| The precipitation of metastable carbide and the decomposition of retained austenite in martensitic Fe-4Cr-O. 4C steel has been studied by micro-Vickers hardness test, transmission electron microscopy and calorimetry. The results obtained are as follows. 1) Under the argon atmosphere of 1.01×10^5 Pa, the relation between apparatus constant k of DSC used in this study and absolute temperature T gives the equation as k＝1.419-9.198×10^(-4) T, where 323˚K≤T≤773˚K. 2) There are three exothermic peaks in DSC curve of martensitic Fe-4Cr-0.4C steel. The first peak corresponds to the precipitation of ξ-carbide in the first stage of tempering, the second to the decomposition of retained austenite in the second stage of tempering, and the third to the precipitation of cementite in the third stage of tempering. 3) Activation energies for the first stage and the second stage of tempering in martensitic Fe-4Cr-0.4C steel are 134.3KJ/㏖ and 153.6KJ/㏖, respectively. 4) The time indices for the first stage of tempering are determined to be 0.86 at 373˚K and 1.00 at 423˚K from the Johnson-Mehl`s equation. 5) It is found that Differential Scanning Calorimetry is convenient to study the kinetics of carbide precipitation from the martensite. |
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