Martensitic stainless steel seamless pipe and method for producing martensitic stainless steel seamless pipe
Abstract
A martensitic stainless steel seamless pipe according to the present disclosure has a chemical composition and the microstructure described in the description, and a yield strength of 862 MPa or more. An observation field of view region which is 1.0 μm long in each of L direction and T direction and which includes an inner surface is composed of an inner surface vicinity region, an interior region that is below contact with the inner surface vicinity region, and a hollow region. An inner surface Cu occupancy OS cu which is defined as the numerical proportion of sections in which a Cu concentration is more than 2.0% in the inner surface vicinity region, and an interior Cu occupancy OI cu which is defined as the numerical proportion of sections in which the Cu concentration is more than 2.0% in the interior region satisfy Formula (2). OS Cu / OI Cu ≥ 1.2 ( 2 )
Claims
exact text as granted — not AI-modified1 . A martensitic stainless steel seamless pipe consisting of, in mass %,
C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Cr: 11.00 to 14.00%, Ni: 5.00 to 7.50%, Mo: 1.50 to 4.50%, Cu: 0.50 to 3.50%, Co: 0.010 to 0.500%, Ti: 0.050 to 0.300%, V: 0.01 to 1.00%, Ca: 0.0005 to 0.0050%, Al: 0.001 to 0.100%, N: 0.0010 to 0.0500%, O: 0.050% or less, W: 0 to 2.00%, Nb: 0 to 0.50%, Mg: 0 to 0.0050%, rare earth metal: 0 to 0.0050%, and B: 0 to 0.0050%, with the balance being Fe and impurities, and satisfying Formula (1), wherein: a microstructure is composed of, in volume percent, retained austenite in an amount of 0 to 15.0% and ferrite in an amount of 0 to 5.0%, with the balance being tempered martensite; a yield strength is 862 MPa or more; when a pipe axis direction of the martensitic stainless steel seamless pipe is defined as an L direction, and a pipe radius direction of the martensitic stainless steel seamless pipe is defined as a T direction, with respect to a square observation field of view region that includes an inner surface of the martensitic stainless steel seamless pipe that extends in the L direction, and whose sides that extend in the L direction are 1.0 μm in length and whose sides that extend in the T direction are 1.0 μm in length, when the observation field of view region is divided into 65,536 sections by being divided equally into 256 sections in the L direction and divided equally into 256 sections in the T direction, the observation field of view region is composed of: an inner surface vicinity region which is a rectangular region that has the inner surface of the martensitic stainless steel seamless pipe as a top edge and includes 256 sections in the L direction and six sections in the T direction, an interior region which is below contact with the inner surface vicinity region, and a hollow region which is above contact with the inner surface vicinity region; and when, among all the sections in the inner surface vicinity region, a numerical proportion of sections in which a Cu concentration is more than 2.0% is defined as inner surface Cu occupancy OS Cu , and among all the sections in the interior region, a numerical proportion of sections in which a Cu concentration is more than 2.0% is defined as interior Cu occupancy OI Cu , the inner surface Cu occupancy OS Cu and the interior Cu occupancy OI Cu satisfy Formula (2);
Mo
+
0.5
×
W
≥
2
.50
(
1
)
OS
Cu
/
OI
Cu
≥
1.2
(
2
)
where, a content of a corresponding element in mass % is substituted for each symbol of an element in Formula (1).
2 . The martensitic stainless steel seamless pipe according to claim 1 , containing one or more elements selected from a group consisting of:
W: 0.01 to 2.00%, Nb: 0.01 to 0.50%, Mg: 0.0001 to 0.0050%, rare earth metal: 0.0001 to 0.0050%, and B: 0.0001 to 0.0050%.
3 . A method for producing the martensitic stainless steel seamless pipe according to claim 1 , including:
a starting material preparation process of preparing a starting material which consists of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Cr: 11.00 to 14.00%, Ni: 5.00 to 7.50%, Mo: 1.50 to 4.50%, Cu: 0.50 to 3.50%, Co: 0.010 to 0.500%, Ti: 0.050 to 0.300%, V: 0.01 to 1.00%, Ca: 0.0005 to 0.0050%, Al: 0.001 to 0.100%, N: 0.0010 to 0.0500%, O: 0.050% or less, W: 0 to 2.00%, Nb: 0 to 0.50%, Mg: 0 to 0.0050%, rare earth metal: 0 to 0.0050%, and B: 0 to 0.0050%, with the balance being Fe and impurities, and which satisfies Formula (1); a hot working process of heating, in a heating furnace, the starting material that is prepared, and thereafter performing hot working in which an area reduction ratio R defined by Formula (A) is 40% or more and a hot working time is 15minutes or less to produce a hollow shell; a quenching process of subjecting the hollow shell that is at a temperature not less than an A 3 point to quenching; and a tempering process of performing tempering of the hollow shell subjected to the quenching, under conditions that satisfy Formula (B);
Mo
+
0.5
×
W
≥
2
.50
(
1
)
R
=
{
1
-
cross
‐
sectional
area
perpendicular
to
pipe
axis
direction
of
the
hollow
shell
after
hot
working
/
cross
‐
sectional
area
perpendicular
to
axial
direction
of
the
starting
material
before
hot
working
}
×
100
(
A
)
(
T
+
273.15
)
×
(
20
+
log
10
(
t
/
60
)
)
×
(
1
-
[
Cu
]
/
100
)
≤
17200
(
B
)
where, a content of a corresponding element in mass % is substituted for each symbol of an element in Formula (1), and
in Formula (B), a tempering temperature in ° C. is substituted for T, a tempering time in minutes is substituted for t, and a content of Cu in the hollow shell in mass % is substituted for [Cu].
4 . The method for producing a martensitic stainless steel seamless pipe according to claim 3 , wherein the starting material contains one or more elements selected from a group consisting of:
W: 0.01 to 2.00%, Nb: 0.01 to 0.50%, Mg: 0.0001 to 0.0050%, rare earth metal: 0.0001 to 0.0050%, and B: 0.0001 to 0.0050%.Cited by (0)
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