HIGH-STRENGTH, HIGH-TOUGHNESS STEEL PLATE AND METHOD FOR PRODUCING THE SAME

• US 20180057908A1
• Filed: 03/25/2016
• Published: 03/01/2018
• Est. Priority Date: 03/31/2015
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Kimura, Hideyuki, Yasuda, Kyono, Ishikawa, Nobuyuki
• Granted Patent: US 10,640,841 B2
• Time in Patent Office: Days
• CPC Class Codes: C21D 1/18 Hardening C21D1/02 takes precedence; Quenching with or without subsequent tempering quenching devices C21D1/62
• CPC Class Codes: C21D 2211/001 Austenite
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 6/001 containing Ni C21D6/004 takes precedence
• CPC Class Codes: C21D 6/002 containing Cr C21D6/004 takes precedence
• CPC Class Codes: C21D 6/005 containing Mn
• CPC Class Codes: C21D 6/008 containing Si
• CPC Class Codes: C21D 8/02 during manufacturing of plates or strips C21D8/12 takes precedence
• CPC Class Codes: C21D 8/0205 of ferrous alloys
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/005 containing rare earths, i.e. Sc, Y, Lanthanides
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/08 containing nickel C22C38/105 takes precedence
• CPC Class Codes: C22C 38/16 containing copper
• CPC Class Codes: C22C 38/22 : with molybdenum or tungsten
• CPC Class Codes: C22C 38/26 : with niobium or tantalum
• CPC Class Codes: C22C 38/28 : with titanium or zirconium
• CPC Class Codes: C22C 38/38 : with more than 1.5% by weight of manganese
• CPC Class Codes: C22C 38/58 : with more than 1.5% by weight of manganese

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.

Claims

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 μ

m or less, and

the steel plate has a Vickers hardness difference (Δ

HV) 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 (Δ

T) 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 (Δ

T) 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.