized steel sheet comprising:
performing hot rolling and cold rolling of a steel slab having the chemical composition of claim 4 ;
then in a continuous galvanizing line (CGL), performing heating in a range of 680° C. to 750° C. at an average heating rate of less than 5.0° C./sec;
subsequently performing annealing at an annealing temperature of 750° C. to 830° C.;
performing cooling to set an average cooling rate from the annealing temperature to immersion in a galvanizing bath to 2° C. to 30° C./sec and to set a holding time in a temperature region of 480° C. or less during cooling to 30 seconds or less;
then performing galvanizing by immersion in a galvanizing bath; and
performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the galvanizing, or further performing an alloying treatment after the galvanizing, and performing cooling to 300° C. or less at an average cooling rate of 5° C. to 100° C./sec after the alloying treatment.

16. A method for manufacturing a galvanized steel sheet comprising:
performing hot rolling and cold rolling of a steel slab having the chemical composition of claim 5 ;
then in a continuous galvanizing line (CGL), perfor

Assignees

• Ono Yoshihiko
• Takahashi Kenji
• Okuda Kaneharu
• Taira Shoichiro
• Sakurai Michitaka
• Fushiwaki Yusuke
• Jfe Steel Corp

Inventors

• Ono Yoshihiko
• Takahashi Kenji
• Okuda Kaneharu
• Taira Shoichiro
• Sakurai Michitaka
• Fushiwaki Yusuke

Classifications

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title

• C22C38/38

  with more than 1.5% by weight of manganese · CPC title

• C22C38/001

  containing N · CPC title

• C22C38/06

  containing aluminium · CPC title