BAINITIC STEELS WITH BORON
First Claim
Patent Images
1. A method of making a steel pipe, comprising:
- providing a steel composition comprising;
about 0.04-0.12 wt. % carbon (C);
about 0.01 to 0.03 wt. % titanium (Ti);
about 0.0005 to 0.003 wt. % boron (B); and
less than or equal to about 0.008 wt. % nitrogen (N);
the concentration of each element being based upon the total weight of the steel composition;
wherein about 0.0005 to 0.002 wt. % boron is in solid solution for improving hardenability;
wherein substantially all of the nitrogen is present in the form TiN particles to avoid the formation of boron nitrides and achieve said boron content in solid solution, andcooling a bar cast from the steel composition, wherein the cooling rate at about the center of the bar is selected such that TiN particles formed in the bar exhibit a mean diameter less than about 50 nm; and
forming a pipe from the bar;
wherein the yield strength of the steel pipe, measured according to ASTM E8, is greater than about 100 ksi (690 MPa).
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Abstract
Steel compositions contain micro-alloying additions of boron and titanium, with yield strength of at least 100 ksi (690 MPa), excellent toughness and good weldability. Boron additions are used to increase hardenability. Strong nitride formers, such as titanium, may be added to the steel composition in order to prevent boron nitrides from forming. These compositions may be cooled from hot rolling in air or using accelerated cooling. After air cooling, the composition may be quenched or quenched and tempered. The compositions are suitable for high strength line pipes (for example, X100 in API 5L standard) and other applications.
64 Citations
26 Claims
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1. A method of making a steel pipe, comprising:
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providing a steel composition comprising; about 0.04-0.12 wt. % carbon (C); about 0.01 to 0.03 wt. % titanium (Ti); about 0.0005 to 0.003 wt. % boron (B); and less than or equal to about 0.008 wt. % nitrogen (N); the concentration of each element being based upon the total weight of the steel composition; wherein about 0.0005 to 0.002 wt. % boron is in solid solution for improving hardenability; wherein substantially all of the nitrogen is present in the form TiN particles to avoid the formation of boron nitrides and achieve said boron content in solid solution, and cooling a bar cast from the steel composition, wherein the cooling rate at about the center of the bar is selected such that TiN particles formed in the bar exhibit a mean diameter less than about 50 nm; and forming a pipe from the bar; wherein the yield strength of the steel pipe, measured according to ASTM E8, is greater than about 100 ksi (690 MPa). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of making a steel composition, comprising:
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providing a steel composition comprising; about 0.04 to 0.12 wt. % carbon (C); about 0.8 to 1.6 wt. % manganese (Mn); about 0.05 to 0.3 wt. % silicon (Si); less than or equal to about 0.5 wt. % nickel (Ni); less than or equal to about 0.5 wt. % chromium (Cr); less than or equal to about 0.5 wt. % molybdenum (Mo); less than or equal to about 0.15 wt. % vanadium (V); less than or equal to about 0.05 wt. % niobium (Nb); about 0.01 to 0.03 wt. % titanium (Ti); about 0.0005 to 0.0030 wt. % boron (B); and less than or equal to 0.008 wt. % nitrogen (N); wherein the concentration of each element is based upon the total weight of the steel composition and wherein about 0.0005 to 0.002 wt. % boron is kept in solid solution for improving hardenability; casting the steel composition, wherein substantially all of the nitrogen in the cast steel composition is present in the form of TiN particles having a size less than about 50 nm to avoid the formation of boron nitrides and achieve said boron content in solid solution; hot rolling the cast steel composition; and cooling the cast steel composition directly after hot rolling at a rate between about 5 to 50°
C./sec. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of making a steel composition, comprising:
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providing a steel composition comprising; about 0.04-0.12 wt. % carbon (C); about 0.8 to 1.6 wt. % manganese (Mn); about 0.05 to 0.3 wt. % silicon (Si); less than or equal to about 0.5 wt. % nickel (Ni); less than or equal to about 0.5 wt. % chromium (Cr); less than or equal to about 0.5 wt. % molybdenum (Mo); less than or equal to about 0.15 wt. % vanadium (V); less than or equal to about 0.05 wt. % niobium (Nb); about 0.01 to 0.03 wt. % titanium (Ti); about 0.0005-0.0030 wt. % boron (B); and less than or equal to 0.008 wt. % nitrogen (N); wherein the concentration of each element is based upon the total weight of the steel composition; wherein about 0.0005 to 0.002 wt. % boron is kept in solid solution for improving hardenability; casting the steel composition, wherein substantially all of the nitrogen in the cast steel composition is present in the form of TiN particles having a size less than about 50 nm to avoid the formation of boron nitrides and achieve said boron content in solid solution; hot rolling the cast steel composition; air cooling the formed steel composition directly after hot rolling at a rate less than about 1°
C./sec; andaustenizing and quenching the composition. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26)
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Specification