Title of Invention | A PROCESS FOR THE PRODUCTION OF 1.27MM THICK HIGH STRENGTH MEDIUM C-Mn STRAPPING QUALITY STEEL THROUGH MODIFIED AUSTEMPERING PRACTICE FOR PACKAGING APPLICATION |
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Abstract | There is proposed a method for the production of 1.27 mm thick high strength C-Mn strapping quality steel through modified austempering practice comprising the following steps: a. Preparing steel in a basic oxygen furnace to provide the alloy chemistry was as follows: Chemistry: %C: 0.38-0.45 %Mn: 1.35-1.45 %P: 0.025 (max.) %S: 0.015 (max.) %Si: 0.2-0.3 %AI: 0.01-0.03 b. Subjecting the steel to a step of ladle furnace treatment for purpose of controlling the sulpher content, c. Subjecting the products of step (b) to a step of continuous casting to produce defect free slabs, d. Re-heating the slabs formed in step (c) by soaking about 1250° C, e. Subjecting the re-heated slabs to a step of hot strip rolling to obtain 2.8 mm strip, f. Subjecting the hard rolled strips to a step of pickling in HCL acid, g. Followed by cold rolling the pickled strips to obtain coils of 1.27 mm thick, h. Where after the cold rolled coils are subjected to slitting to obtain necessary narrow straps of 31.75 mm thickness, i. Subjecting the straps so produced to a step of austenitisation at temperatures in the ranges of 950-970° C, followed by j. Subjecting the austenitised straps to a step of slow and controlled cooling and thereafter subjecting the cooled straps to austempering in a lead bath at a temperature of around 450° C, so as to form about 15% ferrite. |
Full Text | Introduction to the Field of Invention: This invention relates to an improved method of producing strapping steel for packaging applications. Prior Art and the drawbacks; In steel plants, strapping steel of 1.27 mm thickness is used as a packing material for binding the fully processed coils/packets of sheets after they are covered with HDPE cloth and galvanized sheet. Additionally, a number of coils/packets are unitized together with 1.27 mm thick strapping steel in the wagon during their transportation to the customers. Since the strapping material has to withstand severe stresses that may arise during transportation through rail road, it is imperative that the strapping material should have high strength and good ductility. The presently available straps do not meet all these requirements. Objects of the Invention : It is an object of the invention to propose an improved method to produce strapping steel of 1.27 mm thick through a cost effective process. It is another objects to produce such strapping steel by modified austempering process, which is a cost effective route to produce high strength strapping steel. Brief Description of the Invention: According to the basic aspect of the present invention, there is provided a method for the production of 1.27 mm thick high strength C-Mn strapping quality steel through modified austempering practice comprising the following steps: a. Preparing steel in a basic oxygen furnace to provide the alloy composition comprising: %C:0.38-0.45 %Mn: 1.35-1.45 %P:0.025 (max.) %S:0.015 (max.) %Si: 0.2-0.3 %AI:0.01-0.03 b. Subjecting the steel to a step of ladle furnace treatment for the purpose of controlling the sulphur content, c. Subjecting the products of step (b) to a step of continuous casting to produce defect free slabs, d. Re-heating the slabs formed in step (c) by soaking at about 1250° C, e. Subjecting the re-heated slabs to a step of hot strip rolling to obtain 2.8 mm strips, f. Subjecting the hard rolled strips to a step of pickling in HCL acid, g. Followed by cold rolling pickled strips to obtain coils of 1.27 mm thick, h. Where after the cold rolled coils are subjected to slitting to obtain necessary narrow straps of 31.75 mm width, i. Subjecting the straps so produced to a step of austenitisation at temperatures in the ranges of 950° C -970° C, followed by j. Subjecting the austemitised strips to a step of slow and controlled cooling and thereafter subjecting the cooled straps to austempering in a lead bath at a temperature of around 450° C, so as to form about 15% ferrite. Since present austempering is a continuous process. The duration of controlled cooling and residence time in lead bath is automatically fixed depending on duration of austenitisation. The austenitisation step is carried out for about 2 minutes and the finished rolling and coiling are maintained at 850+10° C and 650±10° C. According to another aspect of the present invention, there is provided an austempering unit for carrying out the method of the invention comprising an uncoiler, austenitisitng furnace, lead bath, air cooling tower and coiler, a closed chamber of ~1.2 meter being maintained between austenitising furnace and lead bath. Basic Details of the Invention : The invention will now be more fully described with reference to the accompanying drawing wherein Figure 1 shows a schematic diagram of an austempering unit. Figure 2 indicates influence of ferrite content on tensile properties of austempered strapping material prepared by the invention. Figure 3 shows a flow chart of the process for the production of improved strapping material of the invention. The process development started with the designing of appropriate alloy composition to enhance the hardenability property of the steel and to facilitate formation of bainite during austempering. For this, carbon and manganese contents are optimized with the help of extensive laboratory and commercial scale trials. The alloy composition obtained is as follows: %C:0.38-0.45 %Mn: 1.35-1.45 %P:0.025 (max.) %S:0.015 (max.) %Si: 0.2-0.3 %AI:0.01-0.03 The steel was made in Basic Oxygen Furnace (BOF) and processed through ladle furnace for controlling the sulphur content. The steel is cast into defect free slabs by oOptimizing the casting parameters with casting speed of ~1 meter/minute and super heat of 30° C max. These slabs are soaked at 1250° C and hot rolled into 2.8 mm strips. Finished rolling and coiling temperature were maintained at 850±10° C and 650±10° C. Hot strips were pickled in HCL acid followed by cold rolling into 1.27 mm thick coils. Cold rolled coils are then slitted in narrow width (31.75 mm) straps. These straps were subjected to an optimized austempering process. Optimization of austempering practice was established both throughy laboratory simulation and plant scale trials to achieve best combination of strength and ductility. For plant scale trials, a austempering unit was set up which included an uncoiler, austenitising furnace, lead bath, air cooling tower and coiler. A closed chamber of ~1.2 meter was maintained - — — between austenitising furnace and lead bath. This gap was sealed to prevent excessive heat loss (Figure 1), this resulted m formation of some amount of ferrite before quenching of the steel in lead bath. Based on the plant scale trials, a nomogram was prepared to understand the influence of % ferrite present in the micro-structure on the tensile properties of austempered straps (Figure 2). From nomogram, it was found that -15% ferrite along with fine banite and pearlite was most desirable micro-structure for achieving higher strength [92 kg/mm2 (min.)] and good ductility [% elongation: 9 (min.) at 150 mm gauge length]. Following optimized austempering practice was found suitable for formation of desired micro-structure: • Austenitising furnace temperature: 950° C -970° C. • Duration of austenitisation: ~2 minutes. • Slower and controlled cooling of austenitised strap prior to quenching into lead bath (to ensure formation of-15% ferrite). • Lead bath temperature: 450° C. Since it is a continuous austempering process, the duration of controlled cooling and residence time in lead bath are automatically fixed. The flow chart is given in Figure 3. The straps with designed chemistry when processed with optimum processing parameters, resulted in following properties: UTS: 92 kg/mm2 (min.) % Elongation. 9 (min.) at 150 mm gauge length. Development of above described process resulted in production of high strength strapping steel in a cost-effective manner. Strapping steel, produced by this process, can be confidently used regularly on commercial scale for packing application. We Claim: 1. A method for the production of 1.27 mm thick high strength C-Mn strapping quality steel through modified austempering practice comprising the following steps: a. Preparing steel in a basic oxygen furnace to provide the alloy composition comprising: %C:0.38-0.45 %Mn: 1.35-1.45 %P:0.025 (max.) %S:0.015 (max.) %Si: 0.2-0.3 %AI:0.01-0.03 b. Subjecting the steel to a step of ladle furnace treatment for the purpose of controlling the sulphur content, c. Subjecting the products of step (b) to a step of continuous casting to produce defect free slabs, d. Re-heating the slabs formed in step (c) by soaking at about 1250° C, e. Subjecting the re-heated slabs to a step of hot strip rolling to obtain 2.8 mm strips, f. Subjecting the hard rolled strips to a step of pickling in HCL acid, g. Followed by cold rolling pickled strips to obtain coils of 1.27 mm thick, h. Where after the cold rolled coils are subjected to slitting to obtain necessary narrow straps of 31.75 mm width, i. Subjecting the straps so produced to a step of austenitisation at temperatures in the ranges of 950° C -970° C, followed by j. Subjecting the austernitised strips to a step of slow and controlled cooling and thereafter subjecting the cooled straps to austempering in a lead bath at a temperature of around 450° C, so as to form about 15% ferrite. 2. A method as claim 1, wherein, the austenitisation step is carried out for about 2 minutes, since it is a continuous austempering process, the duration of controlled cooling and residence time in lead bath are automatically fixed. 3. A method as claimed in claims 1 and 2, wherein, the finished rolling and coiling temperatures are maintained at 850±10° C and 650±10° C respectively. 4. An austempering unit for carrying out the method of claims 1 to 3 comprising an uncoiler, austenitising furnace, lead bath, air cooling tower and coiler, a closed chamber of ~1.2 meter being maintained between austenitising furnace and lead bath. 5. A method for the production of 1.27 mm thick high strength C-Mn strapping quality steel through modified austempering practice and an austempering unit for carrying out the same substantially as herein described with reference to the accompanying drawings. There is proposed a method for the production of 1.27 mm thick high strength C-Mn strapping quality steel through modified austempering practice comprising the following steps: a. Preparing steel in a basic oxygen furnace to provide the alloy chemistry was as follows: Chemistry: %C: 0.38-0.45 %Mn: 1.35-1.45 %P: 0.025 (max.) %S: 0.015 (max.) %Si: 0.2-0.3 %AI: 0.01-0.03 b. Subjecting the steel to a step of ladle furnace treatment for purpose of controlling the sulpher content, c. Subjecting the products of step (b) to a step of continuous casting to produce defect free slabs, d. Re-heating the slabs formed in step (c) by soaking about 1250° C, e. Subjecting the re-heated slabs to a step of hot strip rolling to obtain 2.8 mm strip, f. Subjecting the hard rolled strips to a step of pickling in HCL acid, g. Followed by cold rolling the pickled strips to obtain coils of 1.27 mm thick, h. Where after the cold rolled coils are subjected to slitting to obtain necessary narrow straps of 31.75 mm thickness, i. Subjecting the straps so produced to a step of austenitisation at temperatures in the ranges of 950-970° C, followed by j. Subjecting the austenitised straps to a step of slow and controlled cooling and thereafter subjecting the cooled straps to austempering in a lead bath at a temperature of around 450° C, so as to form about 15% ferrite. |
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708-CAL-2001-CANCELLED PAGES.pdf
708-CAL-2001-CORRESPONDENCE 1.1.pdf
708-CAL-2001-CORRESPONDENCE-1.2.pdf
708-cal-2001-correspondence-1.3.pdf
708-cal-2001-correspondence-1.4.pdf
708-cal-2001-correspondence.pdf
708-cal-2001-description (complete)-1.1.pdf
708-CAL-2001-DESCRIPTION (COMPLETE).pdf
708-cal-2001-examination report-1.1.pdf
708-cal-2001-examination report.pdf
708-cal-2001-granted-abstract.pdf
708-cal-2001-granted-claims.pdf
708-cal-2001-granted-description (complete).pdf
708-cal-2001-granted-drawings.pdf
708-cal-2001-granted-form 1.pdf
708-cal-2001-granted-form 2.pdf
708-cal-2001-granted-specification.pdf
708-cal-2001-reply to examination report-1.1.pdf
708-cal-2001-reply to examination report.pdf
708-cal-2001-specification-1.1.pdf
708-cal-2001-specification.pdf
Patent Number | 247595 | |||||||||||||||||||||
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Indian Patent Application Number | 708/CAL/2001 | |||||||||||||||||||||
PG Journal Number | 17/2011 | |||||||||||||||||||||
Publication Date | 29-Apr-2011 | |||||||||||||||||||||
Grant Date | 26-Apr-2011 | |||||||||||||||||||||
Date of Filing | 24-Dec-2001 | |||||||||||||||||||||
Name of Patentee | STEEL AUTHORITY OF INDIA LIMITED | |||||||||||||||||||||
Applicant Address | RESEARCH AND DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI | |||||||||||||||||||||
Inventors:
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PCT International Classification Number | C22C 38/00 | |||||||||||||||||||||
PCT International Application Number | N/A | |||||||||||||||||||||
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