US2021207235A1PendingUtilityA1
Steel sheet for carburizing, and method for manufacturing steel sheet for carburizing
Est. expiryOct 2, 2038(~12.2 yrs left)· nominal 20-yr term from priority
C21D 8/02C21D 8/0226C21D 9/46C21D 8/0263C21D 8/0257C21D 8/0236C21D 1/84C21D 1/76C21D 1/32C22C 38/40C22C 38/38C22C 38/32C22C 38/28C22C 38/26C22C 38/24C22C 38/22C22C 38/18C22C 38/16C22C 38/14C22C 38/12C22C 38/10C22C 38/06C22C 38/04C22C 38/02C22C 38/002C22C 38/001C22C 38/52C22C 1/051C22C 38/44C21D 8/0426C23C 8/22C21D 6/004C22C 38/46C21D 6/008C22C 38/42C22C 38/08C21D 6/005C21D 1/06C22C 38/48C22C 38/50C23C 8/02C21D 6/007C22C 38/54C21D 2211/005C21D 8/0205
52
PatentIndex Score
0
Cited by
0
References
0
Claims
Abstract
[Object] To provide a steel sheet for carburizing having further improved formability and toughness after carburizing, and a method for manufacturing the same.[Solution] A steel sheet consisting of, in mass %, C: more than or equal to 0.02%, and less than 0.30%, Si: more than or equal to 0.005%, and less than or equal to 0.5%, Mn: more than or equal to 0.01%, and less than or equal to 3.0%, P: less than or equal to 0.1%, S: less than or equal to 0.1%, sol. Al: more than or equal to 0.0002%, and less than or equal to 3.0%, N: more than or equal to 0.0001, and less than or equal to 0.035%, and the balance: Fe and impurities, in which average crystal grain size of ferrite is smaller than 10 μm, average equivalent circle diameter of carbide is 5.0 μm or smaller, percentage of number of carbides with an aspect ratio of 2.0 or smaller is 80% or larger relative to the total carbides, percentage of number of carbides present in ferrite crystal grain is 60% or larger relative to the total carbides, and average nitrogen concentration in a region ranging from topmost surface of steel sheet to a depth of 50 μm is 0.040 mass % or higher and 0.200 mass % or lower.
Claims
exact text as granted — not AI-modified1 . A steel sheet for carburizing consisting of, in mass %,
C: more than or equal to 0.02%, and less than 0.30%, Si: more than or equal to 0.005%, and less than or equal to 0.5%, Mn: more than or equal to 0.01%, and less than or equal to 3.0%, P: less than or equal to 0.1%, S: less than or equal to 0.1%, sol. Al: more than or equal to 0.0002%, and less than or equal to 3.0%, N: more than or equal to 0.0001%, and less than or equal to 0.035%, and the balance: Fe and impurities, wherein average crystal grain size of ferrite is smaller than 10 average equivalent circle diameter of carbide is 5.0 μm or smaller, percentage of number of carbides with an aspect ratio of 2.0 or smaller is 80% or larger relative to the total carbides, percentage of number of carbides present in ferrite crystal grain is 60% or larger relative to the total carbides, and average nitrogen concentration in a region ranging from topmost surface of steel sheet to a depth of 50 μm is 0.040 mass % or higher and 0.200 mass % or lower.
2 . The steel sheet for carburizing according to claim 1 , further comprising, in place of part of the balance Fe, one of, or two or more of, in mass %,
Cr: more than or equal to 0.005%, and less than or equal to 3.0%, Mo: more than or equal to 0.005%, and less than or equal to 1.0%, Ni: more than or equal to 0.010%, and less than or equal to 3.0%, Cu: more than or equal to 0.001%, and less than or equal to 2.0%, Co: more than or equal to 0.001%, and less than or equal to 2.0%, Nb: more than or equal to 0.010%, and less than or equal to 0.150%, Ti: more than or equal to 0.010%, and less than or equal to 0.150%, V: more than or equal to 0.0005%, and less than or equal to 1.0%, and B: more than or equal to 0.0005%, and less than or equal to 0.01%.
3 . The steel sheet for carburizing according to claim 1 , further comprising, in place of part of the balance Fe, at least either one of, in mass %,
W: less than or equal to 1.0%, or Ca: less than or equal to 0.01%.
4 . A method for manufacturing the steel sheet for carburizing according to claim 1 , the method comprising:
a hot-rolling step, in which a steel material having the chemical composition of said steel sheet is heated, hot finish rolling is terminated in a temperature range of 800° C. or higher and lower than 920° C., followed by winding at a temperature of 700° C. or lower; and an annealing step, in which the steel sheet obtained by the hot-rolling step, or, the steel sheet having been cold-rolled subsequently to the hot-rolling step is heated in an atmosphere with nitrogen concentration controlled to 25% or higher in volume fraction, at an average heating rate of 5° C./h or higher and 100° C./h or lower, up into a temperature range not higher than point Ac 1 defined by equation (1) below, annealed in the temperature range not higher than the point Ac 1 for 10 h or longer and 100 h or shorter, and then cooled at an average cooling rate of 5° C./h or higher and 100° C./h or lower in a temperature range from a temperature at the end of annealing down to 550° C., in the hot-rolling step, cooling being started within one second after end of the hot finish rolling, at an average cooling rate of higher than 50° C./s, and an average grain size of ferrite after the annealing being controlled to smaller than 10 μm, where in equation (1) below, notation [X] represents the content of element X (in mass %), which is substituted by zero if such element X is absent,
Ac
1
=
750.8
-
26.6
[
C
]
+
17.6
[
Si
]
-
11.6
[
Mn
]
-
22.9
[
Cu
]
-
23
[
Ni
]
+
24.1
[
Cr
]
+
22.5
[
Mo
]
-
39.7
[
V
]
-
5.7
[
Ti
]
+
232.4
[
Nb
]
-
169.4
[
Al
]
-
894.7
[
B
]
.
Equation
(
1
)
5 . A method for manufacturing the steel sheet for carburizing according to claim 4 , further comprising:
a continuous casting step for obtaining the steel material to be subjected to the hot-rolling step, in which at least either soundness enhancing treatment of the steel material, namely production of a predetermined inclusion, or reduction of center segregation of a predetermined element, is carried out.
6 . A steel sheet for carburizing comprising, in mass %,
C: more than or equal to 0.02%, and less than 0.30%, Si: more than or equal to 0.005%, and less than or equal to 0.5%, Mn: more than or equal to 0.01%, and less than or equal to 3.0%, P: less than or equal to 0.1%, S: less than or equal to 0.1%, sol. Al: more than or equal to 0.0002%, and less than or equal to 3.0%, N: more than or equal to 0.0001%, and less than or equal to 0.035%, and the balance comprising Fe and impurities, wherein average crystal grain size of ferrite is smaller than 10 μm, average equivalent circle diameter of carbide is 5.0 μm or smaller, percentage of number of carbides with an aspect ratio of 2.0 or smaller is 80% or larger relative to the total carbides, percentage of number of carbides present in ferrite crystal grain is 60% or larger relative to the total carbides, and average nitrogen concentration in a region ranging from topmost surface of steel sheet to a depth of 50 μm is 0.040 mass % or higher and 0.200 mass % or lower.
7 . The steel sheet for carburizing according to claim 6 , further comprising, in place of part of the balance Fe, one of, or two or more of, in mass %,
Cr: more than or equal to 0.005%, and less than or equal to 3.0%, Mo: more than or equal to 0.005%, and less than or equal to 1.0%, Ni: more than or equal to 0.010%, and less than or equal to 3.0%, Cu: more than or equal to 0.001%, and less than or equal to 2.0%, Co: more than or equal to 0.001%, and less than or equal to 2.0%, Nb: more than or equal to 0.010%, and less than or equal to 0.150%, Ti: more than or equal to 0.010%, and less than or equal to 0.150%, V: more than or equal to 0.0005%, and less than or equal to 1.0%, and B: more than or equal to 0.0005%, and less than or equal to 0.01%.
8 . The steel sheet for carburizing according to claim 6 , further comprising, in place of part of the balance Fe, at least either one of, in mass %,
W: less than or equal to 1.0%, or Ca: less than or equal to 0.01%.
9 . A method for manufacturing the steel sheet for carburizing according to claim 6 , the method comprising:
a hot-rolling step, in which said steel material having the chemical composition of said steel sheet is heated, hot finish rolling is terminated in a temperature range of 800° C. or higher and lower than 920° C., followed by winding at a temperature of 700° C. or lower; and an annealing step, in which the steel sheet obtained by the hot-rolling step, or, the steel sheet having been cold-rolled subsequently to the hot-rolling step is heated in an atmosphere with nitrogen concentration controlled to 25% or higher in volume fraction, at an average heating rate of 5° C./h or higher and 100° C./h or lower, up into a temperature range not higher than point Ac 1 defined by equation (1) below, annealed in the temperature range not higher than the point Ac 1 for 10 h or longer and 100 h or shorter, and then cooled at an average cooling rate of 5° C./h or higher and 100° C./h or lower in a temperature range from a temperature at the end of annealing down to 550° C., in the hot-rolling step, cooling being started within one second after end of the hot finish rolling, at an average cooling rate of higher than 50° C./s, and an average grain size of ferrite after the annealing being controlled to smaller than 10 μm, where in equation (1) below, notation [X] represents the content of element X (in mass %), which is substituted by zero if such element X is absent,
Ac
1
=
750.8
-
26.6
[
C
]
+
17.6
[
Si
]
-
11.6
[
Mn
]
-
22.9
[
Cu
]
-
23
[
Ni
]
+
24.1
[
Cr
]
+
22.5
[
Mo
]
-
39.7
[
V
]
-
5.7
[
Ti
]
+
232.4
[
Nb
]
-
169.4
[
Al
]
-
894.7
[
B
]
.
Equation
(
1
)
10 . A method for manufacturing the steel sheet for carburizing according to claim 9 , further comprising:
a continuous casting step for obtaining the steel material to be subjected to the hot-rolling step, in which at least either soundness enhancing treatment of the steel material, namely production of a predetermined inclusion, or reduction of center segregation of a predetermined element, is carried out.Join the waitlist — get patent alerts
Track US2021207235A1 — get alerts on status changes and closely related new filings.
We store only your email — no account needed. See our privacy policy.