Electric resistance welded oil country tubular goods and manufacturing method of electric resistance welded oil country tubular goods

1. An electric resistance welded oil country tubular goods comprising:

a chemical composition that contains, in mass %,

C: 0.08% to 0.12%,

Si: 0.03 to 0.5%,

Mn: 0.80 to 2.2%,

P: 0.03% or less,

S: 0.003% or less,

Al: 0.08% or less,

Nb: 0.01% to 0.10%,

Ti: 0.005 to 0.03%,

B: 0.0005 to 0.0030%, and

N: 0.008% or less and in which Ti>3.4 N is satisfied, its balance is composed of Fe and inevitable impurities, and V C90 defined by Expression (1) below is 15 to 40, where a C content (%) is represented by [C], an Si content (%) is represented by [Si], an Mn content (%) is represented by [Mn], an Ni content (%) is represented by [Ni], a Cu content (%) is represented by [Cu], a Cr content (%) is represented by [Cr], and a Mo content (%) is represented by [Mo],

wherein the electric resistance welded oil country tubular goods has a yield stress of 758 to 965 MPa, a tensile strength of 862 MPa or more, and a yield to tensile ratio of 85% to 95%, and

the electric resistance welded oil country tubular goods does not have yield point elongation in a test result of a tensile test,

log V C90 =2.94−0.75(2.7[C]+0.4[Si]+[Mn]+0.45[Ni]+0.45[Cu]+0.8[Cr]+2[Mo])  Expression (1),

and wherein

a structure of the electric resistance welded oil country tubular goods other than a structure of an electric resistance welded portion consists of a bainite structure in which cementite exists in a lath-shaped structure,

wherein heat treatment with respect to a pipe body is not performed after the electric resistance welding, and

wherein the pipe body has a thickness of 5-20 mm and an outer diameter of 139.8-273.1 mm.

2. The electric resistance welded oil country tubular goods according to claim 1 , further containing one type or two types or more selected from, in mass %,

Ni: 1% or less,

Cu: 1% or less,

Mo: 0.3% or less,

Cr: 0.8% or less,

V: 0.1% or less, and

Ca: 0.0060% or less.

3. An electric resistance welded oil country tubular goods manufactured by hot-rolling a steel slab and performing coiling at 300° C. or lower to make a hot-rolled steel plate, and then forming the hot-rolled steel plate into a pipe shape and subjecting edge surfaces to electric resistance welding, and wherein heat treatment with respect to a pipe body is not performed after the electric resistance welding, and

wherein the steel slab has a chemical composition that contains, in mass %,

C: 0.08% to 0.12%,

Si: 0.03 to 0.5%,

Mn: 0.80 to 2.2%,

P: 0.03% or less,

S: 0.003% or less,

Al: 0.08% or less,

Nb: 0.01% to 0.10%,

Ti: 0.005 to 0.03%,

B: 0.0005 to 0.0030%, and

N: 0.008% or less and in which Ti>3.4 N is satisfied, its balance is composed of Fe and inevitable impurities, and V C90 defined by Expression (1) below is 15 to 40, where a C content (%) is represented by [C], an Si content (%) is represented by [Si], an Mn content (%) is represented by [Mn], an Ni content (%) is represented by [Ni], a Cu content (%) is represented by [Cu], a Cr content (%) is represented by [Cr], and a Mo content (%) is represented by [Mo],

wherein the electric resistance welded oil country tubular goods has a yield stress of 758 to 965 MPa, a tensile strength of 862 MPa or more, and a yield to tensile ratio of 85% to 95%, and

the electric resistance welded oil country tubular goods does not have yield point elongation in a test result of a tensile test,

log V C90 =2.94−0.75(2.7[C]+0.4[Si]+[Mn]+0.45[Ni]+0.45[Cu]+0.8[Cr]+2[Mo])  Expression (1),

and wherein a structure of the electric resistance welded oil country tubular goods other than a structure of an electric resistance welded portion consists of a bainite structure in which cementite exists in a lath-shaped structure, and

wherein the pipe body has a thickness of 5-20 mm and an outer diameter of 139.8-273.1 mm.

4. The electric resistance welded oil country tubular goods according to claim 3 , further containing

one type or two types or more selected from, in mass %,

Ni: 1% or less,

Cu: 1% or less,

Mo: 0.3% or less,

Cr: 0.8% or less,

V: 0.1% or less, and

Ca: 0.0060% or less.

5. A manufacturing method of an electric resistance welded oil country tubular goods comprising:

hot-rolling a steel slab;

performing coiling at 300° C. or lower to make a hot-rolled steel plate;

then forming the hot-rolled steel plate into a pipe shape; and

subjecting edge surfaces to electric resistance welding, and wherein heat treatment with respect to a pipe body is not performed after the electric resistance welding, and

wherein the steel slab has a chemical composition that contains, in mass %,

C: 0.08% to 0.12%,

Si: 0.03 to 0.5%,

Mn: 0.80 to 2.2%,

P: 0.03% or less,

S: 0.003% or less,

Al: 0.08% or less,

Nb: 0.01% to 0.10%,

Ti: 0.005 to 0.03%,

B: 0.0005 to 0.0030%, and

N: 0.008% or less and in which Ti>3.4 N is satisfied, its balance is composed of Fe and inevitable impurities, and V C90 defined by Expression (1) below is 15 to 40, where a C content (%) is represented by [C], an Si content (%) is represented by [Si], an Mn content (%) is represented by [Mn], an Ni content (%) is represented by [Ni], a Cu content (%) is represented by [Cu], a Cr content (%) is represented by [Cr], and a Mo content (%) is represented by [Mo],

wherein the electric resistance welded oil country tubular goods has a yield stress of 758 to 965 MPa, a tensile strength of 862 MPa or more, and a yield to tensile ratio of 85% to 95%, and

the electric resistance welded oil country tubular goods does not have yield point elongation in a test result of a tensile test,

log V C90 =2.94−0.75(2.7[C]+0.4[Si]+[Mn]+0.45[Ni]+0.45[Cu]+0.8[Cr]+2[Mo])  Expression (1),

wherein a structure of the electric resistance welded oil country tubular goods other than a structure of an electric resistance welded portion consists of a bainite structure in which cementite exists in a lath-shaped structure, and

wherein the pipe body has a thickness of 5-20 mm and an outer diameter of 139.8-273.1 mm.

6. The manufacturing method of the electric resistance welded oil country tubular goods according to claim 5 , further containing one type or two types or more selected from, in mass %,

Ni: 1% or less,

Cu: 1% or less,

Mo: 0.3% or less,

Cr: 0.8% or less,

V: 0.1% or less, and

Ca: 0.0060% or less.

7. The manufacturing method of the electric resistance welded oil country tubular goods according to claim 5 , wherein

a cooling rate in a range of 650 to 300° C. is set to 15 to 50° C./s.