INTRAGRANULAR FERRITE MORPHOLOGIES IN MEDIUM CARBON VANADIUM-MICROALLOYED STEEL

The aim of this work was to determine TTT diagram of medium carbon V-N micro-alloyed steel with emphasis on the development of intragranular ferrite morphologies. The isothermal treatment was carried out at 350, 400, 450, 500, 550 and 600 degrees C. These treatments were interrupted at different times in order to analyze the evolution of the microstructure. Metallographic evaluation was done using optical and scanning electron microscopy (SEM). The results show that at high temperatures (>= 500 degrees C) polygonal intragranulary nucleated ferrite idiomorphs, combined with grain boundary ferrite and pearlite were produced and followed by an incomplete transformation phenomenon. At intermediate temperatures (450, 500 degrees C) an interloced acicular ferrite (AF) microstructure is produced, and at low temperatures (400, 350 degrees C) the sheave of parallel acicular ferrite plates, similar to bainitic sheaves but intragranularly nucleated were observed. In addition to sheaf type acicular ferrite, the grain boundary nucleated bainitic sheaves are observed.