TMT steel bar
TMT bars are thermally mechanically treated steel bars with high strength and good mechanical properties compared to mild steel bars. TMT bar is a new enhanced version of mild steel bras. The treatment process of TMT bars includes 3 stages: quenching, self tempering, and atmospheric cooling. The quality of produced TMT bars depends on the quality of raw materials, quality of rolling mill, and quality of quenching and tempering process.
The output after removal of the impurities introduced into the rotary kiln. In the rotary kiln, 80% of iron reduced to metallic iron over a period of 12 hours. The feed of the multi-hearth furnace is mixed with limestone and fed into the rotary kiln. In the first third of the rotary kiln, the mixture is preheated to a temperature of 900-1000 C. the last portion of the rotary kin is known as the reducing zone. In this portion of the rotary kiln, the solid iron oxide is reduced to metallic iron. This portion's temperature can reach up to 1100 C. air injected into the rotary kiln along with its length. The limestone is converted into lime, which acts as a flux in the melters. The waste gases scrubbed to remove solids and burnt to remove any flammable compounded before being vented to air.
The first stage of thermo-mechanical treatment of steel is quenching. in this process, the hot-rolled bars are cooled by a water spraying system (thermex system). This process cools down the outer layer of the steel bars. The Cooling process will harden the outer core of steel rebar, which results in improving the rebar ductility. Self tempering is the second stage of TMT bars treatment, the hot core of steel rebar will transfer the heat to the outer layer, which results in tempering the outer layer. As a result of this process, a new structure called tempered martensite will be formed. Once the second stage is completed, the bars will be ready for atmospheric cooling. This is done by cooling the bars on the bed at normal temperatures. At this stage, the austenitic core turns into ferrite pearlite. The treated rebar will compose of a strong outer core and ductile inner-core. This process will increase the tensile strength and ductility of rebar. TMT steel bar has different grades, such as Fe415, Fe 415S, Fe 500, Fe 500D, Fe 500S, Fe 550D, Fe 600, etc.