What are TMT bars? What are the grades of TMT bars? How are they made? These are some of the basic questions that may strike our mind when we first get to know about the Thermo Mechanically Treated bars a.k.a TMT bars. Now, while you are out to purchase the rebars, you can’t directly contact the TMT bar manufacturers, rather discussing your needs with the supplier is wiser.
The oligopoly business of TMT bars provides no choice but to trust everyone out there in the market. So, before you finalise the deal you must have some good ideas regarding the manufacturing process and the grades of TMT bars.
What Are the Grades of TMT bars?
Let's first define TMT bars before we discuss their manufacturing process. High-strength reinforcement bars with a soft inner core and a hardened outer core are known as Thermo mechanically treated, or TMT, bars. They get their name from a manufacturing method known as Thermo Mechanical Treatment.
Because of its great tensile strength, steel—an alloy consisting primarily of iron, carbon, and other elements—is utilised extensively in the construction of infrastructure, tools, ships, cars, and other machinery. Thus, to improve its mechanical qualities—such as ductility, hardness, corrosion resistance, and yield strength—steel is put through many operations.
In India, TMT bar producers produce four grades of TMT bars: Fe-415, Fe-500, Fe-550, and Fe-600. The higher the grade, the stronger and more superior the bar is. The numbers state the amount of stress the constructor should apply to deform it.
Manufacturing Process Of TMT Bars
Now let’s talk about the manufacturing process of TMT bars:
1. Extraction Procedure
Iron is removed from its ore and transformed into steel with the help of raw materials like coke, iron ore, and fluxes like limestone and dolomite. Right now the iron is in the molten state. After undergoing pre-treatment and being converted into steel in a conversion device, the molten iron is heated in a ladle to refine the steel's chemistry.
Following this stage, billets (pencil ingots) measuring at least 130 mm2 are formed by pouring the molten steel into a casting machine.
2. Heating, Rolling, and Forming TMT Bars
When trying to reshape the steel billets into the final size of the reinforced bar (rebar), they heat up to between 1200 °C (2192 F) and 1250 °C (2282 F).
3. Quenching
After the hot rolled bars are let out from the finished mill, they go into the "Thermex System," - a water spray system. This process ensures the ductility of TMT Rebars as it rapidly cools the outer core, and serves as a component in the highest-grade TMT bars manufacturing process.
The TMT Rebars' outer core gets hardened by a rapid cooling process that is ideal for each segment, generating a martensitic rim while the core stays hot and soft.
4. Self-tempering
A temperature difference forms across the quenched bar's cross-section as it escapes from the quenching box. The heat therefore moves from the core, which is warmer than outside temperatures.
This results in the development of an intermediate ring of martensite and bainite (a plate-like microstructure) and the proper tempering of the outer martensitic layer into a structure known as Tempered Martensite. At this point, the core continues to remain in the austenitic condition, which is a typical cubicle crystalline structure known as gamma-phase iron.
5. Atmospheric Cooling
When the self-tempering process is over, the producers keep the bars outside for atmospheric cooling. It equalises the temperature difference between the soft inner core and the hard exterior. After they are completely cooled down, they form a ductile ferrite-pearlite structure.
Bottom Line
Hopefully, you have understood the manufacturing process of TMT bars. The above study will also help you hunt reliable TMT Bars Manufacturers in India, who never compromise on their quality.
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