**1. Introduction**

Excellent combination of mechanical and corrosion resistance properties is an initial requirement for high strength low alloyed steel plates which have to be used for the construction of bridge, pipe lines, and ship hull applications [1]. Generally, basic steels do not have the sufficient combination of properties for a direct use for such types of applications. Desirable structural properties may become possible by changes in the chemical composition of steels or by heat treatments such as continuous/isothermal heat treatments with/without thermo-mechanical processing of steels. The compassionate evolved will support in scheming isothermal heat treatment cycles during production of such steels. During steel processing as well as fabrication through welding, the phase transformation has always been a significant research topic for steel users and metallurgists. Isothermal heat treatment

is subsequently possible after casting process in industry on nominal cost. Better properties offer to users to reduce the overall cost for structures by reducing the thickness of steel plates. Presently, most of researchers focus on isothermal transformation treatments for medium and high grade carbon steel [2–5] but they lack such information in wide range of isothermal temperature on micro-alloyed steel.

In the present study, effort has been made to design isothermal transformation (ITT) phase diagram for micro-alloyed steel. Isothermal heat treatments are experimented by using physical thermo-mechanical simulator in an isothermal temperature range from 750 to 100°C. Microstructural evolution is characterized by optical microscopy.
