Title of Invention

METHOD OF MAKING STEEL STRIP AND STEEL STRIP PRODUCED BY SAID METHOD

Abstract Twin roll casting of thin steel strip. Molten steel is introduced between a pair of cooled casting rolls to form a casting pool from which steel solidifies on the rolls to produce a solidified strip. The molten steel has a total oxygen content in the range 100 ppm to 250 ppm and contains metal oxide inclusions comprising any one or more of MnO, SiO2 and Al2O3 distributed throughout the steel at an inclusion density in the range 2gm/cm3 to 4gm/cm3. Typically the inclusions range in size between 2 and 12 microns. The cast strip has a thickness of less than 5 mm and contains solidified metal oxide inclusions distributed such that the regions of the strip contain solidified inclusions to a per unit area density of at least 120 inclusions/mm2.
Full Text WE CLAIM:
1. A method of making a steel strip by continuous casting comprising the
steps of assembling a pair of cooled casting rolls having a nip between them and
with confining closures at adjacent ends of the nip;
introducing steel between the pair of casting rolls to form a casting pool between the casting rolls;
counter-rotating the casting rolls and solidifying the molten steel to form metal shells on the surface of the casting rolls; and
forming solidified thin steel strip through the nip of the casting rolls from the solidified shells;
characterised in that the molten steel is a low carbon steel having a carbon content in the range of 0.001% to 0.01% by weight, a manganese content in the range of 0.01% to 2.0% by weight, and a silicon content in the range of 0.01% to 10% by weight and having a total oxygen content of at least 100 ppm which steel solidifies to form said shells with oxide inclusions comprising any one or more of MnO, SiO2 and AI2O3 distributed through the steel at levels reflected by the total oxygen content to promote the formation of the thin steel strip.
2. A method of making steel strip as claimed in claim 1, wherein the molten steel in the casting pool has an aluminium content on the order of 0.01% or less by weight.
3. A method of making steel strip as claimed in claim 1 or claim 2, wherein the molten steel in the casting pool has an oxygen content between 100 ppm and 250 ppm.
4. A method of making steel strip as claimed in any one of the preceding claims, wherein the oxide inclusions are distributed through the steel at an inclusion density in the range 2 gm/cm3 to 4 gm/cm3.

5. A method of making steel strip as claimed in any one of the preceding claims, wherein more than a majority of the inclusions range in size between 2 and 12 microns.
6. A method of making steel strip as claimed in any one of the preceding claims, wherein the sulphur content of the molten steel is less than 0.01% by weight.
7. A method of making steep strip as claimed in Claim 1, wherein said including step includes refining the molten steel in a ladle prior to forming the casting pool by heating a steel charge and slag forming material in the ladle to form molten steel covered by a slag containing silicon, manganese and calcium oxides, stirring the molten steel in the ladle by injecting an inert gas into molten steel to cause desulphurisation, and thereafter injecting oxygen to produce molten steel having the total oxygen content of greater than 100 ppm.
8. A method of making steel strip as claimed in Claim 7, wherein the desulphurisation reduces the sulphur content of the molten steel to less than 0.01% by weight.
9. A method of making a thin steel strip as claimed in Claim 7 or 8, wherein the solidified steel is a silicon/manganese killed steel and the inclusions comprise any one or more of MnO, SiO2 and AI2O3.
10. A method of making a thin steel strip as claimed in any one of Claims 7 to 9, wherein more than a majority of the inclusions range in size between 2 and 12 microns.
11. A method of making a steel strip as claimed in any one of Claims 7 to 10, wherein the solidified steel has a total oxygen content in the range of 100 ppm to 250 ppm.

12. A thin steel strip produced by twin roll casting to a thickness of less than 5 mm and formed of a solidified low carbon steel having a carbon content in the range of 0.001% to 0.01% by weight, a manganese content in the range of 0.01% to 2.0% by weight and a silicon content in the range of 0.01% to 10% by weight and containing oxide inclusions comprising any one or more of MnO, SiO2 and AI2O3 distributed through the steel to reflect an oxygen content in the solidified steel in the range 100 ppm to 250 ppm.
13. A thin steel strip as claimed in claim 12, wherein the majority of the inclusions range in size between 2 and 12 microns.
14. A thin steel strip as claimed in claim 12 or claim 13, wherein the solidified oxide inclusions are distributed such that surface regions of the strip to a depth of 2 microns from the surface contain such inclusions to a per unit area density of at least 120 inclusions/mm2.

Documents:

953-delnp-2004-Abstract (09-11-2009).pdf

953-delnp-2004-abstract.pdf

953-delnp-2004-amended sheet.pdf

953-delnp-2004-Claims (09-11-2009).pdf

953-delnp-2004-claims.pdf

953-delnp-2004-Correspondence-Others (09-11-2009).pdf

953-delnp-2004-correspondence.pdf

953-delnp-2004-Description (Complete) (09-11-2009).pdf

953-delnp-2004-description.pdf

953-DELNP-2004-Drawings (09-11-2009).pdf

953-delnp-2004-drawings.pdf

953-delnp-2004-Form-1 (09-11-2009).pdf

953-delnp-2004-Form-2 (09-11-2009).pdf

953-delnp-2004-form1.pdf

953-delnp-2004-form2.pdf

953-delnp-2004-form26.pdf

953-delnp-2004-form3.pdf

953-delnp-2004-form5.pdf

953-delnp-2004-pct-ipea-409.pdf

953-delnp-2004-pct-isa-210.pdf

953-delnp-2004-pct-pamphlet a1.pdf

953-delnp-2004-Petition-137 (09-11-2009).pdf


Patent Number 239273
Indian Patent Application Number 953/DELNP/2004
PG Journal Number 12/2010
Publication Date 19-Mar-2010
Grant Date 15-Mar-2010
Date of Filing 12-Apr-2004
Name of Patentee NUCOR CORPORATION
Applicant Address 2100 Rexford Road, Charlotte,
Inventors:
# Inventor's Name Inventor's Address
1 BLEJDE, WALTER 67 Lakeshore Circle, Brownsburg,
2 MAHAPATRA, RAMA BALLAV 5451 Elkhorn Drive, Apartment 1027,
3 STREZOV, LAZAR 7 Marin Street, Adamstown Heights,
PCT International Classification Number C22C
PCT International Application Number PCT/AU02/01257
PCT International Filing date 2002-09-13
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/322,261 2001-09-14 U.S.A.