# US 11,299,798 B2 · Steel plate and method of producing same

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- Number: US 11,299,798 B2
- Document ID: US11299798B2
- Status: Granted
- Kind: B2
- Application number: 16/612,400
- Filed: 2018-05-21
- Published: 2020-04-16
- Granted: 2022-04-12
- Earliest claimed: 2017-05-22
- Assignees: Jfe Steel Corporation
- Applicants: Jfe Steel Corporation
- Inventors: Yoshiko Takeuchi; Katsuyuki Ichimiya; Kazukuni Hase
- Web page: https://patentgrep.com/patent/US11299798B2

## CPC

- C22C 38/04: containing manganese
- C21D 1/02: Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 6/001: {containing Ni (C21D6/004 takes precedence)}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 9/00: Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D 9/46: for sheet metals
- 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 38/06: 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 38/20: with copper
- C22C 38/50: with titanium or zirconium
- C22C 38/58: with more than 1.5% by weight of manganese
- Y02P 10/20: Recycling
- 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)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

Excellent CTOD properties for multilayer welding joint is provided for a steel plate. The steel plate comprises a specific chemical composition with Ceq of 0.45% or less where Ceq (%)=[C]+[Mn]/6+([Cu]+[Ni])/15+([Cr]+[Mo]+[V])/5 . . . (1) and Pcm of 0.22% or less where Pcm (%)=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5 [B] . . . (2); an average effective grain size of 20 μm or less at a mid-thickness part of the steel plate; and porosities having an equivalent circular diameter of 200 μm or more, the number of the porosities per mm2 being 0.1/mm2 or less.

## Claims

### Claim 1

A method of producing a steel plate, comprising:
heating a slab to 1050° C. or higher and 1200° C. or lower, the slab having a chemical composition containing, in mass %,
C: 0.01% to 0.07%,
Si: 0.5% or less,
Mn: 1.0% to 2.0%,
P: 0.01% or less,
S: 0.0005% to 0.0050%,
Al: 0.030% or less,
Ni: 0.5% to 2.0%,
Ti: 0.005% to 0.030%,
N: 0.0015% to 0.0065%,
O: 0.0010% to 0.0050%, and
Ca: 0.0005% to 0.0060%,
with a balance being Fe and inevitable impurities; and
having Ceq of 0.45% or less, where Ceq is defined by the following Formula (1):
Ceq (%)=[C]+[Mn]/6+([Cu]+[Ni])/15+([Cr]+[Mo]+[V])/5 (1); and
having Pcm of 0.22% or less, where Pcm is defined by the following Formula (2):
Pcm (%)=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5[B] (2),
where the brackets in Formula (1) and Formula (2) indicate a content by mass % of an element enclosed in the brackets and have a value of 0 if such an element is not contained;
hot rolling the heated slab to obtain a hot-rolled steel plate;
cooling the hot-rolled steel plate to a stop cooling temperature of 600° C. or lower under a condition of at an average cooling rate of 3° C./sec to 50° C./sec while a mid-thickness part of the hot-rolled steel plate has a temperature from 700° C. to 550° C.,
wherein the hot rolling comprises:
(1) rolling with an average rolling reduction of 10% or more per pass and a cumulative rolling reduction of 20% or more when the temperature at a mid-thickness part of the heated slab is 1050° C. or higher to obtain a heated plate;
(2) rolling with a cumulative rolling reduction of 30% or more when the temperature at the mid-thickness part of the heated plate is lower than 1050° C. and 950° C. or higher; and
(3) rolling with an average rolling reduction of 8% or more per pass and a cumulative rolling reduction of 60% or more when the temperature at the mid-thickness part of the heated plate is lower than 950° C.

### Claim 2 (depends on 1)

The method of producing the steel plate according to claim 1, wherein a tempering treatment is performed at a temperature of 700° C. or lower after the cooling.

### Claim 3

A method of producing a steel plate, comprising:
heating a slab to 1050° C. or higher and 1200° C. or lower, the slab having a chemical composition containing, in mass %
C: 0.01% to 0.07%,
Si: 0.5% or less,
Mn: 1.0% to 2.0%,
P: 0.01% or less,
S: 0.0005% to 0.0050%,
Al: 0.030% or less,
Ni: 0.5% to 2.0%,
Ti: 0.005% to 0.030%,
N: 0.0015% to 0.0065%,
O: 0.0010% to 0.0050%,
Ca: 0.0005% to 0.0060%, and
at least one element selected from the group consisting of
Cu: 0.05% to 2.0%,
Cr: 0.05% to 0.30%,
Mo: 0.05% to 0.30%,
Nb: 0.005% to 0.035%,
V: 0.01% to 0.10%,
W: 0.01% to 0.50%,
B: 0.0005% to 0.0020%,
REM: 0.0020% to 0.0200%, and
Mg: 0.0002% to 0.0060%,
with a balance being Fe and inevitable impurities; and
having Ceq of 0.45% or less, where Ceq is defined by the following Formula (1):
Ceq (%)=[C]+[Mn]/6+([Cu]+[Ni])/15+([Cr]+[Mo]+[V])/5 (1); and
having Pcm of 0.22% or less, where Pcm is defined by the following Formula (2):
Pcm (%)=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5[B] (2),
where the brackets in Formula (1) and Formula (2) indicate a content by mass % of an element enclosed in the brackets and have a value of 0 if such an element is not contained;
hot rolling the heated slab to obtain a hot-rolled steel plate;
cooling the hot-rolled steel plate to a stop cooling temperature of 600° C. or lower under a condition of at an average cooling rate of 3° C./sec to 50° C./sec while a mid-thickness part of the hot-rolled steel plate has a temperature from 700° C. to 550° C.,
wherein the hot rolling comprises:
(1) rolling with an average rolling reduction of 10% or more per pass and a cumulative rolling reduction of 20% or more when the temperature at a mid-thickness part of the heated slab is 1050° C. or higher to obtain a heated plate;
(2) rolling with a cumulative rolling reduction of 30% or more when the temperature at the mid-thickness part of the heated plate is lower than 1050° C. and 950° C. or higher; and
(3) rolling with an average rolling reduction of 8% or more per pass and a cumulative rolling reduction of 60% or more when the temperature at the mid-thickness part of the heated plate is lower than 950° C.

### Claim 4 (depends on 3)

The method of producing the steel plate according to claim 3, wherein a tempering treatment is performed at a temperature of 700° C. or lower after the cooling.