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 TC and θD, 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.

The kinetics of the polymorphic transformation of massicot to litharge during prolonged dry‐grinding in a laboratory pebble mill were studied by quantitative X‐ray diffraction using the direct‐comparison method. The kinetics describe stages of (1) normal comminution and (2) particle agglomeration; the latter was confirmed by measuring relative specific surface areas. Both stages obey a modified logistic growth function which takes into account a strain‐induced martensitic (shear) transformation which occurs during reduction of particle size.

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The Mössbauer effect in 57Fe has been used to study carbide phases appearing during the tempering process of an alloy steel containing 1.33 wt.% Si, 1.13% wt. Mn, and 0.38 Wt.% C. Carbides were chemically extracted from the samples which had been isothermally tempered for 2 h at various temperatures. Carbides obtained from samples tempered at 300° and 400°C were identified as ε and χ phases, respectively. The ε carbide has an isomer shift (I.S.) of 0.18 mm/sec relative to α iron and an effective hyperfine field (Hn) of 162 kOe at 300°K. The χ carbide has an I.S. of 0.28 mm/sec relative to α iron and Hn of 179 kOe at 300°K. Carbides precipitated at and above 500°C were found to have the orthormbic cementite structure, with a composition of (Fe1−xMnx)3C. As the tempering temperature increases from 500° to 700°C the Curie temperature changes from 440° to 270°K, and x increases from 0.02 to 0.10. Curie points and extrapolated values of Hn(0) were found for all the carbides in question. The early stages of tempering in which transition carbides appear are explained as being controlled by the elastic strain. The elastic binding energy between an interstitial carbon atom and a substitutional silicon atom can then be estimated. Other phases which were found in the chemically extracted samples after tempering the alloy at a low temperature, were identified as oxyhydeoxides and iron gel. In a sample tempered at 700°C the carbide was detected in the steel matrix and compared with the same carbide after chemical extraction.