| Title of Invention | "A METHOD FOR PREPARING A STEEL PLATE HAVING A MICRO-LAMINATE MICROSTRUCTURE" |
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| Abstract | An ultra-high strength, weldable, low alloy steel with excellent cryogenic temperature toughness in the base plate and in the heat affected zone (HAZ) when welded, having a tensile strength greater than 830 MPa (120 ksi) and a micro-laminate microstrucrure comprising austenite film layers and fine-grained martensite/lower bainite laths, is prepared by heating a steel slab comprising iron and specified weight percentages of some or all of the additives carbon, manganese, nickel, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum, and boron; reducing the slab to form plate in one or more passes in a temperature range in which austenite recrystallizes; finish rolling the plate in one or more passes in a temperature range below the austenite recrystallization temperature and above the Ara transformation temperature; quenching the finish rolled plate to a suitable Quench Stop Temperature (QST); stopping the quenching; and either, for a period of time, holding the plate substantially isothermally at the QST or slow-cooling the plate before air cooling, or simply air cooling the plate to ambient temperature |
| Full Text | CLAIM: 1. A method for preparing a steel plate having a micro-laminate microstructure comprising about 2 vol% to about 10 vol% of austenite film layers and about 90 vol% to about 98 vol% laths of predominantly fine-grained martensite and fine-grained lower bainite, said method comprising the steps of: (a) heating a steel slab to a reheating temperature sufficiently high to (i) substantially homogenize said steel slab, (ii) dissolve substantially all carbides and carbonitrides of niobium and vanadium in said steel slab, and (iii) establish fine initial austenite grains in said steel slab; (b) reducing said steel slab to form steel plate in one or more hot rolling passes in a first temperature range in which austenite recrystallizes; (c) further reducing said steel plate in one or more hot rolling passes in a second temperature range below about the Tnr temperature and above about the Ar3 transformation temperature; (d) quenching said steel plate at a cooling rate of about 10°C per second to about 40°C per second (I8°F/sec -72°F/sec) to a Quench Stop Temperature below about the Ms transformation temperature plus 100°C (180oC ) and above about the Ms transformation temperature; and (e) stopping said quenching, so as to facilitate transformation of said steel plate to a micro-laminate microstructure of about 2 vol% to about 10 vol% of austenite film layers and about 90 vol% to about 98 vol% laths of predominantly fine-grained martensite and fine-grained lower bainite. 2. The method as claimed in claim 1, wherein said reheating temperature of step (a) is between about 955°C and about 1065°C (17500F-1950°F). 3. The method as claimed in claim 1, wherein said fine initial austenite grains of step (a) have a grain size of less than about 120 microns. 4. The method as claimed in claim 1, wherein a reduction in thickness of said steel slab of about 30% to about 70% occurs in step (b). 5. The method as claimed in claim 1, wherein a reduction in thickness of said steel plate of about 40% to about 80% occurs in step (c). 6. The method as claimed in claim 1 wherein step (e) includes allowing said steel plate to air cool to ambient temperature from said Quench Stop Temperature. 7. The method as claimed in claim 1, wherein step (e) includes holding said steel plate substantially isothermally at said Quench Stop Temperature for up to about 5 minutes. 8. The method as claimed in claim 1, wherein step (e) includes slow-cooling said steel plate at said Quench Stop Temperature at a rate lower than about 1.0° C per second (1.8° F/sec) for up to about 5 minutes. 9. The method as claimed in claim 1, wherein said steel slab of step (a) comprises iron and the following alloying elements in the weight percents indicated: about 0.04% to about 0.12% C, at least about 1 % Ni, about 0.1 % to about 1.0% Cu, about 0.1 % to about 0.8% Mo, about 0.02% to about 0.1 % Nb, about 0.008% to about 0.03% Ti, about 0.001 % to about 0.05% AI, and about 0.002% to about 0.005% N. 10. The method as claimed in claim 9, wherein said steel slab comprises less than about 6 wt% Ni. 11. The method as claimed in claim 9 wherein said steel slab comprises less than about 3 wt% Ni and additionally comprises about 0.5 wt% to about 2.5 wt% Mn. 12. The method as claimed in claim 1, wherein said steel slab of step (a) comprises iron and the following alloying elements in the weight percents indicated about 0.04% to about 0.12% C, at least about 1% to about 1.0% Cu, about 0.02% to about 0.1%Nb, about 0.008% to about 0.03% Ti, about 0.001% to about 0.05% Al, about 0.002% to about 0.005% N, and at least one additive selected from the group consisting of (i) up to about 1.0% Cr, (ii) up to about 0.5% Si, (iii) about 0.02% to about 0.10% V, and (iv) up to about 2.5% Mn. 13. The method as claimed in claim 9, wherein said steel slab of step (a) comprises iron and the following alloying elements in the weight percents indicated: about 0.04% to about 0.12% C, at least about 1% Ni, about 0.1% to about 1.0% Cu, about 0.1% to about 0.8% Mo, about .02% to about 0.1% Nb, about 0.008% to about 0.03% Ti, about 0.001% to about 0.05% Al, about 0.002% to about 0.005% N, and about 0.0004% to about 0.0020 % B. 14. The method as claimed in claim 1 wherein, after step ( e), said steel plate has a DBTT lower than about -730C(-100°F) in both said baseplate and its HAZ and has a tensile strength greater than 830 MPa(120 ksi). 15. A method for enhancing the crack propagation resistance of a steel plate, said method comprising processing said steel plate to produce a micro-laminate microstructure comprising about 2 vol% to about 10 vol% of austenite film layers and about 90 vol% to about 98 vol% laths of predominantly fine-grained martensite and fine-grained lower bainite, said micro-laminate microstructure being optimized to substantially maximize crack path tortuosity by thermo-mechanical controlled rolling processing that provides a plurality of high angle interfaces between said laths of fine-grained martensite and frne- grained lower bainite and said austenite film layers. 15. The method as claimed in claim 14, wherein said crack propagation resistance of said steel plate is further enhanced, and crack propagation resistance of the HAZ of said steel plate when welded is enhanced, by adding at least about 1.0 wt% Ni and at least about 0.1 wt% Cu, and by substantially minimizing addition of BCC stabilizing elements. 16. A method for preparing a steel plate substantially as herein described with reference to the accompanying drawings. |
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1713-del-1998-Correspondence-Others-(02-05-2011).pdf
1713-del-1998-correspondence-others.pdf
1713-del-1998-correspondence-po.pdf
1713-DEL-1998-Description (Complete).pdf
1713-del-1998-Form-27-(02-05-2011).pdf
1713-del-1998-Petition 138-(02-05-2011).pdf
1713-del-1998-petition-137.pdf
1713-del-1998-petition-138.pdf
| Patent Number | 216758 | ||||||||||||
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| Indian Patent Application Number | 1713/DEL/1998 | ||||||||||||
| PG Journal Number | 13/2008 | ||||||||||||
| Publication Date | 31-Mar-2008 | ||||||||||||
| Grant Date | 19-Mar-2008 | ||||||||||||
| Date of Filing | 18-Jun-1998 | ||||||||||||
| Name of Patentee | EXXONMOBIL UPSTREAM RESEARCH COMPANY, | ||||||||||||
| Applicant Address | 100 WEST 10TH STREET, CITY OF WILMINGTON, COUNTY OF NEW CASTLE, UNITED STATES OF AMERICA | ||||||||||||
Inventors:
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| PCT International Classification Number | C21D 8/00 | ||||||||||||
| PCT International Application Number | N/A | ||||||||||||
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PCT Conventions:
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