Title of Invention | A PROCESS FOR DEVELOPMENT OF ULTRA HIGH STRENGTH STEEL FROM FERRITE MARTENSITE STARTING MICROSTRUCTURE |
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Abstract | The present invention relates to a process for development of ultra high strength steel from ferrite martensite starting microstructure. The process comprises of forging the steel at 900° - 1100° with different amount of deformation and temperature at each stoke to achieve homogenized microstructure. The forged material is not rolled and air cooled. The material is then intercritically annealed at the temperature range of 700° C - 800° C for one hour and water quenched from that temperature to produce ferrite - martensite. The hot rolled material is then cold rolled to different percentage of reduction from 20 to 85 % and the said cold rolled material is then recrystallized annealed at 200° C to 700° C for 20 - 60 minutes to produce the ultra high strength steel having a composition by % weight of C - 0.1 - 0.3 %, Mn - 1.5 % or less, Si - 0.50 % or less, S - 0.015 % or less, Ti - 0.01 % or less, P - 0.02 % or less, V - 0.2 % or less, cr - 0.1 % or less. |
Full Text | FIELD OF THE INVENTION The present invention relates to a process for development of an high strength steels. More particularly the present invention relates to a process for development of an ultra high strength steels. BACKGROUND OF THE INVENTION To increase the strength to weight ratio of the automobiles which will eventually lead to a decrease in the fuel consumption and an increase in the passenger safety there has been an increased emphasis on the development of new advanced high strength sheet steels (AHSS), categorically for this purpose. Design applications for steel products have necessitated the development of new steels with unique properties. In general, the strength ductility relationship is some what inverse particularly in steel gamete. But the steel referred to as advance high strength steels (AHSS) possess very high strength with nominal ductility. There are some chemistries and processing routes suggested in the invention which can lead to a development of certain grades of AHSS family. OBJECTS OF THE INVENTION It is therefore, an object of the present invention to propose a process for development of an ultra high strength steels which eliminates the disadvantages of prior art. Another object of the present invention is to propose a process for development of an ultra high strength steels which increases strength to weight ratio. A further object of the present invention is to propose a process for development of an ultra high strength steels which is adaptable to automobile industry A still further object of the present invention is to propose a process for development of an ultra high strength steels which takes care of passengers safety when used in automobile can body. SUMMARY OF THE INVENTION is made in the air induction furnace and subsequently forged at 900-1100° C with different amount of deformation and temperature at each stoke to achieve homogenized microstructure. The forged material is hot rolled and the FRT is kept just above Ar3 temperature. The steel is then air cooled. The hot rolled structure is observed to be ferrite-bainite. After that the material is intercritically annealed at the temperature range of 700°C 800°C for 1 hour and water quenched from that temperature to produce ferrite-martensite. The intercritical annealing temperature are selected to vary the amount of ferrite and austensite at that temperature, which ultimately controlled the amount of two phases after cooling. The basic aim is to achieve two kinds of grain size distribution after the final processing. The hot rolled material is then cold rolled to different percentage of reduction starting from 20 to 85 %. The cold rolled material is then subjected to annealing at various temperatures ranging from 200°C to 700°C for 20-60 mins. RESULT 1. The above chemical composition of steel yield the following properties after subsequent treatment UTS 1200 and EL-8% 2. After hot rolling and inter-critical annealing the microstructure is composed of martensite and (10-35) % ferrite depending on annealing temperature. 3. The final microstructure after cold rolling and annealing composed of bimodal grain size distribution. Ferrite grain size is ~10-15µm and martensite grain size is ~ 1-µm. 4. The hot rolled material when cold rolled (20-85%) and recrystallized annealed at 200° C to 700PC for 20-60 minutes results in YS: ~ 1100MPa, UTS: ~1200MPa and Elongation:~ 8%. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention can now be described in detail with the help of the figure of the accompanying drawing in which Figure 1 shows Fe-C phase diagram (only the steel part) showing the Ar3 and Ar1 lines. WE CLAIM 1. A process for development of ultra high strength steel from ferrite martensite starting microstructure, the process comprising: - forging the steel at 900° - 1100° with different amount of deformation and temperature at each stoke to achieve homogenized microstructure; - hot rolling the forged material; - air cooling the said steel; - annealing inter critically the hot rolled material at the temperature range of 700° - 800° for one hour; - water quenching the annealed material from that temperature to produce ferrite - martensite; characterized in that, - the hot rolled material is then cold rolled to different percentage of reduction from 20 to 85 % and the said cold rolled material is then recrystallized annealed at 200° C to 700° C for 20 - 60 minutes to produce the ultra high strength steel having a composition by % by weight, C-0.1-0.5% Mn - 1.5 % or less Si - 0.50 % or less S - 0.015 % or less Ti - 0.01 % or less P - 0.02 % or less V - 0.2 % or less Cr-0.1 % or less 2. The process as claimed in claim 1, wherein the cold rolling the annealing produces the final microstructure of ultra high strength steel of bimodal grain- size-distribution and yields a ferrite grain size of 10 - 15 µm. 3. The process as claimed in claim 1, wherein the microstructure after hot rolling and inter-critical annealing is composed of martensite and 10-35 % of ferrite depending on the annealing temperature. 4. An ultra high strength steel having a final microstructure of bimodal grain size distribution and ferrite grain size of 10 - 15 µm and martensite grain size of 1 µm comprising by % by weight; C-0.1-0.5% Mn - 1.5 % or less Si - 0.50 % or less S - 0.015 % or less Ti - 0.01 % or less P - 0.02 % or less V - 0.2 % or less Cr - 0.1% or less 5. An ultra high strength steel as claimed in claim 4, wherein the said steel acquires yield strength of 1100MPa, tensile strength of 1200MPa and elongation of 8 %. The present invention relates to a process for development of ultra high strength steel from ferrite martensite starting microstructure. The process comprises of forging the steel at 900° - 1100° with different amount of deformation and temperature at each stoke to achieve homogenized microstructure. The forged material is not rolled and air cooled. The material is then intercritically annealed at the temperature range of 700° C - 800° C for one hour and water quenched from that temperature to produce ferrite - martensite. The hot rolled material is then cold rolled to different percentage of reduction from 20 to 85 % and the said cold rolled material is then recrystallized annealed at 200° C to 700° C for 20 - 60 minutes to produce the ultra high strength steel having a composition by % weight of C - 0.1 - 0.3 %, Mn - 1.5 % or less, Si - 0.50 % or less, S - 0.015 % or less, Ti - 0.01 % or less, P - 0.02 % or less, V - 0.2 % or less, cr - 0.1 % or less. |
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00664-kol-2007-correspondence others 1.1.pdf
00664-kol-2007-correspondence others 1.2.pdf
00664-kol-2007-correspondence others.pdf
00664-kol-2007-description complete.pdf
664-kol-2007-amanded claims.pdf
664-kol-2007-amanded pages of specification.pdf
664-kol-2007-correspondence.pdf
664-kol-2007-description (complete).pdf
664-kol-2007-examination report.pdf
664-kol-2007-granted-abstract.pdf
664-kol-2007-granted-claims.pdf
664-kol-2007-granted-description (complete).pdf
664-kol-2007-granted-drawings.pdf
664-kol-2007-granted-form 1.pdf
664-kol-2007-granted-form 2.pdf
664-kol-2007-granted-specification.pdf
664-kol-2007-reply to examination report.pdf
664-kol-2007-reply to examination report1.1.pdf
Patent Number | 249559 | |||||||||
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Indian Patent Application Number | 664/KOL/2007 | |||||||||
PG Journal Number | 43/2011 | |||||||||
Publication Date | 28-Oct-2011 | |||||||||
Grant Date | 25-Oct-2011 | |||||||||
Date of Filing | 30-Apr-2007 | |||||||||
Name of Patentee | TATA STEEL LIMITED | |||||||||
Applicant Address | RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION JAMSHEDPUR | |||||||||
Inventors:
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PCT International Classification Number | C22C 38/04 | |||||||||
PCT International Application Number | N/A | |||||||||
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