CARMEN OTILIA RUSANESCU1, MARIN RUSANESCU PROCESS DESIGN IN THE MANUFACTURING OF PIPES FOR CHEMICAL AND PETROCHEMICAL INDUSTRY In the present study the influence of vanadium microalloy on kinetics of transformation in medium carbon steel is studied. In order to choose the thermal treatment temperatures at optimal values, the steel transformation points were determined by dilatometric analysis. The bainitic transformation point was obtained under fast cooling conditions. The industrial experiments on the hardening and tempered of steel were performed in five variants of the oil hardening and reversing treatment, with austenitizing temperatures for hardening and the tempered temperature. The steel quality was determined, the influence of the temperature on the microalloyed steel structure with vanadium was highlighted. The mechanical characteristics of the pipes after the thermal hardening and tempering were analyzed after the traction test and the shock break. Electron microscopy analysis on extraction replicas revealed aspects of precipitation, globular constituent after return is finely and uniformly distributed, austenitization at lower temperature, resulted in a finer austenitic grain <20>. The finer structure obtained after hardening resulted in heat treatment to return to precipitation of fine and uniformly distributed carbides. It has been found that the influence on bainitic transformation depends on temperature; the steel structure after the quenching and tempering treatment was analyzed by optical and electronic microscopy. The development of welding consumables is permanently challenged with matching the increasing strength and toughness of thermomechanically treated or hardening and tempered steels.