US2025376747A1PendingUtilityA1
Extremely thick steel material for flange having excellent strength and low temperature impact toughness, and manufacturing method for same
Est. expiryJun 14, 2042(~15.9 yrs left)· nominal 20-yr term from priority
Inventors:Dae-Woo Kim
C21D 8/00C22C 38/50C22C 38/48C22C 38/46C22C 38/44C22C 38/42C22C 38/06C22C 38/02C22C 38/002C21D 2211/009C21D 2211/005C21D 2211/002C21D 2211/001C21D 6/004B21B 2001/028B21B 1/04B21B 1/024C21D 9/50C21D 2261/00C21D 6/02C21D 2211/004C21D 1/28C21D 9/40C21D 9/0068C21D 7/13C22C 38/04C22C 38/58
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Claims
Abstract
The present disclosure relates to an extremely thick steel material for a flange having excellent strength and low-temperature impact toughness, and a method of manufacturing the same.
Claims
exact text as granted — not AI-modified1 . An extremely thick steel material for a flange comprising:
in wt %, C: 0.05 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 2.0%, Al: 0.005 to 0.1%, P: 0.01% or less, S: 0.015% or less, Nb: 0.001 to 0.07%, V: 0.001 to 0.3%, Ti: 0.001 to 0.03%, Cr: 0.01 to 0.3%, Mo: 0.01 to 0.12%, Cu: 0.01 to 0.6%, Ni: 0.05 to 1.0%, Ca: 0.0005 to 0.004%, and a remainder of Fe and other unavoidable impurities, and Ceq thereof according to the following relational expression 1 satisfying a range of 0.35 to 0.55, the extremely thick steel material for a flange, having a thickness of 200 to 500 mm, having a steel microstructure composed of a composite structure of pearlite and ferrite with an average grain size of 30 μm or less, having a maximum size of cementite existing in ferrite-ferrite and/or ferrite-pearlite grain boundary, being 5 μm or less, having a porosity of 0.1 mm 3 /g or less in a central portion of a product, a region of ⅜t to ⅝t (where t means a steel thickness (mm)) in a thickness direction from a steel surface, and having 5 or more fine NbC or NbCN precipitates with a diameter of 5 to 15 nm, per 1 μm 2 , among precipitates observed in a cross section of steel,
[
Relational
expression
1
]
Ceq
=
[
C
]
+
[
Mn
]
/
6
+
(
[
Cr
]
+
[
Mo
]
+
[
V
]
)
/
5
+
(
[
Ni
]
+
[
Cu
]
)
/
15
,
wherein in the relational expression 1, [C], [Mn], [Cr], [Mo], [V], [Ni], and [Cu] represent contents (in weight %) of C, Mn, Cr, Mo, V, Ni, and Cu contained in the steel, respectively, and 0 is substituted if these components are not added intentionally.
2 . The extremely thick steel material for a flange of claim 1 , wherein the steel has a tensile strength of 510 to 690 MPa, a yield strength of 370 MPa or more, and an absorbed energy value of −50° C. Charpy impact test of 50 J or more.
3 . The extremely thick steel material for a flange of claim 1 , wherein a maximum surface crack depth of the steel is 0.1 mm or less (including 0).
4 . The extremely thick steel material for a flange of claim 1 , wherein a fraction of the cementite existing in the ferrite-ferrite or ferrite-pearlite grain boundary is 3 area % or less.
5 . A method of manufacturing an extremely thick steel material for a flange, comprising:
an operation of manufacturing a slab containing, in wt %, C: 0.05 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 2.0%, Al: 0.005 to 0.1%, P: 0.01% or less, S: 0.015% or less, Nb: 0.001 to 0.07%, V: 0.001 to 0.3%, Ti: 0.001 to 0.03%, Cr: 0.01 to 0.3%, Mo: 0.01 to 0.12%, Cu: 0.01 to 0.6%, Ni: 0.05 to 1.0%, Ca: 0.0005 to 0.004%, and a remainder of Fe and other inevitable impurities, the slab satisfying, Ceq according to the following relational expression 1 being in a range of 0.35 to 0.55, and having a thickness of 500 mm or more; an operation of heating the manufactured slab to a temperature within a range of 1100 to 1300° C., and then performing a first upsetting with a forging ratio of 1.3 to 2.4; an operation of bloom forging with a forging ratio of 1.5 to 2.0 after the first upsetting; an operation of reheating the bloom forged material to a temperature within a range of 1100 to 1300° C., and then performing round forging with a forging ratio of 1.65 to 2.25, and then performing a second upsetting with a forging ratio of 1.3 to 2.3; an operation of performing a third upsetting with a forging ratio of 2.0 to 2.8 on the second upsetting material, and then performing hole processing; an operation of reheating the hole-processed material to a temperature within a range of 1100 to 1300° C., and then ring-forging with a forging ratio of 1.0 to 1.6; and an operation of performing a normalizing heat treatment by heating the ring-forged material to a temperature within a range of 820 to 930°° C. based on a temperature measurement standard of a central portion thereof and maintaining the temperature for 5 to 600 minutes and then performing air cooling to room temperature,
[
Relational
expression
1
]
Ceq
=
[
C
]
+
[
Mn
]
/
6
+
(
[
Cr
]
+
[
Mo
]
+
[
V
]
)
/
5
+
(
[
Ni
]
+
[
Cu
]
)
/
15
,
wherein in the relational expression 1, [C], [Mn], [Cr], [Mo], [V], [Ni], and [Cu] represent contents (weight %) of C, Mn, Cr, Mo, V, Ni, and Cu contained in steel, respectively, and 0 is substituted if these components are not intentionally added.
6 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein the slab is manufactured using a continuous casting process or a semi-continuous casting process.
7 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein after manufacturing the slab, a prior austenite grain size of a surface layer of the slab before forging is 1000 μm or less, and a microstructure of the surface layer of the slab before forging is composed of a composite structure of polygonal ferrite of 15% or more and residual bainite.
8 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein a size of a forging surface punched during the first upsetting is 1000-1200 mm×1800-2000 mm when being initially 700 mm×1800 mm.
9 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein in the case of the bloom forging, when forging is completed, a size of a forging surface is 1450-1850 mm×2100-2500 mm when being initially 1000-1200 mm×1800-2000 mm.
10 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein when the round forging and the second upsetting are completed, a size of a product is 1450-1850Ø×1300-1700 mm.
11 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein when the third upsetting is completed, a size of a product is 2300-2800Ø×400-800 mm.
12 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein the flange made of the steel has a maximum thickness of 200 to 500 mm, an inner diameter of 4000 to 7000 mm, and an outer diameter of 5000 to 8000 mm.
13 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , wherein during the normalizing heat treatment, a heat treatment is performed such that an LMP defined by the following relational expression 2 satisfies 20 to 33,
LMP
=
T
(
Log
t
+
20
)
×
(
1
/
1000
)
[
Relational
expression
2
]
wherein in the relational expression 2, T is Kelvin reference temperature, t is time, and an exponent of log is 10.
14 . The method of manufacturing an extremely thick steel material for a flange of claim 5 , further comprising an operation of performing a post-weld heat treatment, a stress relieving heat treatment, or a tempering heat treatment, when welding is performed on the steel after the normalizing heat treatment.
15 . The method of manufacturing an extremely thick steel material for a flange of claim 14 , wherein the post-weld heat treatment is performed in a range where a value defined by the following relational expression 2 is LMP 19.3 or less,
LMP
=
T
(
Log
t
+
20
)
×
(
1
/
1000
)
,
[
Relational
expression
2
]
wherein in the relational expression 2, T is Kelvin reference temperature, t is time, and an exponent of log is 10.
16 . A method of manufacturing an extremely thick steel material for a flange, comprising:
an operation of manufacturing a slab by second-cooling a cast iron discharged from a mold to a temperature within a range of 800 to 850° C. at a cooling rate of 0.01 to 3° C./s, when manufacturing the slab using molten steel containing, in wt %, C: 0.05 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 2.0%, Al: 0.005 to 0.1%, P: 0.01% or less, S: 0.015% or less, Nb: 0.001 to 0.07%, V: 0.001 to 0.3%, Ti: 0.001 to 0.03%, Cr: 0.01 to 0.3%, Mo: 0.01 to 0.12%, Cu: 0.01 to 0.6%, Ni: 0.05 to 1.0%, Ca: 0.0005 to 0.004%, and a remainder of Fe and other inevitable impurities, Ceq thereof according to the following relational expression 1 satisfying a range of 0.35 to 0.55; an operation of heating the manufactured slab to a temperature within a range of 1100 to 1300° C., and then performing a first upsetting with a forging ratio of 1.3 to 2.4; an operation of bloom-forging with a forging ratio of 1.5 to 2.0 after the first upsetting; an operation of reheating the bloom-forged material to a temperature within a range of 1100 to 1300° C., and then performing round forging with a forging ratio of 1.65 to 2.25, and then performing a second upsetting with a forging ratio of 1.3 to 2.3; an operation of performing a third upsetting of the second-upsetting material with a forging ratio of 2.0 to 2.8, and then performing hole processing; an operation of reheating the hole-processed material to a temperature within a range of 1100 to 1300° C., and then performing ring forging with a forging ratio of 1.0 to 1.6; and an operation of performing a normalizing heat treatment by heating the ring-forged material to a temperature within a range of 820 to 930° C. based on a temperature measurement standard of a central portion thereof and maintaining the temperature for 5 to 600 minutes and then air-cooling to room temperature,
[
Relational
expression
1
]
Ceq
=
[
C
]
+
[
Mn
]
/
6
+
(
[
Cr
]
+
[
Mo
]
+
[
V
]
)
/
5
+
(
[
Ni
]
+
[
Cu
]
)
/
15
,
wherein in the relational expression 1, [C], [Mn], [Cr], [Mo], [V], [Ni], and [Cu] represent contents (weight %) of C, Mn, Cr, Mo, V, Ni, and Cu contained in steel, respectively, and 0 is substituted if these components are not intentionally added.
17 . The method of manufacturing an extremely thick steel material having excellent strength and low-temperature impact toughness for a flange of claim 16 , wherein in the normalizing heat treatment, a heat treatment is performed so that an LMP defined by the following relational expression 2 satisfies 20 to 33,
LMP
=
T
(
Log
t
+
20
)
×
(
1
/
1000
)
,
[
Relational
expression
2
]
wherein in the relational expression 2, T is Kelvin reference temperature, t is time, and a exponent of log is 10.Join the waitlist — get patent alerts
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