Welded joint and production method therefor
AssigneeJfe Steel Corporation
InventorsChikaumi SAWANISHI, Katsutoshi TAKASHIMA, Kyohei KONISHI, Koichi TANIGUCHI
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Abstract
Provided is a welded joint formed using relatively thin high-strength steel sheets as base metal and having excellent room-temperature toughness. In the welded joint, each base steel sheet has a sheet thickness of 0.8 mm or more and 10 mm or less, at least one of the base steel sheets has a steel microstructure in which a total area ratio of martensite and bainite is more than 50% and a tensile strength of 980 MPa or more, and an oxygen content of a weld metal in a weld portion and a total area ratio of martensite and bainite in the weld metal satisfy a predetermined relationship.
Claims8
A welded joint comprising:
- two or more base steel sheets;
- and
- a weld portion joining the base steel sheets,
- wherein each of the base steel sheets has a sheet thickness of 0.8 mm or more and 10 mm or less,
- at least one of the base steel sheets has a steel microstructure in which a total area ratio of martensite and bainite is more than 50% and a tensile strength of 980 MPa or more, and
- an oxygen content of a weld metal in the weld portion and a total area ratio of martensite and bainite in the weld metal satisfy the following formulas (1) to (3):
- 1
-
- 0
- ≤
- O
-
- w
- ≤
- 600
- (
- 1
- )
- 10
- -
- (
- Ow
- -
- 10
- )
- /
- 34
- ≤
- M
-
- w
- ≤
- 100
-
- when
-
- 10
- ≤
- Ow
- ≤
- 350
- (
- 2
- )
- 0
- ≤
- Mw
- ≤
- 1
-
- 0
-
- 0
- -
- (
- O
-
- w
- -
- 3
-
- 5
-
- 0
- )
- ×
- 50
- /
- 250
-
- when
-
- 350
- <
- Ow
- ≤
- 600
- ,
- (
- 3
- )
- where Ow is the oxygen content of the weld metal in mass ppm, and Mw is the total area ratio of martensite and bainite in the weld metal in %.
A production method for a welded joint, comprising welding two or more steel sheets as materials to be joined to obtain a welded joint,
- wherein each of the steel sheets has a sheet thickness of 0.8 mm or more and 10 mm or less,
- each of the steel sheets has a surface oxide layer thickness of 50 μm or less,
- at least one of the steel sheets has a steel microstructure in which a total area ratio of martensite and bainite is more than 50% and a tensile strength of 980 MPa or more,
- a total volume fraction of CO2 and O2 in a shielding gas used for the welding and a Ti content and B content in each of the steel sheets satisfy the following formula (4), and
- a heat input amount in the welding, a thickness of the materials to be joined, and an average value of surface oxide layer thicknesses of the steel sheets satisfy the following formula (5),
- 0
- ≤
- Ti
- +
- 100
- ×
- B
- ≤
- 12
- -
- Og
- ×
- 0.8
- /
- 100
- (
- 4
- )
- 1200
- ×
- t
- all
- 1
- /
- 3
- ×
- (
- 1
- +
- 0
- .
- 1
- ×
- t
- 0
- 1
- /
- 5
- )
- ≤
- Q
- ≤
- 4
-
- 0
-
- 00
- ×
- t
- all
- 1
- /
- 3
- ×
- (
- 1
- +
- 0
- .
- 1
- ×
- t
- 0
- 1
- /
- 5
- )
- ,
- (
- 5
- )
- where Og is the total volume fraction of CO2 and O2 in the shielding gas in %, Ti is the Ti content in each of the steel sheets in mass %, B is the B content in each of the steel sheets in mass %, Q is the heat input amount in J/cm, tall is the thickness of the materials to be joined in mm, and to is the average value of the surface oxide layer thicknesses of the steel sheets in μm.
Dependencies are inferred from the claim text.