TECHNICAL FIELD

[0001] The present disclosure relates generally to the technical field of ferrous metallurgy. In particular, the present disclosure pertains to a high strength armour steel plate with hardness 470-520 BHN, and method for production thereof.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Armour plate has found utility in both civilian and military uses to provide protection of objects against damage. Historically, armour plate has been produced from various materials, including ceramics, metals, such as steel and aluminium, as well as composites of metals and other materials. Improvements in armour plate are required to provide greater ballistic protection while providing a more light-weight armour plate.
[0004] At present, generally, steel or steel alloys have been used as the material for armour plates. Armour steel plates have high resistance to bending, shear and crushing forces. Vehicles such as tanks, military sites, vaults etc. have used steel armour plates to provide such protection. Besides, in daily life, there is also need of the armour steel plates to be manufactured into bulletproof doors, bulletproof helmets, bulletproof vests and bulletproof shields which have bullet-proofing and shooting-proofing functions, or to be manufactured into bulletproof components of devices such as bank counters, confidential safes, anti-riot vehicles, bulletproof cash carriers, submarines, landing crafts, anti-smuggling vessels, helicopters. The existing typical steel armour plates have disadvantages such as their manufacturing is expensive, and their specific weight (density) is high.
[0005] There is, therefore a need in the art to provide an improved, efficient, and cost effective high strength armour steel plate and method for production thereof.
[0006] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0007] In some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0008] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0009] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

OBJECTS OF THE INVENTION
[0010] A general object of the present disclosure is to provide high strength steel plates.
[0011] Another object of the present disclosure is to provide an improved and cost effective high strength armour steel plates.
[0012] Another object of the present disclosure is to provide efficient high strength armour steel plate with hardness 470-520 BHN.
[0013] Another object of the present disclosure is to provide method for production of high strength steel plate.
[0014] Another object of the present disclosure is to provide an efficient and cost effective method for producing high strength armour steel plate with hardness 470-520 BHN.

SUMMARY
[0015] The present disclosure relates generally to the technical field of ferrous metallurgy. In particular, the present disclosure pertains to high strength armour steel plate with hardness 470-520 BHN, and method for production thereof.
[0016] In another aspect of the present disclosure provides a high strength steel plate/ high strength armour steel plate having composition in weight percentage comprising: carbon (C) in amount ranging from 0.26 – 0.32%, silicon (Si) in amount ranging from 0.80 – 1.80 %, manganese (Mn) in amount ranging from 0.50 to 1.60%, chromium (Cr) in amount ranging from 0 to 0.60%, copper (Cu) in amount ranging from 0 to 0.20%, Nickel (Ni) in amount ranging from 0.10 to 0.80%, sulphur (S) in amount ranging from 0.002 to 0.01%, boron (B) in amount ranging from 0 to 0.004%, aluminium (Al) in amount ranging from 0.001 to 0.01%, and phosphorus (P) in amount ranging from 0.004 to 0.05%.
[0017] In an embodiment, the high strength steel plate having hardness ranging from 470 to 520 BHN, and charpy impact energy (CVN) at -40 0C along transverse direction greater than 20 Joules when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0018] In an embodiment, the high strength steel plate having yield strength ranging from 1400 to 1700 MPa, tensile strength ranging from 1650 to 1900 MPa when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0019] In an embodiment, the high strength steel plate having percentage elongation ranging from 6 to 10%, and percentage reduction in area ranging from 22 to 32% when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0020] In another aspect, the present disclosure provides a method for producing high strength steel plate (also referred to as high strength armour steel plate hereinafter) comprising steps of: cooling a high strength steel slab; soaking the high strength steel slab; performing hot rolling on the soaked high strength steel slab to convert the high strength steel slab into a high strength steel plate; heating the high strength steel plate; quenching the heated high strength steel plate in oil; and tempering the quenched high strength steel plate.
[0021] In an embodiment, the cooling of the high strength steel slab is a hood cooling performed for a time period of about 72 hours.
[0022] In an embodiment, the soaking of the high strength steel slab is performed at temperature ranging from 1280 to 1300OC for a time period of about 4 to 5 hours.
[0023] In an embodiment, the hot rolling comprising primary descaling, roughing mill descaling and pinch roll descaling in a steckel mill. The hot rolling is performed to convert the high strength steel slab into a high strength steel plate with thickness ranging from 4.5 to 6.0 mm.
[0024] In an exemplary embodiment, the finishing temperature can be maintained at temperature ranging from 850 to 925 0C, and coiling temperature can be ranging from 760 to 830 0C.
[0025] In an embodiment, the heating of the high strength steel plate is performed at temperature ranging from 860 to 910 OC for a time period of about 10 to 30 minutes.
[0026] In an embodiment, the tempering on the high strength steel plate is performed at temperature ranging from 230 to 350OC for a time period of about 45 to 90 minutes to harden the high strength steel plate.
[0027] In an embodiment, the high strength steel plate includes tempered martensite with packet size less than 20 µm.
[0028] In an embodiment, a method for producing a high strength steel plate comprising steps of: charging input material comprising of any or combination of steel scrap, direct-reduced iron (DRI), and hot briquetted iron (HBI) into anelectric arc furnace (EAF) for converting the input material into a molten steel form; adding a flux into the molten steel, and tapping the molten steel in a ladle with addition of ferro-alloy in the molten steel; degassing the molten steel using a vacuum arc degasser (VAD) for removing the dissolved gases from the molten steel; performing continuous casting (CC) of the molten steel to produce a high strength steel slab; cooling the high strength steel slab; soaking the high strength steel slab; performing hot rolling on the soaked high strength steel slab to convert the high strength steel slab into a high strength steel plate; quenching the high strength steel plate in oil; and tempering the quenched high strength steel plate.
[0029] In an embodiment, the cooling is a hood cooling performed for a time period of about 72 hours.
[0030] In an embodiment, the soaking is performed at temperature ranging from 1280 to 1300OC for a time period of about 4 to 5 hours.
[0031] In an embodiment, the hot rolling comprising primary descaling, roughing mill descaling and pinch roll descaling in a steckel mill. The hot rolling is performed to convert high strength steel slab into high strength steel plate with thickness ranging from 4.5 to 6.0 mm.
[0032] In an embodiment, the heating of the high strength steel plate is performed at temperature ranging from 860 to 910 OC for a time period of about 10 to 30 minutes.
[0033] In an embodiment, the tempering is performed at temperature ranging from 230 to 350OC for a time period of about 45 to 90 minutes to harden the high strength steel plate.
[0034] In an embodiment, the high strength steel plate includes tempered martensite with packet size less than 20 µm.
[0035] Those skilled in the art will further appreciate the advantages and superior features of the disclosure together with other important aspects thereof on reading the detailed description that follows in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0037] FIG. 1 illustrates an exemplary flow diagram representation of the proposed method for producing a high strength steel plate, in accordance with an embodiment of the present disclosure.
[0038] FIG. 2 illustrates an exemplary method flow diagram representation for producing a high strength steel plate, in accordance with an embodiment of the present disclosure.
[0039] FIG. 3 illustrates an exemplary graphical representation of Dilation curve at different cooling rate of a high strength steel plate, in accordance with an embodiment of the present disclosure.
[0040] FIGs. 4A and 4B illustrate SEM image representations of high strength steel plates showing ferritic bainite and martensite and austenite (MA) constituent at cooling rate (CR) 1 0C/s, and fully martensite constituent at CR 5 0C /s, respectively, in accordance with an embodiment of the present disclosure.
[0041] FIGs. 5A to 5D illustrate image representations of high strength steel plates showing fracture surfaces, in accordance with an embodiment of the present disclosure.
[0042] FIGs. 6A to 6H illustrate optical and SEM image of representations of high strength steel plates, in accordance with an embodiment of the present disclosure.
[0043] FIGs. 7A to 7D illustrate TEM image of representations of high strength steel plates, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0044] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0045] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0046] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
[0047] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0048] Embodiments explained herein relate to a high strength armour steel plate with hardness 470-520 BHN and method for production thereof.
[0049] In embodiment, the disclosed high strength steel plate/ high strength armour steel plate having composition in weight percentage can include carbon (C) in amount ranging from 0.26 – 0.32%, silicon (Si) in amount ranging from 0.80 – 1.80 %, manganese (Mn) in amount ranging from 0.50 to 1.60%, chromium (Cr) in amount ranging from 0 to 0.60%, copper (Cu) in amount ranging from 0 to 0.20%, Nickel (Ni) in amount ranging from 0.10 to 0.80%, sulphur (S) in amount ranging from 0.002 to 0.01%, boron (B) in amount ranging from 0 to 0.004%, aluminium (Al) in amount ranging from 0.001 to 0.01%, and phosphorus (P) in amount ranging from 0.004 to 0.05%.
[0050] In an embodiment, the high strength steel plate (also referred to as high strength armour steel plate hereinafter) having hardness ranging from 470 to 520 BHN when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0051] In an embodiment, the high strength steel plate having charpy impact energy at -40 0C along transverse direction greater than 20 Joules when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0052] In an embodiment, the high strength steel plate having yield strength ranging from 1400 to 1700 MPa when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0053] In an embodiment, the high strength steel plate having tensile strength ranging from 1650 to 1900 MPa when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0054] In an embodiment, the high strength steel plate having percentage elongation ranging from 6 to 10% when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0055] In an embodiment, the high strength steel plate having percentage reduction in area ranging from 22 to 32% when thickness of the high strength steel plate is 4.5 to 6.0 mm.
[0056] In an embodiment, the high strength steel plate includes tempered martensite with packet size less than 20 µm.
[0057] In an embodiment, the high strength steel plate having high ballistic resistance. Ballistic test has been carried out on the high strength steel plate when thickness of the high strength steel plate is 4.5 to 6.0 mm from 50 meter distance using 7.62 mm ball rimmed ammunition with 730-900 m/sec velocity.
[0058] FIG. 1 illustrates an exemplary flow diagram representation of the proposed method for producing a high strength steel plate, in accordance with an embodiment of the present disclosure. The proposed method 100 comprising at step 102, cooling a high strength steel slab (also referred to as high strength armour steel slab hereinafter). The high strength steel slab is produced through electric arc furnace (EAV)- vacuum arc degassing (VAD)- continuous casting (CC) route of steel making.
[0059] In an exemplary embodiment, the vacuum arc degassing can be carried out for 48 min at < 3.0 Torr. The last VAD temperature is performed at 1565 OC while tundish temperature is ranging from 15210C to 1511 0C.
[0060] In an exemplary embodiment, the casting speed can be 0.72to0.75 m/min at steady state.
[0061] In an exemplary embodiment, dimension of the high strength steel slab can be 170mm × 1160mm × 8500mm.
[0062] In an embodiment, at the step 102, the cooling of the high strength steel slab is a hood cooling performed for a time period of about 72 hours.
[0063] In an embodiment, the method 100 can include at step 104, soaking the cooled high strength steel slab. In an embodiment, the soaking of high strength steel slab the can be performed at temperature ranging from 1280 to 1300OC for a time period of about 4 to 5 hours for homogenization of the material of the high strength steel slab tough out cross section.
[0064] In an embodiment, the method 100 can include at step 106, performing hot rolling on the soaked high strength steel slab to convert the high strength steel slab into a high strength steel plate.
[0065] In an embodiment, at the step 106, primary descaling, roughing mill descaling (first and third pass) and pinch roll descaling in steckel mill can be carried out before and during hot rolling process.
[0066] In an exemplary embodiment, the finishing temperature can be maintained at temperature ranging from 850 to 925 0C, and coiling temperature can be ranging from 760 to 830 0C.
[0067] In an embodiment, the hot rolling is performed to convert the high strength steel slab intoa high strength steel plate with thickness ranging from 4.5 to 6.0mm.
[0068] In an embodiment, the method 100 can include at step 108, heating the high strength steel plate. In an embodiment, the heating of the high strength steel plate can be performed at temperature ranging from 860 to 910 OC for a time period of about 10 to 30 minutes.
[0069] In an embodiment, the method 100 can include at step 110, quenching the heated high strength steel plate in oil.
[0070] In an embodiment, the method 100 can include at step 112, tempering the quenched high strength steel plate. In an exemplary embodiment, the tempering on the high strength steel plate is performed at temperature ranging from 230 to 350OC for a time period of about 45 to 90 minutes to harden the high strength steel plate.
[0071] In an embodiment, the high strength steel plate can include tempered martensite with packet size less than 20 µm.
[0072] FIG. 2 illustrates an exemplary method flow diagram representation for producing high strength steel plate, in accordance with an embodiment of the present disclosure. In an embodiment, the method 200 for producing a high strength steel plate can include at step 202, charging input material into an electric arc furnace (EAF) for converting the input material into a molten steel form. In an embodiment, the charging input material can include any or combination of steel scrap, direct-reduced iron (DRI), and hot briquetted iron (HBI).
[0073] In an embodiment, the method 200 can include at step 204, adding a flux into the molten steel, and tapping the molten steel in a ladle with addition of ferro-alloy in the molten steel.
[0074] In an embodiment, the flux can be selected from any or a combination of a calcined bauxite, calcined dolomite and a burnt lime (CaO). In an embodiment, the ferro-alloy can be high carbon ferro-manganese.
[0075] In an embodiment, the method 200 can include at step 206, degassing the molten steel using a degasser for removing the dissolved gases from the molten steel. In an embodiment, the degasser can be a vacuum arc degasser (VAD).
[0076] In an exemplary embodiment, the vacuum arc degassing can be carried out for 48 min at < 3.0 Torr. The last VAD temperature can be performed at 1565 OC while tundish temperature is ranging from 15210C to 1511 0C.
[0077] In an embodiment, the method 200 can include at step 208, performing continuous casting (CC) of the molten steel to produce a high strength steel slab (also referred to as high strength armour steel slab hereinafter).
[0078] In an exemplary embodiment, the casting speed can be 0.72 to 0.75 m/min at steady state.
[0079] In an exemplary embodiment, dimension of the high strength steel slab can be 170mm × 1160mm × 8500mm.
[0080] In an embodiment, the method 200 can include at step 210, cooling the high strength steel slab.
[0081] In an embodiment, the cooling can be a hood cooling for a time period of about 72 hours.
[0082] In an embodiment, the method 200 can include at step 212, soaking the cooled high strength steel slab. In an embodiment, the soaking of high strength steel slab the can be performed at temperature ranging from 1280 to 1300OC for a time period of about 4 to 5 hours for homogenization of the material of the high strength steel slab tough out cross section.
[0083] In an embodiment, the method 200 can include at step 214, performing hot rolling on the soaked high strength steel slab to convert the high strength steel slab into a high strength steel plate.
[0084] In an embodiment, at the step 214, primary descaling, roughing mill descaling (first and third pass) and pinch roll descaling in steckel mill can be carried out before and during hot rolling process.
[0085] In an exemplary embodiment, the finishing temperature can be maintained at temperature ranging from 922 to 924 0C, and coiling temperature can be ranging from 760 to 830 0C.
[0086] In an embodiment, the hot rolling is performed to convert the high strength steel slab into a high strength steel plate with thickness ranging from 4.5 to 6.0 mm.
[0087] In an embodiment, the method 200 can include at step 216, heating the high strength steel plate. In an embodiment, the heating of the high strength steel plate can be performed at temperature ranging from 860 to 910 OC for a time period of about 10 to 30 minutes.
[0088] In an embodiment, the method 200 can include at step 218, quenching the heated high strength steel plate in oil.
[0089] In an embodiment, the method 200 can include at step 220, tempering the quenched high strength steel plate. In an exemplary embodiment, the tempering on the high strength steel plate is performed at temperature ranging from 230 to 350OC for a time period of about 45 to 90 minutes to harden the high strength steel plate.
[0090] FIG. 3 illustrates an exemplary graphical representation of Dilation curve at different cooling rate of a high strength steel plate, in accordance with an embodiment of the present disclosure. In an embodiment, as shown in FIG. 3, restricting austenite grain growth during austenization before quenching can be taken care through by heating for very less time above Ac3 temperature. Ac3 temperature is determined using Gleeble 3500C at cooling rate of 1 0C/sec and 5 0C/sec as 850 0C while Ms = 355 0C.
[0091] FIGs. 4A and 4B illustrates EM image representations of the high strength steel plates showing ferritic bainite and martensite and austenite (MA) constituent at cooling rate (CR) 1 0C/s, and fully martensite constituent at CR 5 0C /s, respectively, in accordance with an embodiment of the present disclosure.
[0092] In an exemplary embodiment, different condition for austenization and tempering of the high strength steel plates are provided in Table 1. Plate no. 5P 181418R and 5P 181418F are from the same plate but from the rear and front end of the plate respectively.
Plate No. Hardening Condition Tempering Condition
5P 181397 30 min heating at 8750 C 1 hr temp@2500 C
5P 181422 12 min heating at 8950 C 1 hr temp@2500 C
5P 181418R 15 min heating at 8950 C 1 hr temp@2500 C
5P 181418F 15 min heating at 8950 C 1 hr temp@2500 C
5P 181419 11 min heating at 8950 C 1.5 hr temp@2500 C
5P 181367 07 min heating at 8950 C 1 hr temp@2500 C

Table 1(Hardening and tempering condition and hardness data)
[0093] In an exemplary embodiment, the tensile properties and average hardness of quenched and tempered high strength steel plates at different heat conditions are provided in Table 2. Though the hardness at different locations vary in the range of 470 to 520 BHN, the average hardness of each plate varies from 495 to 507 BHN as shown in Table 2. The average values with standard deviation of yield strength (YS), ultimate tensile strength (UTS), % elongation (EL) and % reduction in area (RA) are provided in Table 2. In all cases, YS is above 1400 MPa while UTS is above 1750 MPa and %EL is above 7 respectively. This indicates that the material is having high strength and good ductility in all testing conditions though the YS, UTS and %EL values are lower in the case of plate no. 5P 181397, which is heated for 30 minutes at austenitization temperature. The lower heating at relatively higher temperature may be suitable for obtaining better tensile properties as shown in Table 2. This may lead to finer austenite packet size leading better strength and toughness.
[0094] Further, as provided in Table 3, the Charpy Impact energy (CIE) of ½ width specimens (5 mm thick) of each plate at -40 0C is more than 11 Joule, which implies that CIE of full size specimen at -40 0C will be more than 22 Joule. On increasing test temperature to 00C and room temperature (RT), the CIE value has been also increased though it is not substantial. Fractography in Fig.4A and 4B reveals that all samples failed in ductile dimple rupture mode. As CIE value at -40 0C, 0 0C and room temperature are not very much different and the morphology of fracture surface at - 40 0C is in ductile dimple rupture mode, it can be inferred that even -400C lies above ductile to brittle transition temperature. Thus, both the composition and the processing conditions must have been helped to achieve good strength and toughness.

Plate No. YS (MPa) UTS (MPa) %EL %RA Average Hardness (BHN)
5P 181397 1435 ? 4.95 1764 ? 13.34 7.31 ? 0.41 28.1 ? 1.64 502.5
5P 181422 1466 ? 13.0 1782 ? 13.0 8.13 ? 0.27 24.64 ? 2.1 497.3
5P 181418R 1513 ? 7.06 1835 ? 11.80 8.61 ? 0.20 26.8 ? 1.18 506.4
5P 181418F 1689 ? 66.0 1857 ? 107 7.38 ? 1.6 23.31 ? 4.5 506.4
5P 181419 1481 ? 4.0 1806 ? 2.10 8.47 ? 0.18 27 ? 1.14 495.7
5P 181367 1561 ? 2.38 1784 ? 20.4 7.37 ? 0.64 27.4 ? 2.42 495.1

Table 2 (Tensile properties of quenched and tempered high strength steel plates)

Plate No. CIE at RT (J) CIE at 00C (J) CIE at -400C (J)
5P 181397 17.39 ? 0.49 17.31 ? 0.56 11.85 ? 1.04
5P 181422 18.37 ? 1.23 17.27 ? 3.35 12.79 ? 1.05
5P 181418R 17.85 ? 0.93 15.68 ? 0.8 12.34 ? 1.62
5P 181418F 17.64 ? 0.8 16.26 ? 1.91 11.98 ? 1.75
5P 181419 17.83 ? 2.0 13.23 ? 2 11.31 ? 1.9
5P 181367 18.13 ? 0.56 17.16 ? 0.78 12.62 ? 1.27

Table 3 (Charpy Impact energy (Joule) at different temperature of 1/2 width specimens (5 mm thickness))
[0095] FIGs. 5A to 5D illustrate image representations of high strength steel plates showing fracture surfaces, in accordance with an embodiment of the present disclosure. FIGs. 5A to 5D represent fracture surfaces of high strength steel plates 5P 181418F, 5P 181419, 5P 181422 and 5P 181367, respectively.
[0096] FIGs. 6A to 6H illustrate optical and SEM image of representations of high strength steel plates, in accordance with an embodiment of the present disclosure. FIGs. 6Aand 6B represent optical and SEM image, respectively, of the high strength steel plate 5P 181418F, FIGs. 6Cand 6D represent optical and SEM image, respectively, of the high strength steel plate 5P 181419, FIGs. 6E and 6F represent optical and SEM image, respectively, of the high strength steel plate 5P 181422, and FIGs. 6G and 6H represent optical and SEM image, respectively, of the high strength steel plate 5P 181367. As compared to FIGs.6 A and 6B, the microstructure in other heat-treatment conditions (FIGs. 6 C to FIG. 6H) show slightly refined microstructure of martensitic lath. However, the lath and martensite packet size is less than 20 µm in each case, which leads to better toughness.
[0097] FIGs. 7A to 7D illustrate TEM image of representations of high strength steel plates, in accordance with an embodiment of the present disclosure. FIGs. 7A and 7B represent TEM images of the high strength steel plate 5P 181422, and FIGs. 7C and 7D represent TEM images of the high strength steel plate 5P 181367.The TEM images of the high strength steel plates heat-treated at different conditions are shown in FIG.5. The structure consisted of tempered martensite laths. The elongated carbides are also visible within the laths typically found in these steels due to stage 2 low temperature tempering. The heat-treatment conditions leading to tempered martensitic microstructure resulted in good toughness while maintaining required hardness and strength.
[0098] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[0099] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[00100] The present disclosure provides high strength steel plates.
[00101] The present disclosure provides an improved and cost effective high strength armour steel plates.
[00102] The present disclosure provides efficient high strength armour steel plate with hardness 470-520 BHN.
[00103] The present disclosure provides a method for production of high strength steel plate.
[00104] The present disclosure provides an efficient and cost effective method for producing high strength armour steel plate with hardness 470-520 BHN.

Claims:

1. A high strength steel plate having composition in weight percentage comprising: carbon (C) in amount ranging from 0.26 – 0.32%, silicon (Si) in amount ranging from 0.80 – 1.80 %, manganese (Mn) in amount ranging from 0.50 to 1.60%, chromium (Cr) in amount ranging from 0 to 0.60%, copper (Cu) in amount ranging from 0 to 0.20%, Nickel (Ni) in amount ranging from 0.10 to 0.80%, sulphur (S) in amount ranging from 0.002 to 0.01%, boron (B) in amount ranging from 0 to 0.004%, aluminium (Al) in amount ranging from 0.001 to 0.01%, and phosphorus (P) in amount ranging from 0.004 to 0.05%.
2. The high strength steel plate as claimed in claim 1, wherein the high strength steel plate having hardness ranging from 470 to 520 BHN, and Charpy impact energy (CVN) at -40 0C along transverse direction greater than 20 Joules when thickness of the high strength steel plate is 4.5 to 6.0 mm.
3. The high strength steel plate as claimed in claim 1, wherein the high strength steel plate having yield strength ranging from 1400 to 1700 MPa, tensile strength ranging from 1650 to 1900 MPa, percentage elongation ranging from 6 to 10%, and percentage reduction in area ranging from 22 to 32% when thickness of the high strength steel plate is 4.5 to 6.0 mm.
4. A method for producing high strength steel plate comprising steps of:
cooling a high strength steel slab;
soaking the cooled high strength steel slab;
performing hot rolling on the soaked high strength steel slab to convert the high strength steel slab into a high strength steel plate;
heating the high strength steel plate;
quenching the heated high strength steel plate in oil; and
tempering the quenched high strength steel plate.
5. The method as claimed in claim 4, wherein the cooling of the high strength steel slab is a hood cooling performed for a time period of about 72 hours, and wherein the soaking is performed at temperature ranging from 1280 to 1300 OC for a time period of about 4 to 5 hours.
6. The method as claimed in claim 4, wherein the step of hot rolling comprising primary descaling, roughing mill descaling and pinch roll descaling in a steckel mill, and wherein hot rolling is performed to convert the high strength steel slab into the high strength steel plate with thickness ranging from 4.5 to 6.0 mm.
7. The method as claimed in claim 4, wherein the heating of the high strength steel plate is performed at temperature ranging from 860 to 910 OC for a time period of about 10 to 30 minutes, and wherein the tempering is performed at temperature ranging from 230 to 350 OC for a time period of about 45 to 90 minutes to harden the high strength steel plate, and wherein the high strength steel plate comprising tempered martensite with packet size less than 20 µm.
8. A method for producing high strength steel plate comprising steps of:
charging input material comprising of any or combination of steel scrap, direct-reduced iron (DRI), and hot briquetted iron (HBI) into a furnace for converting the input material into a molten steel form;
adding a flux into the molten steel, and tapping the molten steel in a ladle with addition of ferro-alloy in the molten steel;
degassing the molten steel using a degasser for removing the dissolved gases from the molten steel;
performing continuous casting of the molten steel to produce a high strength steel slab;
cooling the high strength steel slab;
soaking the cooled high strength steel slab;
performing hot rolling on the soaked high strength steel slab to convert the high strength steel slab into a high strength steel plate;
heating the high strength steel plate;
quenching the heated high strength steel plate in oil; and
tempering the quenched high strength steel plate.
9. The method as claimed in claim 8, wherein the cooling is a hood cooling performed for a time period of about 72 hours, wherein the soaking is performed at temperature ranging from 1280 to 1300 OC for a time period of about 4 to 5 hours, wherein the heating of the high strength steel plate is performed at temperature ranging from 860 to 910 OC for a time period of about 10 to 30 minutes, and wherein the tempering is performed at temperature ranging from 230 to 350 OC for a time period of about 45 to 90 minutes to harden the high strength steel plate.
10. The method as claimed in claim 8, wherein the step of hot rolling comprising primary descaling, roughing mill descaling and pinch roll descaling in a steckel mill, and wherein hot rolling is performed to convert the high strength steel slab into the high strength steel plate with thickness ranging from 4.5 to 6.0 mm.