Three-dimensional distribution, morphology, and nucleation site of intragranular ferrite formed in association with inclusions

The three-dimensional (3-D) distribution, morphology and nucleation site of intragranular ferrite formed in association with MnS particles were observed by computer-aided reconstruction of images obtained by serial sectioning in an Fe–0.1mass% C–1.5mass% Mn alloy isothermally reacted at 610 and 640 °C. 3-D analysis indicated that essentially all the intragranular ferrite precipitates nucleate at inclusions. The 3-D shape of idiomorphic ferrite precipitates was considerably more irregular than would be expected from their shape on polished specimen surfaces. Electron backscattering diffraction analysis showed that ferrite particles nucleated at inclusions were often composed of several grains and subgrains, and most of them were in contact with the surfaces of inclusions. Widmanstätten ferrite which grew radially from inclusions had a lath rather than a plate shape at the temperature studied.