Tailored blank for hot stamping, hot stamped member, and methods for manufacturing same
View Patent ↗A tailored blank for hot stamping includes a welded portion formed by butt-welding a first aluminum-plated steel sheet and a second aluminum-plated steel sheet, an Average Al concentration of a weld metal in the welded portion is in a range of 0.3 mass % to 1.5 mass %, an Ac 3 point of the weld metal is 1250° C. or lower, and furthermore, an aluminum layer formed during the butt-welding is present on a surface of the welded portion.
1. A tailored blank for hot stamping comprising:
a welded portion formed by butt-welding a first aluminum-plated steel sheet and a second aluminum-plated steel sheet,
wherein an average Al concentration of a weld metal in the welded portion is 0.3 mass % to 1.5 mass %, in the following formula (1), an Ac 3 point of the weld metal defined in unit ° C. is 1250° C. or lower, and
an aluminum layer formed during the butt-welding is present on a surface of the welded portion,
Ac 3 =910−230×C 0.5 −15.2×Ni+44.7×Si+104×V+31.5×Mo+13.1×W−30×Mn−11×Cr−20×Cu+700×P+400×Al+120×As+400×Ti Formula (1)
where, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti in Formula (1) represent amounts of individual elements in the weld metal in mass %, and elements not contained are considered to have an amount of zero in computation.
2. The tailored blank for hot stamping according to claim 1 ,
wherein, in the following formula (2), Δt M defined in unit of second is 0.5 seconds or longer,
Δ
t
M
=
exp
{
10.6
(
C
+
Si
+
5
×
Al
24
+
Mn
6
+
Cu
15
+
Ni
12
+
Mo
6
+
Cr
×
(
1
-
0.16
×
Cr
)
8
+
Δ
H
)
-
4.8
}
Formula
(
2
)
where, C, Si, Al, Mn, Cu, Ni, Mo, and Cr in Formula (2) represent amounts of individual elements in the weld metal in mass %, elements not contained are considered to have an amount of zero in computation, and ΔH represents a numeric value defined as described below in accordance with the amount of B in mass % and fN when the fN is set to (0.02−N)/0.02 using the amount of N in the weld metal in mass %,
when B≦0.0001, ΔH=0,
when 0.0001<B≦0.0002, ΔH=0.03×fN,
when 0.0002<B≦0.0003, ΔH=0.06×fN, and
when 0.0003<B, ΔH=0.09×fN.
3. The tailored blank for hot stamping according to claim 2 ,
wherein, an Ac 1 point of the weld metal defined in unit ° C. in the following formula (3) is 860° C. or lower,
Ac
1
=
exp
(
6.5792
-
0.038058
×
C
+
0.052317
×
Si
+
0.011872
×
Ni
-
0.045575
×
V
+
0.18057
×
Al
+
0.011442
×
W
-
0.013403
×
Cu
+
5.5207
×
B
+
0.91209
×
S
-
1.1002
×
P
+
0.60014
×
Mn
×
C
-
0.096628
Cr
×
C
+
0.050625
×
Cr
×
Si
+
0.39802
×
Mo
×
C
-
0.34782
×
Mo
×
Mn
+
0.40986
×
Mo
×
Si
-
0.12959
×
Mo
×
Cr
-
0.048128
×
Ni
×
C
-
0.01090
×
Mn
2
-
0.03550
×
Si
2
+
0.010207
×
Cr
2
+
0.36074
×
Mo
2
-
0.0030705
×
Ni
2
)
Formula
(
3
)
where, C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo in Formula (3) represent amounts, in mass %, of individual elements in the weld metal, and elements not contained are considered to have an amount of zero in computation.
4. The tailored blank for hot stamping according to claim 2 ,
wherein a thickness of a thinnest portion of the weld metal is represented by t in unit of mm, a sheet thickness of the first aluminum-plated steel sheet is represented by t1 in unit of mm, and a sheet thickness of the second aluminum-plated steel sheet is represented by t2 in unit of mm,
when the t1 is equal to the t2, the t is 80% or more of the t1; and
when the t1 is different from the t2, the t is 80% or more of the smaller of the t1 and the t2.
5. The tailored blank for hot stamping according to claim 2 ,
wherein, when t1, which is a sheet thickness of the first aluminum-plated steel sheet, is equal to t2, which is a sheet thickness of the second aluminum-plated steel sheet, a maximum height of the weld metal is 300 μm or shorter from an extended line of a surface of the first aluminum-plated steel sheet; and
when the t1 is different from the t2, a maximum height of the weld metal is 300 μm or shorter from an extended line of a surface of thicker of the first aluminum-plated steel sheet and the second aluminum-plated steel sheet.
6. The tailored blank for hot stamping according to claim 1 ,
wherein, an Ac 1 point of the weld metal defined in unit ° C. in the following formula (3) is 860° C. or lower,
Ac
1
=
exp
(
6.5792
-
0.038058
×
C
+
0.052317
×
Si
+
0.011872
×
Ni
-
0.045575
×
V
+
0.18057
×
Al
+
0.011442
×
W
-
0.013403
×
Cu
+
5.5207
×
B
+
0.91209
×
S
-
1.1002
×
P
+
0.60014
×
Mn
×
C
-
0.096628
Cr
×
C
+
0.050625
×
Cr
×
Si
+
0.39802
×
Mo
×
C
-
0.34782
×
Mo
×
Mn
+
0.40986
×
Mo
×
Si
-
0.12959
×
Mo
×
Cr
-
0.048128
×
Ni
×
C
-
0.01090
×
Mn
2
-
0.03550
×
Si
2
+
0.010207
×
Cr
2
+
0.36074
×
Mo
2
-
0.0030705
×
Ni
2
)
Formula
(
3
)
where, C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo in Formula (3) represent amounts, in mass %, of individual elements in the weld metal, and elements not contained are considered to have an amount of zero in computation.
7. The tailored blank for hot stamping according to claim 6 ,
wherein a thickness of a thinnest portion of the weld metal is represented by t in unit of mm, a sheet thickness of the first aluminum-plated steel sheet is represented by t1 in unit of mm, and a sheet thickness of the second aluminum-plated steel sheet is represented by t2 in unit of mm,
when the t1 is equal to the t2, the t is 80% or more of the t1; and
when the t1 is different from the t2, the t is 80% or more of the smaller of the t1 and the t2.
8. The tailored blank for hot stamping according to claim 1 ,
wherein a thickness of a thinnest portion of the weld metal is represented by t in unit of mm, a sheet thickness of the first aluminum-plated steel sheet is represented by t1 in unit of mm, and a sheet thickness of the second aluminum-plated steel sheet is represented by t2 in unit of mm,
when the t1 is equal to the t2, the t is 80% or more of the t1; and
when the t1 is different from the t2, the t is 80% or more of the smaller of the t1 and the t2.
9. The tailored blank for hot stamping according to claim 1 ,
wherein, when t1, which is a sheet thickness of the first aluminum-plated steel sheet is equal to t2, which is a sheet thickness of the second aluminum-plated steel sheet, a maximum height of the weld metal is 300 μm or shorter from an extended line of a surface of the first aluminum-plated steel sheet; and
when the t1 is different from the t2, a maximum height of the weld metal is 300 μm or shorter from an extended line of a surface of thicker of the first aluminum-plated steel sheet and the second aluminum-plated steel sheet.
10. The tailored blank for hot stamping according to claim 1 ,
wherein an oxygen content in the weld metal is 50 ppm or more higher than an average oxygen content in a first steel sheet that is a base material for plating of the first aluminum-plated steel sheet and a second steel sheet that is a base material for plating of the second aluminum-plated steel sheet.
11. A method for manufacturing a hot-stamped member including performing hot stamping on the tailored blank for hot stamping according to claim 1 ,
wherein, after the hot stamping, a product of a hardness of the weld metal and a thickness of a thinnest portion of the weld metal is set to be greater than both a product of a hardness of the first aluminum-plated steel sheet and a sheet thickness of the first aluminum-plated steel sheet and a product of a hardness of the second aluminum-plated steel sheet and a sheet thickness of the second aluminum-plated steel sheet.
12. A method for manufacturing a tailored blank for hot stamping in which butt welding is performed using a first aluminum-plated steel sheet and a second aluminum-plated steel sheet, the method comprising:
determining welding conditions so that an average Al concentration of a weld metal in a welded portion falls in a range of 0.3 mass % to 1.5 mass %, and an Ac 3 point (° C.) of the weld metal defined by the following formula (1) is 1250° C. or lower; and
forming an aluminum layer derived from aluminum-plated layers of the first aluminum-plated steel sheet and the second aluminum-plated steel sheet on a surface of the weld metal in the welded portion by performing welding under the welding conditions,
Ac 3 =910−230×C 0.5 −15.2×Ni+44.7×Si+104×V+31.5×Mo+13.1×W−30×Mn−11×Cr−20×Cu+700×P+400×Al+120×As+400×Ti Formula (1)
where, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti in Formula (1) represent amounts of individual elements in the weld metal in mass %, and elements not contained are considered to have an amount of zero in computation.
13. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the welding conditions are determined so that Δt M defined by the following formula (2) in unit of second is 0.5 seconds or longer,
Δ
t
M
=
exp
{
10.6
(
C
+
Si
+
5
×
Al
24
+
Mn
6
+
Cu
15
+
Ni
12
+
Mo
6
+
Cr
×
(
1
-
0.16
×
Cr
)
8
+
Δ
H
)
-
4.8
}
Formula
(
2
)
where, C, Si, Al, Mn, Cu, Ni, Mo, and Cr in Formula (2) represent amounts of individual elements in the weld metal in mass %, and elements not contained are considered to have an amount of zero in computation, and ΔH represents a numeric value defined as described below in accordance with the amount of B in mass % and fN when the fN is set to (0.02−N)/0.02 using the amount of N in the weld metal in mass %,
when B≦0.0001, ΔH=0,
when 0.0001<B≦0.0002, ΔH=0.03×fN,
when 0.0002<B≦0.0003, ΔH=0.06×fN, and
when 0.0003<B, ΔH=0.09×fN.
14. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the welding conditions are determined so that an Ac 1 point defined by the following formula (3) in unit ° C. is 860° C. or lower,
Ac
1
=
exp
(
6.5792
-
0.038058
×
C
+
0.052317
×
Si
+
0.011872
×
Ni
-
0.045575
×
V
+
0.18057
×
Al
+
0.011442
×
W
-
0.013403
×
Cu
+
5.5207
×
B
+
0.91209
×
S
-
1.1002
×
P
+
0.60014
×
Mn
×
C
-
0.096628
Cr
×
C
+
0.050625
×
Cr
×
Si
+
0.39802
×
Mo
×
C
-
0.34782
×
Mo
×
Mn
+
0.40986
×
Mo
×
Si
-
0.12959
×
Mo
×
Cr
-
0.048128
×
Ni
×
C
-
0.01090
×
Mn
2
-
0.03550
×
Si
2
+
0.010207
×
Cr
2
+
0.36074
×
Mo
2
-
0.0030705
×
Ni
2
)
Formula
(
3
)
where, C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo in Formula (3) represent amounts, in mass %, of individual elements in the weld metal, and elements not contained are considered to have an amount of zero in computation.
15. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the welding conditions are determined so that a thickness of a thinnest portion of the weld metal is represented by t in unit of mm, a sheet thickness of the first aluminum-plated steel sheet is represented by t1 in unit of mm, and a sheet thickness of the second aluminum-plated steel sheet is represented by t2 in unit of mm,
when the t1 is equal to the t2, the t is 80% or more of the t1; and when the t1 is different from the t2, the t is 80% or more of the smaller of the t1 and the t2.
16. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the welding conditions are determined so that, when t1, which is a sheet thickness of the first aluminum-plated steel sheet, is equal to t2, which is a sheet thickness of the second aluminum-plated steel sheet, a maximum height of the weld metal is 300 μm or shorter from an extended line of a surface of the first aluminum-plated steel sheet; and when the t1 is different from the t2, a maximum height of the weld metal is 300 μm or shorter from an extended line of a surface of thicker of the first aluminum-plated steel sheet and the second aluminum-plated steel sheet.
17. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the welding conditions are determined so that an oxygen content in the weld metal is 50 ppm or more higher than an average oxygen content in a steel sheet that is a base material for plating of the first aluminum-plated steel sheet and the second aluminum-plated steel sheet.
18. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the butt welding is any one of laser welding, electron beam welding, and plasma welding.
19. The method for manufacturing a tailored blank for hot stamping according to claim 12 ,
wherein the butt welding is laser welding performed while supplying a filler wire.