Microstructural Modifications of As-Cast High-Chromium White Iron by Heat Treatment

The initial as-cast microstructure of a high-chromium (2.35% C, 18.23% Cr) white cast iron consisting of primary austenitic dendrites and a eutectic mixture of M₇C₃ carbides/austenite was extensively modified by four different heat treatments: H.T.A: destabilization (970 °C-2.5 h), H.T.B: destabilization/subcritical treatments (970 °C-2.5 h + 600 °C-13 h), H.T.C: subcritical treatment (600 °C-13 h) and H.T.D: subcritical/destabilization treatments (600 °C-13 h + 970 °C-2.5 h). H.T.A leads to martensitic structures that present considerable precipitation of cubic secondary carbide particles of M₂₃C₆ type. H.T.B produces pearlitic structures and causes further carbide precipitation and pre-existent carbide particle shape modifications. H.T.C extensively modifies the initial as-cast structure to more pearlitic morphologies accompanied with spheroidization/degradation of the M₇C₃ primary carbide structure. H.T.D causes extensive formation of secondary carbide particles within the primary austenitic matrix; the latter has been mainly transformed to martensite. The effect of each heat treatment on the hardness of the alloy was correlated with the attained microstructure.