Steel plate having superior toughness in weld heat-affected zone and welded structure made therefrom

• US 7,105,066 B2
• Filed: 11/16/2001
• Issued: 09/12/2006
• Est. Priority Date: 11/16/2001
• Status: Expired due to Term

• Current Assignee: Posco Holdings Incorporated
• Original Assignee: Posco Holdings Incorporated
• Inventors: Choi, Hae-Chang, Jeong, Hong-Chul
• Primary Examiner(s): Yee, Deborah
• Application Number:
  US10/476,442
• Publication Number:
  US 20040144454A1
• Time in Patent Office: 1,761 Days
• Field of Search: 148/320, 148330-336
• US Class Current: 148/330
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 2211/009 Pearlite
• CPC Class Codes: C21D 8/021 involving a particular fabrication or treatment of ingot or slab
• CPC Class Codes: C21D 8/0226 Hot rolling
• 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 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• 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 38/60 containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Abstract

A welding structural steel product exhibiting a superior heat affected zone toughness, comprising, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% 0.00 1 to 0.2% W, at most 0.03% P, at most 0.03% S, at most 0.005% 0, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, and 6.5≦(Ti 2Al 4B)/N≦14, and having a microstructure essentially consisting of a complex structure of ferrite and pearlite having a grain size of 20 μm or less. The method includes the steps of preparing a slab of the above-described composition, heating the slab to 1,100° C. to 1,250° C. for 60-180 minutes, hot rolling the heated slab in an austenite recrystallization range at a 40% or more rolling reduction followed by controlled cooling.

Claims

1. A welding structural steel product exhibiting a superior heat affected zone toughness. comprising, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, at most 0.03% P, at most 0.03% 5, at most 0.005% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦

Ti/N≦

2.5, 10≦

N/B≦

40, 2.5 Al/N≦

7, and 6.5≦

(Ti 2Al 4B)/N≦

14, and having a microstructure essentially consisting of a complex structure of ferrite and pearlite having a grain size of 20 μ

m or less.

2. The welding structural steel product according to claim 1, further comprising 0.01 to 0.2% V while satisfying conditions of 0.3≦

V/N≦

9, and 7≦

(Ti 2Al 4B V)/N≦

17.

3. The welding structural steel product according to claim 1, further comprising one or more selected from a group consisting of Ni:

0.1 to 3.0%, Cu;

0.1 to 1.5%, Nb;

0.01 to 0.1%, Mo;

0.05 to 1.0%, and Cr;

0.05 to 1.0%.

4. The welding structural steel product according to claim 1, further comprising one or both of Ca:

0.0005 to 0.005% and REM;

0.005 to 0.05%.

5. The welding structural steel product according to claim 1, wherein TiN prebipitates having a grain size of 0.01 to 0.1 μ

m are dispersed at a density of 1.0×

10⁷/mm² or more and a spacing of 0.5 μ

m or less.

6. The welding structural steel product according to claim 1, wherein a toughness difference between a matrix and a heat treated zone is within a range of ±

30 J when the steel product is heated to a temperature of 1,400°

C. or more, and then cooled within 60 seconds over a cooling range of from 800°

C. to 500°

C.;

is within a range of ±

70 J when the steel product is heated to a temperature of 1,400°

C. or more, and then cooled within 60 to 120 seconds over a cooling range of from 800°

C. to 500°

C.; and

is within a range of 0 to 100 J when the steel product is heated to a temperature of 1,400°

C. or more, and then cooled within 120 to 180 seconds over a cooling range of from 800°

C. to 500°

C.

7. A welded structure having a superior heat affected zone toughness, manufactured using a welding structural steel product according to claim 1.