US 2026/0243287 A1Published application

Spot-welded joint and method for manufacturing spot-welded joint

AssigneeNippon Steel Corporation

InventorsTohru OKADA, Masafumi AZUMA, Takuya NISHIO, Seiji FURUSAKO

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Abstract

A spot-welded joint according to one aspect of the present disclosure includes a first steel sheet, a second steel sheet, and a spot-welding portion that joins the first steel sheet and the second steel sheet, in which the first steel sheet and the second steel sheet are directly overlapped with each other, the tensile strength of the first steel sheet is 1500 MPa or more, the tensile strength of the second steel sheet is equal to or less than the tensile strength of the first steel sheet, the Vickers hardness from a surface of the first steel sheet to a depth of 20 μm is 95% or less of the Vickers hardness at a position of ¼ of a sheet thickness of a base material portion of the first steel sheet, a carbon equivalent Ceq of the base material portion of the first steel sheet is 0.22% or more, HC=Ceq×TS2×(1−(TS2×t23)/(TS1×t13))/√t2 is 170 or more, and the spot-welding portion includes a nugget and a corona bond area that joins the first steel sheet and the second steel sheet around the nugget, and the Vickers hardness of 20 μm on a first steel sheet side at an outer peripheral side end portion of the corona bond area is lower by 50 Hv or more than the Vickers hardness at the position of ¼ of the sheet thickness of the base material portion of the first steel sheet.

Claims12

Dependent claims

A spot-welded joint comprising:

a first steel sheet;
a second steel sheet;
and
a spot-welding portion which joins the first steel sheet and the second steel sheet, wherein
the first steel sheet and the second steel sheet are directly overlapped with each other,
a tensile strength of the first steel sheet is 1500 MPa or more,
a tensile strength of the second steel sheet is equal to or less than the tensile strength of the first steel sheet,
a Vickers hardness from a surface of the first steel sheet to a depth of 20 μm is 95% or less of a Vickers hardness at a position of ¼ of a sheet thickness of a base material portion of the first steel sheet,
a carbon equivalent Ceq defined by a formula 1 of the base material portion of the first steel sheet is 0.22% or more,
an index HC defined by a formula 2 is 170 or more,
the spot-welding portion includes a nugget and a corona bond area which joins the first steel sheet and the second steel sheet around the nugget, and
a Vickers hardness of 20 μm on a first steel sheet side at an outer peripheral side end portion of the corona bond area is lower by 50 Hv or more than the Vickers hardness at the position of ¼ of the sheet thickness of the base material portion of the first steel sheet:
Ceq
=
C
+
Si
/
90
+
(
Mn
+
Cr
)
/
100
(
formula
⁢
1
)
HC
=
C
⁢
e
⁢
q
×
T
⁢
S
2
×
(
1
-
(
T
⁢
S
2
×
t
2
3
)
/
(
TS
1
×
t
1
3
)
)
/
√
t
2
(
formula
⁢
2
)
wherein an element symbol described in the formula 1 is a content in mass % of an element corresponding to the element symbol in a sheet thickness ¼ portion of the base material portion of the first steel sheet, and
a symbol TS1 described in the formula 2 is the tensile strength in MPa of the first steel sheet, t1 is a sheet thickness in mm of the first steel sheet, TS2 is the tensile strength in MPa of the second steel sheet, and t2 is a sheet thickness in mm of the second steel sheet.

76 more elements

A method for manufacturing a spot-welded joint, comprising:

overlapping a first steel sheet and a second steel sheet;
and
spot-welding the first steel sheet and the second steel sheet, wherein
a tensile strength of the first steel sheet is 1500 MPa or more,
a tensile strength of the second steel sheet is equal to or less than the tensile strength of the first steel sheet,
a Vickers hardness from a surface of the first steel sheet to a depth of 20 μm is 95% or less of a Vickers hardness at a position of ¼ of a sheet thickness of a base material portion of the first steel sheet,
a carbon equivalent Ceq defined by a formula 1 of the base material portion of the first steel sheet is 0.22% or more, and
an index HC defined by a formula 2 is 170 or more:
Ceq
=
C
+
Si
/
90
+
(
Mn
+
Cr
)
/
100
(
formula
⁢
1
)
HC
=
C
⁢
e
⁢
q
×
T
⁢
S
2
×
(
1
-
(
T
⁢
S
2
×
t
2
3
)
/
(
TS
1
×
t
1
3
)
)
/
√
t
2
(
formula
⁢
2
)
wherein an element symbol described in the formula 1 is a content in mass % of an element corresponding to the element symbol in a sheet thickness ¼ portion of the base material portion of the first steel sheet, and
a symbol TS1 described in the formula 2 is the tensile strength in MPa of the first steel sheet, t1 is a sheet thickness in mm of the first steel sheet, TS2 is the tensile strength in MPa of the second steel sheet, and t2 is a sheet thickness in mm of the second steel sheet.

72 more elements

Dependencies are inferred from the claim text.

Facts

Application: 18/870,327Filed 1 Jun 2023
Priority: JP 2022-0895511 Jun 2022
Published: 20 Aug 2026
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

F16B 5/08
Joining sheets or plates , e.g. panels, to one another or to strips or bars parallel to them: by means of welds or the like
B23K 11/11
Spot welding; Stitch welding: spot welding
B23K 11/115
Spot welding: by means of two electrodes placed opposite one another on both sides of the welded parts
B23K 11/16
Resistance welding; Severing by resistance heating: taking account of the properties of the material to be welded

Family

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