In-situ observation on the growth of Widmanstätten sideplates in an Fe–C–Mn steel

•Widmanstätten sideplate growth behavior was conducted by in-situ observation.•Face-to-face nucleation was observed in the formation of Widmanstätten sideplate.•Widmanstätten sideplate was lengthened faster on specimen free surface than in bulk.

The growth behavior of Widmanstätten plates as well as their lengthening rate in an Fe–0.09C–1.48Mn (weight percent) alloy were examined in-situ on the specimen surface and in bulk specimen by the traditional quench-arrest experiments. Widmanstätten plates directly emanated from austenite grain boundaries and/or from the existing ferrite allotriomorphs, i.e. through the mechanism of edge-to-face sympathetic nucleation. Simultaneously, face-to-face sympathetic nucleation could also occur on the broad face of pre-formed plates. The growth of Widmanstätten plates on the free surface did not occur at a constant lengthening rate but was accompanied by acceleration and deceleration. The average plate lengthening rate measured on the free surface was about one order of magnitude larger than that measured in bulk specimen. The former was close to the plate lengthening rate predicted by the modified Zener–Hillert model assuming paraequilibrium, while, the latter was close to the one that assumes negligible partition local equilibrium.