US2025243556A1PendingUtilityA1
Ultra-high strength cold-rolled steel sheet and method for manufacturing same
Est. expirySep 16, 2042(~16.1 yrs left)· nominal 20-yr term from priority
C21D 8/02C21D 2211/003C21D 1/22C22C 38/04C22C 38/02C22C 38/28C22C 38/24C22C 38/38C22C 38/32C22C 38/22C22C 38/06C22C 38/002C21D 2211/008C21D 2211/005C21D 2211/002C21D 8/0278C21D 8/0263C21D 8/0236C21D 8/0226C21D 6/008C21D 6/005C21D 6/002C21D 9/46C21D 8/0273C21D 2211/004C21D 8/0205
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Claims
Abstract
Provided is a cold-rolled steel sheet consisting of carbon (C): 0.23 wt % to 0.35 wt %, silicon (Si): 0.05 wt % to 0.5 wt %, manganese (Mn): 0.3 wt % to 2.3 wt %, phosphorus (P): more than 0 wt % and not more than 0.02 wt %, sulfur (S): more than 0 wt % and not more than 0.005 wt %, aluminum (Al): 0.01 wt % to 0.05 wt %, chromium (Cr): more than 0 wt % and not more than 0.8 wt %, molybdenum (Mo): more than 0 wt % and not more than 0.4 wt %, titanium (Ti): 0.01 wt % to 0.1 wt %, vanadium (V): more than 0 wt % and not more than 0.3 wt %, boron (B): 0.001 wt % to 0.005 wt %, and a balance of iron (Fe) and other unavoidable impurities, wherein a final microstructure of the cold-rolled steel sheet includes cementite, a transition carbide, and a fine precipitate, the transition carbide including E-carbide having an atomic ratio of a substitutional element selected from Fe, Mn, Cr, and Mo to C of 2.5:1, or η-carbide having an atomic ratio of the substitutional element to C of 2:1.
Claims
exact text as granted — not AI-modified1 . A cold-rolled steel sheet consisting of carbon (C): 0.23 wt % to 0.35 wt %, silicon (Si): 0.05 wt % to 0.5 wt %, manganese (Mn): 0.3 wt % to 2.3 wt %, phosphorus (P): more than 0 wt % and not more than 0.02 wt %, sulfur (S): more than 0 wt % and not more than 0.005 wt %, aluminum (Al): 0.01 wt % to 0.05 wt %, chromium (Cr): more than 0 wt % and not more than 0.8 wt %, molybdenum (Mo): more than 0 wt % and not more than 0.4 wt %, titanium (Ti): 0.01 wt % to 0.1 wt %, vanadium (V): more than 0 wt % and not more than 0.3 wt %, boron (B): 0.001 wt % to 0.005 wt %, and a balance of iron (Fe) and other unavoidable impurities,
wherein a final microstructure of the cold-rolled steel sheet comprises cementite, a transition carbide, and a fine precipitate, the transition carbide comprising ε-carbide having an atomic ratio of a substitutional element selected from Fe, Mn, Cr, and Mo to C of 2.5:1, or η-carbide having an atomic ratio of the substitutional element to C of 2:1, and the fine precipitate having an atomic ratio of an alloying element selected from Mo, V, and Ti to C of 1:1, and wherein the cold-rolled steel sheet has a yield strength (YP) of 1170 MPa or more, a tensile strength (TS) of 1400 MPa or more, an elongation (El) of 3.0% or more, a yield ratio of 70% or more, and a bendability (R/t) of 4.0 or less.
2 . The cold-rolled steel sheet of claim 1 , wherein the cementite, the transition carbide, and the fine precipitate each has an average size of 50 nm or less and an average aspect ratio of 4.0 or less.
3 . The cold-rolled steel sheet of claim 1 , wherein the cementite, the transition carbide, and the fine precipitate each has an area fraction of more than 0% and not more than 5%.
4 . The cold-rolled steel sheet of claim 1 , wherein the final microstructure consists of only tempered martensite.
5 . The cold-rolled steel sheet of claim 1 , wherein the final microstructure consists of tempered martensite, ferrite, and bainite, the tempered martensite having an area fraction of 70% or more and less than 100%, and the ferrite and bainite having an area fraction of more than 0% and not more than 20%.
6 . A method of manufacturing a cold-rolled steel sheet, the method comprising:
(a) hot rolling a steel material consisting of carbon (C): 0.23 wt % to 0.35 wt %, silicon (Si): 0.05 wt % to 0.5 wt %, manganese (Mn): 0.3 wt % to 2.3 wt %, phosphorus (P): more than 0 wt % and not more than 0.02 wt %, sulfur (S): more than 0 wt % and not more than 0.005 wt %, aluminum (Al): 0.01 wt % to 0.05 wt %, chromium (Cr): more than 0 wt % and not more than 0.8 wt %, molybdenum (Mo): more than 0 wt % and not more than 0.4 wt %, titanium (Ti): 0.01 wt % to 0.1 wt %, vanadium (V): more than 0 wt % and not more than 0.3 wt %, boron (B): 0.001 wt % to 0.005 wt %, and a balance of iron (Fe); (b) cold rolling the hot-rolled steel material; and (c) sequentially performing annealing, first heat treatment, and second heat treatment on the cold-rolled steel material, wherein a final microstructure of the cold-rolled steel sheet obtained by performing steps (a) to (c) comprises cementite, a transition carbide, and a fine precipitate, the transition carbide comprising ε-carbide having an atomic ratio of a substitutional element selected from Fe, Mn, Cr, and Mo to C of 2.5:1, or η-carbide having an atomic ratio of the substitutional element to C of 2:1, and the fine precipitate having an atomic ratio of an alloying element selected from Mo, V, and Ti to C of 1:1.
7 . The method of claim 6 wherein the cementite is formed during the first heat treatment, the transition carbide is formed during the second heat treatment, and the fine precipitate is formed during the hot rolling.
8 . The method of claim 6 , wherein step (a) is performed under conditions of a reheating temperature of 1150° C. to 1300° C., a finishing delivery temperature of 800° C. to 1000° C., and a coiling temperature of 500° C. to 650° C.
9 . The method of claim 6 wherein step (c) is performed under conditions of an annealing temperature of 800° C. to 900° C. and a first heat treatment temperature of 100° C. to 300° C., and the second heat treatment comprises maintaining a second heat treatment temperature T satisfying Inequality 1 for a second heat treatment holding time t.
3
8
0
0
≤
(
T
+
3
0
0
)
×
(
1
0
+
log
(
t
)
)
≤
5
6
5
0
Inequality
1
(where a unit of T is ° C. and a unit of t is hours).
10 . The method of claim 8 wherein step (c) is performed under conditions of an annealing temperature of 800° C. to 900° C. and a first heat treatment temperature of 100° C. to 300° C., and the second heat treatment comprises maintaining a second heat treatment temperature T satisfying Inequality 1 for a second heat treatment holding time t.
3
8
0
0
≤
(
T
+
3
0
0
)
×
(
1
0
+
log
(
t
)
)
≤
5
6
5
0
Inequality
1
(where a unit of T is ° C. and a unit of t is hours).
11 . The method of claim 6 , wherein step (a) is performed under conditions of a reheating temperature of 1150° C. to 1300° C., a finishing delivery temperature of 800° C. to 1000° C., and a coiling temperature of 500° C. to 650° C., and
wherein step (c) comprises performing coating and is performed under conditions of an annealing temperature of 800° C. to 900° C. and a first heat treatment temperature of 450° C. to 600° C., and the second heat treatment comprises maintaining a second heat treatment temperature T satisfying Inequality 1 for a second heat treatment holding time t.
3
8
0
0
≤
(
T
+
3
0
0
)
×
(
1
0
+
log
(
t
)
)
≤
5
6
5
0
Inequality
1
(where a unit of T is ° C. and a unit of t is hours).
12 . The method of claim 6 wherein step (c) comprises performing coating and is performed under conditions of an annealing temperature of 800° C. to 900° C. and a first heat treatment temperature of 450° C. to 600° C., and the second heat treatment comprises maintaining a second heat treatment temperature T satisfying Inequality 1 for a second heat treatment holding time t.
3
8
0
0
≤
(
T
+
3
0
0
)
×
(
1
0
+
log
(
t
)
)
≤
5
6
5
0
Inequality
1
(where a unit of T is ° C. and a unit of t is hours).
13 . The method of claim 6 , wherein, in step (c), the first heat treatment, following the annealing, is performed after cooling to a first heat treatment temperature.
14 . The method of claim 6 , wherein, in step (c), the second heat treatment, following the first heat treatment, is performed after cooling to room temperature and then raising the temperature.Join the waitlist — get patent alerts
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