US2024247349A1PendingUtilityA1
High strength cold rolled steel sheet having excellent surface quality and low mechanical property deviation and manufacturing method of same
Est. expirySep 24, 2041(~15.2 yrs left)· nominal 20-yr term from priority
C21D 8/02C22C 38/02C22C 38/12C21D 1/18C21D 8/0247C22C 38/002C22C 38/001C22C 38/06C22C 38/32C22C 38/22C22C 38/38C22C 38/04C21D 8/0226C21D 2211/005C21D 2211/002C21D 6/005C21D 8/0273C21D 8/0236C21D 2211/008C21D 8/0263C21D 9/46C21D 8/0205
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Claims
Abstract
Provided is a high-strength cold-rolled steel sheet having excellent surface quality and low mechanical property deviation; and a manufacturing method thereof and, more particularly, to: a high-strength cold-rolled steel sheet that can be suitably used for automotive parts by ensuring high strength and elongation with little surface defects and low mechanical property deviation; and a manufacturing method thereof.
Claims
exact text as granted — not AI-modified1 . A high-strength cold-rolled steel sheet comprising:
by weight %, C: 0.05 to 0.3%, Si: 0.01 to 2.0%, Mn: 1.5 to 3.0%, Al: 0.01 to 0.1%, P: 0.001 to 0.015%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, with a remainder of Fe, and other unavoidable impurities, wherein a value defined by Relational Expression 1 satisfies 0.6 or more and less than 0.9, as a microstructure, by area %, ferrite: 50% or more, a remainder: bainite and martensite, wherein an average number of surface defects satisfying one or more conditions of a depth of 100 μm or more and a short side length of 1 μm or more, is less than 10/m 2
C
+
(
13
×
Si
+
Mn
)
/
6
+
(
Cr
+
12
×
Mo
)
/
5
+
100
×
B
[
Relational
Expression
1
]
In Relational Expression 1, C, Si, Mn, Cr, Mo, and B represent an average weight percentage for each element. when each of the above-described elements is not added, 0 is substituted.
2 . The high-strength cold-rolled steel sheet of claim 1 , wherein the microstructure comprises, by area %, ferrite: 50 to 85% and a sum of bainite and martensite: 15 to 50%.
3 . The high-strength cold-rolled steel sheet of claim 1 , wherein the microstructure comprises, by area %, ferrite: 66 to 75%.
4 . The high-strength cold-rolled steel sheet of claim 3 , wherein the microstructure comprises, by area %, bainite: 3 to 7%.
5 . The high-strength cold-rolled steel sheet of claim 3 , wherein the microstructure comprises, by area %, martensite: 19 to 31%.
6 . The high-strength cold-rolled steel sheet of claim 1 , further comprising one or more selected elements from, by weight %, Cr: 1.0% or less (including 0%), Mo: 0.2% or less (including 0%), and B: 0.005% or less (including 0%).
7 . The high-strength cold-rolled steel sheet of claim 1 , wherein a tensile strength is 780 MPa or more and a yield strength is 380 MPa or more.
8 . The high-strength cold-rolled steel sheet of claim 1 , wherein a product of the tensile strength and elongation is 12,000 MPa % or more.
9 . The high-strength cold-rolled steel sheet of claim 1 , wherein a difference in yield strength between both end portions and a center portion is 100 MPa or less, in a width direction of the cold-rolled steel sheet.
10 . A method for manufacturing a high-strength cold-rolled steel sheet, the method comprising:
reheating a steel slab including, by weight %, C: 0.05 to 0.3%, Si: 0.01 to 2.0%, Mn: 1.5 to 3.0%, Al: 0.01 to 0.1%, P: 0.001 to 0.015%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, with a remainder of Fe, and other unavoidable impurities, wherein a value defined by Relational Expression 1 satisfies 0.6 or more and less than 0.9, to a temperature of 1100 to 1350° C.; hot rolling the reheated steel slab at a temperature within a range of 850 to 1150° C.; cooling the hot-rolled steel sheet to a temperature within a range of 450 to 700° C. at an average cooling rate of 10 to 70° C./s; coiling the cooled steel sheet at a temperature within a range of 450 to 700° ° C.; cold rolling the wound steel sheet at a reduction rate of 40 to 70%; and continuously annealing the cold-rolled steel sheet at a temperature within a range of 740 to 900° C., wherein in the coiling, based on an entire width of the steel sheet, a surface temperature (Te) of both end portions in a width direction is controlled to satisfy 601 to 700° C., and a surface temperature (Tc) of a center portion is controlled to satisfy 450 to 600° ° C.
C
+
(
13
×
Si
+
Mn
)
/
6
+
(
Cr
+
12
×
Mo
)
/
5
+
100
×
B
[
Relational
Expression
1
]
In Relational Expression 1, C, Si, Mn, Cr, Mo and B represent an average weight percentage of each element. In addition, if each of the above-described elements is not added, 0 is substituted.
11 . The method of claim 10 , further comprising:
after the coiling, moving the wound steel sheet into a heat retaining cover and maintaining at a temperature within a range of 400 to 500° ° C. for more than 6 hours.
12 . The method of claim 10 , wherein in the coiling, a difference (Te−Tc) between the surface temperature of both end portions and the surface temperature (Tc) of the center portion is controlled to satisfy a temperature of 150° C. or less.
13 . The method of claim 10 , wherein in the cooling, based on an entire width of the steel sheet, an amount of coolant provided onto a center portion excluding the both end portions is controlled to be greater than an amount of coolant provided onto the both end portions in a width direction.Join the waitlist — get patent alerts
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