Our TMT process is a method of quenching and  self-tempering of steel rods at the end of the rolling-mill process. After having left the final rolling-mill process (at temperature 900 to 1050° C), the steel rod enters a water-cooling chamber in which it is subjected to strong quenching on its surface, thus acquiring a martensitic (bonded iron and carbide) structure, whereas the core of the rod, having a higher temperature, acquires an austenitic structure. After quenching, the bar is left in still air and during this time heat flows from the center of the bar to the surface, caused by the temperature gradient between these two parts.


The martensite surface layer is thereby subjected to self-tempering that continues until the internal and external temperatures of the bar are equal (approx. 600° C). This process is monitored on the cooling bed. The characteristics of the steel thus obtained derive clearly from its chemical composition, diameter, final temperature and intensity of cooling. The product resulting from the process is highly ductile (with an increase in the elasticity limit equal to 150-250 MPa) and weldable (the chemical analysis, particularly of its carbon and carbon equivalent, shows values in line with normal values - C<=0.24% and Ceq<=0.40%).

The on-line heat treatment is completed in 3 successive stages :

• As soon as it leaves the final mill stand, the product is rapidly and energetically cooled in a short cooling installation, where it undergoes a surface hardening (marten site layer)
• As soon as this quenching operation is stopped, the surface layer undergoes Tempering by using the residual heat left in the core of the bar (self tempering of the marten site layer)
• The third stage takes place while the product lies on the cooling bed where the bar is subjected to normal air cooling down to ambient temperature (transformation of the residual austenite in the core).