The manufacturing process of TMT Bar involves the following steps
Step 1- Manufacturing of billets from raw materials:
Step 2 - Heating, Rolling and formation of reinforced bar:
Step 3 - Quenching:
Step 4 - Self-tempering:
Step 5 - Atmospheric Cooling:
Manufacture of Steel Billets
Billets are rectangular rods which are created by the Continuous Casting Process. In this process,
steel is molten and heated to a temperature of 1700°C. It is subsequently poured into casting
moulds to give the form of billets.
The hot billets are sent to a Rolling / Reduction Mill where the thickness is further reduced and
elongated across three stands – Roughing, Intermediate and the Finishing stands.
Quenching
Undesirable property changes might occur in case freshly cast rods are consistently kept at a
higher temperature.
However, this is prevented by passing the bars through a Quenching Chamber where they
undergo Rapid Cooling system and are sprayed with cold water.
This leads to a unique layer called Martensite being formed on the exterior surface of the bar.
Self Tempering
During the cooling down process of the steel bars, the outer core of the bar is at a lower
temperature and the inner core is at a much higher temperature.
The Martensite is further tempered on exposure to air and conduction, which leads to heat flix
being transferred to the outer core from the inner core.
Eventually, the process leads to the formation of Bainite and Martensite rings around the bars.
This helps the bar to achieve higher yield strength. The core remains hot and malleable,
otherwise called austenitic during this phase.
Atmospheric Cooling
The temperature of the inner core of the bars are gradually reduced to room temperature by
passing them through special cooling beds. At this point the differentiation of outer and inner
core becomes cognizable. The bar becomes more weldable and tensile since it has Ferrite- Pearlite structure in the center.
The bars are then tested, bundled, and made ready for despatch.
