THE PROCESS
Equipment of the Water Box
The above schematic illustrates the exclusive TMT process which converts low carbon steel into high strength bars with a guaranteed yield strength of .500 mpa. In Bangladesh, SARM is the company to procure and implement this technology commercially and successfully.
Mechanical Graph
High strength, ductilily and weldabiliy together was an almost impossible combination – a civil engineer’s dream, and a steel metallurgist’s nightmare. The unique heat treatment technology in the TMT makes this possible. SARM rebars have typically high strengths. shown in the stress-strain graph above, yet retain the modulus of plain carbon steel. 2 1 0 Cpa [29,000,000 psi].
The TMT Process at SARM
How the TMT Process Works
SARM SUPREME rebars are hot-roHed from prime qualily steel billets and subjected to on-line thermo-mechanical treatment in three successive stages.
(a) Quenching:
The hot rolled bar leaving the final mill stand is rapidly quenched by high pressure water in special venturi tubes. This hardens the surface of the bar to a depth optimized for each section through formation of martensitic rim, while the core remains hot and austenitic.
(b) Self Tempering:
As the bar leaves the quenching venturi tube the core remains hot compared to the surface, allowing heat to flow from the core to the surface which causes tempering of the outer martensitic layer into a structure called Tempered Martensite. The core still remains austenitic at this stage.
(c) Atmospheric Cooling:
This takes place on the cooling bed, where the austenitic core is transformed into a ductile ferrite-pearlite structure. Thus the final structure consists of an optimum combination of strong outer layer (tempered martensite) with a ductile core (ferrite-pearlite). This gives SARM TMT bars a unique combination of high strength and ductility.
A close-up view of the dual phase rebar made by SARM Steels Ltd – a hard outer shell of tempered martensite and an inner core of very tough and ductile ferrite-pearlite core. This unique technology at SARM enables very high strength in the reinforcing bar without sacrificing ductility and weld ability.