Precipitation of Iron Carbides in Tempered Martensite

Abstract

The precipitation of carbides in 0.7 wt%‐carbon steel as a function of tempering temperature has been studied through the Mössbauer effect, magnetic measurements, and x‐ray observations. The magnetic behavior of the extracted precipitates is discussed. The tiny clusters obtained by extraction after the early stages of tempering (up to 250°C) show the relation of these clusters to martensitic bct cells (``Johnson clusters''). The results obtained by further stages of tempering (250–500°C) show a decrease in the relative amount of the Johnson clusters, followed by a precipitation of ferromagnetic carbides. The behavior of the internal field, the T_C and θ_D, as a function of the tempering temperature suggests a decrease of the relative carbon content with the increasing tempering temperatures. The Fe₃C is formed toward 550°C.