Zinc-plated steel sheet and manufacturing method thereof
A zinc-plated steel sheet of an aspect of the present invention includes a steel sheet having a predetermined chemical composition and a zinc-plated layer. In the steel sheet, steel microstructures in a range of ⅛ thickness to ⅜ thickness, having the center at ¼ thickness from a steel sheet surface, include, by vol %, ferrite: 0% to 10%, bainite: 0% to 20%, tempered martensite: 70% or more, fresh martensite: 0% to 10%, retained austenite: 0% to 10%, and pearlite: 0% to 5%. In the zinc-plated steel sheet, the amount of hydrogen emitted when the steel sheet is heated to 200° C. from a room temperature after removal of the zinc-plated layer is 0.40 ppm or less per mass of the steel sheet, the tensile strength is 1470 MPa or more, and no cracking occurs in a U-shape bending test where a stress equivalent to 1000 MPa is applied for 24 hours.
1. A zinc-plated steel sheet comprising:
a steel sheet; and
a zinc-plated layer disposed on a surface of the steel sheet,
the steel sheet has a chemical composition containing, by mass %,
C: 0.150% to 0.500%,
Si: 0.01% to 2.50%,
Mn: 1.00% to 5.00%,
P: 0.100% or less,
S: 0.0100% or less,
Al: 0.001% to 1.000%,
N: 0.0100% or less,
O: 0.0100% or less,
Cr: 0% to 2.00%,
Mo: 0% to 1.00%,
B: 0% to 0.010%,
Cu: 0% to 1.00%,
Ni: 0% to 1.00%,
Co: 0% to 1.00%,
W: 0% to 1.00%,
Sn: 0% to 1.00%,
Sb: 0% to 0.50%,
Ti: 0% to 0.30%,
Nb: 0% to 0.30%,
V: 0% to 1.00%,
Ca: 0% to 0.0100%,
Mg: 0% to 0.0100%,
Ce: 0% to 0.0100%,
Zr: 0% to 0.0100%,
La: 0% to 0.0100%,
Hf: 0% to 0.0100%,
Bi: 0% to 0.0100%, and
REM: 0% to 0.0100%
with a remainder including Fe and an impurity,
steel microstructures in a range of ⅛ thickness to ⅜ thickness, having a center at ¼ thickness from the surface of the steel sheet, include, by vol %,
ferrite: 0% to 10%,
bainite: 0% to 20%,
tempered martensite: 70% or more,
fresh martensite: 0% to 10%,
retained austenite: 0% to 10%, and
pearlite: 0% to 5%,
an amount of hydrogen that is emitted when the steel sheet is heated up to 200° C. from a room temperature after removal of the zinc-plated layer is 0.40 ppm or less per mass of the steel sheet,
a tensile strength is 1470 MPa or more, and
cracking does not occur in a U-shape bending test in which a stress equivalent to 1000 MPa is applied for 24 hours.
2. The zinc-plated steel sheet according to claim 1 ,
wherein the chemical composition of the steel sheet contains one or more of
Cr: 0.001% to 2.00%,
Mo: 0.001% to 1.00%,
B: 0.0001% to 0.010%,
Cu: 0.001% to 1.00%,
Ni: 0.001% to 1.00%,
Co: 0.001% to 1.00%,
W: 0.001% to 1.00%,
Sn: 0.001% to 1.00%, and
Sb: 0.001% to 0.50%.
3. The zinc-plated steel sheet according to claim 1 ,
wherein the chemical composition of the steel sheet contains one or more of
Ti: 0.001% to 0.30%,
Nb: 0.001% to 0.30%, and
V: 0.001% to 1.00%.
4. The zinc-plated steel sheet according to claim 1 ,
wherein the chemical composition of the steel sheet contains one or more of
Ca: 0.0001% to 0.0100%,
Mg: 0.0001% to 0.0100%,
Ce: 0.0001% to 0.0100%,
Zr: 0.0001% to 0.0100%,
La: 0.0001% to 0.0100%,
Hf: 0.0001% to 0.0100%,
Bi: 0.0001% to 0.0100%, and
REM: 0.0001% to 0.0100%.
5. The zinc-plated steel sheet according to claim 1 ,
wherein a ductile-brittle transition temperature is −40° C. or lower.
6. A manufacturing method of the zinc-plated steel sheet according to claim 1 , wherein each of (I) to (IV) is sequentially carried out on the steel sheet:
(I) annealing the steel sheet under conditions of a heating temperature: an Ac 3 point to 950° C. and a retention time in a temperature range of the Ac 3 point to 950° C.: 1 to 500 s and maintaining a concentration of hydrogen in a furnace at 1.0 to 15.0 vol % at all times from when a steel sheet temperature reaches 600° C. until when retention of the steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the steel sheet in a temperature range of an Ms point to 600° C. for 20 to 500 s and maintaining the concentration of hydrogen in the furnace at 1.0 to 10.0 vol % at all times during the retention of the steel sheet;
(IIT) immersing the steel sheet in a hot-dip galvanizing bath and then cooling the steel sheet until the steel sheet temperature reaches lower than the Ms point −150° C.; and
(IV) retaining the steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 200° C. or higher and lower than 350° C. for 10 to 1000 s and then coiling the steel sheet in a coil shape; thereby producing the zinc-plated steel sheet of claim 1 .
7. The manufacturing method of the zinc-plated steel sheet according to claim 6 ,
wherein the (III) is cooling of the steel sheet until the steel sheet temperature reaches lower than the Ms point −150° C. after immersion of the steel sheet in the hot-dip galvanizing bath and then an alloying treatment that is carried out in a temperature range of 460° C. to 600° C.
8. The zinc-plated steel sheet according to claim 2 ,
wherein the chemical composition of the steel sheet contains one or more of
Ti: 0.001% to 0.30%,
Nb: 0.001% to 0.30%, and
V: 0.001% to 1.00%.
9. The zinc-plated steel sheet according to claim 2 ,
wherein the chemical composition of the steel sheet contains one or more of
Ca: 0.0001% to 0.0100%,
Mg: 0.0001% to 0.0100%,
Ce: 0.0001% to 0.0100%,
Zr: 0.0001% to 0.0100%,
La: 0.0001% to 0.0100%,
Hf: 0.0001% to 0.0100%,
Bi: 0.0001% to 0.0100%, and
REM: 0.0001% to 0.0100%.
10. The zinc-plated steel sheet according to claim 3 ,
wherein the chemical composition of the steel sheet contains one or more of
Ca: 0.0001% to 0.0100%,
Mg: 0.0001% to 0.0100%,
Ce: 0.0001% to 0.0100%,
Zr: 0.0001% to 0.0100%,
La: 0.0001% to 0.0100%,
Hf: 0.0001% to 0.0100%,
Bi: 0.0001% to 0.0100%, and
REM: 0.0001% to 0.0100%.
11. The zinc-plated steel sheet according to claim 2 ,
wherein a ductile-brittle transition temperature is −40° C. or lower.
12. The zinc-plated steel sheet according to claim 3 ,
wherein a ductile-brittle transition temperature is −40° C. or lower.
13. The zinc-plated steel sheet according to claim 4 ,
wherein a ductile-brittle transition temperature is −40° C. or lower.
14. A manufacturing method of the zinc-plated steel sheet according to claim 2 , wherein each of (I) to (IV) is sequentially carried out on the steel sheet:
(1) annealing the steel sheet under conditions of a heating temperature: an Ac 3 point to 950° C. and a retention time in a temperature range of the Ac 3 point to 950° C.: 1 to 500 s and maintaining a concentration of hydrogen in a furnace at 1.0 to 15.0 vol % at all times from when a steel sheet temperature reaches 600° C. until when retention of the steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the steel sheet in a temperature range of an Ms point to 600° C. for 20 to 500 s and maintaining the concentration of hydrogen in the furnace at 1.0 to 10.0 vol % at all times during the retention of the steel sheet;
(IIT) immersing the steel sheet in a hot-dip galvanizing bath and then cooling the steel sheet until the steel sheet temperature reaches lower than the Ms point −150° C.; and
(IV) retaining the steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 200° C. or higher and lower than 350° C. for 10 to 1000 s and then coiling the steel sheet in a coil shape; thereby producing the zinc-plated steel sheet of claim 2 .
15. A manufacturing method of the zinc-plated steel sheet according to claim 3 , wherein each of (I) to (IV) is sequentially carried out on the steel sheet:
(I) annealing the steel sheet under conditions of a heating temperature: an Ac 3 point to 950° C. and a retention time in a temperature range of the Ac 3 point to 950° C.: 1 to 500 s and maintaining a concentration of hydrogen in a furnace at 1.0 to 15.0 vol % at all times from when a steel sheet temperature reaches 600° C. until when retention of the steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the steel sheet in a temperature range of an Ms point to 600° C. for 20 to 500 s and maintaining the concentration of hydrogen in the furnace at 1.0 to 10.0 vol % at all times during the retention of the steel sheet;
(III) immersing the steel sheet in a hot-dip galvanizing bath and then cooling the steel sheet until the steel sheet temperature reaches lower than the Ms point −150° C.; and
(IV) retaining the steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 200° C. or higher and lower than 350° C. for 10 to 1000 s and then coiling the steel sheet in a coil shape; thereby producing the zinc-plated steel sheet of claim 3 .
16. A manufacturing method of the zinc-plated steel sheet according to claim 4 , wherein each of (I) to (IV) is sequentially carried out on the steel sheet:
(I) annealing the steel sheet under conditions of a heating temperature: an Ac 3 point to 950° C. and a retention time in a temperature range of the Ac 3 point to 950° C.: 1 to 500 s and maintaining a concentration of hydrogen in a furnace at 1.0 to 15.0 vol % at all times from when a steel sheet temperature reaches 600° C. until when retention of the steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the steel sheet in a temperature range of an Ms point to 600° C. for 20 to 500 s and maintaining the concentration of hydrogen in the furnace at 1.0 to 10.0 vol % at all times during the retention of the steel sheet;
(III) immersing the steel sheet in a hot-dip galvanizing bath and then cooling the steel sheet until the steel sheet temperature reaches lower than the Ms point −150° C.; and
(IV) retaining the steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 200° C. or higher and lower than 350° C. for 10 to 1000 s and then coiling the steel sheet in a coil shape; thereby producing the zinc-plated steel sheet of claim 4 .