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US 6,554,925 B2Granted
Method for manufacturing cold-rolled steel sheet
AssigneeNKK Corporation
InventorsTadashi Inoue, Yasuhide Ishiguro, Yoichi Motoyashiki, Sadanori Imada, Toru Inazumi
Life of this patent
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Abstract
The method for manufacturing cold-rolled steel sheet comprises the steps of: rough-rolling a slab using a rough-rolling unit; finish-rolling the sheet bar using a continuous hot finishing-rolling mill; cooling the hot-rolled steel strip on a runout table; coiling thus cooled hot-rolled steel strip; and applying picking, cold-rolling the hot-rolled steel strip, and final annealing to the cold-rolled steel strip.
Claims22
A method for manufacturing a cold-rolled steel sheet comprising the steps of:
- (a) providing a slab consisting essentially of 0.02% or less C, 0.5% or less Si, 2.5% or less Mn, 0.10% or less P, 0.05% or less S. 0.003% or less O, 0.003% or less N, 0.01to 0.40% of at least one element selected from the group consisting of Ti, Nb, V, and Zr, by weight, optionally 0.0001 to 0.005% by weight of B, and a balance being Fe;
- (b) rough-rolling the slab by a rough-rolling mill to form a sheet bar;
- (c) finish-rolling the sheet bar by a continuous hot finish-rolling mill to form a hot-rolled steel strip,
- the finish-rolling comprising finish-rolling the sheet bar so that a material temperature at a final stand of the finish-rolling mill becomes an Ar3 transformation point or more over the whole range of from a front end of the sheet bar to a rear end thereof;
- (d) cooling the hot-rolled steel strip on a runout table and coiling the cooled hot-rolled steel strip at a coiling temperature,
- the cooling on the runout table beginning with a time range of from more than 0.1 second and less than 1.0 second after completing the finish-rolling,
- the cooling on the runout table being conducted at an average cooling speed in a temperature range of from a hot-rolling finish temperature to 700° C. being 120° C./sec or more,
- an average cooling speed in a temperature range of from 700° C. to the coiling temperature being 50° C./sec or less,
- the coiling temperature of the hot-rolled steel strip being less than 700° C.;
- and
- (e) pickling and cold rolling the hot-rolled steel strip, and final annealing the cold-rolled steel strip.
8 more elements
A method for manufacturing a cold-rolled steel sheet comprising the steps of:
- (a) heating a slab consisting essentially of 0.0003 to 0.004% C, 0.05% or less Si, 0.05 to 2.5% Mn, 0.003 to 0.1% P, 0.0003 to 0.02% S, 0.005 to 0.1% sol.Al, 0.0003 to 0.004% N, by weight, optionally (i) 0.005 to 0.1% by weight of at least one element selected from the group consisting of Ti, Nb, V and Zr, or (ii) 0.015 to 0.8% Cu by weight or (iii) 0.0001 to 0.001% B by weight, and a balance of Fe;
- (b) hot-rolling the slab to form a hot-rolled steel strip;
- and
- (c) cold-rolling the hot-rolled steel strip to form a cold-rolled steel strip and annealing the cold-rolled steel strip,
- the step of hot-rolling comprising finish-rolling, cooling, and coiling,
- the finish-rolling having a total reduction in thickness of two passes before a final pass being in a range of from 25 to 45%, a reduction in thickness at the final pass being in a range of from 5 to 25%, and a finishing temperature being in a range of from the Ar3 transformation point to the (Ar3 transformation point+50° C.), and
- the cooling being carried out by a rapid cooling at a cooling speed in a range of from 200 to 2,000° C./sec within 1 second after completing the finish rolling, a temperature reduction from the finishing temperature of the finish rolling in the rapid cooling being in a range of from 50 to 250° C., and a temperature to stop the rapid cooling being in a range of from 650 to 850° C., followed by applying slow cooling or air cooling at a rate of 100° C./sec or less,
- the coiling being carried out at a coiling temperature of 550 to 750° C.
5 more elements
A method for manufacturing a cold-rolled steel sheet comprising the steps of:
- (a) heating a slab consisting essentially of 0.0003 to 0.004% C, 0.05% or less Si, 0.05 to 2.5% Mn, 0.003 to 0.1% P, 0.0003 to 0.02% S, 0.005 to 0.1% sol.Al, 0.0003 to 0.004% N, by weight, optionally (i) 0.005 to 0.1% by weight of at least one element selected from the group consisting of Ti, Nb, V and Zr, or (ii) 0.015 to 0.8% Cu by weight or (iii) 0.0001 to 0.001% B by weight, and a balance of Fe;
- (b) hot-rolling the heated slab to form a hot-rolled steel strip;
- and
- (c) cold-rolling the hot-rolled steel strip to form a cold-rolled steel sheet and annealing the cold-rolled steel sheet;
- the step of hot-rolling comprising finish-rolling, cooling, and coiling,
- a total reduction in thickness of two passes before a final pass being in a range of from 45 to 70%, a reduction in thickness at the final pass being in a range of from 5 to 35%, and a finishing temperature being in a range of from the Ar3 transformation point to the (Ar3 transformation point+50° C.), and
- the cooling being carried out by a rapid cooling at a cooling speed of from 200 to 2,000° C./sec within 1 second after completing the finish rolling, a temperature reduction from the finishing temperature of the finish-rolling in the rapid cooling being in a range of from 50 to 250° C., and a temperature to stop the rapid cooling being in a range of from 650 to 850° C., followed by applying slow cooling or air cooling at a rate of 100° C./sec or less,
- the coiling being carried out at a coiling temperature of 550 to 750° C.
5 more elements
Dependencies are inferred from the claim text.