HIGH STRENGTH BAINITIC STEEL FOR OCTG APPLICATIONS
First Claim
1. Process for the production of high strength bainitic steel seamless pipes comprising the following steps:
- a) providing a steel having a composition comprising 0.2-0.4% by weight of C 0.05-1.5% by weight of Mn;
1.0-2.0% by weight of Si and 0-0.5% by weight of Al or, alternatively, 1.0-2.0% by weight of Al and 0-0.5% by weight of Si;
0.5-2.0% by weight of Cr;
0.2-0.5% by weight of Mo;
0.5-3.7% by weight of Ni;
the remainder being iron and inevitable impurities;
b) hot rolling said steel at a predetermined temperature such as to obtain a seamless steel pipe;
c) continuously cooling the steel from the rolling temperature naturally in air or by a controlled cooling with an average cooling rate comprised between 0.10 and 1.0°
C. per second in order to obtain mainly bainitic structures.
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Abstract
A high strength bainitic steel and a process for producing seamless pipes for OCTG applications are described. In particular, the advantages ensuing to the steel of the invention are the improvement in strength-toughness over tempered martensitic steels, and a simplified thermal treatment. Quenching is not necessary and by avoiding the quenching treatment the microstructure results far more homogeneous, which allows thick walled tubes to be produced. For the same steel composition, in comparison to conventional tempered martensitic structures, a better combination of strength and toughness can be achieved, in particular by tempering as rolled carbide-free bainitic structures.
102 Citations
18 Claims
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1. Process for the production of high strength bainitic steel seamless pipes comprising the following steps:
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a) providing a steel having a composition comprising 0.2-0.4% by weight of C 0.05-1.5% by weight of Mn;
1.0-2.0% by weight of Si and 0-0.5% by weight of Al or, alternatively, 1.0-2.0% by weight of Al and 0-0.5% by weight of Si;
0.5-2.0% by weight of Cr;
0.2-0.5% by weight of Mo;
0.5-3.7% by weight of Ni;
the remainder being iron and inevitable impurities;b) hot rolling said steel at a predetermined temperature such as to obtain a seamless steel pipe; c) continuously cooling the steel from the rolling temperature naturally in air or by a controlled cooling with an average cooling rate comprised between 0.10 and 1.0°
C. per second in order to obtain mainly bainitic structures. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. High strength bainitic steel having the following composition:
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0.2-0.4% by weight of C; 0.05-1.5% by weight of Mn; 1.0-2.0% by weight of Si and 0-0.5% by weight of Al or, alternatively, 1.0-2.0% by weight of Al and 0-0.5% by weight of Si; 0.5-2.0% by weight of Cr; 0.2-0.5% by weight of Mo; 0.5-3.7% by weight of Ni; 0-0.005% by weight of S; 0-0.015% by weight of P; 0-0.005% by weight of O; 0-0.003% by weight of Ca; 0-0.01% by weight of N; 0-0.15% by weight of Cu; balanced iron and incidental impurities. - View Dependent Claims (16, 17)
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18. Use of a high strength bainitic steel having the following composition:
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0.2-0.4% by weight of C; 0.05-1.5% by weight of Mn; 1.0-2.0% by weight of Si and 0-0.5% by weight of Al or, alternatively, 1.0-2.0% by weight of Al and 0-0.5% by weight of Si; 0.5-2.0% by weight of Cr; 0.2-0.5% by weight of Mo; 0.5-3.7% by weight of Ni; 0-0.005% by weight of S; 0-0.015% by weight of P; 0-0.005% by weight of O; 0-0.003% by weight of Ca; 0-0.01% by weight of N; 0-0.15% by weight of Cu; balanced iron and incidental impurities, for the production of articles intended for OCTG applications.
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Specification