Effect of heating rate on nucleation and growth of austenite in cold rolled dual phase steel

Abstract

In this study, the effect of heating rate on austenite nucleation and growth in a cold rolled dual phase (DP) steel during annealing was investigated by microstructural analysis and electron probe microanalysis (EPMA). Two heating rates, 5 and 300 K s⁻¹, and different holding times ranging from 1 to 300 s were applied to study the austenisation progress. It was found that the austenite nucleated at recrystallised ferrite grain boundaries and grew along them at low heating rate (5 K s⁻¹), and a high carbon rim is observed in the formed austenite at low heating rate. An increase in heating rate resulted in austenite nucleating at the carbide/ferrite interface and growing into deformed ferrite. In addition, a higher carbon concentration existed at original carbide particle area. Higher heating rate could improve the strength. But long holding time minimises the strength difference caused by a difference in heating rate.