Direct evidence of cementite dissolution in drawn pearlitic steels observed by tomographic atom probe

The dissolution of cementite during cold-drawing of pearlitic steels has been directly observed with the tomographic atom probe (TAP). Because of the nanometric interlamellar spacing and size of cementite lamellae, the TAP is shown to be extremely well suited for such a study. Analysis conditions and mass spectra peak deconvolution are shown to lead to quantitative analysis of both ferrite and cementite. It is also shown that specimen preparation always aligns the cementite lamellae habit plane with the analysis direction so that the analysed area is always perpendicular to their habit plane. Local magnification effects are also shown not to affect the carbon concentration measurement in the cementite. The first direct atomic scale quantitative concentration data across a few nanometer-thick cementite lamellae are given, and confirm the dissolution of cementite after cold-drawing. The derived compositions of ferrite, cementite and interfacial areas are obtained, giving information on the cementite dissolution mechanism as well as on its extent.