Electric resistance welded steel pipe excellent in weld zone and method of production of same
View Patent ↗Electric resistance welded steel pipe excellent in weld zone quality suitable for oil country tubular goods and line pipe wherein steel plate forming the base metal of the electric resistance welded steel pipe has a predetermined chemical composition, the contents of Ca, O, S, Ce, La, and Al satisfy XCASO = ( Ca O + Ca S + 0.285 Ce + La O + 0.285 Ce + La S ) × ( Al Ca ) > 78 the oxide-based inclusions in the weld zone of the electric resistance welded steel pipe contains one or both of Ce and La, and the long axis/short axis of the oxide-based inclusions is 2.5 or less.
1. An electric resistance welded steel pipe excellent in weld zone quality,
wherein a chemical composition of a steel plate forming a base metal of the electric resistance welded steel pipe contains, by mass %,
C: 0.03 to 0.15%,
Si: 0.1 to 0.3%,
Mn: 0.5 to 2.0%,
Al: 0.01 to 0.06%,
Ti: 0.011 to 0.023%,
Ca: 0.001 to 0.005%,
one or both of Ce and La: 0.001 to 0.005%,
P: 0.03% or less,
S: 0.0015% or less,
O: 0.002% or less, and
N: 0.005% or less,
further contains one or more of
Nb: 0.1% or less,
V: 0.1% or less,
Mo: 0.2% or less, and
B: 0.002% or less, and
a balance of iron and unavoidable impurities;
the contents of Ca, O, S, Ce, La, and Al satisfying formula:
XCASO
=
(
Ca
O
+
Ca
S
+
0.285
Ce
+
La
O
+
0.285
Ce
+
La
S
)
×
(
Al
Ca
)
>
78
;
oxide-based inclusions at a weld zone of the electric resistance welded steel pipe contain one or both of Ce and La; and
a long axis/short axis of the oxide-based inclusions is 2.5 or less.
2. The electric resistance welded steel pipe excellent in weld zone quality according to claim 1 , wherein the chemical composition of the steel plate further contains, by mass %, one or more of
Cu: 0.1 to 2%,
Ni: 0.05 to 1%,
Cr: 0.01 to 1%, and
Zr: 0.001 to 0.01%.
3. The electric resistance welded steel pipe excellent in weld zone quality according to claim 1 or 2 , wherein
a tensile strength of the base metal is 860 MPa or more,
a toughness of the base metal at 0° C. is 100 J or more, and
a toughness of a weld zone of the electric resistance welded steel pipe at 0° C. is 40 J or more.
4. The electric resistance welded steel pipe excellent in weld zone quality according to claim 1 or 2 , wherein
a tensile strength of the base metal is 500 MPa to 620 MPa,
a toughness of the base metal at −40° C. is 100 J or more, and
a weld zone toughness of a weld zone of the electric resistance welded steel pipe at −40° C. is 100 J or more.
5. A method of production of electric resistance welded steel pipe excellent in weld zone quality, comprising the steps of:
in a refining process of steelmaking, adjusting a chemical composition of a molten steel so as to contain, by mass %,
C: 0.03 to 0.15%,
Si: 0.1 to 0.3%,
Mn: 0.5 to 2.0%,
Al: 0.01 to 0.06%,
Ti: 0.011 to 0.023%,
P: 0.03% or less,
S: 0.0015% or less,
O: 0.002% or less, and
N: 0.005% or less,
further contain one or more of
Nb: 0.1% or less,
V: 0.1% or less,
Mo: 0.2% or less, and
B: 0.002% or less, and
a balance of iron and unavoidable impurities;
then adding one or both of Ce and La to the molten steel to give total contents of Ce and La of 0.001 to 0.005%;
then adding Ca to the molten steel to give a content of Ca of 0.0010 to 0.0050%, and adjusting the contents of Ca, O, S, Ce, La, and Al so as to satisfy the formula:
XCASO
=
(
Ca
O
+
Ca
S
+
0.285
Ce
+
La
O
+
0.285
Ce
+
La
S
)
×
(
Al
Ca
)
>
78
;
manufacturing a steel slab from the molten steel;
hot rolling the steel slab to obtain hot rolled steel plate;
coiling the hot rolled steel plate; and
manufacturing electric resistance welded steel pipe from the coiled hot rolled steel plate.
6. The method of production of electric resistance welded steel pipe excellent in weld zone quality according to claim 5 , wherein in the refining process of steelmaking, the chemical composition before adding one or both of Ce and La to the molten steel further contains, by mass %,
one or more of
Cu: 0.1 to 2%
Ni: 0.05 to 1%
Cr: 0.01 to 1%, and
Zr: 0.001 to 0.01%.