In Situ Observations of the Formation of Fine-Grained Mixed Microstructures of Acicular Ferrite and Bainite in the Simulated Coarse-Grained Heated-Affected Zone



The formation of fine-grained mixed microstructure of acicular ferrite and bainite in the simulated coarse-grained heated-affected zone was investigated by means of in situ observation and EBSD analysis. Single, multiple, and sympathetic nucleation of acicular ferrite were observed. Acicular ferrite laths or plates were formed prior to bainite and effectively partitioned austenite grains into many smaller and separated regions. The later formed bainite at lower temperature was confined in those smaller regions, thus resulting in the fine-grained mixed microstructures of acicular ferrite and fine bainite plate.