Thick-walled, high tensile strength steel with excellent CTOD characteristics of the weld heat-affected zone, and manufacturing method thereof

• US 9,777,358 B2
• Filed: 09/04/2013
• Issued: 10/03/2017
• Est. Priority Date: 09/06/2012
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Ichimiya, Katsuyuki, Yuga, Masao, Hayashi, Kenji
• Primary Examiner(s): Yee, Deborah
• Application Number:
  US14/416,960
• Publication Number:
  US 20150203945A1
• Time in Patent Office: 1,490 Days
• Field of Search: None
• CPC Class Codes: C21D 1/20 Isothermal quenching, e.g. bainitic hardening
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 6/001 containing Ni C21D6/004 takes precedence
• CPC Class Codes: C21D 6/004 containing Cr and Ni
• CPC Class Codes: C21D 6/005 containing Mn
• CPC Class Codes: C21D 6/008 containing Si
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 9/46 for sheet metals
• 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 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/08 containing nickel C22C38/105 takes precedence
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/16 containing copper
• CPC Class Codes: C22C 38/42 : with copper
• CPC Class Codes: C22C 38/46 : with vanadium
• CPC Class Codes: C22C 38/48 : with niobium or tantalum
• CPC Class Codes: C22C 38/50 : with titanium or zirconium
• CPC Class Codes: C22C 38/58 : with more than 1.5% by weight of manganese

Abstract

A thick-walled high-strength steel plate with excellent low-temperature toughness (Charpy impact and CTOD properties of a weld bond) in a multilayer weld zone, and a method for manufacturing the steel plate.

Claims

1. A thick-walled high-strength steel plate with an excellent low-temperature toughness property (“

CTOD property”

) of a heat-affected zone, the steel plate having a chemical composition comprising;

C;

0.020% or more and 0.080% or less by mass %;

Si;

0.01% or more and 0.35% or less by mass %;

Mn;

1.20% or more and 2.30% or less by mass %;

P;

0.008% or less by mass %;

S;

0.0035% or less by mass %;

Al;

0.010% or more and 0.060% or less by mass %;

Cu;

0.70% or more and 1.50% or less by mass %;

Ni;

0.40% or more and 2.00% or less by mass %;

Nb;

0.005% or more and 0.040% or less by mass %;

Ti;

0.005% or more and 0.025% or less by mass %;

N;

0.0020% or more and 0.0050% or less by mass %;

O;

0.0030% or less by mass %; and

the balance being Fe and inevitable impurities,

wherein (a) Ceq defined by the relational expression (1) is 0.520% or less,

Ceq=[C]+[Mn]/6+([Cu]+[Ni])/15+([Cr]+[Mo]+[V])/5, 

 

(1)

where [M] represents the content (mass %) of the chemical element represented by M,

(b) Ti/N (mass ratio) is 1.50 or more and 4.00 or less,

(c) relational expression (2) is satisfied,

5.5[C]^4/3+15[P]+0.90[Mn]+0.12[Ni]+7.9[Nb]^1/2+0.53[Mo]≦

3.50 

 

(2),

where [M] represents the content (mass %) of the chemical element represented by M, and

(d) the hardness of a center segregation part satisfies relational expression (3)

H_Vmax/H_Vave≦

1.35+0.006/[C]−

t/500, 

 

(3)

where H_Vmax represents a maximum value of the Vickers hardness of a center segregation part, H_Vave represents an average value of the Vickers hardness of portions other than portions within ¼

of a thickness from upper and lower surfaces of the steel plate and the center segregation part, [C] represents C content (mass %), and t represents the thickness of the steel plate (mm).

2. The thick-walled high-strength steel plate according to claim 1, the chemical composition further comprising at least one of the group (e) or (f),

wherein (e) the chemical composition further comprising at least one of Cr:

0.10% or more and 1.00% or less by mass %, Mo;

0.05% or more and 0.50% or less by mass %, and V;

0.005% or more and 0.050% or less by mass %, and

(f) Ca;

0.0005% or more and 0.0050% or less by mass %, wherein relational expression (4) is satisfied,

0<

{[Ca]−

(0.18+130×

[Ca])×

[O]}/1.25/[S]<

1.00, 

 

(4)

where [M] represents the content (mass %) of the chemical element represented by M.

3. A method for manufacturing a thick-walled high-strength steel plate with an excellent CTOD property of a heat-affected zone, the method comprising:

heating steel having the chemical composition according to claim 1 at a temperature of 1030°

C. or higher and 1200°

C. or lower;

performing hot rolling on the heated steel such that the cumulative rolling reduction in a temperature range of 950°

C. or higher is 30% or more and that the cumulative rolling reduction in a temperature range of lower than 950°

C. is 30% or more and 70% or less;

performing accelerated cooling on the hot-rolled steel plate down to a temperature of 600°

C. or lower at a cooling rate of 1.0°

C./s or more; and

performing a tempering treatment on the cooled steel plate at a temperature of 450°

C. or higher and 650°

C. or lower.

4. The thick-walled high-strength steel plate according to claim 1, wherein the steel plate has a yield stress of 420 MPa or more.

5. The thick-walled high-strength steel plate according to claim 1, wherein the steel plate has a tensile strength of 520 MPa or more.

6. The thick-walled high-strength steel plate according to claim 1, wherein the steel plate has a thickness in the range of 50 to 100 mm.

7. The thick-walled high-strength steel plate according to claim 1, wherein the steel plate exhibits an absorbed energy at a temperature of −

40°

C. (vE<sub>−

40°

C.</sub>) of 200 J or more.

8. A method for manufacturing a thick-walled high-strength steel plate with an excellent CTOD property of a heat-affected zone, the method comprising:

heating steel having the chemical composition according to claim 2 at a temperature of 1030°

C. or higher and 1200°

C. or lower;

performing hot rolling on the heated steel such that the cumulative rolling reduction in a temperature range of 950°

C. or higher is 30% or more and that the cumulative rolling reduction in a temperature range of lower than 950°

C. is 30% or more and 70% or less;

performing accelerated cooling on the hot-rolled steel plate down to a temperature of 600°

C. or lower at a cooling rate of 1.0°

C./s or more; and

performing a tempering treatment on the cooled steel plate at a temperature of 450°

C. or higher and 650°

C. or lower.

9. The thick-walled high-strength steel plate according to claim 2, wherein the steel plate has a yield stress of 420 MPa or more.

10. The thick-walled high-strength steel plate according to claim 2, wherein the steel plate has a tensile strength of 520 MPa or more.

11. The thick-walled high-strength steel plate according to claim 2, wherein the steel plate has a thickness in the range of 50 to 100 mm.

12. The thick-walled high-strength steel plate according to claim 2, wherein the steel plate exhibits an absorbed energy at a temperature of −

40°

C. (vE<sub>−

40°

C.</sub>) of 200 J or more.

13. The thick-walled high-strength steel plate according to claim 1, wherein the chemical composition comprises Cu:

0.80% or more and 1.50% or less by mass %.

14. The thick-walled high-strength steel plate according to claim 2, wherein the chemical composition comprises Cu:

0.80% or more and 1.50% or less by mass %.