# US 9,039,847 B2 · High strength cold rolled steel sheet and method for manufacturing the same

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- Number: US 9,039,847 B2
- Document ID: US9039847B2
- Status: Granted
- Kind: B2
- Application number: 13/387,393
- Filed: 2010-07-27
- Published: 2012-07-19
- Granted: 2015-05-26
- Earliest claimed: 2009-07-28
- Assignees: Jfe Steel Corporation
- Applicants: Yoshihiko Ono; Kenji Takahashi; Kaneharu Okuda; Shoichiro Taira; Michitaka Sakurai; Yusuke Fushiwaki
- Inventors: Yoshihiko Ono; Kenji Takahashi; Kaneharu Okuda; Shoichiro Taira; Michitaka Sakurai; Yusuke Fushiwaki
- Web page: https://patentgrep.com/patent/US9039847B2

## CPC

- C21D 8/0236: {Cold rolling}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/58: with more than 1.5% by weight of manganese
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- Y02P 10/20: Recycling
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A multiphase steel sheet has a steel composition containing, in percent by mass, more than 0.015% to less than 0.100% of carbon, less than 0.40% of silicon, 1.0% to 1.9% of manganese, more than 0.015% to 0.05% of phosphorus, 0.03% or less of sulfur, 0.01% to 0.3% of soluble aluminum, 0.005% or less of nitrogen, less than 0.30% of chromium, 0.0050% or less of boron, less than 0.15% of molybdenum, 0.4% or less of vanadium, 0.02% or less of titanium, wherein [Mneq] is 2.0 to 2.8, the balance being iron and incidental impurities.

## Claims

### Claim 1

A cold rolled steel sheet having a steel composition comprising, in percent by mass, more than 0.015% to less than 0.100% of carbon, less than 0.40% of silicon, 1.0% to 1.9% of manganese, more than 0.015% to 0.05% of phosphorus, 0.03% or less of sulfur, 0.01% to 0.3% of soluble aluminum, 0.005% or less of nitrogen, 0.04% or less of chromium, 0.0050% or less of boron, 0.4% or less of vanadium, 0.18% or less of copper, 0.02% or less of molybdenum, and 0.02% or less of titanium, and satisfying formula (1):
0.6[% Si]+[% Cr]+2[% Mo]<0.35 (1)
wherein [% A] is content (% by mass) of alloying element A, the balance being iron and incidental impurities, the steel sheet having a microstructure that is a multiphase structure comprising, in percent by volume, ferrite and 3% to 12% of a second phase, the multiphase structure comprising, as the second phase, 1.0% to 10% of martensite and 1.0% to 5.0% of retained γ, wherein a ratio of total amount of martensite and retained γ to a volume fraction of second phase is 70% or more, a proportion of volume fraction of retained γ to a volume fraction of second phase is 30% to 80%, and an average grain size of the second phase is 0.9 to 5 μm, and further satisfying formulas (2), (3) and (4):
2.2≦[Mneq]≦2.8 (2)
[% Mn]+3.3[% Mo]≦1.9 (3)
0.42≦12[% P]+150B*≦0.93 (4)
wherein B*=[% B]+[% Ti]/48×10.8×0.9+[% sol.Al]/27×10.8×0.025, wherein if [% B]=0, B*=0, and if B*≧0.0022, B*=0.0022; and [% A] is the content (% by mass) of alloying element A; and [Mneq]=[% Mn]+1.3 [% Cr]+8 [% P]+150B*+2 [% V]+3.3 [% Mo].

### Claim 2 (depends on 1)

The cold rolled steel sheet according to claim 1, further satisfying formula (5):
0.49≦12[% P]+150B*≦0.93 (5)
wherein B*=[% B]+[% Ti]/48×10.8×0.9+[% sol.Al]/27×10.8×0.025, wherein if [% B]=0, B*=0, and if B*≧0.0022, B*=0.0022; and [% A] is the content (% by mass) of alloying element A.

### Claim 3 (depends on 1)

The cold rolled steel sheet according to claim 1, further comprising, in percent by mass, one or more of less than 0.02% of niobium, 0.005% or less of tungsten, 0.1% or less of zirconium, 0.5% or less of nickel, 0.2% or less of tin, 0.2% or less of antimony, 0.01% or less of calcium, 0.01% or less of cerium, 0.01% or less of lanthanum, and 0.01% or less of magnesium.

### Claim 4 (depends on 2)

The cold rolled steel sheet according to claim 2, further comprising, in percent by mass, one or more of less than 0.02% of niobium, 0.005% or less of tungsten, 0.1% or less of zirconium, 0.5% or less of nickel, 0.2% or less of tin, 0.2% or less of antimony, 0.01% or less of calcium, 0.01% or less of cerium, 0.01% or less of lanthanum, and 0.01% or less of magnesium.

### Claim 5 (depends on 1)

The cold rolled steel sheet according to claim 1, wherein the YP is 225 MPa or less.