What is a TMT bar? - salient features, types, and their manufacturing process.

 1. What is a TMT Bar?

TMT stands for thermomechanical treatment. These bars have a tough outer rim known as martensite and soft inner cores made of ferrite & pearlite. The combination of these two characters in a single bar makes them a better choice for the construction field fulfilling all the required specifications. 

In other words, we can say that TMT bars are the right mix of two main features i.e. strength & flexibility.

2. What is the manufacturing process of TMT bars?

Hot rolled rebars are subjected to thermomechanical treatment in 3 steps.

Cross-section of TMT bar.

a. Quenching: 

Hot-rolled bars are quenched rapidly by spraying water over them. This forms a hardened rim known as martensite. The inner core portion still remains hot in the austenite phase.

b. Tempering:

When the bar leaves a quenching system, due to the temperature difference between the inner core portion and the outer surface, the inner heat gets transferred to the outer surface, forming a strong tempered martensite rim.

c. Cooling:

The bar is passed through the cooling bed, where the austenitic core is transferred to the ferrite+ pearlite structure. In this atmospheric cooling process, the inner core portion remains soft having good ductility.

Thus the finally manufactured TMT bars consist of strong outer martensite and a ductile inner core made of ferrite + pearlite.

3. What are the main features of TMT bars?

TMT bars have

 1. High tensile strength.

 2. Good anti-corrosive properties.

 3. High malleability & ductility.

 4. Superior weldability. 

 5. Extra grip with good bonding strength.

 6.  Good resistance to fire hazards.

 7.  Excellent fatigue strength.

 8. Cost-effective. 

To get the answer to all types of your construction queries,

Click 👀.  Terms & definition.

4. How many grades are there in the TMT bars?

TMT bars are manufactured in 9 different grades. However, the most common grades that are widely used are Fe-415, Fe-500, Fe-500D & Fe- 550. 

Here, Fe denotes iron, and the number 415, 500, 550, stands for minimum yield stress in N/mm2.The letter D signifies that the particular TMT bars have a higher value of ductility.

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