High-strength galvanized hot-rolled steel sheet and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-10927441-B2
Application number	US-201816481646-A
Country	US
Kind code	B2
Filing date	Jan 9, 2018
Priority date	Jan 31, 2017
Publication date	Feb 23, 2021
Grant date	Feb 23, 2021

Abstract

Provided are a high-strength galvanized hot-rolled steel sheet and a method for manufacturing the steel sheet. A steel sheet has a chemical composition, and a galvanized layer is disposed on the steel sheet. The chemical composition includes, in mass %, C: 0.02% or greater and 0.30% or less, Si: 0.01% or greater and 2.5% or less, Mn: 0.3% or greater and 3.0% or less, P: 0.08% or less, S: 0.02% or less, and Al: 0.001% or greater and 0.20% or less. The galvanized layer has a coating weight per side of 20 to 120 g/m2. A surface of the steel sheet has a specific surface area ratio, r, of 2.5 or less, and an amount of Si present in the galvanized layer and an amount of Mn present in the galvanized layer respectively satisfy: amount of Si×r≤0.06, and amount of Mn×r≤0.10.

First claim

The invention claimed is:

1. A high-strength galvanized hot-rolled steel sheet comprising:
a steel sheet having a chemical composition; and
a galvanized layer disposed on the steel sheet having the chemical composition, the chemical composition including, in mass %,
C in the range of 0.02% to 0.30%,
S in the range of 0.01% to 2.5%,
Mn in the range of 0.3% to 3.0%,
P in the range of 0.08% or less,
S in the range of 0.02% or less, and
Al in the range of 0.001% to 0.20%, with a balance of Fe and incidental impurities,

the galvanized layer having a coating weight per side of 20 to 120 g/m 2 , wherein
a surface of the steel sheet having the chemical composition has a specific surface area ratio, r, of 2.5 or less, and
an amount (g/m 2 ) of Si present in the galvanized layer and an amount (g/m 2 ) of Mn present in the galvanized layer respectively satisfy:
amount of Si×r≤0.06, and
amount of Mn×r≤0.10
wherein the high-strength galvanized hot-rolled steel sheet has a tensile strength of 590 MPa or greater.

2. The high-strength galvanized hot-rolled steel sheet according to claim 1 , wherein the chemical composition further includes, in mass %, one or more of the following components:
Ti in the range of 0.01% to 0.40%,
Nb in the range of 0.001% to 0.200%,
V in the range of 0.001% to 0.500%,
Mo in the range of 0.01% to 0.50%, and
W in the range of 0.001% to 0.200%.

3. A method for manufacturing a high-strength galvanized hot-rolled steel sheet of claim 1 , the method comprising:
hot-rolling and pickling a steel slab having the chemical composition according to claim 1 ;
subsequently, performing rolling by using a roll having a surface roughness (Ra) of 0.3 to 1.0 μm at a rolling reduction ratio of 1 to 10%; and
subsequently, performing hot-dip galvanizing.

4. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 3 , wherein,
in the hot-rolling, descaling by high-pressure water spraying is performed at an impact pressure of 0.3 MPa or greater and less than 1.8 MPa after rough rolling and prior to finish rolling,
the finish rolling is performed at a finish rolling temperature of 800° C. or higher, and
coiling is performed at a coiling temperature of 400 to 650° C.

5. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 4 , wherein, prior to the hot-dip galvanizing, continuous annealing is performed in a furnace atmosphere having a hydrogen concentration of 2 to 30 vol % and a dew point of −60 to −10° C., with a steel sheet end-point temperature being 600 to 950° C.

6. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 5 , the method further comprising performing alloying after the hot-dip galvanizing.

7. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 4 , the method further comprising performing alloying after the hot-dip galvanizing.

8. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 3 , wherein, prior to the hot-dip galvanizing, continuous annealing is performed in a furnace atmosphere having a hydrogen concentration of 2 to 30 vol % and a dew point of −60 to −10° C., with a steel sheet end-point temperature being 600 to 950° C.

9. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 8 , the method further comprising performing alloying after the hot-dip galvanizing.

10. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 3 , the method further comprising performing alloying after the hot-dip galvanizing.

11. A method for manufacturing a high-strength galvanized hot-rolled steel sheet of claim 2 , the method comprising:
hot-rolling and pickling a steel slab having the chemical composition according to claim 2 ;
subsequently, performing rolling by using a roll having a surface roughness (Ra) of 0.3 to 1.0 μm at a rolling reduction ratio of 1 to 10%; and
subsequently, performing hot-dip galvanizing.

12. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 11 , the method further comprising performing alloying after the hot-dip galvanizing.

13. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 11 , wherein,
in the hot-rolling, descaling by high-pressure water spraying is performed at an impact pressure of 0.3 MPa or greater and less than 1.8 MPa after rough rolling and prior to finish rolling,
the finish rolling is performed at a finish rolling temperature of 800° C. or higher, and
coiling is performed at a coiling temperature of 400 to 650° C.

14. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 13 , wherein, prior to the hot-dip galvanizing, continuous annealing is performed in a furnace atmosphere having a hydrogen concentration of 2 to 30 vol % and a dew point of −60 to −10° C., with a steel sheet end-point temperature being 600 to 950° C.

15. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 14 , the method further comprising performing alloying after the hot-dip galvanizing.

16. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 13 , the method further comprising performing alloying after the hot-dip galvanizing.

17. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 11 , wherein, prior to the hot-dip galvanizing, continuous annealing is performed in a furnace atmosphere having a hydrogen concentration of 2 to 30 vol % and a dew point of −60 to −10° C., with a steel sheet end-point temperature being 600 to 950° C.

18. The method for manufacturing a high-strength galvanized hot-rolled steel sheet according to claim 17 , the method further comprising performing alloying after the hot-dip galvanizing.

Assignees

• Jfe Steel Corp

Inventors

• Koba Masaki
• Fushiwaki Yusuke
• Nagataki Yasunobu

Classifications

• C21D8/04

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

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/02

  containing silicon · CPC title

• C23C2/022

  by heating · CPC title