US2024295000A1PendingUtilityA1
High strength coated dual phase steel strip and method to produce it
Est. expiryJul 7, 2041(~15 yrs left)· nominal 20-yr term from priority
Inventors:Joost Willem Hendrik Van Krevel
C25D 3/44C25D 3/22C23C 2/40C23C 2/12C23C 2/06C22C 38/60C22C 38/06C22C 38/04C22C 38/02C22C 38/002C22C 38/001C21D 2211/008C21D 2211/005C21D 2211/003C21D 2211/002C21D 2211/001C21D 8/0273C21D 8/0263C21D 8/0236C23C 2/28C21D 9/46C21D 8/0226C22C 38/54C22C 38/50C22C 38/48C22C 38/46C22C 38/44C23C 2/0224C23C 2/02C21D 8/0473C21D 8/0436C21D 8/0426C21D 8/0478C21D 8/0278C22C 38/38C22C 38/32C22C 38/28C22C 38/24C22C 38/22C22C 38/14C22C 38/12C22C 38/58
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Claims
Abstract
A coated and optionally temper-rolled dual phase steel strip with a tensile strength Rm of 580-720 MPa and a yield strength Rp of 310-430 MPa high strength having improved formability. The invention also relates to a method for producing such steel strip and the use thereof.
Claims
exact text as granted — not AI-modified1 . A dual phase steel strip consisting of, in wt. %:
C:
0.090-0.140
B:
0.0010-0.0050
Mn:
1.200-1.900
S:
at most 0.050
Si:
0.200-0.800
P:
at most 0.050
Al:
0.200-0.800
N:
at most 0.015
and optionally one or more of the elements selected from:
Cr:
at most 0.500
Nb:
at most 0.060
Mo:
at most 0.400
Ti:
at most 0.060
V:
at most 0.200
Ca:
at most 0.0050
the remainder being iron and unavoidable impurities,
wherein the steel has a tensile strength Rm of 580-720 MPa and a yield strength Rp of 310-430 MPa, and
wherein the steel strip is optionally i) a hot-dip galvanised or ii) electrogalvanized or iii) electroplated.
2 . The dual phase steel strip according to claim 1 , consisting of, in wt. %:
C:
0.090-0.130
B:
0.0010-0.0040
Mn:
1.400-1.800
S:
at most 0.004
Si:
0.250-0.750
P:
at most 0.040
Al:
0.200-0.750
N:
at most 0.012
and optionally one or more of the elements selected from:
Cr:
at most 0.400
Nb:
at most 0.050
Mo:
at most 0.300
Ti:
at most 0.050
V:
at most 0.150
Ca:
at most 0.0050
the remainder being iron and unavoidable impurities.
3 . The dual phase steel strip according to claim 1 , consisting of, in wt. %:
C:
0.090-0.130
B:
0.0010-0.0030
Mn:
1.400-1.750
S:
at most 0.003
Si:
0.250-0.700
P:
at most 0.015
Al:
0.200-0.650
N:
at most 0.006
and optionally one or more of the elements selected from:
Cr:
at most 0.120
Nb:
at most 0.010
Mo:
at most 0.015
Ti:
at most 0.010
V:
at most 0.010
Ca:
at most 0.0050
the remainder being iron and unavoidable impurities.
4 . The dual phase steel strip according to claim 1 , consisting of, in wt. %:
C:
0.110-0.130
B:
0.0012-0.0028
Mn:
1.400-1.750
S:
at most 0.003
Si:
0.500-0.700
P:
at most 0.015
Al:
0.200-0.400
N:
at most 0.006
and optionally one or more of the elements selected from:
Cr:
at most 0.040
Nb:
at most 0.010
Mo:
at most 0.015
Ti:
at most 0.010
V:
at most 0.010
Ca:
at most 0.0050
the remainder being iron and unavoidable impurities.
5 . The dual phase steel strip according to claim 1 , consisting of, in wt. %:
C:
0.110-0.130
B:
0.0012-0.0028
Mn:
1.400-1.750
S:
at most 0.003
Si:
0.500-0.700
P:
at most 0.015
Al:
0.200-0.400
N:
at most 0.006
Cr:
0.020-0.150
and optionally one or more of the elements selected from:
Mo:
at most 0.015
Ti:
at most 0.010
V:
at most 0.010
Ca:
at most 0.0050
Nb:
at most 0.010
the remainder being iron and unavoidable impurities.
6 . The dual phase steel strip according to claim 1 , consisting of, in wt. %:
C:
0.090-0.130
B:
0.0010-0.0035
Mn:
1.300-1.800
S:
at most 0.003
Si:
0.250-0.750
P:
at most 0.030
Al:
0.200-0.650
N:
at most 0.010
and optionally one or more of the elements selected from:
Cr:
at most 0.150
Nb:
at most 0.040
Mo:
at most 0.200
Ti:
at most 0.040
V:
at most 0.100
Ca:
at most 0.0050
the remainder being iron and unavoidable impurities.
7 . The dual phase steel strip according to claim 1 , wherein one or more or all of Cr, Mo, V, Nb and Ti is present only as an impurity which means that, if applicable, Cr is below 0.020 wt. %, Ti is below 0.010 wt. %, V is below 0.010 wt. %, Mo is below 0.015 wt. %, Nb is below 0.010 wt. %.
8 . The dual phase steel strip according to claim 1 , wherein the steel has a tensile strength Rm of 590-720 MPa and/or a yield strength Rp of 320-430 MPa.
9 . The dual phase steel strip according to claim 1 , wherein the steel has a uniform elongation Ag of at least 18%.
10 . The dual phase steel strip according to claim 1 , wherein the steel has a hole expansion capacity HEC of at least 35%.
11 . The dual phase steel strip according to claim 1 , wherein the steel has an average strain hardening exponent or n-value of at least 0.16.
12 . The dual phase steel strip according to claim 1 , which is provided with the metallic coating by hot-dip coating immediately subsequent to continuous annealing or by electrodeposition of the strip after cooling the continuously annealed strip to ambient temperature.
13 . A method for producing a coated and optionally temper-rolled dual phase steel strip with a tensile strength Rm of 580-720 MPa and a yield strength Rp of 310-430 MPa according to claim 1 , comprising the following steps:
providing a hot-rolled steel strip by hot rolling a continuously cast slab with a composition consisting of, in wt. %:
C:
0.090-0.140
B:
0.0010-0.0050
Mn:
1.200-1.900
S:
at most 0.050
Si:
0.200-0.800
P:
at most 0.050
Al:
0.200-0.800
N:
at most 0.015
and optionally one or more of the elements selected from:
Cr:
at most 0.500
Nb:
at most 0.060
Mo:
at most 0.400
Ti:
at most 0.060
V:
at most 0.200
Ca:
at most 0.0050
the remainder being iron and unavoidable impurities,
to a hot-rolled strip having a thickness of 2.0-4.5 mm, wherein finish-rolling is performed while the strip has an austenitic microstructure;
Cooling the hot-rolled strip after finish-rolling with a cooling rate of at least 30° C./s;
Coiling the cooled strip at a coiling temperature CT in the range of 500 to 650° C. wherein the amount of austenite is more than 60% and the coiled strip is subsequently allowed to cool to ambient temperatures;
Uncoiling the coiled hot-rolled strip, followed by pickling and cold-rolling with a reduction of 40-80%;
Continuous annealing of the cold-rolled strip by:
i. heating the strip to a temperature T 1 in the range of 550-710° C. with a heating rate HR 1 of at least 3° C./s to allow the recrystallisation of the cold-rolled strip to proceed for at least 60% prior to the start of the austenite formation;
ii. further heating of the strip with an average heating rate HR 2 to a temperature T 2 in the range of (Ac1+50° C.) to (Ac3−30° C.) to form a partially austenitic microstructure;
iii. subsequently either:
a. keeping the strip at T 2 for a time period t 2 of up to 300 s, followed by slow cooling of the strip with a cooling rate CR 1 in the range of 0.5-12° C./s to a temperature T 3 in the range of 600-790° C., preferably 620-790° C. so that 16-30% austenite is present in the slow cooled strip, or
b. immediately slowly cooling the strip from T 2 with a cooling rate CR 1 in the range of 0.5-12° C./s to a temperature T 3 in the range of 600-790° C. so that 16-30% austenite is present in the slow cooled strip;
iv. rapidly cooling the slowly cooled strip comprising 16-30% austenite with an average cooling rate CR 2 in the range of 5-70° C./s either:
a. to a temperature T 4 in the range of 330-470° C.; or
b. to an overaging temperature T_oa for a time t_oa in the range of 5 to 100 s, wherein T_oa is between 390 and 465° C.;
v. cooling the steel strip at a cooling rate CR 3 of at least 4° C./s to a temperature below 300° C.;
wherein the strip is a). provided with a metallic coating by hot-dip coating between step iv. and v., optionally followed by galvannealing the hot-dip coated strip, or b). with a metallic coating by electrodeposition after step v.;
Optionally temper rolling or tension levelling of the coated steel strip with a reduction of at most 0.70%;
Coiling the coated steel strip or cutting the coated steel strip into sheets or blanks;
Optionally shaping the coated steel strip, sheet or blank via cold-forming operations like stamping, bending, deep drawing or via warm press forming or hot press forming.
14 . The method according to claim 13 , wherein one or more of the following process parameters apply:
Coiling temperature is below 630° C.; Coiling temperature is above 520° C.; Cold rolling reduction is at least 44%; T 3 is between 400 and 470° C.
15 . The method according to claim 13 to produce a coated steel strip, sheet or blank having one or more of
a uniform elongation Ag of at least 18%;
a total elongation A80 or JIS of at least 26%;
a hole expansion capacity HEC of at least 35%;
a total elongation minus uniform elongation of at least 7.0%.
16 . A car or truck component, such as an automotive chassis or safety component, a B-pillar, a reinforcement (crash) part, a front crash beam, a seat member, a bumper part, a door part, a component of the body in white, a component of the frame or the sub-frame, an electric battery holder or container part, said component having been produced from the steel according to claim 1 .
17 . The dual phase steel strip according to claim 1 , wherein the steel has a uniform elongation Ag of at least 30%.
18 . The dual phase steel strip according to claim 1 , wherein the steel has an average strain hardening exponent or n-value of at least 0.24.
19 . The method of claim 13 , wherein the temperature T 3 is in the range of 620-790° C.
20 . The method according to claim 13 , wherein one or more of the following process parameters apply:
Coiling temperature is below 600° C.; Coiling temperature is above 530° C.; Cold rolling reduction is at least 67%; T 3 is between 400 and 470° C.Join the waitlist — get patent alerts
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