US2024327962A1PendingUtilityA1
Hot dip galvanized steel sheet and method for producing same
Est. expiryJan 13, 2042(~15.5 yrs left)· nominal 20-yr term from priority
Inventors:Takafumi YokoyamaChisato YoshinagaTakuya KuwayamaKengo TakedaTakuya MitsunobuSeiji FurusakoTatsuya Obuchi
C21D 8/02C22C 38/18C21D 8/0278C21D 6/008C22C 38/10C23C 2/29C21D 8/0263C22C 38/08C22C 38/12C22C 38/14C22C 38/16C23C 2/02C23C 2/024C23C 2/0224C22C 38/02C23C 2/28C21D 8/0273C21D 8/0236C21D 6/005C22C 38/04C22C 38/06C21D 8/0226C22C 38/60C23C 2/20C23C 2/40C21D 9/46C23C 2/06C21D 2211/009C21D 2211/008C21D 2211/005C21D 2211/003C21D 2211/002C21D 2211/001C21D 8/0436C21D 8/0463C21D 8/0426C22C 38/58C23C 2/26C21D 8/0205
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Claims
Abstract
Provided are a hot dip galvanized steel sheet having a predetermined chemical composition, and a steel microstructure comprising, by vol %, ferrite: 0 to 50%, tempered martensite: 1% or more, retained austenite: 5% or more, fresh martensite: 0 to 15%, total of pearlite and cementite: 0 to 5%, and balance: bainite, when measuring by GDS, a maximum value of Al concentration of an Al rich layer present at an interface of the base steel sheet and the hot dip galvanized layer is 2.0 mass % or more and an Sis/Sib right under the interface is 0.90 or less, a number density of recessed parts with a depth of more than 2 μm at the interface is 2.0/100 μm or less per interface length, and a tensile strength is 980 MPa or more, and a method for producing the same.
Claims
exact text as granted — not AI-modified1 . A hot dip galvanized steel sheet comprising a base steel sheet and a hot dip galvanized layer formed on at least one surface of the base steel sheet, wherein the base steel sheet has a chemical composition comprising, by mass %,
C: 0.15 to 0.30%, Si: 0.30 to 2.50%, Mn: 1.40 to 3.49%, P: 0.050% or less, S: 0.0100% or less, Al: 0.001 to 1.50%, N: 0.0100% or less, O: 0.0100% or less, Cr: 0 to 1.00%, Mo: 0 to 1.00%, 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%, Nb: 0 to 0.200%, Ti: 0 to 0.200%, V: 0 to 1.00%, B: 0 to 0.0050%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Ce: 0 to 0.0150%, Zr: 0 to 0.0100%, La: 0 to 0.0150%, Hf: 0 to 0.0100%, Bi: 0 to 0.0100%, REM other than Ce and La: 0 to 0.0100% and balance: Fe and impurities, and a steel microstructure in a range of ⅛ thickness to ⅜ thickness centered on ¼ thickness from the surface of the base steel sheet comprising, by vol %, ferrite: 0 to 50%, tempered martensite: 1% or more, retained austenite: 5% or more, fresh martensite: 0 to 15%, total of pearlite and cementite: 0 to 5%, and balance: bainite, when measuring the hot dip galvanized steel sheet by a high frequency glow discharge optical emission spectrometer (GDS), a maximum value of Al concentration of an Al rich layer present at an interface of the base steel sheet and the hot dip galvanized layer is 2.0 mass % or more and an Si s /Si b at the base steel sheet right under the interface of the base steel sheet and the hot dip galvanized layer is 0.90 or less, a number density of recessed parts with a depth of more than 2 μm at the interface of the base steel sheet and the hot dip galvanized layer is 2.0/100 μm or less per interface length, and a tensile strength is 980 MPa or more, where Si s : local minimum value of Si emission intensity at base steel sheet right under interface of base steel sheet and hot dip galvanized layer Si b : average value of Si emission intensity at base steel sheet.
2 . The hot dip galvanized steel sheet according to claim 1 , wherein the chemical composition comprises, by mass %,
Si: 0.30 to 1.20% and Al: 0.30 to 1.50%.
3 . A method for producing the hot dip galvanized steel sheet according to claim 1 , comprising
(A) a hot rolling step including hot rolling a slab having the chemical composition according to claim 1 , then coiling and cooling the obtained hot rolled steel sheet, wherein the cooling satisfies the following formula (1):
[
Mathematical
1
]
0.05
<
2
·
∑
t
=
0
tf
(
Do
·
No
N
x
·
Δ
t
)
<
1.5
(
1
)
where
,
[
Mathematical
2
]
D
o
=
2.9
·
10
-
7
·
exp
(
-
90
,
000
8.314
·
T
(
t
)
)
(
2
)
[
Mathematical
3
]
N
o
=
0.381
·
exp
(
-
104
,
000
8.314
·
T
(
t
)
)
(
3
)
T(t): steel sheet temperature (K) after elapse of “t” seconds from coiling
tf: time (s) until steel sheet temperature reaches 673K
Nx: total of atomic percents (-) of Si, Mn, and Al in steel
(B) a pickling step including applying at least one bending/unbending deformation to the hot rolled steel sheet, then running the hot rolled steel sheet through a temperature 70 to 90° C. aqueous solution containing 1.0 to 5.0 mol/L of HCl, less than 3.0 mol/L of Fe 2+ , and less than 0.10 mol/L of Fe 3+ by an average speed of 10 m/min or more as pickling treatment for 30 seconds or more,
(C) a cold rolling step of cold rolling the hot rolled steel sheet after the pickling treatment by a rolling reduction of 30 to 75%,
(D) a heat treatment and plating step including heat treating and plating the obtained cold rolled steel sheet, wherein the heat treatment and plating step satisfies the conditions of the following (D1) to (D4)
(D1) heating the cold rolled steel sheet to give an average heating speed from 600° C. to an Ac1+30° C. to 950° C. maximum heating temperature of 0.2 to 20° C./s, wherein an atmosphere around the cold rolled steel sheet satisfies the following formula (4):
[
Mathematical
4
]
-
1.
<
log
(
p
H
2
O
p
H
2
)
<
-
0.1
(
4
)
pH 2 O: steam partial pressure
pH 2 : hydrogen partial pressure
(D2) holding the cold rolled steel sheet at the maximum heating temperature for 1 to 1000 seconds,
(D3) the time after dipping in the plating bath until gas wiping is 0.1 to 5 seconds and the steel sheet temperature after gas wiping is 440° C. or less, and
(D4) cooling the steel sheet to a range of Ms to Ms−200° C., then reheating to a temperature region of 300 to 420° C. and holding at the temperature region for 100 to 600 seconds.
4 . A method for producing the hot dip galvanized steel sheet according to claim 2 , comprising
(A) a hot rolling step including hot rolling a slab having the chemical composition according to claim 2 , then coiling and cooling the obtained hot rolled steel sheet, wherein the cooling satisfies the following formula (1):
[
Mathematical
1
]
0.05
<
2
·
∑
t
=
0
tf
(
Do
·
No
N
x
·
Δ
t
)
<
1.5
(
1
)
where
,
[
Mathematical
2
]
D
o
=
2.9
·
10
-
7
·
exp
(
-
90
,
000
8.314
·
T
(
t
)
)
(
2
)
[
Mathematical
3
]
N
o
=
0.381
·
exp
(
-
104
,
000
8.314
·
T
(
t
)
)
(
3
)
T(t): steel sheet temperature (K) after elapse of “t” seconds from coiling
tf: time (s) until steel sheet temperature reaches 673K
Nx: total of atomic percents (-) of Si, Mn, and Al in steel
(B) a pickling step including applying at least one bending/unbending deformation to the hot rolled steel sheet, then running the hot rolled steel sheet through a temperature 70 to 90° C. aqueous solution containing 1.0 to 5.0 mol/L of HCl, less than 3.0 mol/L of Fe 2+ , and less than 0.10 mol/L of Fe 3+ by an average speed of 10 μm/min or more as pickling treatment for 30 seconds or more,
(C) a cold rolling step of cold rolling the hot rolled steel sheet after the pickling treatment by a rolling reduction of 30 to 75%,
(D) a heat treatment and plating step including heat treating and plating the obtained cold rolled steel sheet, wherein the heat treatment and plating step satisfies the conditions of the following (D1) to (D4)
(D1) heating the cold rolled steel sheet to give an average heating speed from 600° C. to an Ac1+30° C. to 950° C. maximum heating temperature of 0.2 to 20° C./s, wherein an atmosphere around the cold rolled steel sheet satisfies the following formula (4):
[
Mathematical
4
]
-
1.
<
log
(
p
H
2
O
p
H
2
)
<
-
0.1
(
4
)
pH 2 O: steam partial pressure
pH 2 : hydrogen partial pressure
(D2) holding the cold rolled steel sheet at the maximum heating temperature for 1 to 1000 seconds,
(D3) the time after dipping in the plating bath until gas wiping is 0.1 to 5 seconds and the steel sheet temperature after gas wiping is 440° C. or less, and
(D4) cooling the steel sheet to a range of Ms to Ms−200° C., then reheating to a temperature region of 300 to 420° C. and holding at the temperature region for 100 to 600 seconds.Join the waitlist — get patent alerts
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