TMT STEEL RODS – MANUFACTURING & PROPERTIES



TMT STEEL RODS

For year’s, Bamboo has been used by man for construction activities, later it has been replaced by CTD (Cold Twisted Deformed steel rods) or TOR steel rods. The manufacturers adopted the “Cold Twisting Process” in which the naturally cooled rods were twisted by means of motors. Thus the molecular structure of the core steel is weakened. Thus it should not be used for construction activities.

Now, the TMT (THERMO MECHANICALLY TREATED) steel rods have emerged. This rod is not twisted; instead it is treated with the WATER JACKETING PROCESS and allowed to cool in the ambient condition.

TMT STEEL BARS

COMPOSITION:

The TMT chemistry

 

BIS (bUREAU OF INDIAN STANDARDS)

Rosun TMT

Carbon (Max%)

0.30

0.25 to  0.30

Manganese (%)

0.5 to 1.2

0.5 to 0.8

Sulphur & Phosphorous

as per IS:1786/85

as per IS:1786/85

MANUFACTURE:

TMT STEEL MANUFACTURING PROCESS

WATER JACKETING:

TMT STEEL MANUFACTURING PROCESS

The steel rebar are at high temperature when they leave the last rolling stand. They are immediately passed through a pre-determined quantity of a high-pressure water-cooling system. These instant cooling tempers the outer surface and it becomes very hard. The next phase involves cooling at an ambient temperature that allows the hot core to temper the surface through thermal exchange. This result in a unique tempered structure of MARTENSITE (outer) and a fine-grained BAINITE-FERRITE / PEARLITE (core) that is stronger, more flexible and far better suited for construction.

TMT STEEL MANUFACTURING PROCESS

COMPARISON OF TMT & CTD:

TMT & CTD COMPARISON

 

  Properties

                    CTD Bars

                             TMT Bars

 

Strength

High (Normally up to Grade Fe-415)

Very High as grades of Fe-500 & 550 are easily achievable

 

Elongation

As per IS: 1786/ ’85

Very High in all grades and over- achieves the elongation requirement in the recent amendment to IS: 1786 for earthquake resistance

 

Weld-ability

Preferably avoided as welded joints are weak

Better and no loss of strength

 

Formability

Bend 3D – 5D, Re-bend 5D – 8D

Excellent due to uniform elongation

 

Ductility & Fatigue Strength

High

Very High, Most suited for earthquake resistant structures

 

Fire Hazards

Loss of Strength on temperature rise

Negligible loss in strength up to 500 deg. C

 

Corrosion Resistance

Scale fall down during cold twisting

Pre-welded meshes can be used

 

Workability

Easy working at site

Availability of Grade Fe-500 & 550 results in steel saving

 

Overall Economy

 

Availability of Grades Fe-500 & 550 results in steel Saving

 

 

 

Advantages of TMT:

Special Features of TMT Bars:

 

 

  1. Savings of 14 – 19% steel                    

  2. Reduction in Costs

  3. Better safety of structures

  4. Easy working at site

  5. Better ductility & bend-ability

  6. Better Corrosion Resistance

  7. Good Weld-ability

  8. Resistant to fire hazards

  1. Higher strength with better elongation

  2. Excellent Weld-ability

  3. Resistance to fire hazards

  4. Excellent Ductility

  5. Higher Fatigue Strength

  6. Easy work – ability at site

  7. Better Bonding Strength

  8. Better Corrosion Resistance

  9. Achieves better results than BIS Standards