Heavy wall quenched and tempered seamless steel pipes and related method for manufacturing said steel pipes
First Claim
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1. A seamless quenched and tempered steel pipe comprising:
- a yield strength from 415 MPa to 635 MPa and a wall thickness (WT) higher than or equal to 35 mm and lower than or equal to 80 mm;
wherein the steel pipe has a chemical composition consisting of;
0.050-0.085 wt % C;
0.80-1.65 wt % Mn;
0.10-0.45 wt % Si;
0.10-0.70 wt % Cr;
0.08-0.45wt % Ni;
0.08-0.40 wt % Mo;
0.015-0.040 wt % Al;
0.0008-0.0050 wt % Ca;
0.0030-0.0090 wt % N;
0.000-0.040 wt % Nb;
0.000-.020 wt % Ti;
0.000-0.030 wt % Zr;
0.000-0.030 wt % Ta;
0.000-0.010 wt % V;
0.000-0.25 wt % Cu;
0.000-0.003 wt % S;
0.000-0.015 wt % P; and
0.000-0.0005 wt % B;
the remainder being Fe;
wherein CEIIW=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15) is in the range of 0.36% to 0.43%;
wherein, defining a first parameter P1=50×
C+Cr+10×
Mo+70×
V, the chemical composition satisfies a first condition 4.2<
P1<
8.0;
wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 50% and ferrite (VF) lower than or equal to 50%,wherein the quenched and tempered steel pipe has, at a distance up to 2 mm starting from outer and inner surfaces of the steel pipe, a microstructure comprising, in volume percentage, tempered martensite lower than 70% and tempered bainite higher than 30%;
wherein the microstructure of the quenched and tempered steel pipe has an average prior austenite grain size, measured by ASTM Standard E112, smaller than 25 μ
m;
and wherein the maximum hardness values, measured at 1.5-2.0 mm depth from the outer and inner surfaces, are not higher than 235 HV10.
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Abstract
Disclosed herein are embodiments of a seamless quenched and tempered steel pipe having a wall thickness (WT) higher than or equal to 35 mm and lower than or equal to 80 mm. Embodiments of the steel pipe can comprise C, Mn, Cr, Ni, Mo, Al, Ca, N, Nb, Ti, Zr, and Ta. Further, for some embodiments of the steel pipe wherein, defining a first parameter P1=50×C+Cr+10×Mo+70×V, the chemical composition can satisfy a first condition P1≦8.0.
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Citations
18 Claims
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1. A seamless quenched and tempered steel pipe comprising:
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a yield strength from 415 MPa to 635 MPa and a wall thickness (WT) higher than or equal to 35 mm and lower than or equal to 80 mm; wherein the steel pipe has a chemical composition consisting of; 0.050-0.085 wt % C; 0.80-1.65 wt % Mn; 0.10-0.45 wt % Si; 0.10-0.70 wt % Cr; 0.08-0.45wt % Ni; 0.08-0.40 wt % Mo; 0.015-0.040 wt % Al; 0.0008-0.0050 wt % Ca; 0.0030-0.0090 wt % N; 0.000-0.040 wt % Nb; 0.000-.020 wt % Ti; 0.000-0.030 wt % Zr; 0.000-0.030 wt % Ta; 0.000-0.010 wt % V; 0.000-0.25 wt % Cu; 0.000-0.003 wt % S; 0.000-0.015 wt % P; and 0.000-0.0005 wt % B; the remainder being Fe; wherein CEIIW=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15) is in the range of 0.36% to 0.43%; wherein, defining a first parameter P1=50×
C+Cr+10×
Mo+70×
V, the chemical composition satisfies a first condition 4.2<
P1<
8.0;wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 50% and ferrite (VF) lower than or equal to 50%, wherein the quenched and tempered steel pipe has, at a distance up to 2 mm starting from outer and inner surfaces of the steel pipe, a microstructure comprising, in volume percentage, tempered martensite lower than 70% and tempered bainite higher than 30%; wherein the microstructure of the quenched and tempered steel pipe has an average prior austenite grain size, measured by ASTM Standard E112, smaller than 25 μ
m;and wherein the maximum hardness values, measured at 1.5-2.0 mm depth from the outer and inner surfaces, are not higher than 235 HV10. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18)
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16. A method for manufacturing a seamless quenched and tempered steel pipe comprising:
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hot forming a seamless steel pipe having a wall thickness (WT) higher than or equal to 35 mm and lower than or equal to 80 mm and a chemical composition consisting of; 0.050-0.085 wt % C; 0.80-1.65 wt % Mn; 0.10-0.45 wt % Si; 0.10-0.70 wt % Cr; 0.08-0.45 wt % Ni; 0.08-0.40 wt % Mo; 0.015-0.040 wt % Al; 0.0008-0.0050 wt % Ca; 0.0030-0.0090 wt % N; 0.000-0.040 wt % Nb; 0.000-0.020 wt % Ti; 0.000-0.030 wt % Zr; 0.000-0.030 wt % Ta; 0.000-0.010 wt % V; 0.00-0.25 wt % Cu; 0.000-0.003 wt % S; 0.000-0.015 wt % P; and 0.0000-0.0005 wt % B; the remainder being Fe; cooling in air the seamless steel pipe down to reach room temperature; heating the seamless steel pipe, with a first heating rate between 0.1°
C./s and 10°
C./s, to an austenitizing temperature above the Ac3 transformation point, in a range between 880°
C. and 980°
C., and providing a soaking time between 180 s and 5400 s;quenching the seamless steel pipe using external and internal cooling, with a cooling rate greater than 6°
C./s and up to 30°
C./s at mid thickness of the pipe, and with a cooling rate of 100-200°
C./s in proximity of the outer and inner surfaces of the pipe;heating the seamless steel pipe, with a second heating rate between 0.1°
C./s and 10°
C./s, to a tempering temperature comprised in a predetermined range, and providing a holding time at said tempering temperature between 600 s and 7200 s;wherein said predetermined range is calculated with a tolerance of ±
20°
C. using the following equation;
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Specification