US2025197981A1PendingUtilityA1
Hot rolled steel sheet having excellent cold bendability after heating and quenching-tempering heat treatment, steel pipe, member and manufacturing methods therefor
Est. expiryDec 21, 2041(~15.4 yrs left)· nominal 20-yr term from priority
C21D 8/02C22C 38/50C22C 38/48C22C 38/46C22C 38/44C22C 38/42C22C 38/06C22C 38/04C22C 38/02C22C 38/001C21D 2211/009C21D 2211/008C21D 2211/005C21D 2211/001C21D 9/085C21D 8/0263C21D 8/0226C21D 6/004C21D 1/18B21C 47/02C21D 8/0273C22C 38/54C22C 38/08C22C 38/40C21D 6/005C21D 9/46C21D 9/08C21D 8/0205
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Claims
Abstract
A hot rolled steel sheet having excellent cold bendability after heating and quenching-tempering heat treatment, a steel pipe, a member and manufacturing methods therefor are provided. The present invention relates to: a hot rolled steel sheet comprising, by weight %, 0.20% or greater and less than 0.3% of C, 0.5-1.3% of Mn, 0.3% or less of Si (excluding 0%), 0.03% or less of P (including 0%), 0.004% or less of S (including 0%), 0.04% or less of Al (excluding 0%), 0.3% or less of Cr, 0.1-0.4% of Ni, 0.05% of Ti (including 0%), 0.0005-0.0050% of B, 0.01% or less of N (excluding 0%) and the balance of Fe and other impurities, and satisfying relational expressions 1-3; a steel pipe; and a member.
Claims
exact text as granted — not AI-modified1 - 19 . (canceled)
20 . A hot-rolled steel sheet for a cold-forming member, the hot-rolled steel sheet comprising:
by weight %, 0.20% or greater and less than 0.3% of C, 0.5-1.3% of Mn, 0.3% or less of Si (excluding 0%), 0.03% or less of P (including 0%), 0.004% or less of S (including 0%), 0.04% or less of Al (excluding 0%), 0.3% or less of Cr, 0.1-0.4% of Ni, 0.05% of Ti (including 0%), 0.0005-0.0050% of B, 0.01% or less of N (excluding 0%) and a balance of Fe and inevitable impurities, and satisfying relational expressions 1-3, wherein a hardness difference value between a surface portion and a thickness/4 position portion of the steel sheet is less than 15, wherein, by volume %, the hot-rolled steel sheet has a microstructure including 20-65% of ferrite and 35-80% of pearlite, and wherein an average grain size of prior austenite is 15 μm or more,
(
Mn
/
Si
)
≥
2
(
weight
ratio
)
[
Relational
expression
1
]
(
Ni
)
/
(
Mn
)
≥
0.05
(
weight
ratio
)
[
Relational
expression
2
]
(
Si
+
Ni
)
/
(
C
+
M
n
)
≥
0.2
(
weight
ratio
)
.
[
Relational
expression
3
]
21 . The hot-rolled steel sheet of claim 20 , wherein one or more of Mo: 0.01-0.2%, Cu: 0.05-0.2%, Nb: 0.005-0.02% and V: 0.01-0.05% are included.
22 . The hot-rolled steel sheet of claim 20 , wherein the hot-rolled steel sheet has tensile strength of 320 to 950 MPa.
23 . A cold-forming member, comprising:
by weight %, 0.20% or greater and less than 0.3% of C, 0.5-1.3% of Mn, 0.3% or less of Si (excluding 0%), 0.03% or less of P (including 0%), 0.004% or less of S (including 0%), 0.04% or less of Al (excluding 0%), 0.3% or less of Cr, 0.1-0.4% of Ni, 0.05% of Ti (including 0%), 0.0005-0.0050% of B, 0.01% or less of N (excluding 0%) and a balance of Fe and inevitable impurities, satisfying relational expressions 1-3, and having, by volume %, a microstructure including 95% of one or more of martensite and tempered martensite and a balance of 5% or less of retained austenite, wherein an average grain size of prior austenite is 15 μm or more, and the number of Fe 3 C carbides having an average circle equivalent size of 300 nm or less is 30 or less per unit area (μm 2 ),
(
Mn
/
Si
)
≥
2
(
weight
ratio
)
[
Relational
expression
1
]
(
Ni
)
/
(
Mn
)
≥
0.05
(
weight
ratio
)
[
Relational
expression
2
]
(
Si
+
Ni
)
/
(
C
+
M
n
)
≥
0.2
(
weight
ratio
)
[
Relational
expression
3
]
24 . The cold-forming member of claim 23 , wherein one or more of Mo: 0.01-0.2%, Cu: 0.05-0.2%, Nb: 0.005-0.02% and V: 0.01-0.05% are included.
25 . The cold-forming member of claim 23 , wherein the forming member has tensile strength of 1300 MPa or more and a maximum bending angle of 40° or more.
26 . A method of manufacturing a cold-forming member, the method comprising:
heating a slab including, by weight %, 0.20% or greater and less than 0.3% of C, 0.5-1.3% of Mn, 0.3% or less of Si (excluding 0%), 0.03% or less of P (including 0%), 0.004% or less of S (including 0%), 0.04% or less of Al (excluding 0%), 0.3% or less of Cr, 0.1-0.4% of Ni, 0.05% of Ti (including 0%), 0.0005-0.0050% of B, 0.01% or less of N (excluding 0%) and a balance of Fe and inevitable impurities and satisfying relational expressions 1-3 in a temperature range of 1150-1300° C.; obtaining a hot-rolled steel sheet by hot-rolling the heated slab at an Ar 3 temperature or higher, the hot-rolling including rough-rolling and finishing rolling; cooling the hot-rolled steel sheet on a run-out table and coiling the hot-rolled steel sheet at a temperature of 550 to 750° C.; obtaining a steel pipe by welding the hot-rolled steel sheet; performing annealing heat treatment and drawing out the steel pipe; performing a reheating step of heating the annealing-heat treated or drawn steel pipe to a temperature of Ar 3 —970° C. at a heating rate of 10° C./sec or more and maintaining the steel pipe for less than 60 seconds; performing a quenching step of cooling the reheated steel pipe to room temperature at a cooling rate of 20-350° C./sec more; a tempering heat treatment step of heating the quenched steel pipe at a heating rate of 2-20° C./sec to a temperature range of 150-350° C. and maintaining the steel pipe at the above temperature; and cold-forming the tempering-heat treated steel pipe into a member.
27 . The method of claim 26 , wherein one or more of Mo: 0.01-0.2%, Cu: 0.05-0.2%, Nb: 0.005-0.02% and V: 0.01-0.05% are included.
28 . The method of claim 26 , wherein the forming member has tensile strength of 1300 MPa or more and a maximum bending angle of 40° or more.
29 . The method of claim 26 , wherein annealing heat treatment is performed on the steel pipe for 3-60 minutes at a temperature of Ac 1 −50° C.-Ac 3 +150° C.
30 . The method of claim 26 , wherein, during cold-forming the heat treated steel pipe, the cold-forming is performed in a range of bending radius of 30-60R.Join the waitlist — get patent alerts
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