US 2026/0085392 A1Published application

Hot-rolled steel sheet

AssigneeNippon Steel Corporation

InventorsHiroshi SHUTO, Kazumasa TSUTSUI, Masaaki URANAKA, Yuko SOKUNO, Jun ANDO, Mutsumi YOSHITAKE

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Abstract

This hot-rolled steel sheet has a predetermined chemical composition, in a microstructure at a position of ¼ from a surface in a sheet thickness direction, in terms of area %, residual austenite is less than 3.0%, ferrite is 15.0% or more and less than 60.0%, and pearlite is less than 5.0%, an E value is 10.7 or more, an I value is 1.020 or more, a CS value is −8.0×105 to 8.0×105, a standard deviation of Mn concentrations is 0.60 mass % or less, at the surface, a number density of Si—Al—Cr oxides having a sphere equivalent radius of 0.500 μm or more is 2.0×103 pieces/cm2 or less, and a number density of Si—Al—Cr oxides having a sphere equivalent radius of 0.005 μm to 0.050 μm is 1.0×105 pieces/cm2 or more.

A hot-rolled steel sheet comprising, in terms of mass %, as a chemical composition:

C:
0.050% to 0.250%,
Si:
0.40% to 1.00%,
Mn:
1.00% to 1.50%,
sol. Al:
0.100% to 0.500%,
Cr:
0.50% to 2.00%,
P:
0.100% or less,
S:
0.0300% or less,
N:
0.1000% or less,
O:
0.0100% or less,
Ti:
0% to 0.500%,
Nb:
0% to 0.500%,
V:
0% to 0.500%,
Cu:
0% to 2.00%,
Mo:
0% to 1.00%,
Ni:
0% to 2.00%,
B:
0% to 0.0100%;
Ca:
0% to 0.0200%;
Mg:
0% to 0.0200%;
REM:
0% to 0.1000%;
Bi:
0% to 0.0200%;
As:
0% to 0.100%;
Zr:
0% to 1.00%;
Co:
0% to 1.00%;
Zn:
0% to 1.00%;
W:
0% to 1.00%;
Sn:
0% to 0.05%;
a remainder comprising Fe and impurities, and
the following formulas (A) and (B) are satisfied,
wherein, a microstructure at a position of ¼ from a surface in a sheet thickness direction having, in terms of area %,
residual austenite at less than 3.0%,
ferrite at 15.0% or more and less than 60.0%, and
pearlite at less than 5.0%,
an Entropy value indicated by the following formula (1) is 10.7 or more,
an Inverse difference normalized value indicated by the following formula (2) is 1.020 or more,
a Cluster Shade value indicated by the following formula (3) is −8.0×105 to 8.0×105, which are obtained by analyzing SEM images of the microstructure with a gray level co-occurrence matrices method,
a standard deviation of Mn concentrations is 0.60 mass % or less,
at the surface, a number density of Si—Al—Cr oxides having a sphere equivalent radius of 0.500 μm or more is 2.0×103 pieces/cm2 or less, and a number density of Si—Al—Cr oxides having a sphere equivalent radius of 0.005 μm to 0.050 μm is 1.0×105 pieces/cm2 or more,
0.06
%
≤
Ti
+
Nb
+
V
≤
0.5
%
,
(
A
)
Zr
+
Co
+
Zn
+
W
≤
1.
%
,
(
B
)
here, each element symbol in the formulas (A) and (B) indicates the content of the element in terms of mass %, and 0% is substituted when the element is not contained,
P(i,j) in the following formulas (1) to (5) is a gray level co-occurrence matrix, L in the following formula (2) is possible Quantization levels of grayscale of the SEM images, i and j in the following formulas (2) and (3) are natural numbers from 1 to the L, μx and μy in the following formula (3) are indicated by the in the following formulas (4) and (5),
[
Formula
⁢
1
]

Entropy
=
-
∑
i
⁢
∑
j
⁢
P
⁡
(
i
,
j
)
⁢
log
⁡
(
P
⁡
(
i
,
j
)
)
(
1
)
[
Formula
⁢
2
]

Inverse
⁢
difference
⁢
normalized
=
∑
i
⁢
∑
j
⁢
P
⁡
(
i
,
j
)
1
+
❘
"\[LeftBracketingBar]"
i
-
j
❘
"\[RightBracketingBar]"
L
(
2
)
[
Formula
⁢
3
]

Cluster
⁢
Shade
=
∑
i
⁢
∑
j
⁢
(
i
+
j
-
μ
x
-
μ
y
)
3
⁢
P
⁡
(
i
,
j
)
(
3
)
[
Formula
⁢
4
]

μ
x
=
∑
i
⁢
∑
j
⁢
i
⁡
(
P
⁡
(
i
,
j
)
)
(
4
)
[
Formula
⁢
5
]

μ
y
=
∑
i
⁢
∑
j
⁢
j
⁡
(
P
⁡
(
i
,
j
)
)
.
(
5
)

264 more elements

Facts

Application

19/109,902Filed 23 Oct 2023

Priority

JP 2022-17463031 Oct 2022

Published

26 Mar 2026

Term ends

Not estimatedThe source records don’t support an estimate.

Classification34 codes

C22C 38/32
Containing chromium: with boron
C21D 1/02
General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering: hardening articles or materials formed by…
C21D 6/002
Heat treatment of ferrous alloys: containing Cr
C21D 8/0226
Characterised by the working steps: hot rolling

Abstract

Claims2