Thermo-mechanical treatment (TMT)发表评论(0)编辑词条

    TMT is an acronym for the phrase ‘thermo-mechanical treatment’. The Bureau of Indian Standards while issuing the new code IS: 1786-1985  TMT Bars is an acronym for “thermo-mechanical treatment”.     Thermo Mechanically Treated (TMT) bars are manufactured using the 'Quenching & Tempering' (Q & T) technology. TMT bars gets its strength properties from quenching and tempering. No mechanical treatment is involved in TMT Bars. 

    Quenching: Hot TMT bars coming out from rolling mills are treated(cooled) with water on the surface to form marten site on the surface, the core remain austenitic. The TMT steel bars are passed through a water-cooling system where they are kept till the outer surface of the bars becomes colder while the core remains hot. This creates a temperature gradient in the bars.      

    Temp core: TMT BARS are removed from cooling zone. A temperature gradient is established in the  cross section. It causes heat to flow from centre to surface. The marten site left at centre is tempered by heat flow. So it is known as temp core. After the intensive cooling, the TMT bar is exposed to air and the core reheats the quenched surface layer by conduction, therefore tempering the external marten site. Helps them attain higher yield strength. The resulting heat-treated structure imparts superior strength and toughness to the bars. Depending upon the yield strength and ductility required percentage of transformed core area and temperature ranges are chosen. 

    Isothermal Transformation: Austenite remaining at the core is transformed. During atmospheric cooling , austenite transforms into a very fine-grained pearlite structure. 

    After thermo mechanical treatment, surface consists of tempered marten site and core of ferrite pearlite .The tempered marten site surface layer is very hard while the microstructure of the core is a very fine-grained pearlite which is soft. The result is a structure in TMT bar with a high yield strength combined with high ductility. 

    TMT bars are also known as 'Quenched and Tempered Rebars', because of the quenching and tempering processes involved in making the TMT bars.