Zinc-plated steel sheet and manufacturing method thereof
A zinc-plated steel sheet 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 30%, tempered martensite: 50% or more, fresh martensite: 0% to 10%, retained austenite: more than 10% and 30% or less, 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 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 base steel sheet; and
a zinc-plated layer disposed on a surface of the base steel sheet,
wherein the base steel sheet has a chemical composition containing, by mass %,
C: 0.200% to 0.500%,
Si: 1.00% to 2.50%,
Mn: 1.50% to 5.00%,
P: greater than 0% to 0.100%,
S: greater than 0% to 0.0100%,
Al: 0.001% to 1.000%,
N: greater than 0% to 0.0100%,
O: greater than 0% to 0.0100%,
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 base steel sheet, include, by vol %,
ferrite: 0% to 10%,
bainite: 0% to 30%,
tempered martensite: 50% or more,
fresh martensite: 0% to 10%,
retained austenite: more than 10% and 30% or less, and
pearlite: 0% to 5%,
an amount of hydrogen that is emitted when the base steel sheet is heated up to 200° C. from room temperature after removal of the zinc-plated layer is 0.40 ppm or less per mass of the base 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 base 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 base 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 base 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 , the method comprising:
sequentially carrying out each of (I) to (IV) on the base steel sheet having said chemical composition:
(I) annealing the base steel sheet to form an annealed 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 base steel sheet temperature reaches 600° C. until when retention of the base steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the annealed 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 annealed steel sheet;
(III) immersing the annealed steel sheet in a hot-dip galvanizing bath to form a plated steel sheet, and then cooling the plated steel sheet until the plated steel sheet temperature reaches a temperature range of the Ms point −150° C. to the Ms point −30° C.; and
(IV) retaining the plated steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 330° C. to 430° C. for 50 to 1000 s and then coiling the plated steel sheet in a coil shape thereby forming the zinc-plated steel sheet.
7. The manufacturing method of the zinc-plated steel sheet according to claim 6 ,
wherein the (III) is cooling of the plated steel sheet until the plated steel sheet temperature reaches a temperature range of the Ms point −150° C. to the Ms point −30° C. after immersion of the annealed 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 base 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 base 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 base 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 , the method comprising:
sequentially carrying out each of (I) to (IV) on the base steel sheet having said chemical composition:
(I) annealing the base steel sheet to form an annealed 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 base steel sheet temperature reaches 600° C. until when retention of the base steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the annealed 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 annealed steel sheet;
(III) immersing the annealed steel sheet in a hot-dip galvanizing bath to form a plated steel sheet, and then cooling the plated steel sheet until the plated steel sheet temperature reaches a temperature range of the Ms point −150° C. to the Ms point −30° C.; and
(IV) retaining the plated steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 330° C. to 430° C. for 50 to 1000 s and then coiling the plated steel sheet in a coil shape thereby forming the zinc-plated steel sheet.
15. A manufacturing method of the zinc-plated steel sheet according to claim 3 , the method comprising:
sequentially carrying out each of (I) to (IV) on the base steel sheet having said chemical composition:
(I) annealing the base steel sheet to form an annealed 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 base steel sheet temperature reaches 600° C. until when retention of the base steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the annealed 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 annealed steel sheet;
(III) immersing the annealed steel sheet in a hot-dip galvanizing bath to form a plated steel sheet, and then cooling the plated steel sheet until the plated steel sheet temperature reaches a temperature range of the Ms point −150° C. to the Ms point −30° C.; and
(IV) retaining the plated steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 330° C. to 430° C. for 50 to 1000 s and then coiling the plated steel sheet in a coil shape thereby forming the zinc-plated steel sheet.
16. A manufacturing method of the zinc-plated steel sheet according to claim 4 , the method comprising:
sequentially carrying out each of (I) to (IV) on the base steel sheet having said chemical composition:
(I) annealing the base steel sheet to form an annealed 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 base steel sheet temperature reaches 600° C. until when retention of the base steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the annealed 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 annealed steel sheet;
(III) immersing the annealed steel sheet in a hot-dip galvanizing bath to form a plated steel sheet, and then cooling the plated steel sheet until the plated steel sheet temperature reaches a temperature range of the Ms point −150° C. to the Ms point −30° C.; and
(IV) retaining the plated steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 330° C. to 430° C. for 50 to 1000 s and then coiling the plated steel sheet in a coil shape thereby forming the zinc-plated steel sheet.
17. A manufacturing method of the zinc-plated steel sheet according to claim 5 , the method comprising:
sequentially carrying out each of (I) to (IV) on the base steel sheet having said chemical composition:
(I) annealing the base steel sheet to form an annealed 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 base steel sheet temperature reaches 600° C. until when retention of the base steel sheet in the temperature range of the Ac 3 point to 950° C. ends;
(II) retaining the annealed 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 annealed steel sheet;
(III) immersing the annealed steel sheet in a hot-dip galvanizing bath to form a plated steel sheet, and then cooling the plated steel sheet until the plated steel sheet temperature reaches a temperature range of the Ms point −150° C. to the Ms point −30° C.; and
(IV) retaining the plated steel sheet in an atmosphere having a concentration of hydrogen of less than 0.50 vol % in a temperature range of 330° C. to 430° C. for 50 to 1000 s and then coiling the plated steel sheet in a coil shape thereby forming the zinc-plated steel sheet.