SEAMLESS STEEL PIPE AND METHOD FOR PRODUCING SAME
First Claim
Patent Images
1. A seamless steel pipe comprising, as a chemical composition, by mass %:
- C;
0.02% to 0.10%;
Si;
0.05% to 0.5%;
Mn;
1.0% to 2.0%;
Mo;
0.5% to 1.0%;
Cr;
0.1% to 1.0%;
Al;
0.01% to 0.10%;
P;
0.03% or less;
S;
0.005% or less;
Ca;
0.0005% to 0.005%;
V;
0.010% to 0.040%;
N;
0.002% to 0.007%;
at least one selected from the group consisting of Ti;
0.008% or less and Nb;
0.02% to 0.05%; and
a balance consisting of Fe and impurities,wherein a carbon equivalent Ceq defined by the following Formula (1) is 0.50% to 0.58%, andspecified carbides containing Mo at a ratio of 50 mass % or more, V, and at least one selected from the group consisting of Ti and Nb, and having a size defined by an average value of major axes of 20 nm or more are contained.
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15
(1)here, into each of the symbols of elements in the Formula (1), the amount of a unit mass % of a corresponding element is substituted, and in the case where an element corresponding to the symbol of the element is not contained, “
0”
is substituted into the corresponding symbol of the element.
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Abstract
A seamless steel pipe has a carbon equivalent Ceq of 0.50% to 0.58%, and contains specified carbides containing Mo at a ratio of 50 mass % or more, V, and at least one selected from the group consisting of Ti and Nb, and having a size of 20 nm or more.
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12 Claims
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1. A seamless steel pipe comprising, as a chemical composition, by mass %:
-
C;
0.02% to 0.10%;Si;
0.05% to 0.5%;Mn;
1.0% to 2.0%;Mo;
0.5% to 1.0%;Cr;
0.1% to 1.0%;Al;
0.01% to 0.10%;P;
0.03% or less;S;
0.005% or less;Ca;
0.0005% to 0.005%;V;
0.010% to 0.040%;N;
0.002% to 0.007%;at least one selected from the group consisting of Ti;
0.008% or less and Nb;
0.02% to 0.05%; anda balance consisting of Fe and impurities, wherein a carbon equivalent Ceq defined by the following Formula (1) is 0.50% to 0.58%, and specified carbides containing Mo at a ratio of 50 mass % or more, V, and at least one selected from the group consisting of Ti and Nb, and having a size defined by an average value of major axes of 20 nm or more are contained.
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15
(1)here, into each of the symbols of elements in the Formula (1), the amount of a unit mass % of a corresponding element is substituted, and in the case where an element corresponding to the symbol of the element is not contained, “
0”
is substituted into the corresponding symbol of the element. - View Dependent Claims (2, 3, 4, 8, 9, 10, 11)
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-
5. A method for producing a seamless steel pipe comprising:
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heating a steel material including, as a chemical composition, by mass %, C;
0.02% to 0.10%,Si;
0.05% to 0.5%,Mn;
1.0% to 2.0%,Mo;
0.5% to 1.0%,Cr;
0.1% to 1.0%,Al;
0.01% to 0.10%,P;
0.03% or less,S;
0.005% or less,Ca;
0.0005% to 0.005%,V;
0.010% to 0.040%,N;
0.002% to 0.007%,at least one selected from the group consisting of Ti;
0.008% or less and Nb;
0.02% to 0.05%, anda balance consisting of Fe and impurities and having a carbon equivalent Ceq defined by the following Formula (2) of 0.50% to 0.58%; producing a raw pipe by piercing-rolling the heated steel material; producing a seamless steel pipe by rolling the raw pipe; quenching the seamless steel pipe at a quenching temperature of an Ac3 point or higher; and tempering the seamless steel pipe after the quenching at a tempering temperature of 660°
C. to 700°
C.
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15
(2)here, into each of the symbols of elements in the formula (2), the amount (mass %) of the corresponding element is substituted, and in the case where an element corresponding to the symbol of the element is not contained, “
0”
is substituted into the corresponding symbol of the element. - View Dependent Claims (6, 7, 12)
-
Specification