High-strength, high-toughness steel plate and method for producing the same

Patent metadata

Field	Value
Publication number	US-10640841-B2
Application number	US-201615562192-A
Country	US
Kind code	B2
Filing date	Mar 25, 2016
Priority date	Mar 31, 2015
Publication date	May 5, 2020
Grant date	May 5, 2020

Abstract

A high-strength, high-toughness steel plate having excellent surface properties and a high absorbed energy includes, by mass %, C: 0.03% to 0.08%, Si: 0.01% to 0.50%, Mn: 1.5% to 2.5%, P: 0.001% to 0.010%, S: 0.0030% or less, Al: 0.01% to 0.08%, Nb: 0.010% to 0.080%, Ti: 0.005% to 0.025%, and N: 0.001% to 0.006%, and further includes at least one selected from Cu: 0.01% to 1.00%, Ni: 0.01% to 1.00%, Cr: 0.01% to 1.00%, Mo: 0.01% to 1.00%, V: 0.01% to 0.10%, and B: 0.0005% to 0.0030%, with the balance being Fe and unavoidable impurities. In a surface portion and a central portion in the thickness direction, the area fraction of Martensite-Austenite constituent is less than 3% and the area fraction of bainite is 90% or more, and in the central portion in the thickness direction, the average particle size of cementite in bainite is 0.5 μm or less.

First claim

The invention claimed is:

1. A high-strength, high-toughness steel plate having a composition containing, by mass %,
C: 0.03% or more and 0.08% or less,
Si: 0.01% or more and 0.50% or less,
Mn: 1.5% or more and 2.5% or less,
P: 0.001% or more and 0.010% or less,
S: 0.0030% or less,
Al: 0.01% or more and 0.08% or less,
Nb: 0.010% or more and 0.080% or less,
Ti: 0.005% or more and 0.025% or less,
N: 0.001% or more and 0.006% or less,
and further containing at least one selected from
Cu: 0.01% or more and 1.00% or less,
Ni: 0.01% or more and 1.00% or less,
Cr: 0.01% or more and 1.00% or less,
Mo: 0.01% or more and 1.00% or less,
V: 0.01% or more and 0.10% or less, and
B: 0.0005% or more and 0.0030% or less,
with the balance being Fe and unavoidable impurities,
wherein the steel plate has a microstructure in which an area fraction of Martensite-Austenite constituent in each of a surface portion and a central portion in a thickness direction is less than 3%, an area fraction of bainite in each of the surface portion and the central portion in the thickness direction is 90% or more, and an average particle size of cementite present in the bainite in the central portion in the thickness direction is 0.5 μm or less, and
the steel plate has a Vickers hardness difference (ΔHV) between the surface portion and the central portion in the thickness direction of 20 or less.

2. The high-strength, high-toughness steel plate according to claim 1 , wherein the composition further contains, by mass %, at least one selected from
Ca: 0.0005% or more and 0.0100% or less,
REM: 0.0005% or more and 0.0200% or less,
Zr: 0.0005% or more and 0.0300% or less, and
Mg: 0.0005% or more and 0.0100% or less.

3. A method for producing the high-strength, high-toughness steel plate according to claim 1 , the method comprising:
heating a steel slab to 1000° C. or higher and 1250° C. or lower;
performing rolling in an austenite recrystallization temperature range;
performing rolling at an accumulated rolling reduction ratio of 60% or more in an austenite non-recrystallization temperature range;
finishing the rolling at a temperature of 770° C. or higher and 850° C. or lower;
performing accelerated cooling to achieve a temperature drop (ΔT) of 350° C. or more from a cooling start temperature of 750° C. or higher and 830° C. or lower to a cooling stop temperature of 250° C. or higher and 400° C. or lower at a cooling rate of 10° C./s or more and 80° C./s or less; and then
immediately performing reheating to a temperature of 400° C. or higher and 500° C. or lower at a heating rate of 3° C./s or more.

4. A method for producing the high-strength, high-toughness steel plate according to claim 2 , the method comprising:
heating a steel slab to 1000° C. or higher and 1250° C. or lower;
performing rolling in an austenite recrystallization temperature range;
performing rolling at an accumulated rolling reduction ratio of 60% or more in an austenite non-recrystallization temperature range;
finishing the rolling at a temperature of 770° C. or higher and 850° C. or lower;
performing accelerated cooling to achieve a temperature drop (ΔT) of 350° C. or more from a cooling start temperature of 750° C. or higher and 830° C. or lower to a cooling stop temperature of 250° C. or higher and 400° C. or lower at a cooling rate of 10° C./s or more and 80° C./s or less; and then
immediately performing reheating to a temperature of 400° C. or higher and 500° C. or lower at a heating rate of 3° C./s or more.

Assignees

• Jfe Steel Corp

Inventors

• Kimura Hideyuki
• Yasuda Kyono
• Ishikawa Nobuyuki

Classifications

• C21D6/001

  containing Ni (C21D6/004 takes precedence) · CPC title

• C22C38/001

  containing N · CPC title

• C21D2211/001

  Austenite · CPC title

• C22C38/02

  containing silicon · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title