Tailored blank for hot stamping, hot stamped member, and methods for manufacturing same
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 hot-stamped member obtained by performing hot stamping on a tailored blank for hot stamping,
wherein the tailored blank for hot stamping includes
a welded portion comprising a weld metal formed by butt-welding a first aluminum-plated steel sheet and a second aluminum-plated steel sheet,
wherein an average Al concentration of the weld metal of the hot-stamped member 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
wherein an aluminum layer formed during the butt-welding is present on a surface of the welded portion of the hot-stamped member,
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 of the hot-stamped member in mass %, and elements not contained are considered to have an amount of zero in computation, and
wherein a product of a hardness of the weld metal of the hot-stamped member and a thickness of a thinnest portion of the weld metal of the hot-stamped member is greater than both a product of a hardness of the first aluminum-plated steel sheet of the hot-stamped member and a sheet thickness of the first aluminum-plated steel sheet of the hot-stamped member and a product of a hardness of the second aluminum-plated steel sheet of the hot-stamped member and a sheet thickness of the second aluminum-plated steel sheet of the hot-stamped member.
2. The hot-stamped member according to claim 1 ,
wherein, furthermore, in the following formula (2), Δt M defined in unit of second is 0.5 seconds or longer,
Formula
(
2
)
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
}
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 hot-stamped member 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+0.060014×Mn×C−0.096628Cr×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 hot-stamped member according to claim 1 ,
wherein a thickness of a thinnest portion of the weld metal is represented by t in unit mm, a sheet thickness of the first aluminum-plated steel sheet is represented by t1 in unit mm, and a sheet thickness of the second aluminum-plated steel sheet is represented by t2 in unit 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 hot-stamped member according to claim 1 ,
wherein when the 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 hot-stamped member 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 coating of the first aluminum-plated steel sheet and a second steel sheet that is a base material for coating of the second aluminum-plated steel sheet.