What makes Thermo Mechanically Treated bars so special? Talks about the properties and process

Since more than 2 decades, Agni Steels has been a leading manufacturer of finished and semi-finished steel products in India. During our journey from the humble 3-ton furnace in 1992, to the two 15-ton induction furnaces, we have constantly upgraded our manufacturing facility to offer the best steel products for our valued customers. A lot of technological developments contributed to making this transition possible. Here is a brief account of the same:

            Before the advent of TMT technology, Agni Steels manufactured carbon steel bars with the help of ingots. Realising the drawbacks of carbon steel rebars, and developments in casting machines and TMT tech, we shifted to manufacturing superior quality TMT Steel rods. TMT stands for Thermo Mechanically Treated steel bars, which combine mechanical processes like compression, forging, rolling, etc. with thermal processes like re-heating, quenching, etc. Ingots were soon replaced by Billets, and moulds were superseded by our CCM (Continuous Casting Machine). TMT rods soon replaced carbon steel rods worldwide, due to their superior physical properties.

      Here are a few reasons why TMT bars are perfect for their usage as rebars:
  1. Strength: Billets are hot-rolled through the CCM, to form/cast rods that are rapidly cooled(quenched) to form a hardened surface of martensite on its periphery. This layer of martensite imparts the rod its characteristic compressive strength. It is caused by the slow quenching that shrinks the rod’s outer layer forming bainite along with martensite. Bainite adds to the brittle strength of the rod. Thus it helps in reinforcing the RCC construction with a strong TMT steel rod.                                                                                                                                    
  2. Ductility: Paired with compression due to shrinkage of the outer layer, a core of austenite is formed in the rod. This eventually leads to the formation of further layers; ferrite, cementite, and pearlite are also formed. Austenite is formed due to diffusion of carbon from cementite to ferrite. Presence of a softer core surrounded by a layer of martensite and cementite results in a rod that possesses great tensile strength, while maintaining high ductility. This ductility thus helps the rod survive sudden shocks and impacts, and for preserving structural integrity during seismic activity.                                                                                                                                  
  3. Other properties: When the cut ends of TMT bars are etched, three distinct rings must appear: 1) A tempered outer ring of martensite, 2) A semi-tempered middle ring of martensite and bainite, and 3) A mild circular core of bainite, ferrite, and pearlite. This is the desired microstructure for a quality construction rebar. This microstructure thus improves the physical properties of a standard TMT bar to the point that its strength, ductility, corrosion resistance, bendability, weldability, etc. are improved drastically. The whole process is controlled with sensors for the formation of uniform layers throughout the length of the rod, and to avoid any irregularities.

 These properties are maintained during the manufacture of a TMT steel rod, due to the modernized machinery we incorporate at our leading-edge manufacturing facility. This leads to casting a pristine quality TMT steel rod that is on par with the international standards. Here at Agni Steels, we believe in offering the best-in-class TMT Steel rods for the Indian masses at competitive prices. Our drive to do so enables us to incorporate developments in the technology for improving the quality of our high strength steel rods.

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