Effect of melt superheating on the sub-rapidly solidified microstructure of AISI 304 austenitic stainless steel strip

The effect of melt superheating on the sub-rapidly solidified microstructure of AISI 304 austenitic stainless steel strip cast by water-cooled copper mould casting was investigated. The results show that the solidified microstructures from surface to center of the as-cast strip are cellular austenite, columnar ferrite dendrite and equiaxed ferrite dendrite, respectively. With the increase of superheating, both the primary arm spacing of cellular austenite and the secondary arm spacing of ferrite dendrite raise, while the delta ferrite fraction decreases. As the melt superheating raises, the supercooling of melt falls, then the cooling rate of melt decreases, resulting in the increase of dendritic arm spacings of austenite and delta ferrite. The decrease of cooling rate also accelerates the transformation from delta ferrite to austenite during the subsequent cooling process after solidification, leading to the reduction of residual delta ferrite fraction.