Abstract The process and characteristics of high-temperature ferrite (δ) → austenite (γ) phase transformation during cooling of an AISI30 stainless steel have been observed in-situ by using a confocal laser scanning microscope. The results show γ phase appears prior at the δ grain boundaries. The cooling rate affects the growth morphology of γ phase which representatively includes polygon, block-like, round, dendritic, plat-form, network, and calabash-like. The independent γ dendrite becomes coarse, and may converge with others surrounding γ dendrites. The convergence degree for the γ dendrite at the δ grain boundary is clearly higher than that in the grain at the same cooling rate. The secondary dendrites become coarse, and grow competitively during cooling. The growth interface becomes unstable as the cooling rate increases. Meanwhile, the movement rate increases, along with the sudden rise and then fall of temperature.
