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: 1786-1985
TMT 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 Reinforcement
Chemical Composition
Constituent
Per cent, Maximum

Fe 415
Fe 415D
Fe 500
Fe 500D
Fe 550
Fe 550D
Fe600
Carbon, Max
0.30
0.25
0.30
0.25
0.30
0.25
0.30
Sulphur, Max
0.060
0.045
0.055
0.040
0.055
0.040
0.040
Phosphorus, Max
0.060
0.045
0.055
0.040
0.050
0.040
0.040
S + P, Max
0.110
0.085
0.105
0.075
0.100
0.075
0.075

MECHANICAL PROPERTIES Element IS 1786: 2008

Fe 415
Fe 415D
Fe 500
Fe 500D
Fe 550
Fe 550D
Fe600
Yield Strength, Min (N/mm2)
415

500

550

Ultimate tensile Strength, Min (N/mm 2)
485

545

585

Elongation, Min (A 5) (%)
14.5

12

8

Nominal Cross-Sectional Area and Mass
Sl. No.
Nominal Size mm
Cross Sectional Area mm2
Mass per Metric kg
(1)
(2)
(3)
(4)
1
4
12.6
0.099
2
5
19.6
0.154
3
6
28.3
0.222
4
8
50.3
0.395
5
10
78.6
0.617
6
12
113.1
0.888
7
16
201.2
1.58
8
20
314.3
2.47
9
25
491.1
3.85
10
28
615.8
4.83
11
32
804.6
6.31
12
36
1018.3
7.99
13
40
1257.2
9.86

Tolerance on Nominal Mass
Sl. No.
Nominal Size mm
Tolerance on the Nominal Mass, Percent

Batch
Individual Sample1
Individual Sample for coils Only2
(1)
(2)
(3)
(4)
(5)
1
Up to and including 10
±7
-8
±8
2
Over 10 up to and including 16
±5
-6
±6
3

±3
-4
±4
1) 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 STRENGTH
DEFORMED BARS AND WIRES
SI.
Property

No.

Fe 415
Fe 415D
Fe 500
Fe 500D
Fe 550
Fe 550D
Fe600
1
2
3
4
5
6
7
8
9
(I)
0.2 per cent proof stress/yield stress, Min N / mm2
415.0
415.0
500.0
500.0
550.0
550.0
600.0
(ii)
Elongation,per cent, Min, on gauge length 5.65 ÖA, Where A is the cross-sectional area of the test piece
14.5
18.0
12.0
16.0
10.0
14.5
10.0
(iii)
Tensile strength, Min
10 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 485.0 N/mm2
12 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 500.0 N/mm2
8 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 545.0 N/mm2
10 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 565.0 N/mm2
6 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 585.0 N/mm2
8 per cent more than the actual 0.2 per cent proof stress/yield stress but not less than 600.0 N/mm2
6 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 ÖA, where A is the cross-sectional area of the test piece
-
5
-
5
-
5
-

BEND PROPERTIES
NOMINAL SIZE mm MANDRAL DIAMETER FOR DIFFERENT GRADES (IS 1786: 2008)

Fe 415
Fe 415D
Fe 500
Fe 500D
Fe 550
Fe 550D
Fe 600
Up to and including 20
3d
2d
4d
3d
5d
4d
5d
Over 22
4d
3d
5d
4d
6d
5d
6d
d is the normal size in mm of the test piece.

REBEND PROPERTIES
NOMINAL SIZE mm MANDRAL DIAMETER FOR DIFFERENT GRADES (IS 1786: 2008)

Fe 415 and 500
Fe 415D and 500D
Fe 550 and 600
Fe 550D
Up to and including 10
5d
4d
7d
6d
Over 10
7d
6d
8d
7d

WEIGHT TOLERANCE
Size Of Bar (mm2)
Cross-Sectional Area (mm2)
IS 1786

Lower
Standard
Upper
8
50.3
0.367
0.395
0.423
10
78.6
0.574
0.617
0.66
12
113.1
0.844
0.888
0.932
16
201.2
1.501
1.58
1.659
20
314.3
2.396
2.47
2.544
25
491.1
3.735
3.85
3.966