US2026098330A1PendingUtilityA1
Case-hardening steel
Est. expiryOct 8, 2044(~18.1 yrs left)· nominal 20-yr term from priority
C22C 38/48C21D 1/28C22C 33/04C22C 38/001C22C 38/06C21D 1/32C22C 38/50C22C 38/04C22C 38/02C22C 38/002C22C 38/42
62
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0
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0
Claims
Abstract
The present invention relates to a case-hardening steel containing: 0.10 mass %≤C≤0.20 mass %, 0.05 mass %≤Si≤2.00 mass %, 0.30 mass %≤Mn≤2.00 mass %, P≤0.030 mass %, S≤0.030 mass %, 0.01 mass %≤Cu≤1.00 mass %, 0.01 mass %≤Ni≤1.00 mass %, 0.30 mass %≤Cr≤3.00 mass %, 0.0001 mass %≤Ti≤0.2000 mass %, 0.040 mass %≤Nb≤0.080 mass %, 0.002 mass %≤Al≤0.060 mass %, and 0.003 mass %≤N≤0.040 mass %, with the balance being Fe and inevitable impurities, and satisfying Pinning Nb Content ≥0.020 mass %, and 2.0×10 −6 ≤[Ti]×[N]≤2.0×10 −3 .
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A case-hardening steel comprising:
0.1
mass
%
≤
C
≤
0.2
mass
%
,
0.05
mass
%
≤
Si
≤
2.
mass
%
,
0.3
mass
%
≤
Mn
≤
2.
mass
%
,
P
≤
0.
0
30
mass
%
,
S
≤
0.03
mass
%
,
0.01
mass
%
≤
Cu
≤
1.
mass
%
,
0.01
mass
%
≤
Ni
≤
1.
mass
%
,
0.3
mass
%
≤
Cr
≤
3.
mass
%
,
0.0001
mass
%
≤
Ti
≤
0.2
mass
%
,
0.04
mass
%
≤
Nb
≤
0.08
mass
%
,
0.002
mass
%
≤
Al
≤
0.06
mass
%
,
and
0.
03
mass
%
≤
N
≤
0
.
0
40
mass
%
,
with the balance being Fe and inevitable impurities, and
satisfying the following formulas (1) and (2):
Pinning
Nb
Content
≥
0.02
mass
%
(
1
)
2.
×
10
-
6
≤
[
Ti
]
×
[
N
]
≤
2.
×
10
-
3
(
2
)
wherein
,
Pinning
Nb
content
=
[
Nb
]
-
area
ratio
(
area
%
)
of
NbC
-
based
inclusions
×
0.892
,
[X] is the content (mass %) of the element X,
the “NbC-based inclusions” refers to NbC-based particles having a Nb content of 50 mass % or more and a maximum length of 0.1 μm or more,
the “area ratio of NbC-based inclusions” refers to the ratio of the area of NbC-based inclusions included in the visual field area of 4000 μm×4000 μm in the measurement range, and
in a cross-section perpendicular to the longitudinal direction of a rolled material or a forged material, where the length of the line connecting the center of gravity of the cross-section and the boundary of the cross-section closest to the center of gravity is d/2 and a closed curve on the cross-section at which the separation distance from the boundary is d/4 is referred to as a d/4 portion, the “measurement range” refers to the range of the length d/4 extending the boundary to the d/4 portion.
2 . The case-hardening steel according to claim 1 , further comprising:
B
≤
0
.
0
1
0
mass
%
,
and
/
or
Mo
≤
1.
mass
%
.
3 . A method for producing a case-hardening steel, comprising:
a melting and casting step of melting and casting a raw material blended so as to have the following composition, to thereby obtain an ingot, and a hot-forging step of performing hot-forging on the ingot, to thereby obtain a hot-forged body, and optionally, at least one of the following steps:
a normalizing step of performing normalizing on the hot-forged body, to thereby obtain a normalized body,
a spheroidizing and annealing step of performing spheroidizing and annealing on the hot-forged body or the normalized body, to thereby obtain a spheroidized and annealed body, and
a cold-working step of performing cold-working on the hot-forged body, the normalized body, or the spheroidized and annealed body,
wherein the composition comprises:
0.1
mass
%
≤
C
≤
0.2
mass
%
,
0.05
mass
%
≤
Si
≤
2.
mass
%
,
0.3
mass
%
≤
Mn
≤
2.
mass
%
,
P
≤
0.
30
mass
%
,
S
≤
0.03
mass
%
,
0.01
mass
%
≤
Cu
≤
1.
mass
%
,
0.01
mass
%
≤
Ni
≤
1.
mass
%
,
0.3
mass
%
≤
Cr
≤
3.
mass
%
,
0.0001
mass
%
≤
Ti
≤
0.2
mass
%
,
0.04
mass
%
≤
Nb
≤
0.08
mass
%
,
0.002
mass
%
≤
Al
≤
0.06
mass
%
,
and
0.
03
mass
%
≤
N
≤
0
.
0
40
mass
%
,
with the balance being Fe and inevitable impurities, and
wherein in the hot-forging step, the ingot is heated at a heating temperature of 900+1500×[C] ° C. or higher, where [X] is the content (mass %) of the element X.
4 . The method according to claim 3 , wherein the composition further comprises:
B
≤
0.
0
1
0
mass
%
,
and
/
or
Mo
≤
1.
mass
%
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