High strength medium wall quenched and tempered seamless steel pipes and related method for manufacturing said steel pipes
First Claim
Patent Images
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 6 mm and lower than 35 mm;
wherein the steel pipe has a chemical composition consisting of;
0.050-0.090 wt % C;
0.80-1.65 wt % Mn;
0.10-0.45 wt % Si;
0.10-0.60 wt % Cr;
0.05-0.45 wt % Ni;
0.05-0.40 wt % Mo;
0.020-0.040 wt % Al;
0.0030-0.0090 wt % N;
0.0008-0.0050 wt % Ca;
0.000-0.040 wt % Nb;
0.000-0.020 wt % Ti;
0.000-0.070 wt % V;
0.000-0.030 wt % Zr;
0.000-0.030 wt % Ta;
0.00-0.25 wt % Cu;
0.000-0.003 wt % S;
0.000-0.018 wt % P; and
0.0000-0.0005 wt % B;
the remainder being Fe;
wherein at least one of Nb and V is present, (V+Nb) content being lower than 0.07 wt %;
wherein, defining a first parameter;
P1=(60×
C)+Cr+[5×
e(35×
Mo/WT)]+50×
(V+Nb),the chemical composition satisfies a first condition 10≦
P1≦
14.5;
wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 40% and ferrite (VF) lower than or equal to 60%, and has at a distance up to 2 mm, starting from the outer surface, a microstructure comprising, in volume percentage, tempered martensite lower than 70%, tempered bainite higher than 30% and traces of ferrite less than or equal to 10%;
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 which can have a wall thickness WT higher than or equal to 6 mm and lower than or equal to 35 mm. Some embodiments of the steel pipe can have a chemical composition comprising C, Mn, Si, Cr, Ni, Mo, Al, N, Ca, Nb, Ti, V, Zr, and Ta based on the composition weight, the remaining being iron and impurities. In some embodiments, wherein (V+Nb) content is lower than 0.07 wt %; defining a first parameter P1=(60×C)+Cr+[5×e(35×Mo/WT)]+50×(V+Nb), the chemical composition satisfies a first condition P1≦14.5.
284 Citations
26 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 6 mm and lower than 35 mm; wherein the steel pipe has a chemical composition consisting of; 0.050-0.090 wt % C; 0.80-1.65 wt % Mn; 0.10-0.45 wt % Si; 0.10-0.60 wt % Cr; 0.05-0.45 wt % Ni; 0.05-0.40 wt % Mo; 0.020-0.040 wt % Al; 0.0030-0.0090 wt % N; 0.0008-0.0050 wt % Ca; 0.000-0.040 wt % Nb; 0.000-0.020 wt % Ti; 0.000-0.070 wt % V; 0.000-0.030 wt % Zr; 0.000-0.030 wt % Ta; 0.00-0.25 wt % Cu; 0.000-0.003 wt % S; 0.000-0.018 wt % P; and 0.0000-0.0005 wt % B; the remainder being Fe; wherein at least one of Nb and V is present, (V+Nb) content being lower than 0.07 wt %; wherein, defining a first parameter;
P1=(60×
C)+Cr+[5×
e(35×
Mo/WT)]+50×
(V+Nb),the chemical composition satisfies a first condition 10≦
P1≦
14.5;wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 40% and ferrite (VF) lower than or equal to 60%, and has at a distance up to 2 mm, starting from the outer surface, a microstructure comprising, in volume percentage, tempered martensite lower than 70%, tempered bainite higher than 30% and traces of ferrite less than or equal to 10%; 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; andwherein 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, 16, 17, 18, 19, 24, 25, 26)
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20. A method of 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 6 mm and lower than 35 mm and a chemical composition consisting of; 0.050-0.090 wt % C; 0.80-1.65 wt % Mn; 0.10-0.45 wt % Si; 0.10-0.60 wt % Cr; 0.05-0.45 wt % Ni; 0.05-0.40 wt % Mo; 0.020-0.040 wt % Al; 0.0030-0.0090 wt % N; 0.0008-0.0050 wt % Ca; 0.000-0.040 wt % Nb; 0.000-0.020 wt % Ti; 0.000-0.070 wt % V; 0.000-0.030 wt % Zr; 0.000-0.030 wt % Ta; 0.00-0.25 wt % Cu; 0.000-0.003 wt % S; 0.000-0.018 wt % P; and 0.0000-0.0005 wt % B; the remainder being Fe; cooling the seamless steel pipe in air 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 180s and 5400s;quenching the seamless steel pipe with a cooling rate in the range of 20 to 80°
C./s at mid thickness of the pipe, or at mid thickness and at the inner surface of the pipe, and with a cooling rate of 100-200°
C./s in proximity of the outer and inner surfaces of the pipe or in proximity of the outer surface only; andheating 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 600s and 7200s;wherein said predetermined range is calculated with a tolerance of ±
20°
C. using the following equation; - View Dependent Claims (21, 22, 23)
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Specification