Title of Invention	A PROCESS FOR PRODUCING NOVEL ALLOY STEEL OF IMPROVED TENSILE STRENGTH
Abstract	This invention relates to a new process for producing novel alloy steel of improved tensile strength Niobium is inoculated into the alloy melt which is subsequently refined electroslag treatment. The alloy steel obtained by this process may be tempered by heat treatment.

Full Text

This invention relates to a process for producing novel alloy steel of improved tensile strength. Alloy steel is a steel to which elements not present in carbon steel have been added or in which the manganese or silicon content is increased above that in the normal carbon steel. High strength alloy steel is used to build motorcases for satellite launch vehicles. Alloy steel is also used for constructing strap-on motors of launch vehicles. The tensile strength of the steel hitherto used in the art is about lOOOMPa and a 0.2% proof strength of 850MPa. However, present generation satellite launch vehicles require steel with higher or better tensile strength. The quest for high tensile strength alloy steel which may be used to construct solid booster motorcases of launch vehicles resulted in the development of the subject invention. The chemical composition of the new high tensile strength alloy steel is given below: Carbon 0.27 to 0.31% Manganese 0.80 to 1.00% Molybdenum 0.80 to 1.00% Vanadium 0.20 to 0.30% Chromium 1.20 to 1.50% Niobium 0.08 to 0.12% Silicon 0.25% Max. Sulphur 0.015% max. Phosphorous 0.020% max. the balance being Fe. The charge materials consisting of required ferro alloys and clean mild steel scrap are subjected to electric arc or induction melting. The melt is then transferred to a ladle to which Niobium or ferro-niobium lumps are added. The melt is stirred well by bottom purging using argon gas to effect uniform distribution of the inoculant, Niobium. This inoculated melt is then cast into ingots of the desired size and shape and are called primary ingots. The primary ingots are melted in an electric furnace and is subjected to conventional electroslag refining process. The top slag is removed, to clean the steel of extraneous and undesired impurities. The clean melt is then solidified in water cooled molds. The sequence followed according to our invention is electric arc melting of the alloy making components other than Niobium, ladle inoculation of Niobium and electros lag refining technique for further refining and purifying the alloy. The alloy steel produced may be subjected to conventional heat-treatment for hardening and tempering. Hardening is carried out at a temperature of about 920°C which is followed by tempering at 150°C, 200°C, 300°C, 450°C, 500°C and 600°C. Grain size of the alloy thus obtained is found to be in the order of up to 7 to 10 microns in diameter. The alloy steel made by this process exhibits strength levels exceeding 1650 MPa which is one of the major advantages of this invention. Further, agitation during Niobium inoculation prior to refining step results in uniform micrograins. Strength and toughness qualities are also improved due to the inoculation of Niobium. This invention relates to a process for producing novel alloy steel of improved tensile strength having a chemical composition of: Carbon 0.27 to 0.31% Manganese 0.80 to 1.00% Molybdenum 0.80 to 1.00% Vanadium 0.20 to 0.30% Chromium 1.20 to 1.50% Niobium 0.08 to 0.12% Silicon 0.25% Max. Sulphur 0.015% max. Phosphorous 0.020%) max. the balance being iron which comprises the steps of melting a charge of the desired alloy making components other than Niobium, inoculating said melt with Niobium, heating said inoculated alloy in an electric furnace and removing the slag from the resultant melt to obtain alloy steel of high tensile strength. The percentage of the alloy making component required for primary melt may be regulated by known means or techniques. Though this invention has been described hereinabove with respect to a specific embodiment, obvious alterations and modifications known to persons skilled in the art are within its scope and that of the appended claims. WE CLAIM; 1. A process for producing novel alloy steel of improved tensile strength having a chemical composition of: Carbon 0.21 to 0.31% Manganese 0.80 to 1.00% Molybdenum 0.80 to 1.00% Vanadium 0.20 to 0.30% Chromium 1.20 to 1.50% Niobium 0.08 to 0.12% Silicon 0.25% Max. Sulphur 0.015% max. Phosphorous 0.020% max. the balance being iron comprising the steps of melting a charge of the desired alloy making components other than Niobium, inoculating said melt with Niobium, heating said inoculated alloy in an electric furnace and removing the slag from the resultant melt to obtain alloy steel of high tensile strength. 2. The process as claimed in claim 1, wherein the charge is melted in an electric arc furnace and the melt is transferred to a ladle. 3. The process as claimed in claim 2, wherein Niobium is inoculated to the melt in the ladle. 4. The process as claimed in claims 1 to 3, wherein the charge consists of ferroalloys and clear mild steel scraps. 5. The process as claimed in claims 1 to 4, wherein Niobium is inoculated as Ferro-Niobium. 6. The process as claimed in claim 5, wherein the melt is agitated by passing argon gas therethrough. 7. The process as claimed in any of the preceding claims wherein said melt obtained after inoculating with Niobium is cast into ingots. 8. The process as claimed in claim 7, wherein said ingot is melted in an electric furnace for electroslag refining. 9. The process as claimed in claim 8, wherein the melt after slag removal is cast into ingots. 10. The process as claimed in any of the preceding claims wherein said alloy steel is tempered by heat treatment. 11. The process as claimed in claim 10, wherein said alloy is heated to 950°C and then cooled to 150°C to 650°C for hardening and tempering said alloy steel. 12. A process for producing novel alloy steel of improved tensile strength substantially as herein described.

Documents:

0870-mas-1999 abstract.pdf

0870-mas-1999 claims-duplicate.pdf

0870-mas-1999 claims.pdf

0870-mas-1999 correspondence-others.pdf

0870-mas-1999 correspondence-po.pdf

0870-mas-1999 description (complete)-duplicate.pdf

0870-mas-1999 description (complete).pdf

0870-mas-1999 form-1.pdf

0870-mas-1999 form-26.pdf

0870-mas-1999 form-3.pdf

0870-mas-1999 form-8.pdf