Title of Invention

PRECAST STEEL COMPOSITION AND PROCESS FOR MANUFACTURE OF ARMOUR STEEL PLATES USING THE SAME.

Abstract

Pre-cast composition and a process for manufacture of steel plates with yield strength of atleast about 150 kg/mm2, ultimate tensile strength of atleast about 170 kg/mm2, and elongation atleast about 5% with thickness in the range of about 3-6 mm. Such steel plates are obtained of a selective pre-cast steel composition comprising Carbon in the range of 0.3 to 0.35 wt% preferably 0.30 wt%, Mn in the range of 0.8 to 1.0 wt% preferably 0.80 wt%, Si in the range of 0.7 to 1.0 wt% preferably 0.7wt%, Cr in the range of 0.8 to 1.1 wt% preferably 0.80 wt%, Mo in the range of 0.25 to 0.40 wt% preferably 0.25 wt%, S in the range of upto 0.01 wt% , P in the range of upto 0.015 wt% , Al in the range of 0.02 to 0.04 wt% preferably 0.02 max, H2 in the range of upto 2.5 ppm max. The steel composition is useful as bulletproof safety appliances and for patrolling vehicles especially as armour steels. Other applications of armour steel include manufacture of safety bunkers for army personnel and safety screens for police for protection against rioting mobs. The above steel composition and its process of manufacture avoids the problems and disadvantages associated with the manufacture of armour plates such as higher decarburisation during soft annealing before heat treatment and internal defects, which are responsible for piercing of bullets and fracture in steel plates thereby making the process more cost effective and designed. The steel obtained is also easy to weld if required and free from harmful oxides.

Full Text

FIELD OF THE INVENTION The present invention relates to pre-cast composition and a process for manufacture of steel plates in particular, to pre-cast composition and manufacture of steel plates with yield strength of atleast about 150 kg/mm2, ultimate tensile strength of atleast about 170 Kg/mm2, and elongation atleast about 5% with thickness in the range of about 3-6 mm. Importantly, the steel plates produced by the process are useful as bulletprroof safety appliances and for patrolling vehicles and are conventionally known as armour steels. Other applications of armour steel include manufacture of safety bunkers for army personnel and safety screens for police for protection against rioting mobs. US 5458704 relates to a process for the production of very hard armour plates from steel slabs, wherein the slabs are hot rolled to a final thickness above 50 mm and then hardened and possibly tempered. FR 2619577 A1 relates to steel composition containing silicon-chromium- molybdenum-vanadium which is specifically directed to application to piercing cores of armour-piercing projectiles. DE 3735715 A1 relates to armour plate for strongboxes, safes, burglar-proof wall claddings and the like and process for producing it. It involves a perforated plate fastened on a base plate. One or more hard particles are inserted into the chambers formed by the holes of the perforated plate. Moreover, these chambers are filled partially or completely with a metal powder. A covering layer consisting of high-alloy rust-resistant or carbide-containing material is applied over the perforated plate and its holes by build-up welding. During this build-up welding, the powder cakes a little in the chambers, but without the hard particles contained therein being embedded with complete firmness. DE 3820342 A1 also relates to armour plate for strongboxes, safes, burglar-proof wall claddings or the like, a perforated sheet is arranged between an outward- facing cover sheet made of special steel proof against oxyacetylene cutting and a baseplate. The cavities limited by these three components are filled alternately with two different layered structures : the first layered structure comprises a first later adjacent to the cover sheet and consisting of high-alloy, stainless or carbide- containing material (called the "wearing layer" in brief), a layer located above it and consisting of hard-metal particles and a second wearing layer which is welded over the layer of hard-metal particles. The second layered structure II likewise comprises a first wearing layer which is applied to the cover sheet, but over which a small ceramic plate then lies. This is covered, in turn, by a second wearing layer. The armour plate thus constructed successfully withstands even the attack of highly specialised grinding tools. DE 4125100 A1 discloses an armour plate obtained of a ductile carrier plate made of high strength steel and a layer contg. Cr-Ni alloy and hard material. The plate is relatively thin and light. DRAWBACKS OF THE INVENTION Most of the above prior art on manufacture of armour steel plates are directed to manufacture of thick armour plates which some of the other known prior art are related to production of armour piercing cores and to manufacturing of burglar- proof strong boxes using cladded steel and ceramic plates. Importantly, most of the armour plates manufacturing process discussed above include higher decarburisation during soft annealing before heat treatment and lead to internal defects, which are responsible for piercing of bullets and fracture in steel plates. Also, the majority of the armour steel plates are produced in a batch prpcess and are batch rolled in a piece mill and soft annealed in furnace thus resulting in decarburisation of surface layers. Apart from limitations of thickness variation along length and width of such armour steel plate productions, the conventional processes also result in precipitation of harmful oxides of alloying elements in the steel. OBJECTS OF THE INVENTION It is thus the basic objective of the present invention to provide for armour steel which would have the desired high yield strength, tensile strength and also elongation characteristics at a lower thickness in the range of 3-6 mm thus providing for thin armour plates. Another object of the present invention is to provide for simple and cost effective process for manufacture of thin armour plates which would have the desired strength and characteristics. Yet further object of the present invention is to avoid the problems and disadvantages associated with the manufacture of armour plates such as higher decarburisation during soft annealing before heat treatment and internal defects, which are responsible for piercing of bullets and fracture in steel plates thereby making the process more cost effective and designed. Yet another object of the present invention is to provide for a process for manufacture of thin armour plate in the range of 3-6 mm thickness and would provide for continuous process for manufacture of armour steel plates not known in the art. Yet another object of the present invention is directed to provide for thin armour plates with required characteristics and strength involving use of leaner chemistry thinner armour plate production not known in the art before. Thus according to one aspect of the present invention there is provided a precast steel composition for use in manufacture of armour plates and the like comprising: Carbon in the range of 0.3 to 0.35 wt% preferably 0.30 wt% Mn in the range of 0.8 to 1.0 wt% preferably 0.80 wt% Si in the range of 0.7 to 1.0 wt% preferably 0.7wt% Cr in the range of 0.8 to 1.1 wt% preferably 0.80 wt% Mo in the range of 0.25 to 0.40 wt% preferably 0.25 wt% S in the range of upto 0.01 wt% P in the range of upto 0.015 wt% Al in the range of 0.02 to 0.04 wt% preferably 0.02 max H2 in the range of upto 2.5 ppm max. In the above disclosed composition is selectively provided to produce steel therefrom having a yield strength of atleast 150 kg/mm2, ultimate tensile strength of atleast 180 kg/mm2 and elongation of atleast 5%. Steel plates can be obtained of the above composition in large sizes such as about 1050 mm wide and up to 6000mm length. This helps in reducing weld joints during manufacture and achieving proper armour quality and character. Preferably, the steel plates such as armour steel plates obtained of the above composition have a thickness of 3-6 mm, length of 2-6 meters and width of 1050 mm. The steel obtained of the above composition is suitable for use as armour steel which is also easy to weld if required and free from harmful oxides. In accordance with another aspect there is provided a process for manufacture of armour steel with high yield strength of atleast 150kg/mm2, ultimate tensile strength of atleast 170kg/mm2 and elongation atleast 5% comprising: - providing a selective pre cast steel composition; - casting the said liquid steel composition; - hot rolling the thus cast steel; - self annealing to control de-carburization; and finally - subjecting the same to heat treatment of quenching and tempering. In particular, in accordance with a preferred aspect of the present invention there is provided a process for manufacture of the armpur steel comprising : i. providing a selective pre-cast composition comprising : Carbon in the range of 0.3 to 0.35 wt% preferably 0.30 wt% Mn in the range of 0.8 to 1.0 wt% preferably 0.80 wt% Si in the range of 0.7 to 1.0 wt% preferably 0.7wt% Cr in the range of 0.8 to 1.1 wt% preferably 0.80 wt% Mo in the range of 0.25 to 0.40 wt% preferably 0.25 wt% S in the range of upto 0.01 wt% P in the range of upto 0.015 wt% Al in the range of 0.02 to 0.04 wt% preferably 0.02 max. H2 in the range of upto 2.5 ppm max ii. casting of the liquid steel composition; iii. hot rolling preferably, in continuous mill for better gauge control; iv. self-annealing for controlling decarburisation; and v. heat treatment to thereby obtain the armour plate. THE DETAILED DESCRIPTION The above disclosed steel of the invention is suitable for application as armour steel include manufacturing of safety bunkers for army personnel and safety screens for police for protection against rioting mobs. Importantly, the process of obtaining the armour steel of the invention provides for achieving desired quality and character of steel with thickness in the range of 3-6 mm. The prior art on the subject deal mostly with the manufacturing of thicker armour plates. It may be noted that steel plates of the invention are used in thickness of 3-6 mm, thus putting them in the category of thinner armour plates. Also, the armour plate manufacturing processes include step of self annealing to control decarburisation and avoids problems of internal defects, which are responsible for piercing of bullets and fracture in steel plates. Also, the armour steel plates of the invention are produced in a continuous process thus avoiding limitations of batch process. The steel of the invention effectively uses leaner chemistry for thinner armour plate production. Higher coiling temperatures are employed during stacking of coils to take advantage of their "self annealing effect" to minimize decarburisation in the product and heat treatment of plate to achieve a good impact resistance against the bullets. No separate soft annealing step is carried out in this process. The comparative process flow diagrams for process according to the invention and other known process as illustrated in Fig. 1. The steel plates of the invention have a new composition and are hot rolled in a continuous mill with better gauge control. The hot rolled coils are self annealed as against conventional armour steel plates which are batch rolled in a piece mill and are soft annealed in a furnace, thus resulting in the decarburisation of surface layers. In particular, the advantages flowing from the process of the invention are as follows: i. Steel can be rolled in 5 stand hot rolling mill under strict control of finishing and coiling temperatures. Roll crown and profile at different stands and temperature gradient across the work rolls has been controlled. This has reduced the variation in thickness along the width and length of the coil. ii. Coiling temperature is kept sufficiently high to enable pack annealing of coils to minimize the decarburization on the surface of the plates. Thus, the effective thickness of the plate does not reduce. iii. Steel has sufficiently high strength and toughness as compared to other bullet-proof steels, available in the market. Due to high strength and toughness, steel plates in 5 mm thickness are adapted to stop bullets of SLR 7.62 rifle from a distance of 10 meter distance at 90° impact. iv. Steel plates can be produced in large sizes such as 1050mm wide and up to 6000 mm in length. This reduces weld joints while using the steel plates for bullet proofing the patrolling vehicles. v. Surface of the plates is free from pits, holes and other harmful surface defects. The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to non- limiting exemplary illustrations as per examples discussed hereunder: Example 1: The armour steel was obtained in accordance with present invention is discussed hereunder: The steel composition was selectively used comprising Carbon 0.30, Mn 0.80, Si 0.7, Cr 0.80, Mo 0.25, S 0.01 max. P 0.015 max, Al 0.02 and H22.5 ppm max. The above steel was subjected to casting followed by hot rolling in a continuous mill to facilitate desired gauge control. After the rolling step the steel was subjected to self annealing to control de-carburization to the extent of less than 2%. Finally, after the step of self annealing steel was subjected to heat treatment involving quenching and tempering. Example 2: Under this example, the conventional process of manufacture of armour was followed. For the purpose, steel composition was provided which was next subjected to step of casting followed by hot rolling piece mill, furnace annealing and finally heat treatment to obtain the desired product. The comparative end properties of the steel manufacture following the process under Example 1 of the invention and that following conventional process under Example 2 was next studied and the results are reproduced hereunder in Table I: As would be evident from the above properties of the steel obtained, the process of the invention is superior in terms of light weight and at the same time achieving higher yield strength, ultimate tensile strength and percentage elongation. The Steel plates of the invention are light weight and can resist the bullets of SLR 7.62 compared to other armour plate. • It is thus possible by way of present invention to provide armour plates with greater protections inspite of lighter weight as compared to other similar armour materials. Further comparative studies are carried out on the steel obtained in accordance with the invention (Example 1) and the known armour steel plates and the results are provided in Table II hereunder: Star stands for threat level * First degree ** Second degre6 *** Third degree. As would be evident from the above the steel of the invention offer greater protection inspite of lighter weight as compared to other similar amour materials. We Claim: . 1. A pre-cast steel composition for use in manufacture of armour plates and the like comprising: Carbon in the range of 0.3 to 0.35 wt% preferably 0.30 wt% Mn in the range of 0.8 to 1.0 wt% preferably 0.80 wt% Si in the range of 0.7 to 1.0 wt% preferably 0.7wt% Cr in the range of 0.8 to 1.1 wt% preferably 0.80 wt% Mo in the range of 0.25 to 0.40 wt% preferably 0.25 wt% S in the range of up to 0.01 wt% P in the range of up to 0.015 wt% Al in the range of 0.02 to 0.04 wt% preferably 0.02 max H2 in the range of up to 2.5 ppm max. 2. A pre-cast steel composition as claimed in claim 1 wherein the composition is selectively provided to produce steel there from having yield strength of at least 150 kg/mm2, ultimate tensile strength of at least 180 kg/mm2 and elongation of at least 5%. 3. A pre-cast steel composition as claimed in anyone one of claims 1 or 2 for producing steel armour plates preferably having a thickness of 3-6 mm length of 2-6 meters and width of 1050 mm. 4. A process for the manufacture of steel plates with high yield strength of atleast 150kg/mm2, ultimate tensile strength of at least 170kg/mm2 and elongation atleast 5% comprising: - providing a selective pre-cast steel composition as claimed in claim 1; - casting the said liquid steel composition; - hot rolling the thus cast steel; - self annealing to control de-carburization; and finally - subjecting the same to heat treatment of quenching and tempering. 5. A process as claimed in claim 4 comprising: i. providing a selective pre-cast composition comprising: Carbon in the range of 0.3 to 0.35 wt% preferably 0.30 wt% Mn in the range of 0.8 to 1.0 wt% preferably 0.80 wt% Si in the range of 0.7 to 1.0 wt% preferably 0.7wt% Cr in the range of 0.8 to 1.1 wt% preferably 0.80 wt% Mo in the range of 0.25 to 0.40 wt% preferably 0.25 wt% S in the range of upto 0.01 wt% P in the range of upto 0.015 wt% Al in the range of 0.02 to 0.04 wt% preferably 0.02 max H2 in the range of upto 2.5 ppm max. ii. casting of the liquid steel composition; iii. hot rolling preferably, in continuous mill for better gauge control; iv. self-annealing for controlling decarburisation; and v. heat treating to thereby obtain the armour plate. 6. A process as claimed in claim 5 wherein said steel is rolled in 5 stand hot rolling mill preferably 5 stand rolling mill under control of finishing and coiling temperatures. 7. A precast steel composition for use in manufacture of armour plates and a process of manufacture using the same substantially as herein described and illustrated with reference to the accompanying examples. Pre-cast composition and a process for manufacture of steel plates with yield strength of atleast about 150 kg/mm2, ultimate tensile strength of atleast about 170 kg/mm2, and elongation atleast about 5% with thickness in the range of about 3-6 mm. Such steel plates are obtained of a selective pre-cast steel composition comprising Carbon in the range of 0.3 to 0.35 wt% preferably 0.30 wt%, Mn in the range of 0.8 to 1.0 wt% preferably 0.80 wt%, Si in the range of 0.7 to 1.0 wt% preferably 0.7wt%, Cr in the range of 0.8 to 1.1 wt% preferably 0.80 wt%, Mo in the range of 0.25 to 0.40 wt% preferably 0.25 wt%, S in the range of upto 0.01 wt% , P in the range of upto 0.015 wt% , Al in the range of 0.02 to 0.04 wt% preferably 0.02 max, H2 in the range of upto 2.5 ppm max. The steel composition is useful as bulletproof safety appliances and for patrolling vehicles especially as armour steels. Other applications of armour steel include manufacture of safety bunkers for army personnel and safety screens for police for protection against rioting mobs. The above steel composition and its process of manufacture avoids the problems and disadvantages associated with the manufacture of armour plates such as higher decarburisation during soft annealing before heat treatment and internal defects, which are responsible for piercing of bullets and fracture in steel plates thereby making the process more cost effective and designed. The steel obtained is also easy to weld if required and free from harmful oxides.

Documents:

676-cal-2001-granted-abstract.pdf

676-cal-2001-granted-claims.pdf

676-cal-2001-granted-correspondence.pdf

676-cal-2001-granted-description (complete).pdf

676-cal-2001-granted-drawings.pdf

676-cal-2001-granted-examination report.pdf

676-cal-2001-granted-form 1.pdf

676-cal-2001-granted-form 2.pdf

676-cal-2001-granted-form 3.pdf

676-cal-2001-granted-pa.pdf

676-cal-2001-granted-reply to examination report.pdf

676-cal-2001-granted-specification.pdf