Steel sheet for excellent panel appearance and dent resistance after panel-forming
AssigneeNKK Corporation
InventorsYoshihiro Hosoya, Fusato Kitano, Yasunobu Nagataki
Life of this patent
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Abstract
A cold-rolled steel sheet or a zinc or zinc alloy layer coated steel sheet containing 0.0010 to 0.01 wt % of C and having a steel composition containing one or two kinds of 0.005 to 0.08 wt % of Nb and 0.01 to 0.07 wt % of Ti in the ranges given by {(12/93)Nb+(12/48)Ti*} .gtoreq.0.0005, 0.ltoreq.C-{(12/93)Nb+(12/48)Ti*}.ltoreq.0.0015, and Ti*=Ti-{(48/32)S+(48/14)N } , in which a bake hardenability BH f the steel sheet at 170.degree. C..times.20 min after 2% tensile prestrain is 10 to 35 MPa and the BH (MPa) and a yield strength YP (MPa) of the steel sheet satisfy the ranges given by BH.gtoreq.exp(-0.115.multidot.YP+23.0) and 0.67.multidot.BH+160.ltoreq.YP.ltoreq.-0.8.multidot.BH+280.
Claims11
A cold-rolled steel sheet for excellent panel appearance and dent resistance after panel-forming, comprising a steel composition containing 0.0010 to 0.01 wt % of C, 0 to 0.2 wt % of Si, 0.1 to 1.5 wt % of Mn, 0 to 0.05 wt % of P, 0 to 0.02 wt % of S, 0.03 to 0.10 wt % of sol. Al, and 0 to 0.0040 wt % of N, and further containing one or both of 0.005 to 0.08 wt % of Nb and 0.01 to 0.07 wt % of Ti in the ranges given by the following formulae (1) and (2):
- {(12/93)Nb+(12/48)Ti*}.gtoreq.0.0005 (1)
- 0.ltoreq.C-{(12/93)Nb+(12/48)Ti*}.ltoreq.0.0015 (2)
- wherein Ti*=Ti-{(48/32)S+(48/14)N}
- said cold-rolled steel sheet having a bake hardenability BH of 10 to 35 MPa obtained by a 2% tensile prestrain and 170.degree. C..times.20 min heat treatment;
- said bake hardenability BH (MPa) and a yield strength YP (MPa) of said steel sheet satisfying the following formulae (3a) and (4a)
- BH.gtoreq.exp (-0.115.multidot.YP+23.0) (3a)
- 0.67.multidot.BH+160.ltoreq.YP.ltoreq.-0.8.multidot.BH+280 (4a).
A cold-rolled steel sheet for excellent panel appearance and dent resistance after panel-forming, comprising a steel composition containing 0.0010 to 0.01 wt % of C, 0 to 0.2 wt % of Si, 0.1 to 1.5 wt % of Mn, 0-to 0.05 wt % of P, 0 to 0.02 wt % of S, 0.03 to 0.10 wt % of sol. Al, and 0 to 0.0040 wt % of N, and further containing one or both of 0.005 to 0.08 wt % of Nb and 0.01 to 0.07 wt % of Ti in the ranges given by the following formulae (1) and (2):
- {(12/93)Nb+(12/48)Ti*}.gtoreq.0.0005 (1)
- 0.ltoreq.C-{(12/93)Nb+(12/48)Ti*}.ltoreq.0.0015 (2)
- wherein Ti*=Ti-{(48/32)S+(48/14)N}
- said cold-rolled steel sheet having a bake hardenability BH of 10 to 30 MPa obtained by 2% tensile prestrain and 170.degree. C..times.20 min heat treatment;
- said bake hardenability BH (MPa) and a yield strength YP (MPa) of said steel sheet satisfying the following formulae (3b) and (4b)
- BH.gtoreq.exp (-0.115.multidot.YP+25.3) (3b)
- 0.67.multidot.BH+177.ltoreq.YP.ltoreq.-0.8.multidot.BH+260 (4b).
- 3.
A cold-rolled steel sheet for excellent panel appearance and dent resistance after panel-forming, comprising a steel composition containing 0.0010 to 0.0025 wt % of C, 0 to 0.2 wt % of Si, 0.1 to 1.5 wt % of Mn, 0 to 0.05 wt % of P, 0 to 0.02 wt % of S, 0.03 to 0.10 wt % of sol. Al, and 0 to 0.0040 wt % of N, and further containing one or both of 0.005 to 0.020 wt % of Nb and 0.01 to 0.05 wt % of Ti in the ranges given by the following formulae (1) and (2):
- {(12/93)Nb+(12/48)Ti*}.gtoreq.0.0005 (1)
- 0.ltoreq.C-{(12/93)Nb+(12/48)Ti*}.ltoreq.0.0015 (2)
- wherein Ti*=Ti-{(48/32)S+(48/14)N}
- said cold-rolled steel sheet having a bake hardenability BH of 10 to 35 MPa obtained by a 2% tensile prestrain and 170.degree. C..times.20 min heat treatment;
- said bake hardenability BH (MPa) and a yield strength YP (MPa) of said steel sheet satisfying the following formulae (3a) and (4a)
- BH.gtoreq.exp (-0.115.multidot.YP+23.0) (3a)
- 0.67.multidot.BH+160.ltoreq.YP.ltoreq.-0.8.multidot.-BH+280(4a).
A cold-rolled steel sheet for excellent panel appearance and dent resistance after panel-forming, comprising a steel composition containing 0.0010 to 0.0025 wt % of C, 0 to 0.2 wt % of Si, 0.1 to 1.5 wt % of Mn, 0 to 0.05 wt % of P, 0 to 0.02 wt % of S, 0.03 to 0.10 wt % of sol. Al, and 0 to 0.0040 wt % of N, and further containing one. or both of 0.005 to 0.020 wt % of Nb and 0.01 to 0.05 wt % of Ti in the ranges given by the following formulae (1) and (2):
- {(12/93)Nb+(12/48)Ti*}.gtoreq.0.0005 (1)
- 0.ltoreq.C-{(12/93)Nb+(12/48)Ti*}.ltoreq.0.0015 (2)
- wherein Ti*=Ti-{(48/32)S+(48/14)N}
- said cold-rolled steel sheet having a bake hardenability BH of 10 to 30 MPa obtained by 2% tensile prestrain and 170.degree. C..times.20 min heat treatment;
- said bake hardenability BH (MPa) and a yield strength YP (MPa) of said steel sheet satisfying the following formulae (3b) and (4b)
- BH.gtoreq.exp (-0.115.multidot.YP+25.3) (3b)
- 0.67.multidot.BH+177.ltoreq.YP.ltoreq.-0.8.multidot.BH+260 (4b).
Dependencies are inferred from the claim text.