Interlamellar Spacing of Pearlite in a Near-eutectoid Fe–C Alloy Measured by Serial Sectioning

Abstract

The interlamellar spacings of pearlite formed isothermally at 700 and 680°C in a near-eutectoid Fe–0.82mass%C alloy were measured by serial sectioning coupled with scanning electron and atomic force microscopy. The intersection angle of cememtite lamellae with the metallographic surface was determined from the variation of horizontal displacement of cementite lamellae with removal depth. The true lamellar spacing was then calculated from the apparent lamellar spacing on the surface. When the angle was small, i.e. less than ~20°, it was measured directly by atomic force microscope. The minimum and mean true lamellar spacings are in good agreement with those measured by other methods. The distribution of interlamellar spacings on the specimen surface back calculated from the spectra of true interlamellar spacing assuming the random orientation of cementite lamellae was in fair agreement with the measured one. It is likely that the distribution of true lamellar spacings is primarily due to recalescence and the minimum true spacings rather than the mean value may be relevant to the thermodynamic theory of pearlite transformation.