Crack-containing hot-stamped coated steel part with excellent spot-weldability and excellent painting adhesion
A hot-stamped coated steel part includes a steel substrate and an aluminum alloy coating comprising, proceeding from steel substrate outwards, an interdiffusion layer and an outer layer. The total thickness of the coating e coating and the thickness of the interdiffusion layer e IDL satisfy the following condition: with 40 ≤ E pc ≤ 80 E pc = ( 33.3 - e IDL 0.9 + e IDL - e coating ) 2 - 148 ( e IDL - e coating ) - ( 33.3 - e IDL 0.9 + e IDL - E coating ) The hot-stamped coated steel part comprises an undeformed portion having a thickness e Pflat from 0.6 mm to 3.5 mm, and at least one deformed portion. A lineic density of cracks dC in the coating in the undeformed portion is higher than or equal to a minimum lineic density of cracks dC min (e Pflat ) defined as: dc min ( e pflat ) - 15.5 + 91 * e - 7.44 - 2.88 * arctan ( 5.49 * ( e pflat - 1.71 ) ) - 106.5 * e - 8.62 - 3.34 * arctan ( 5.49 * ( e pflat - 1.71 ) )
1 . A hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating on at least one face of the steel substrate, the coating comprising, proceeding from steel substrate outwards, an interdiffusion layer and an outer layer, wherein a total thickness of the coating e coating and a thickness of the interdiffusion layer e IDL satisfy the following condition:
4
0
≤
E
p
c
≤
80
E
p
c
=
(
3
3
.
3
-
e
IDL
0
.
9
+
e
IDL
-
e
c
o
a
t
i
n
g
)
2
-
1
4
8
(
e
D
L
-
e
c
o
a
t
i
n
g
)
-
(
3
3
.
3
-
e
IDL
0
.
9
+
e
IDL
-
e
c
o
a
t
i
n
g
)
e IDL designating the thickness of the interdiffusion layer in μm, and e coating designating the total thickness of the coating in μm,
and wherein, the hot-stamped coated steel part comprises an undeformed portion having a thickness e Pflat from 0.6 mm to 3.5 mm, and at least one deformed portion, a lineic density of cracks dC in the coating in the undeformed portion is higher than or equal to a minimum lineic density of cracks dC min (e Pflat ) defined as:
d
C
min
(
e
pflat
)
=
1
5
.
5
+
9
1
*
e
-
7.44
-
2
.
8
8
*
arctan
(
5.49
*
(
e
p
flat
-
1.71
)
)
-
1
0
6.5
*
e
-
8.62
-
3
.
3
4
*
arctan
(
5.49
*
(
e
pflat
-
1.71
)
)
wherein dC and dC min (e Pflat ) are expressed in numbers of cracks per mm, and e pflat designates the thickness of the undeformed portion in mm.
2 . The hot-stamped coated steel part according to claim 1 , wherein the hot-stamped coated steel part has a uniform thickness e P of between 0.6 mm and 3.5 mm.
3 . The hot-stamped coated steel part according to claim 1 , wherein the hot-stamped coated steel part has a variable thickness, the hot-stamped coated steel part consisting of two or more regions with distinct thicknesses e Pi each of between 0.6 and 3.5 mm, the hot-stamped coated steel part having an average thickness e P of between 0.6 mm and 3.5 mm.
4 . The hot-stamped coated steel part according to claim 1 , wherein the hot-stamped coated steel part comprising two or more undeformed portions each having a thickness e pflat (i) from 0.6 mm to 3.5 mm, a lineic density of cracks dC (i) in the coating in each undeformed portion is higher than or equal to dC min (e pflat (i)) with:
d
C
min
(
e
pflat
(
i
)
)
=
1
5
.
5
+
9
1
*
e
-
7.44
-
2
.
8
8
*
arctan
(
5.49
*
(
e
p
flat
-
1.71
)
)
-
1
0
6.5
*
e
-
8.62
-
3
.
3
4
*
arctan
(
5.49
*
(
e
pflat
-
1.71
)
)
wherein e pflat (i) designates the thickness of the considered undeformed portion expressed in mm, with i=1 . . . n, n≥2, and dC(i) and dC min (e pflat (i)) are expressed in numbers of cracks per mm and designate respectively the lineic density of cracks and the minimum lineic density of cracks in the coating of the considered undeformed portion of thickness e pflat (i).
5 . The hot-stamped coated steel part according to claim 1 , wherein in cross-section, the cracks in the coating of the undeformed portion extend from an uppermost surface of the coating towards the steel substrate, in a direction orthogonal to the surface of the steel substrate, over a depth of at least 5 μm, the cracks each having a width lower than 2 μm in a direction parallel to the surface of the steel substrate.
6 . The hot-stamped coated steel part according to claim 1 , wherein the lineic density of cracks is determined as a ratio between a total number of cracks observed in several cross-sections of the undeformed portion with a bright field optical microscope, over a total length of observation of at least 5 mm in a direction parallel to a surface of the steel substrate, and the total length of observation.
7 . The hot-stamped coated steel part according to claim 1 , wherein the hot-stamped coated steel part is a monolithic part, or a hot-stamped welded part consisting of at least two hot-stamped coated sub-parts and at least one hot-stamped weld joining together the hot-stamped coated sub-parts.
8 . The hot-stamped coated steel part according to claim 7 , wherein the hot-stamped coated steel part or each hot-stamped coated sub-part has a structure consisting of, by volume, at least 60% martensite, at most 20% bainite, at most 5% ferrite and at most 15% austenite.
9 . The hot-stamped coated steel part according to claim 7 , wherein the steel in the hot-stamped coated steel part or in each hot-stamped coated sub-part has a chemical composition comprising, by weight %:
0.062
%
≤
C
≤
0.04
%
0.4
%
≤
Mn
≤
3.9
%
0.1
%
≤
Si
≤
1.5
%
0.005
%
≤
Al
≤
1.
%
0.001
%
≤
Cr
≤
2.
%
0.001
%
≤
Ti
≤
0.2
%
0.0002
%
≤
B
≤
0.01
%
Ni
≤
2
%
Nb
≤
0.1
%
Mo
≤
0.65
%
W
≤
0.3
%
N
≤
0.01
%
0.0001
%
≤
S
≤
0.05
%
0.0001
%
≤
P
≤
0.1
%
Ca
≤
0.005
%
and
a remainder being Fe and unavoidable impurities resulting from elaboration.
10 . The hot-stamped coated steel part according to claim 9 , wherein the steel in the hot-stamped coated steel part or in at least one hot-stamped coated sub-part has a chemical composition comprising, by weight %:
0.062
%
≤
C
≤
0.095
%
1.4
%
≤
Mn
≤
1.9
%
0.2
%
≤
Si
≤
0.5
%
0.02
%
≤
Al
≤
0.07
%
0.02
%
≤
Cr
≤
0.1
%
0.0035
%
≤
Ti
≤
0.072
%
0.0002
%
≤
B
≤
0.004
%
0.04
%
≤
Nb
≤
0.06
%
with
0.044
%
≤
(
Nb
+
Ti
)
≤
0.09
%
0.001
%
≤
N
≤
0.009
%
0.0005
%
≤
S
≤
0.003
%
0.0001
%
≤
P
≤
0.02
%
Ca
≤
0.005
%
,
and
a remainder being Fe and unavoidable impurities resulting from elaboration.
11 . The hot-stamped coated steel part according to claim 9 , wherein the steel in the hot-stamped coated steel part or in at least one hot-stamped coated sub-part has a chemical composition comprising, by weight %:
0.15
%
≤
C
≤
0.3
%
0.5
%
≤
Mn
≤
3.
%
0.1
%
≤
Si
≤
0.5
%
0.005
%
≤
Al
≤
0.1
%
0.01
%
≤
Cr
≤
1.
%
0.001
%
≤
Ti
≤
0.2
%
0.0002
%
≤
B
≤
0.01
%
0.0005
%
≤
N
≤
0.01
%
0.0001
%
≤
S
≤
0.05
%
0.0001
%
≤
P
≤
0.1
%
Ca
≤
0.005
%
and
a remainder being Fe and unavoidable impurities resulting from elaboration.
12 . The hot-stamped coated steel part according to claim 9 , wherein the steel in the hot-stamped coated steel part or in at least one hot-stamped coated sub-part has a chemical composition comprising, by weight %:
0.3
%
≤
C
≤
0.4
%
0.5
%
≤
Mn
≤
1.
%
0.4
%
≤
Si
≤
0.8
%
0.01
%
≤
Al
≤
0.1
%
0.1
%
≤
Cr
≤
1.
%
0.008
%
≤
Ti
≤
0.03
%
0.0005
%
≤
B
≤
0.003
%
Ni
≤
0.5
%
0.01
%
≤
Nb
≤
0.1
%
0.1
%
≤
Mo
≤
0.5
%
N
≤
0.005
%
0.0001
%
≤
S
≤
0.004
%
0.0001
%
≤
P
≤
0.02
%
Ca
≤
0.001
%
and
a remainder being Fe and unavoidable impurities resulting from elaboration.