TMT Rebar Manufacturing Process: A Behind-the-Scenes Look

 

TMT Rebar

Before we delve deep into the ways through which TMT bars are manufactured, it is crucial to get familiar with what they are. Thermo-mechanically treated bars are high-strength reinforcement bars that feature a hard external core and a soft inner core. It is normally manufactured under a unique process named Thermo-mechanically treatment.

Steel which is designed out of iron, carbon, and similar elements, is commonly used in massive structures, machines, and tools owing to its extreme strength. But, frequent exposure to fire and corrosion might weaken the steel structures. This particular component undergoes a process known as Thermo mechanical treatment to improve properties such as resistance and ductility. It is an integration of thermal and mechanical techniques.

The steps involved in the process of a TMT rebar are as follows

Extracting iron from its ore and converting it to steel

It is a process where raw materials such as coke, iron ore, and fluxes are utilized to extract iron which is placed in a molten form. Later, this molten iron is pre-treated and transformed into steel inside a converter. It is refined via ladle heating and then transferred to a casting machine to generate billets.

Rolling, heating, and formation of a reinforced bar

Steel billets are allowed to heat to nearly one thousand two hundred degree centigrade. Then, it is rolled to reshape the billets into the ultimate size and shape of a reinforced bar.

Quenching

Quenching is a heat treatment procedure that would enable swift cooling of the hot reinforced bars using water. It is carried out once they leave the final rolling mill. One of the benefits of rapid cooling is that it avoids unnecessary changes inside the material while improving the durability and strength of the bar. The external layer is hardened into Martensite whereas the core remains hot, while assisting them to develop an appropriate crystal structure.

Self-tempering

A temperature gradient is developed via a cross-section of the quenched TMT rebar once it leaves the quenched box. Therefore, it would ensure a smooth flow of heat from the inner core since the temperature is comparatively higher than that of the external core. This would also trigger an accurate tempering of the outer martensitic layer into a structure known by the name Tempered Martensite. 

However, the core still stays intact within the austenitic state during this phase.

Atmospheric cooling

Soon after the completion of self-tempering, these bars are allowed to cool in the atmosphere to stabilize the temperature. This would lead to the conversion of the core into ductile ferrite-pearlite.

The cross-section of the final product showcases a rigid external layer of tempered martensite. It is an intermediate layer consisting of Martensite and Bainite along with a refined core of strong pearlite and ferrite.

Conclusion

Lower grades of rebar are allowed to be twisted amidst cold conditions. This is crucial to enhance their overall strength. However, TMT bars do not undergo this type of process, as quenching would harden them.