Nucleation Stages of Isothermal Transformation in Titanium and Titanium Free Micro-Alloyed Steels

Abstract

This work is focused on nucleation stages during
isothermal austenite transformation in two types of
Vanadium micro-alloyed steels. Isothermal treatment was
carried out in the temperature range 350 to 600
C.
Metallographic evaluation using optical and scanning
electron microscopy (SEM) enabled determination of the
nucleation curves of isothermally decomposed austenite.
Three curves are found to be relevant to this initiation stage
of transformation: first curve is related to grain boundary
nucleated ferrite (GBF), second curve is related to intragranularly

nucleated ferrite (IGF) and the third to pearlite
(P) curve. GBF and IGF curves are divided into two regions,
which represents the high temperature and the low
temperature segments as consequence of either displacive
nature of transformation or diffusion transformation.
Addition of Ti to V – micro-alloyed steel in this work seems
to be balanced by a slightly higher C and Mn content,
leading to limited effect on nucleation stage of austenite
decomposition.