Welded steel pipe for linepipe having high compressive strength and excellent sour gas resistance and manufacturing method thereof
First Claim
1. A welded steel pipe for a linepipe having the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0008% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance, whereinC(%)−
- 0.065Nb(%) is 0.025 or more,a CP value is 0.95 or less,a Ceq value is 0.28 or more,Ti/N is a value which falls within a range of 1.5 to 4.0, andthe steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of martensite-austenite constituent (MA) is 2% or less, and an average grain size of bainite is 5 μ
m or less, wherein the CP value is expressed by the formula;
CP=4.46C(%)+2.37Mn(%)/6+{1.18Cr(%)+1.95Mo(%)+1.74V(%)}/5+{1.74Cu(%)+1.7Ni(%)}/15+22.36P(%); and
wherein the Ceq value is expressed by the formula;
Ceq=C(%)+Mn(%)/6+{Cr(%)+Mo(%)+V(%)}/5+{Cu(%)+Ni(%)}/15.
1 Assignment
0 Petitions
Accused Products
Abstract
Provided is a steel pipe for a linepipe having high compressive strength, a heavy wall thickness and sour gas resistance. The steel pipe has the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0015% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of M-A constituent is 2% or less and an average grain size of bainite is 5 μm or less.
-
Citations
4 Claims
-
1. A welded steel pipe for a linepipe having the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0008% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance, wherein
C(%)− - 0.065Nb(%) is 0.025 or more,
a CP value is 0.95 or less, a Ceq value is 0.28 or more, Ti/N is a value which falls within a range of 1.5 to 4.0, and the steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of martensite-austenite constituent (MA) is 2% or less, and an average grain size of bainite is 5 μ
m or less, wherein the CP value is expressed by the formula;
CP=4.46C(%)+2.37Mn(%)/6+{1.18Cr(%)+1.95Mo(%)+1.74V(%)}/5+{1.74Cu(%)+1.7Ni(%)}/15+22.36P(%); andwherein the Ceq value is expressed by the formula;
Ceq=C(%)+Mn(%)/6+{Cr(%)+Mo(%)+V(%)}/5+{Cu(%)+Ni(%)}/15. - View Dependent Claims (2, 3, 4)
- 0.065Nb(%) is 0.025 or more,
Specification