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Ex situ and in situ TEM investigations of carbide precipitation in a 10Cr martensitic steel

Wang, Hongcai
Journal of materials science 2018 v.53 no.10 pp. 7845-7856
carbides, differential scanning calorimetry, heat production, microstructure, steel, temperature, transmission electron microscopy
An ex situ approach combining fast quenching experiments in a dilatometer and postmortem microstructural observation in transmission electron microscopy (TEM) has been used to observe the dynamic microstructure change during differential scanning calorimetry (DSC) ramping of an Fe–10Cr–0.15C (wt%) alloy fabricated from high-purity components. The DSC measurements reveal two exothermic events at temperatures about 270 and 600 °C in a heating process. The two events were discerned by TEM investigations on specimens interrupted during thermal ramping in a dilatometer. It is found that precipitation and growth of M₃C carbide occurred first in a temperature range between 200 and 400 °C, following the Bagaryatskii orientation relationship. Subsequently, M₇C₃ carbides precipitate on prior martensitic laths boundaries in a temperature range between 500 and 700 °C at the expense of M₃C. M₂₃C₆ carbides were found precipitating on the interface between M₇C₃ and matrix at approximately the same time with the precipitation of M₇C₃. The obtained results are also compared with an in situ TEM heating experiment, and differences between the two approaches are discussed.