US2024191319A1PendingUtilityA1
Steel strip made of a high-strength multiphase steel and process for producing such a steel strip
Est. expiryApr 1, 2041(~14.7 yrs left)· nominal 20-yr term from priority
C21D 8/02C22C 38/38C22C 38/32C22C 38/28C22C 38/26C22C 38/24C22C 38/22C22C 38/20C22C 38/06C22C 38/02C22C 38/002C22C 38/001C21D 2211/009C21D 2211/008C21D 2211/005C21D 2211/002C21D 2211/001C21D 6/008C21D 6/005C21D 6/002C21D 1/18C21D 9/52C21D 1/28C21D 9/46C21D 8/0263C21D 1/84C22C 38/48C22C 38/54C22C 38/46C22C 38/50C22C 38/44C22C 38/58C22C 38/16C21D 9/663C21D 9/0043C21D 8/0247C22C 38/04
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Claims
Abstract
A steel strip made of a high-strength multiphase steel with a tensile strength of at least 780 MPa in the longitudinal direction and consists of the following elements in % by weight: 0.08≤C≤0.23, 1.5≤Mn≤3.5, 0.25≤Si+Al≤2, 0.0020≤N≤0.0160, P<0.05, S<0.01. Cu<0.20; iron; and a carbon equivalent CEV which is greater than 0.49 and smaller than 0.9, wherein the carbon equivalent CEV results from the contents of the corresponding elements in % by weight according to the following formula: CEV=C+Mn/6 (Cu+Ni)/15+(Cr+Mo+V)/5 and wherein the ratio of the carbon equivalent CEV and the sum of the contents of Si and Al in % by weight is less than 2.3, wherein the multiphase steel constituents martensite, tempered martensite, residual austenite, upper bainite and/or lower bainite where the sum of the volume fractions of the microstructure is at least 30% by volume, and residual microstructure consists of ferrite and perlite.
Claims
exact text as granted — not AI-modified1 . A steel strip consisting of a high-strength multiphase steel which has a tensile strength of at least 780 MPa in the longitudinal direction, the multiphase steel consisting of the following elements in wt. %:
C
≥
0.08
to ≤
0.23,
Mn
≥
1.5
to ≤
3.5,
Si + Al
≥
0.25
to ≤
2,
N
≥
0.0020
to ≤
0.0160,
P
<
0.05,
S
<
0.01,
Cu
<
0.20,
optionally one or more of the following elements:
Ca
≥
0.0005
to ≤
0.0060,
Cr
≥
0.05
to ≤
1.0,
Mo
≥
0.05
to ≤
1.0,
Ni
≥
0.05
to ≤
0.50,
Nb
≥
0.005
to ≤
0.15,
Ti
≥
0.005
to ≤
0.15,
V
≥
0.001
to ≤
0.30 and
B
≥
0.0005
to ≤
0.0050
with the remainder being iron including typical steel-associated, melting-induced impurities, and having a carbon equivalent CEV which is greater than 0.49 and less than 0.9, preferably greater than 0.49 and less than 0.75, wherein the carbon equivalent CEV is determined according to the formula
CEV=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5
from the contents of the corresponding elements in wt. % and wherein the ratio of the carbon equivalent CEV and the sum of the contents of Si and Al in wt. % is less than 2.3, wherein the multiphase steel has a microstructure, in which the sum of the volume proportions of the microstructure constituents of martensite, tempered martensite, residual austenite, upper bainite and/or lower bainite is at least 30 vol. % and the remaining microstructure consists of ferrite and pearlite.
2 . The steel strip as claimed in claim 1 , wherein the ratio of elasticity limit to tensile strength R p0.2 /R m is less than 0.8 and the elongation at fracture A 80 is >5%.
3 . The steel strip as claimed in claim 1 , wherein the content in wt. % of the element C is between 0.09 and 0.2 and/or the content in wt. % of the element Mo is less than 0.4.
4 . The steel strip as claimed in claim 1 , wherein the content in wt. % of the element Mn is between 1.8 and 2.5 and/or that the content in wt. % of the sum of the elements Si+Al is between 0.25 and 1.
5 . The steel strip as claimed in claim 1 , wherein the carbon equivalent CEV is less than 0.7.
6 . The steel strip as claimed in claim 1 , wherein the sum of the volume proportions of the microstructure constituents of martensite, tempered martensite, residual austenite, upper bainite and/or lower bainite in the microstructure of the multiphase steel is at least 50 vol. %, preferably at least 70 vol. %, and the remaining microstructure consists of ferrite and pearlite.
7 . The steel strip as claimed in claim 1 , wherein the steel strip has a thickness which specifically varies in the longitudinal extension, wherein the ratio between maximum thickness and minimum thickness is, in particular, between 1.16 and 3.
8 . The steel strip as claimed in claim 1 , wherein the thickness D of the steel strip is in the range ≥4 mm to ≤18 mm.
9 . A method for producing a steel strip consisting of a high-strength multiphase steel, in particular a steel strip, as claimed in claim 1 which has a tensile strength of at least 780 MPa in the longitudinal direction, wherein a rolled strip sheet of steel consisting of the following elements in wt. %:
C
≥
0.08
to ≤
0.23,
Mn
≥
1.5
to ≤
3.5,
Si + Al
≥
0.25
to ≤
2.
N
≥
0.0020
to ≤
0.0160,
P
<
0.05,
S
<
0.01,
Cu
<
0.20,
optionally one or more of the following elements:
Ca
≥
0.0005
to ≤
0.0060,
Cr
≥
0.05
to ≤
1.0,
Mo
≥
0.05
to ≤
1.0,
Ni
≥
0.05
to ≤
0.50,
Nb
≥
0.005
to ≤
0.15,
Ti
≥
0.005
to ≤
0.15,
V
≥
0.001
to ≤
0.30 and
B
≥
0.0005
to ≤
0.0050
with the remainder being iron including typical steel-associated, melting-induced impurities, and having a carbon equivalent CEV which is greater than 0.49 and less than 0.9, preferably greater than 0.49 and less than 0.75, wherein the carbon equivalent CEV is determined according to the formula
CEV=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5
from the contents of the corresponding elements in wt. % and wherein the ratio of the carbon equivalent CEV and the sum of the contents of Si and Al in wt. % is less than 2.3, is heat-treated as a whole—in particular rolled up into a coil—such that it assumes a temperature above 750° C. and after this heat treatment is cooled to a temperature below 200° ° C., wherein the cooling between 750° C. and 200° ° C. is effected at an average cooling rate greater than 1 K/h and less than 300 K/h.
10 . The method as claimed in claim 9 , wherein the strip sheet is heated during the heat treatment from 100° C. to a temperature of 750° C. at an average heating rate between 1 K/h and 300 K/h.
11 . The method as claimed in claim 9 wherein the strip sheet remains for at least 1 h in the temperature range of 750° C. to Ar 3 +70° C., wherein the numerical value of the temperature Ar 3 is calculated by means of the following formula from the contents of the corresponding elements in wt. %:
Ar 3 =910−203√{square root over (C)}−30Mn+44.7Si−11Cr+31.5Mo−15.2Ni
12 . The method as claimed in claim 9 , wherein the strip sheet consisting of steel reaches, during the heat treatment, a maximum temperature of at least 780° C. and at most 900° ° C., preferably of at least 790° C. and at most 850° ° C.
13 . The method as claimed in claim 9 , wherein the steel strip is provided with a surface coating in the form of a metallic coating, organic coating or lacquer after cooling.
14 . The method as claimed in claim 11 , wherein the steel strip has a thickness which specifically varies in the longitudinal extension, wherein the ratio between maximum thickness and minimum thickness is, in particular, between 1.16 and 3.
15 . The method as claimed claim 12 , wherein the strip sheet remains for at least 1 h in the temperature range of 750° ° C. to Ar 3 +70° C., wherein the numerical value of the temperature Ar 3 is calculated by means of the following formula from the contents of the corresponding elements in wt. %:
Ar 3 =910−203√{square root over (C)}−30Mn+44.7Si−11Cr+31.5Mo−15.2Ni
16 . The method as claimed in claim 10 , wherein the strip sheet consisting of steel reaches, during the heat treatment, a maximum temperature of at least 780° ° C. and at most 900° C., preferably of at least 790° ° C. and at most 850° C.
17 . The method as claimed in claim 16 , wherein the steel strip is provided with a surface coating in the form of a metallic coating, organic coating or lacquer after cooling.
18 . A method of using a steel strip as claimed in claim 1 for producing a motor vehicle component.
19 . The Steel strip as claimed in claim 2 , wherein the content in wt. % of the element C is between 0.09 and 0.2 and/or the content in wt. % of the element Mo is less than 0.4.
20 . The steel strip as claimed in claim 9 , wherein the content in wt. % of the element Mn is between 1.8 and 2.5 and/or that the content in wt. % of the sum of the elements Si+Al is between 0.25 and 1.Join the waitlist — get patent alerts
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