Title of Invention | PROCESS FOR MANUFACTURE OF HOT ROLLED HIGH STRENGTH VANADIUM CONTAINING STEEL PLATES IN UNDER POWERED PLATE MILLS |
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Abstract | A process for production of high-strength steel plates and, in particular, to the production of hot rolled high-strength steel plates in underpowered plate mills involving high-strength imparting vanadium content. Importantly, the process can be carried out in underpowered plate mills with rolling load capacity of up to about 5000 tons comprising by way of a selective heat composition having strength enhancing Vanadium content of up to about 0.22 % by wt.; and processing followed by finally subjecting the slabs thus treated to rolling in Plate Mill having load capacity of up to about 5000 tons such as to thereby obtain high strength plates with Vanadium content without significant increase in rolling load. The use of high vanadium content in steel plate manufacturing to increase the strength of plates without any significant increase in rolling load thus favour producing high-strength plates with low rolling load up to about 5000 tones. |
Full Text | FIELD OF THE INVENTION The present invention relates to the process for production of high-strength steel plates and, in particular, to the production of hot rolled high-strength steel plates in under powered plate mills involving high-strength imparting vanadium content. The process of the invention achieves advantageous use of high vanadium content in steel plate manufacture to increase the strength of plates without anY significant increase in rolling load. The process of the invention would thus favour producing high-strength plates in under powered plate mills with rolling load capacity of up to about 5000 tones. The steel plates obtained by the process of the invention involve high-strength and is found suitable for wide application such as in manufacture of ATM chests, earth moving equipments, dams, bridges etc. BACKGROUND ART It is well known to meet requirements of providing high-strength steel plates for various applications/uses and there are several processes for producing steel plates of high-strength to meet such diverse end use requirements/applications. WO9905328A1 discloses the manufacture of ultra high-strength linepipe steel - of fine grained lower bainite or lath-martensite microstructure by a sequence of heating, two-stage hot rolling and quenching to a Quench Stop Temperature. In this process a method is provided for producing an ultra-high strength steel having a tensile strength of at least about 900 Mpa (130 Ksi), a toughness as measured by Charpy V-notch impact test at -40° C (-40° F) of at least about 120 joules (90Ft-lbs) and a microstructure comprising predominantly fine-grained lower bainite, fine-grained lath martensite or mixtures thereof transformed from substantially unrecrystailized austenite grains and comprising iron and specified weight percentages of the additives: carbon, silicon, manganese, copper, nickel, niobium, vanadium, molybdenum, chromium, titanium, aluminum, calcium, Rare Earth Metals, and magnesium. A steel slab is heated to a suitable temperature; the slab is reduced to form plate in one or more hot rolling passes in a first temperature range in which austenite recrystallized; said plate is further reduced in ore or more hot rolling passes (10) in a second temperature range below said first temperature range and above the temperature at which austenite begins. US 5906690 also discloses manufacture cold-rolled, high strength steel strip with good shapability - by hot rolling steel contg. silicon, manganese, phosphorus, sulphur, aluminum, nitrogen and one or more of titanium, vanadium, niobium and zirconium, cold rolling, recrystallisation annealing and finishing. In particular, the method of producing coid-rolled, high-strength steel strip with good plasticity and isotropic properties out of steel comprises no more than 0.08% carbon, no more than 10% silicon, no more than 1.8% manganese, between 0.010 and 0.10% phosphorus, no more than 0.02% sulfur, no more than 0.08% aluminum and no more than 0.008% nitrogen by weight plus one or more of the elements titanium, vanadium, niobium, and zirconium, the remainder being iron, by hot rolling, cold rolling, and recrystallization annealing; followed by temper rolling. The steei contains either three times as much titanium or six times as much niobium or zirconium as nitrogen. JP 04232209A2 teaches the manufacture of a steel pipe for oil well excellent in sulfide stress corrosive cracking resistance even in a sulfide stress corrosive environment involving hot piercing continuous rolling to a steel billet incorporating boron and titanium or further selectively incorporating a little quantity of chromium, molybdenum, nickel and vanadium at 900-700° C temperature in a final stage and 3-15% rolling reduction ratio and reheating a hollow raw pipe lowered to Ar3-100 ° C-Ar3+50 ºCat 900-1000 ° C and rapidly cooling a finished steel pipe, which is obtained by executing hot finish rolling at ≥, Ar3+50 ° C finish temperature from ≥ Ar3 point and successively, executing tempering treatment at ≤ Ac1 point. By this method, the steel pipe for oil well having high strength and excellent sulfide stress corrosive cracking resistance is obtained. US 4938266 discloses method of producing steel having a low yield ratio strength and a dual-phase mixed microstructure of ferrite and second phase carbide comprises heating to at least 950 ° C low-carbon slab steel having 0.30% or less carbon, 0.05% to 0.60% silicon, 0.5 to 2.5% manganese and 0.01 to 0.10% aluminum as the basic components, with the balance being iron and unavoidable impurities, or low-carbon low-alloy slab steel comprising in addition to the above basic components one or more elements selected from copper, nickel, chromium, molybdenum, niobium, vanadium, titanium, boron and calcium, hot rolling it, reheating it and tempering it. EP0320003A1 provides for a method of producing steel plate having a low yield ratio and high strength and a dual phase mixed microstructure of ferrite and second phase carbide comprises heating to at least 950 ° C low-carbon slab steel having 0.300r less carbon, 0.05 to 0.60 ilicon, 0.5 to 2.5% manganese, and 0.01 to 0.10% aluminum as the basic components, with the balance being iron and unavoidable impurities, or low-carbon low-alloy slab steel comprising in addition to the above basic components one or more elements selected from copper, nickel, chromium, molybdenum, niobium, vanadium, titanium, boron and calcium, hot rolling it, reheating it and tempering it. It would be apparent from the above various states of the art that while the use of vanadium and titanium as minor additives in steel plate manufacture has been known and followed over the years, however, usually the manner of obtaining high strength steel plates involved the essential stages of tempering and quenching which make such processes complex and cost-extensive. It was thus been difficult to provide for the selective heat chemistry involving high-strength contributing vanadium which would while facilitating obtaining of high-strength steel plates would avoid the complexities of the steps of tempering and quenching and at the same time would not significantly affect the rolling load adversely during commercial rolling of the plate. OBJECTS OF THE INVENTION It is thus the basic object of the present invention to provide a process for manufacture of high strength steel plates in under powered plate mills which would favour avoiding the complex and cost expensive method of producing high-strength steel plates through quenching and tempering technology. Another object of the present invention is to provide for high-strength steel plates in hot rolled conditions in underpowered plate mills which would favour producing such high-strength steel plates for diverse and wide applications such as in manufacture of ATM chests, earth moving equipments, dams, bridges and the like. Another object of the present invention is to provide for a simple and cost effective manner of producing high strength steel plates in hot rolled conditions in underpowered plate mills which would provide for meeting the huge demand of high-strength hot rolled steel plates. Yet another object of the present invention is directed to the development of technology for production of high-strength steel plates in hot rolled conditions in underpowered plate mills thereby avoiding the complex and cost expensive process of producing high-strength steel plates through quenching and tempering technology. Yet another object of the present invention is directed to identification of selected heat chemistry for producing high-strength steel plates involving high vanadium content which would be adopted for processing in underpowered plate mills under controlled rolling load during plate rolling. Yet another object of the present invention is directed to providing for a process for producing high-strength steel plates involving selective heat chemistry and controlled rolling technology to favour providing high strength plates with good tensile properties and microstructure comprising polygonal ferrite-pearlite near surface and banded ferrite-pearlite in the mid thickness. SUMMARY OF THE INVENTION Thus according to the basic aspect of the present invention there is provided a process for manufacture of hot rolled high strength vanadium containing steel plates in underpowered plate mills with rolling load capacity of up to about 5000 tons comprising: i) providing a selective heat composition having strength enhancing Vanadium content of up to 0.22 about % by wt; ii) processing the heat through Vacuum Arc Refining to lower sulphur content and dissolved gases; iii) casting the heat into slabs in a continuous casting machine; iv) subjecting the slabs thus obtained to reheating in a reheating furnace and soaking; v) subjecting the slabs thus treated to rolling in Plate Mill having load capacity of up to about 5000 tons such as to thereby obtain high strength plates with Vanadium content without significant increase in rolling load. Importantly, the above process for manufacture of hot rolled high strength vanadium containing steel plates comprise of heat composition selected from: C in the range of 0.19 to 0.22 %by wt.; Mn in the range of 1.4 to 1.6 % by wt.; Si in the range of 0.40 to 0.60 % by wt.; S in the range of up to 0.01% Max. by wt.; P in the range of up to 0.025% Max. by wt.; Al. in the range of up to 0.02% Min. by wt; and V in the range of 0.18 to 0.22 % by wt.; Fe: Balance Preferably, the vanadium content in the above heat composition is preferably in the range of 0.18 to 0.22 % by wt. In accordance with a preferred aspect of the present invention, the heat composition used in the above process comprise added Fe-Ti for defect free casting of slabs preferably: C in the range of 0.19 to 0,22 %by wt. preferably 0.21% by wt.; Mn in the range of 1.4 to 1.6 % by wt. preferably 1.57 % by wt.; Si in the range of 0.40 to 0.60 % by wt. preferably 0.51 % by wt.; S in the range of up to 0.010 % Max. by wt. preferably 0.01% by wt.; P in the range of Up to 0.025 % Max. by wt. preferably 0.025% by wt.; Al. in the range of 0.02 to 0.05 % by wt preferably 0.016 by wt.; V in the range of 0.18 to 0.22 % by wt. preferably 0.18% by wt.; and Ti in the range of 0.015 to 0.020 % by wt. preferably 0.018% by wt. Fe: balance In accordance with a further preferred aspect of the invention in the above process the slabs from the heat are charged into reheating furnaces and soaked at 1230+/-10°C for a period of 6 hrs. to 8 hrs. preferably 6 Hrs; rolled into 12.4 mm to 13.3 mm preferably about 12.7 mm thick and 2250 mm to 2350 mm preferably 2250 mm wide plates in a two-stand four high plate mill. The step of controlled rolling comprising roughing rolling wherein the thickness of slab is brought down from the range of 240 mm to 250 mm preferably 242 mm to the range of 37 mm to 40 mm preferably 37 mm in 8 to 10 passes preferably 10 passes with reduction varying between ll-23%.The temperature after roughing rolling is between 1000-1030°C and the maximum load was up to about 4200 tons during rough rolling. Further the step of finish rolling comprising finish rolling wherein total reduction of about 70% was given in 6 to 8 passes preferably 8 passes to bring down the thickness of plates in the range of 12.4 mm to 13.3 mm preferably 12.7 mm and the finish rolling temperature maintained at about 800-830°C while the maximum finish rolling load is upto about 3800 tons during finish rolling. Following the above process of the invention, the tensile properties of the steel plates obtained comprised YS: in the range of 550 to 660 Mpa, preferably about 576 to 659 MPa, UTS: in the range of 690 to 850 Mpa, preferably about 726 to 824 MPa and El in the range of 16 % to 18 %, preferably about 16% and the through thickness microstructure of the plates comprised polygonal ferrite-pearlite near surface and banded ferrite-pearlite in the mid thickness. It is thus possible by way of the above-disclosed process of the invention to provide a simple and cost effective process, technology for producing high-strength plates in hot rolled conditions even in underpowered plated mills. This process of the invention would therefore favour producing high-strength steel plates in hot rolled conditions involving underpowered plate mills without requiring the complex and cost extensive quenching and tempering technology. Importantly, the selective heat chemistry used in the process of the invention would enable including high vanadium content to achieve high strength steel plates without adverse effecting the rolling load during plate rolling. The selective heat chemistry and the processing conditions followed favour achieving controlled production of the high strength plates of varying thickness even in under powered plate mills with maximum rolling load capacity of up to about 5000 tons. The process of the invention further demonstrate the surprising and selective possible incorporation of up to about 0.2% vanadium to increase the strength of the plates without any excessive load on the mill. Importantly the invention and in particular the process is found to achieve such advantages by way of vanadium precipitation has VC and VN at a temperature in the vicinity of the finish rolling temperature and therefore did not significantly increase the rolling load during hot rolling of plates. The visual and ultrasonic tests of the high-strength plates produced by the process of the invention confirm not only tensile properties of the plates but also that the rolled plates produced following the above process where free of surface and internal defects. The through thickness microstructure of the plates produced showed that the plates comprised of polygonal ferrite-pearlite near surface and banded ferrite-pearlite in the mid-thickness. DETAILED DESCRIPTION IN RELATION TO ACCOMPANYING FIGURE: The details of the invention, in particular the process of producing high-strength steel plates of the invention involving selective heat chemistry and processing in under powered steel mills is described hereunder in greater detail in relation to accompanying figure 1 and the following examples wherein: Figure 1 illustrates by way of flow diagram the process of manufacture of the high-strength steel plates involving selective heat chemistry and TMCP technology. Reference is invited to accompanying in figure 1 which illustrates the process sequence followed by the process of the invention to produce the desired high-strength steel plates involving underpowered rolling mills. As shown in said figure the selective high vanadium containing heat chemistry was obtained involving a basic oxygen furnace. Thereafter, the heat was processed through vacuum arc refining unit to lower the sulphur content and to minimize the dissolved gasses. Subsequently as further represented in said figure the heat was caste into slabs of defined sizes in a continuous casting machine. Slabs from this heat were next charged into re-heating furnaces and soaked. Finally the slabs were rolled into plates in an underpowered plate mill. The above-disclosed process of the invention is illustrated hereunder in further detailed by way of the following examples: EXAMPLES: EXAMPLE I Under this example a selective 100 Kg. heat, micro alloyed with high vanadium content was made in an air induction furnace. The chemistry of the heat used was as hereunder: C: 0.25% Mn: 1.43% Si: 0.67% S: 0.03% P: 0.026% V: 0.24% and Al: 0.024% Fe: Balance As would be apparent from the above the selected chemistry Involved high vanadium content and study was carried out to ascertain the rolling load of the heat during plate rolling as discussed hereunder: The heat was rolled into 12.7 mm thick plates under controlled rolled condition in a two-high rolling mill. The finishing temperature was maintained at about 810± 10° C. The tensile properties achieved by the plates produced were noted as hereunder: YS: 659 Mpa; UTS: 824 Mpa; and Percent: Elongation: 17.6 on 25 mm GL. In the above process of the invention the maximum rolling load was found to be 66 tons for 150 mm wide samples. The above results favour identification of expected maximum rolling load during commercial rolling of plates and it was found that slabs of high vanadium chemistry could be rolled even in under powered plate mills with maximum rolling load capacity of 4500 tons. It is thus possible by way of the above process to achieve increase strength of plates by addition of up to about 0.2% vanadium without any excessive load on the mill. Importantly, it was identified that because vanadium precipitated as VC and VN at a temperature in the viscidity of the finish rolling and therefore did not significantly increase the rolling load during hot rolling of plates. EXAMPLE II Under this example the above process of the invention was carried out with selective heat involving C-Mn-V-Ti chemistry in a 150 tons Basic Oxygen Furnace. In the above process Fe-Ti was added to ensure defect free casting of slabs. The selective heat composition was processed through Vacuum Arc Refining Unit to lower the Sulphur content and to minimize the dissolved gasses. The heat was caste into slabs of 242 X 1500 mm size in continuous casting machine. The chemistry of the heat used was identified as follows: C: 0.21% Mn: 1.57% Si: 0.51% S: 0.01% P: 0.025% V: 0.18% Al: 0.016% and Ti: 0.018% Fe: Balance The slabs from the above selective heat composition were next charged into reheating furnaces and soaked at 1230±_10° C for 6 hours. These slabs were then rolled into 12.7 mm thick and 2550 mm wide plates in a two-stand four high plate mill. During rolling, controlled rolling technology was adopted. In particular, in roughing rolling, thickness of slab was brought down from 242 mm to 237 mm in 10 passes with reduction varying between 11-23%. The temperature after roughing rolling was between 1000-1030° C. The maximum load was found to be 4200 tons during rough roiling. During finish rolling, total reduction of 70% was given in 8 passes to bring down the thickness of plates to 12.7 mm. Finish rolling temperature was maintained at 800-830° C. The maximum finishing rolling load was found to be about 3800 tons during finish rolling. Visual and ultrasonic inspection showed that the rolled plates were free from surface and internal defects. The tensile properties of plates were evaluated and noted as hereunder: YS: 576 Mpa; UTS: 726 Mpa The through thickness microstructure of these plates were found to comprise polygonal ferrite-pearlite near surface and branded ferrite-pearlite in the mid-thickness. It is thus possible by way of the above disclosed process of the invention to provide and meet demands for high-strength hot rolled plates for variety of end use/applications such as in manufacture of ATM chests, earth moving equipments, dams, bridged etc. It is possible therefore to provide for fabrication of cost effective high strength steel plate based units/structures such as ATM chests to meet the growing demands of such products of high strength steel. Importantly the process of the invention provides for a simple and cost effective alternative to the usual complex and cost expensive manufacture of high strength plates through quenching and tempering technology by providing for possible manufacture of such high strength steel plates in under powered plate mills with rolling capacity of only up to about 5000 tons. The invention therefore favour in meeting the wide scale demands for such high strength steel plates for variety of end use applications and makes possible the manufacture of such quality steel plates even in underpowered plate mills. WE CLAIM: 1. A process for manufacture of hot rolled high strength vanadium containing steel plates in plate mills with rolling load capacity of less than 5000 tons, comprising: i) providing a selective steel composition having strength enhancing Vanadium content in the range of 0.18 to 0.22 % by wt.; ii) processing the steel composition through Vacuum Arc Refining to lower sulphur content and dissolved gases; iii) casting the steel composition into slabs in a continuous casting machine; iv) subjecting the slabs thus obtained to reheating in a reheating furnace and soaking; v) subjecting the slabs thus treated to rolling in Plate Mill having load capacity of upto 5000 tons such as to thereby obtain high strength plates with Vanadium content without significant increase in rolling load. 2. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in claim 1 comprising of heat composition selected from: C in the range of 0.19 to 0.22 %by wt.; Mn in the range of 1.4 to 1.6 % by wt.; Si in the range of 0.40 to 0.60 % by wt.; S 0.01% Max. by wt., P 0.025% Max. by wt.; Al. in the range of 0.02 to 0.05 % by wt; and V in the range of 0.18 to 0.22 % by wt.; Fe: Balance 3. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in anyone of claims 1 or claim 2, wherein the heat composition used comprise added Fe-Ti for defect free casting of slabs preferably: C in the range of 0.19 to 0.22 %by wt. preferably 0.21% by wt; Mn in the range of 1.4 to 1.6 % by wt. preferably 1.57 % by wt.; Si in the range of 0.40 to 0.60 % by wt. preferably 0.51 % by wt.; S in the range of 0.00 to 0.01 % Max. by wt. preferably 0.01% by wt.; P in the range of 0.00 to 0.25 % Max. by wt. preferably 0.025% by wt.; Al. in the range of 0.02 to 0.05 % by wt preferably 0.02 % by wt., V in the range of 0.18 to 0.22 % by wt. preferably 0.18% by wt.; and Ti in the range of 0.015 to 0.020 % by wt. preferably 0.018% by wt. Fe: balance 4. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in anyone of claims 1 to 3 wherein slabs from the heat are charged into reheating furnaces and soaked at 1230+/-10°C for a period of 6 hrs. to 8 hrs. preferably 6 Hrs; rolled into 12.4 mm to 13.3 mm preferably about 12.7 mm thick and 2250 mm to 2350 mm preferably 2250 mm wide plates in a two-stand four high plate mill. 5. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in anyone of claims 1 to 4 comprising roughing rolling wherein the thickness of slab is reduced from the range of 240 mm to 250 mm preferably 242 mm to the range of 37 mm to 40 mm preferably 37 mm in 8 to 10 passes preferably 10 passes with reduction varying between 11-23%. 6. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in claim 5 wherein the temperature after roughing rolling is between 1000°C-1030°C and the maximum load is up to 4200 tons during rough rolling. 7. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in anyone of claims 1 to 6 comprising finish rolling wherein total reduction of about: 70% was given in 6 to 8 passes preferably 8 passes to bring down the thickness of plates in the range of 12.4 mm to 13.3 mm preferably 12.7 mm and the finish rolling temperature maintained in the range of 800°C -830°C while the maximum finish rolling load is up to about 3800 tons during finish rolling. 8. A process for manufacture of hot rolled high strength vanadium containing steel plates as claimed in anyone of claims 1 to 7 wherein the tensile properties of the steel plates obtained comprised YS:in the range of 550 to 660 Mpa preferably about 576 to 659 MPa, UTS: in the range of 690 to 850 Mpa, preferably about 726 to 824 MPa and El in the range of 16 % to 18 %, preferably about 16% and the through thickness microstructure of the plates comprised polygonal ferrite- pearlite near surface and banded ferrite-pearlite in the mid thickness. 9. A process for manufacture of hot rolled high strength vanadium containing steel plates substantially as herein described and illustrated with reference to the accompanying examples. A process for production of high-strength steel plates and, in particular, to the production of hot rolled high-strength steel plates in underpowered plate mills involving high-strength imparting vanadium content. Importantly, the process can be carried out in underpowered plate mills with rolling load capacity of up to about 5000 tons comprising by way of a selective heat composition having strength enhancing Vanadium content of up to about 0.22 % by wt.; and processing followed by finally subjecting the slabs thus treated to rolling in Plate Mill having load capacity of up to about 5000 tons such as to thereby obtain high strength plates with Vanadium content without significant increase in rolling load. The use of high vanadium content in steel plate manufacturing to increase the strength of plates without any significant increase in rolling load thus favour producing high-strength plates with low rolling load up to about 5000 tones. |
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834-KOL-2005-CORRESPONDENCE 1.1.pdf
834-KOL-2005-CORRESPONDENCE.pdf
834-kol-2005-granted-abstract.pdf
834-kol-2005-granted-claims.pdf
834-kol-2005-granted-correspondence.pdf
834-kol-2005-granted-description (complete).pdf
834-kol-2005-granted-drawings.pdf
834-kol-2005-granted-examination report.pdf
834-kol-2005-granted-form 1.pdf
834-kol-2005-granted-form 18.pdf
834-kol-2005-granted-form 2.pdf
834-kol-2005-granted-form 3.pdf
834-kol-2005-granted-reply to examination report.pdf
834-kol-2005-granted-specification.pdf
Patent Number | 232523 | ||||||||||||||||||
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Indian Patent Application Number | 834/KOL/2005 | ||||||||||||||||||
PG Journal Number | 12/2009 | ||||||||||||||||||
Publication Date | 20-Mar-2009 | ||||||||||||||||||
Grant Date | 18-Mar-2009 | ||||||||||||||||||
Date of Filing | 12-Sep-2005 | ||||||||||||||||||
Name of Patentee | STEEL AUTHORITY OF INDIA LIMITED | ||||||||||||||||||
Applicant Address | RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI | ||||||||||||||||||
Inventors:
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PCT International Classification Number | H01F 5/00 | ||||||||||||||||||
PCT International Application Number | N/A | ||||||||||||||||||
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PCT Conventions:
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