Effect of austenitizing temperature on intergranular proeutectoid ferrite nucleation in a V-N steel

Intergranular proeutectoid ferrite nucleation in a V-N steel has been exami ned at isothermal transformation at 600 degrees C with respect to the auste nitizing temperatures. While substantial grain growth takes place, the numb er of intergranular ferrite grains per unit grain boundary area decreases w ith increasing austenitizing temperatures. Non-stationary increasing rate w ith time is observed. Overall transformation during isothermal transformati on delays after austenitizing at higher temperatures and follows the Johnso n-Mehl-Avrami formula for the case of fast grain boundary nucleation. It is discussed that the decrease in the intergranular ferrite nucleation rate a ssociated with higher austenitizing temperatures is partially due to grain boundary structures, not merely to the decrease in the nucleation sites ass ociated with grain growth. Use of high austenitizing temperature is requisi te for the intragranular ferrite precipitation.