印度螺纹钢标准TMT Rebar Standard.docx

Thermo-mechanical treatment (TMT):TMT is an acronym for the phrase thermo-mechanical treatment. The Bureau of Indian Standards while issuing the new code IS: 1786-1985TMT Bars is an acronym for “thermo-mechanical treatment”. Thermo Mechanically Treated (TMT) bars are manufactured using the Quenching & Tempering (Q & T) technology. TMT bars gets its strength properties from quenching and tempering. No mechanical treatment is involved in TMT Bars.Quenching: Hot TMT bars coming out from rolling mills are treated(cooled) with water on the surface to form marten site on the surface, the core remain austenitic. The TMT steel bars are passed through a water-cooling system where they are kept till the outer surface of the bars becomes colder while the core remains hot. This creates a temperature gradient in the bars. Temp core: TMT BARS are removed from cooling zone. A temperature gradient is established in the cross section. It causes heat to flow from centre to surface. The marten site left at centre is tempered by heat flow. So it is known as temp core. After the intensive cooling, the TMT bar is exposed to air and the core reheats the quenched surface layer by conduction, therefore tempering the external marten site. Helps them attain higher yield strength. The resulting heat-treated structure imparts superior strength and toughness to the bars. Depending upon the yield strength and ductility required percentage of transformed core area and temperature ranges are chosen.Isothermal Transformation: Austenite remaining at the core is transformed. During atmospheric cooling , austenite transforms into a very fine-grained pearlite structure.After thermo mechanical treatment, surface consists of tempered marten site and core of ferrite pearlite .The tempered marten site surface layer is very hard while the microstructure of the core is a very fine-grained pearlite which is soft. The result is a structure in TMT bar with a high yield strength combined with high ductility.TMT bars are also known as Quenched and Tempered Rebars, because of the quenching and tempering processes involved in making the TMT bars.IS 1786:2008 High Strength Deformed Steel Bars and Wires for Concrete ReinforcementChemical Composition ConstituentPer cent, MaximumFe 415Fe 415DFe 500Fe 500DFe 550Fe 550DFe600Carbon, Max 0.300.250.300.250.300.250.30Sulphur, Max 0.0600.0450.0550.0400.0550.0400.040Phosphorus, Max 0.0600.0450.0550.0400.0500.0400.040S + P, Max 0.1100.0850.1050.0750.1000.0750.075MECHANICAL PROPERTIES Element IS 1786: 2008Fe 415Fe 415DFe 500Fe 500DFe 550Fe 550DFe600Yield Strength, Min (N/mm2)415500550Ultimate tensile Strength, Min (N/mm 2)485545585Elongation, Min (A 5) (%)14.5128Nominal Cross-Sectional Area and MassSl. No.Nominal Size mmCross Sectional Area mm2Mass per Metric kg(1)(2)(3)(4)1412.60.0992519.60.1543628.30.2224850.30.39551078.60.617612113.10.888716201.21.58820314.32.47925491.13.851028615.84.831132804.66.3112361018.37.9913401257.29.86Tolerance on Nominal MassSl. No.Nominal Size mmTolerance on the Nominal Mass, PercentBatchIndividual Sample1Individual Sample for coils Only2(1)(2)(3)(4)(5)1Up to and including 107-882Over 10 up to and including 165-6633-441) For individual sample plus tolerance is not specified. A single sample taken from a batch as defined in 3.1 shall not be considered as individual sample.2) For coil batch tolerance is not specified.Physical Properties MECHANICAL PROPERTIES OF HIGH STRENGTHDEFORMED BARS AND WIRESSI.PropertyNo.Fe 415Fe 415DFe 500Fe 500DFe 550Fe 550DFe600123456789(I)0.2 per cent proof stress/yield stress, Min N / mm2415.0415.0500.0500.0550.0550.0600.0(ii)Elongation,per cent, Min, on gauge length 5.65 A, Where A is the cross-sectional area of the test piece14.518.012.016.010.014.510.0(iii)Tensile strength, Min10 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 485.0 N/mm212 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 500.0 N/mm28 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 545.0 N/mm210 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 565.0 N/mm26 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 585.0 N/mm28 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 600.0 N/mm26 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 660.0 N/mm2(iv)Total elongation at maximum force, percent, Min on gauge length 5.65 A, where A is the cross-sectional area of the test piece -5-5-5-BEND PROPERTIESNOMINAL SIZE mm MANDRAL DIAMETER FOR DIFFERENT GRADES (IS 1786: 2008)Fe 415Fe 415DFe 500Fe 500DFe 550Fe 550DFe 600Up to and including 203d2d4d3d5d4d5dOver 224d3d5d4d6d5d6dd is the normal size in mm of the test piece.REBEND PROPERTIESNOMINAL SIZE mm MANDRAL DIAMETER FOR DIFFERENT GRADES (IS 1786: 2008) Fe 415 and 500Fe 415D and 500DFe 550 and 600Fe 55