Thick steel plate having good multipass weld joint CTOD characteristics and method for manufacturing the same

• US 10,450,627 B2
• Filed: 09/05/2014
• Issued: 10/22/2019
• Est. Priority Date: 09/05/2014
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Ichimiya, Katsuyuki, Terazawa, Yusuke, Hase, Kazukuni
• Primary Examiner(s): Wu, Jenny R
• Application Number:
  US15/509,092
• Publication Number:
  US 20170275727A1
• Time in Patent Office: 1,873 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 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 2211/005 Ferrite
• 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: C21D 9/50 for welded joints
• CPC Class Codes: C21D 9/505 Cooling thereof
• 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 38/04 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 38/18 containing chromium
• CPC Class Codes: C22C 38/42 with copper
• CPC Class Codes: C22C 38/44 : with molybdenum or tungsten
• 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 steel plate comprising, by mass %: C: 0.03% to 0.12%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, 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 optionally one or two or more of Cu and the like. Ti/N, Ceq, Pcm, and ACR are in particular ranges, a base metal of the plate has an effective grain size of 20 μm or less at half the thickness of the plate, and the plate contains a particular number of complex inclusions at ¼ and ½ of the thickness of the plate. The complex inclusions comprise a sulfide containing Ca and Mn and an oxide containing Al and having an equivalent circular diameter of 0.1 μm or more.

Claims

1. A thick steel plate having multipass weld joint CTOD characteristics, the steel plate having a chemical composition comprising, by mass %:

C;

0.03% to 0.12%;

Si;

0.5% or less;

Mn;

1.0% to 2.0%;

P;

0.015% or less;

S;

0.0005% to 0.0050%;

Al;

0.005% to 0.060%;

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

the remainder being Fe and incidental impurities,

wherein a base metal of the plate has an effective grain size of 20 μ

m or less at half a thickness of the plate, and the plate contains 25 to 250/mm² of complex inclusions at ¼ and

½

of the thickness of the plate where the thickness is in mm, the complex inclusions (i) comprising a sulfide containing Ca and Mn and an oxide containing Al and (ii) having an equivalent circular diameter of 0.1 μ

m or more, and

formulae (1) to (4) are satisfied;

1.5≤

Ti/N≤

5.0 

 

(1),

0.43≤

Ceq≤

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

 

(2),

0.18≤

Pcm≤

0.24 wherein Pcm=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5[B] 

 

(3),

and

0.2≤

(Ca−

(0.18+130*Ca)*O)/(1.25*S)≤

1.4 

 

(4)

the alloying elements in the formulae (1) to (4) denote the corresponding content in mass %.

2. The thick steel plate having multipass weld joint CTOD characteristics according to claim 1, further comprising, by mass %, at least one 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%.

5. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 1 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 30% or more with a rolling reduction of 8% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 1.

6. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 1 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 33% or more with a rolling reduction of 5% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 1.

7. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 5, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

8. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 2 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 30% or more with a rolling reduction of 8% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 2.

11. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 2 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 33% or more with a rolling reduction of 5% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 2.

14. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 6, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

15. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 8, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

18. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 11, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

3. A thick steel plate having multipass weld joint CTOD characteristics, the steel plate having a chemical composition comprising, by mass %:

C;

0.03% to 0.12%;

Si;

0.5% or less;

Mn;

1.0% to 2.0%;

P;

0.015% or less;

S;

0.0005% to 0.0050%;

Al;

0.005% to 0.060%;

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

the remainder being Fe and incidental impurities,

wherein a base metal of the plate has an effective grain size of 20 μ

m or less at half a thickness of the plate, and the plate contains 25 to 250/mm² of complex inclusions at ¼ and

½

of the thickness of the plate where the thickness is in mm, the complex inclusions (i) comprising a sulfide containing Ca and Mn and an oxide containing Al and (ii) having an equivalent circular diameter of 0.1 μ

m or more,

formulae (1) to (4) are satisfied;

1.5≤

Ti/N≤

5.0 

 

(1),

0.43≤

Ceq≤

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

 

(2),

0.18≤

Pcm≤

0.24 wherein Pcm=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5[B] 

 

(3),

and

0.2≤

(Ca−

(0.18+130*Ca)*O)/(1.25*S)≤

1.4 

 

(4)

the alloying elements in the formulae (1) to (4) denote the corresponding content in mass %.

4. The thick steel plate having multipass weld joint CTOD characteristics according to claim 3, further comprising, by mass %, at least one 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%.

9. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 3 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 30% or more with a rolling reduction of 8% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 3.

10. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 4 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 30% or more with a rolling reduction of 8% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 4.

12. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 3 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 33% or more with a rolling reduction of 5% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.;

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 3.

13. A method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics, the method comprising:

heating a slab having the composition according to claim 4 to a temperature in a range of 950°

C. or more and 1200°

C. or less;

hot rolling the slab at a cumulative rolling reduction of 33% or more with a rolling reduction of 5% or more at a half-thickness temperature of 950°

C. or more and at a cumulative rolling reduction of 40% or more at a half-thickness temperature of less than 950°

C.; and

cooling the hot-rolled plate to 600°

C. or less with an average cooling rate between 700°

C. and 500°

C. at half the thickness of the plate being in a range of 3°

C./s to 50°

C./s; and

thereby producing the thick steel plate of claim 4.

16. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 9, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

17. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 10, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

19. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 12, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.

20. The method for manufacturing a thick steel plate having multipass weld joint CTOD characteristics according to claim 13, further comprising performing tempering treatment at a temperature of 700°

C. or less after the cooling.