steel bars or Manufacturing process, types and uses of TMT steel bars

TMT stands for Thermo Mechanical Treatment. Thermo Mechanical Treatment, or TMT, is a metallurgical process that is used to make TMT steel bars which are one of the most important construction materials. These bars made by reputed, reliable TMT steel bar manufacturers are used to build strong, long lasting and safe structures.

The ribbed TMT bars are used in construction because they provide better reinforcement to concrete structures, thereby minimizing damages during earthquakes and other natural calamities. They are also corrosion resistant, ductile, flexible and can bear great load without any problem.

How are TMT steel bars made?

At the manufacturing unit, there are three main steps in the manufacturing process of TMT Steel bars.

Step 1

Raw material such as iron ore, coal/coke, limestone and dolomite are sourced from specific locations, stacked, reclaimed and blended in a specified proportion. The iron content in the iron ore is increased and it is converted into pellets to enhance productivity. The reduction of iron ore takes place in a blast furnace and the molten iron pools ate the bottom of the furnace.

Step 2

The molten iron is then pre treated and converted to steel in a convertor or a Basic Oxygen Furnace. The carbon in the iron is eliminated at this stage. The steel is subjected to Ladle heating in a Ladle heating furnace and RH De-gasifier so the chemistry of the steel is further refined.  Next, the steel goes through a process called the continuous casting process where the molten steel is poured into a casting machine and converted into billet form with a cross section of 165mm2. The molten steel is heated up to 1250 degrees Celsius to reach the desired shape and then rolled in a rolling mill to be reshaped into reinforced bars.

Step 3

When a hot rolled bar comes out of the final mill stand, it is immediately quenched in a quenching box, using a special water spray system. This hardens the outside while the core still stays hot and soft. Even after leaving the quenching box, the core continues to self-temper by giving heat to the surface. This causes tempering of the outer martensitic layer into a substance called Tempered Martensitic. After this, the bars are atmospherically cooled on special cooling beds. Here the core gets transformed to a ductile ferrite-pearlite structure which has a strong outer surface and a ductile core.

In other words, the Tempered Martensite gives the bar its superior strength to the bar while the ductility to is due to the Ferrite- Pearlite layer. This ideal ratio of strength and ductility in the TMT steel bars results in construction grade steel, which requires minimum reinforcement and yet makes the structure safe in the face of earthquakes and other calamities.

What are the different types of TMT bars available in the market and what are their uses?

Different grades of TMT steel bars are available in the market, with grade being the number of stress level used to deform it. The four main grades of TMT bars are Fe 415, Fe 500, Fe 550 & Fe 600. Depending on the size and strength of the construction variations, a different grade of TMT steel bar is chosen

 Fe-415 grade TMT Steel bars:  Fe 415 TMT is used in smaller construction projects and residential construction, because of its ductile properties and its cost effectiveness. It can be easily bent to form complex shapes. The grade’s uniform elongation property makes it suitable for use in earthquake prone areas

Fe-500 grade TMT Steel bars:These bars have excellent bending ability and excellent load resistance. Fe-500 grade TMT bars are considered a market standard across different construction projects. This grade of TMT steel bars is mostly used in RCC constructions, buildings, bridges, flyovers and other concrete structures. They are specially manufactured to provide stability to high-rise projects and better load resisting properties.

Fe-550 grade TMT Steel bars: Similar to Fe-500, this grade of TMT steel bars differs in the yield and tensile strength. It is used in RCC construction that is exposed to coastal, marine or underground environment. This grade is also used for industrial and large-format infrastructure projects like brides and structures requiring high load-bearing capacities.

e 600 grade

Fe-600 grade TMT Steel bars: This is one of the strongest TMT grades available in the market. These TMT steel bars are used in heavy-duty infrastructure projects, bridges, marine facilities, expressways, metro projects, plants, towers, commercial properties, and industrial zones. They offer durability, greater tensile strength, reduce overall consumption, and ensure lesser steel congestion within the reinforcement.

Binding Wire: Binding wires are used to tie the rebars at the joints. They help to enhance the structural integrity of the construction.

TMT Steel bars sizes

Different sizes of TMT steel bars are chosen, based on the design requirement and project specifications.

TMT steel bars are available in different diameters: 8mm and10mm and12mm and16mm and 25mm and 32mm and 36mm

8mm-10mm size TMT steel bars are used in slabs and stairways which bear a lot of load

12mm-25mm size bars are used in beams & columns, and they can withstand heavy external loads

32mm-36mm size bars are used in the construction of very complex projects like dams, bridges

How do you choose the proper TMT steel bar for your construction?

TMT bars selection must be based on core project requirements, quality standards and project specifications drawn up by the civil engineers, builders and architects. No compromise should be made on quality and durability of the project as the safety of several millions of people often ride on the quality of construction material that is used. Project managers and procurement teams should study the requirement closely and should procure best-quality, feature-driven TMT steel bars that are manufactured by the reputed manufacturers in the steel industry.