# US 2014/0190597 A1 · Hot coil for line pipe use and method of production of same

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- Number: US 2014/0190597 A1
- Document ID: US20140190597A1
- Status: Published application
- Kind: A1
- Application number: 14/236,957
- Filed: 2012-09-27
- Published: 2014-07-10
- Earliest claimed: 2011-09-27
- Assignees: Nippon Steel & Sumitomo Metal Corporation
- Applicants: Nippon Steel & Sumitomo Metal Corporation
- Inventors: Takuya Hara; Takeshi Kinoshita; Kazuaki Tanaka
- Web page: https://patentgrep.com/patent/US20140190597A1

## CPC

- C22C 38/58: with more than 1.5% by weight of manganese
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- C21D 9/46: for sheet metals
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/18: containing chromium
- C22C 38/22: with molybdenum or tungsten
- C22C 38/24: with vanadium
- C22C 38/26: with niobium or tantalum
- C22C 38/28: with titanium or zirconium
- C22C 38/32: with boron
- C22C 38/38: with more than 1.5% by weight of manganese
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/48: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C21D 8/10: during manufacturing of tubular bodies
- C21D 2211/002: Bainite
- C21D 2211/005: Ferrite
- C21D 2221/10: Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- 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)

## Abstract

The present invention provides a hot coil for line pipe use which can reduce deviation in ordinary temperature strength and improve low temperature toughness despite the numerous restrictions in production conditions due to the coiling step and provides a method of production of the same, specifically makes the steel plate stop for a predetermined time between rolling passes in the recrystallization temperature range and performs cooling by two stages after hot rolling so as to thereby make the steel structure at the center part of plate thickness and effective crystal grain size of 3 to 10 μm, make the total of the area ratios of bainite and acicular ferrite 60 to 99%, and make the absolute value of A-B 0 to 30% when the totals of the area ratios of bainite and acicular ferrite at any two portions are designated as respectively A and B.

## Claims

### Claim 1

Hot coil for line pipe use which has a chemical composition which contains, by mass %,
C: 0.03 to 0.10%,
Si: 0.01 to 0.50%,
Mn: 0.5 to 2.5%,
P: 0.001 to 0.03%,
S: 0.0001 to 0.0030%,
Nb: 0.0001 to 0.2%,
Al: 0.0001 to 0.05%,
Ti: 0.0001 to 0.030% and
B: 0.0001 to 0.0005%
and has a balance of iron and unavoidable impurities, which has a steel structure at a center of plate thickness with an effective crystal grain size of 2 to 10 μm, which has a total of the area ratios of bainite and acicular ferrite of 60 to 99%, which has an absolute value of A-B of 0 to 30% when designating the totals of the area ratios of bainite and acicular ferrite at any two portions as respectively A and B, which has a plate thickness of 7 to 25 mm, and which has a tensile strength TS in the width direction of 400 to 700 MPa.

### Claim 2 (depends on 1)

The hot coil for line pipe use as set forth in claim 1, characterized in that said hot coil further contains, by mass %, one or more of
Cu: 0.01 to 0.5%,
Ni: 0.01 to 1.0%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
V: 0.001 to 0.10%,
W: 0.0001 to 0.5%,
Zr: 0.0001 to 0.050%
Ta: 0.0001 to 0.050%
Mg: 0.0001 to 0.010%,
Ca: 0.0001 to 0.005%,
REM: 0.0001 to 0.005%,
Y: 0.0001 to 0.005%,
Hf: 0.0001 to 0.005% and
Re: 0.0001 to 0.005%.

### Claim 3

A method of production of hot coil for line pipe use characterized by heating a steel slab which has a chemical composition which contains, by mass %,
C: 0.03 to 0.10%,
Si: 0.01 to 0.50%,
Mn: 0.5 to 2.5%,
P: 0.001 to 0.03%,
S: 0.0001 to 0.0030%,
Nb: 0.0001 to 0.2%,
Al: 0.0001 to 0.05%,
Ti: 0.0001 to 0.030%, and
B: 0.0001 to 0.0005% and
which has a balance of iron and unavoidable impurities to 1000 to 1250° C., then hot rolling it, during which making a draft ratio in a recrystallization temperature range 1.9 to 4.0 and making the steel plate in the middle of the hot rolling stop at least once between rolling passes in the recrystallization temperature range for 100 to 500 seconds, and cooling the obtained hot rolled steel plate divided between a front stage and a back stage, during which, in the front stage cooling, cooling by a cooling rate of 0.5 to 15° C./sec at a center part of plate thickness of the hot rolled steel plate until a surface temperature of said hot rolled steel plate becomes 600° C. from the cooling start temperature of the front stage, and, in the back stage cooling, cooling by a cooling rate which is faster than the front stage at the center part of plate thickness of the hot rolled steel plate.

### Claim 4 (depends on 3)

The method of production of hot coil for line pipe use as set forth in claim 3 characterized by said steel slab further containing one or more of, by mass %,
Cu: 0.01 to 0.5%,
Ni: 0.01 to 1.0%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
V: 0.001 to 0.10%,
W: 0.0001 to 0.5%,
Zr: 0.0001 to 0.050%
Ta: 0.0001 to 0.050%
Mg: 0.0001 to 0.010%,
Ca: 0.0001 to 0.005%,
REM: 0.0001 to 0.005%,
Y: 0.0001 to 0.005%,
Hf: 0.0001 to 0.005% and
Re: 0.0001 to 0.005%.

### Claim 5 (depends on 3, 4)

The method of production of hot coil for line pipe use as set forth in claim 3 or 4 characterized by hot rolling by a draft ratio in the non-recrystallization temperature range of 2.5 to 4.0.

### Claim 6 (depends on 3, 4)

The method of production of hot coil for line pipe use as set forth in claim 3 or 4 characterized by starting said front stage cooling from a 800 to 850° C. temperature range and cooling through the 800 to 600° C. temperature range by a cooling rate at the center part of plate thickness of 0.5 to 10° C./sec.

### Claim 7 (depends on 5)

The method of production of hot coil for line pipe use as set forth in claim 5 characterized by starting said front stage cooling from a 800 to 850° C. temperature range and cooling through the 800 to 600° C. temperature range by a cooling rate at the center part of plate thickness of 0.5 to 10° C./sec.

### Claim 8 (depends on 3, 4)

The method of production of hot coil for line pipe use as set forth in claim 3 or 4 characterized by coiling the steel plate, after said back stage cooling, at 450 to 600° C.

### Claim 9 (depends on 5)

The method of production of hot coil for line pipe use as set forth in claim 5 characterized by coiling the steel plate, after said back stage cooling, at 450 to 600° C.

### Claim 10 (depends on 6)

The method of production of hot coil for line pipe use as set forth in claim 6 characterized by coiling the steel plate, after said back stage cooling, at 450 to 600° C.

### Claim 11 (depends on 7)

The method of production of hot coil for line pipe use as set forth in claim 7 characterized by coiling the steel plate, after said back stage cooling, at 450 to 600° C.