| Title of Invention | A FIRE RESISTANT STEEL ADAPTABLE TO STRUCTURAL APPLICATIONS AND THE PROCESS OF PRODUCTING THEREOF |
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| Abstract | The present invention is provided with a fire resistant steel adaptable to structural appliances comprises a steel having a composition (wt%): C - 0.10 - 0.15, Mn - 0.45 - 0.65, Si - 0.10 max, S - 0.020 max, P - 0.025 max, Cu - 0.60 - 1.0, Al - 0.02 - 0.06 and rest Fe; characterized in that post heat treatment steel contains copper precipitation in the hot band of steel which in turn compensate the loss in yield strength during fire. |
| Full Text | FIELD OF THE INVENTION The present invention relates to a heat resistance steel. More practically, the present invention relates to fire resistance steel adaptable to structural application and the process of producing fire resistance steel for structural application through deformation of sheet of Cu added low carbon steel encouraging precipitation of copper during breakout of fire attaining a temperature of 500°C or above. BACKGROUND OF THE INVENTION All commonly used structural materials lose some of their strength when exposed to fire. The development of fire resistant steel for building is aimed at increasing steel's elevated temperature strength while assuring other properties equal to or better than those of temperature strength while assuring other properties equal to or better than those of conventional steels for building. Mild steel structural is safe up to 400°C and beyond this the yield strength decreases faster. Thermo mechanically processed steel with combined addition of molybdenum, niobium and or chromium increases the elevated temperature yield strength so that two thirds of room temperature yield strength can be retained at 600°C. Ni, V and Ti are also added as micro alloying elements to obtain specified ambient temperature and elevated temperature yield strength. Hence, there is a need to provide a product from fore resistance point of view by modifying the chemistry such that when subjected to fire, the steel should retain minimum 2/3 of its room temperature yield strength. The proposed invention has been developed to solve the difficulties of using space consuming fire coating elements or costlier alloying steel by providing economical grade of steel sheet for structural application on developing. OBJECTS OF THE INVENTION It is therefore, an object of the present invention to propose a fire resistance steel adaptable to structural steel which eliminates the disadvantages in the prior art. Another object of the present invention is to propose a fire resistance steel adaptable to structural steel and the process of producing the same which modifies the chemistry of steel making such that the add cost does not exceed Rs 1000 per tone. A further object of the present invention is to propose a fire resistance steel adaptable to structural steel and the process of producing the same which can be widely used in building construction including multi-storey open car parks, sport facility,railway stations, external steel frames and many other structure. A still further object of the present invention is to propose a fire resistance steel adaptable to structural steel and the process of producing the same which successfully reduces the amount of fire protection and structural members may even be imported in cases where the steel temperature would not exceeds 600°C. The intention of fire proofing a structure is to save lives, allow safe evacuation provide safe access for fire fighter and protect the building from structural failure. SUMMARY OF THE INVENTION The beneficial role of Cu has recently received renewed attention due to potential of developing post heat treatment steel which combine high strength and good elongation. The precipitation of copper in both the iron and steel is usually observed in temperature range of 450°C to 650°C. Since, during the fire in a building, the materials can attain a temperature of 600oC,/the chemistry was designed as shown in Table 1 with the addition of 0.65-10% copper. The loss in yield strength during fire as in the case of conventional steel will be compensated by precipitation of copper during the aging temperature encountered in the event of fire breakout in steel intensive building. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS Fig-1: Comparative hardness of FR and reference steel at elevated temperature. Fig-2: Stress-strain curve for reference steel at 600°C for 2 hours. Fig-3: Stress-strain curve for FR steel at 600°C for 2 hours. Fig-4: TEM Micro graph of aged sample showing precipitation after 2 hr at 600°C. Fig-5: EDS Spectra showing precipitates composed of Cu. DETAILED DESCRIPTION OF THE INVENTION The heat was melted in 25 kg air induction furnace and cast in to ingot. The ingot was forged in to 150x300x45mm plate. The forged plates were soaked at (1170oC-1190oC) hot-rolled in to 2.8 mm thick with a finishing temperature of 890°C and air cooled. Samples were cut from the hot band for tensile test as well as laboratory heat treatment for aging (15 minutes, 30 minutes, 1 hr and 2 hrs at 600°C) in order to study the copper precipitates in hot band. The samples after soaking were water quenched to retain the precipitates. Simulated hot tensile tests at 600°C were conducted in Gleeble 1500 to determine the loss in yield strength. Changed in hardness for different holding times at 600°C for copper added steel as well as reference steel (without copper while other elements remaining the same) is shown in Figure 1. It may be seen that there is no increase in the hardness of reference material where as copper added steel is showing the increase in hardness due to copper precipitation. The peak hardness is attained within 15 minutes. It is also interesting to see that there is marginal reduction in hardness even at holding for 2 hrs at 600°C. This indicates that the loss in strength at elevated temperature is compensated due to pecipitation of copper in the fire resistant steel. The strength of steels at room temperature and 600°C, using simulated test with Gleeble is shown in table 2. The % ratio of yield strength at 600°C to room temperature yield strength increased with the addition of copper. It is evident from the Fig 2 and 3 that yield strength drops to as much as 170 Mpa for reference steel where as in the case of FR steel it drops to only 290Mpa respectively. The yield ratio is about 80% for FR steel. TEM micrograph of hot- rolled and aged sample (soaked at 600°C for 2 hrs) as shown in Figure 4 reveals the dislocation and sub grain structure. The copper precipitates, located on dislocation are spherical and disturbed homogeneously. EDS spectra as shown in Figure 5 confirmed the presence of copper in precipitates. WE CLAIM: 1. A fire resistance steel adaptable to structural appliances comprises:- a steel having a composition (wt%) C -0.10-0.15 Mn - 0.45- 0.65 Si -0.10 max S - 0.020 max P - 0.025 max Cu -0.60-1.0 Al - 0.02-0.06 and rest Fe characterized in the post heat treatment steel contains copper precipitation in the hot band of steel which in turn compensate the loss in yield strength during fire. 2. The process of producing fire resistance steel as claimed in claim 1 comprising - melting of steel in Induction furnace at 1600°C-1650°C; - liquid steel cast into ingot; - forging of ingot to form a size 150 x 300 x 45 mm plate; - soaking the plate at 1170°C; - hot-rolling the plate to make 2.8mm thick with a finishing temperature 890°C; - air cooling the plate from 890°C to room temperature; - heat treating for aging at 600°C for a soaking period 15 minutes, 30 minutes, 1 hour and 2 hours time in order to study the copper precipitates in hot band; - water quenching after soaking to retain the precipitates; characterized in that the said steel should retain minimum 2/3rd times of its room temperature yield strength at high temperature. 3. The fire resistance steel as claimed in claim 1, wherein the yield ratio is about 80% is achieved at 600°C. 4. The fire resistance steel as claimed in claim 1, wherein the copper precipitates at 600°C. ABSTRACT A FIRE RESISTANT STEEL ADAPTABLE TO STRUCTURAL APPLICATIONS AND THE PROCESS OF PRODUCTING THEREOF The present invention is provided with a fire resistant steel adaptable to structural appliances comprises a steel having a composition (wt%): C - 0.10 - 0.15, Mn - 0.45 - 0.65, Si - 0.10 max, S - 0.020 max, P - 0.025 max, Cu - 0.60 - 1.0, Al - 0.02 - 0.06 and rest Fe; characterized in that post heat treatment steel contains copper precipitation in the hot band of steel which in turn compensate the loss in yield strength during fire. |
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00622-kol-2008-correspondence others.pdf
00622-kol-2008-description complete.pdf
622-KOL-2008-AMANDED CLAIMS.pdf
622-KOL-2008-CORRESPONDENCE 1.1.pdf
622-KOL-2008-CORRESPONDENCE.pdf
622-KOL-2008-DESCRIPTION (COMPLETE) 1.1.pdf
622-KOL-2008-EXAMINATION REPORT.pdf
622-KOL-2008-GRANTED-ABSTRACT.pdf
622-KOL-2008-GRANTED-CLAIMS.pdf
622-KOL-2008-GRANTED-DESCRIPTION (COMPLETE).pdf
622-KOL-2008-GRANTED-DRAWINGS.pdf
622-KOL-2008-GRANTED-FORM 1.pdf
622-KOL-2008-GRANTED-FORM 2.pdf
622-KOL-2008-GRANTED-SPECIFICATION.pdf
622-KOL-2008-PETITION UNDER RULE 137.pdf
622-KOL-2008-REPLY TO EXAMINATION REPORT.pdf
622-KOL-2008-REPLY TO EXAMINATION REPORT1.1.pdf
| Patent Number | 255307 | |||||||||
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| Indian Patent Application Number | 622/KOL/2008 | |||||||||
| PG Journal Number | 07/2013 | |||||||||
| Publication Date | 15-Feb-2013 | |||||||||
| Grant Date | 11-Feb-2013 | |||||||||
| Date of Filing | 28-Mar-2008 | |||||||||
| Name of Patentee | TATA STEEL LIMITED | |||||||||
| Applicant Address | RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DEVISION, JAMSHEDPUR | |||||||||
Inventors:
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| PCT International Classification Number | C22C38/20 | |||||||||
| PCT International Application Number | N/A | |||||||||
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