Contribution to the Mechanism of Unstable Flow in Martensite

ABSTRACT Five FeNiC alloys with graded carbon contents were examined for changes in their strain rate sensitivity of flow stress [δσ/δlogɛ˙]T, in the as-quenched martensite, at two deformation rates, ɛ˙ 1 = 4.16. 10 -4 s -1 and ɛ˙ 2 = 4.16 . 10 -3 s -2 , in the temperature interval from 77 to 300 K. At test temperatures between 150 and 300 K, the δ-e dependence displayed signs of unstable flow. Its development in the martensitic matrix could not be accounted for by the Snoek interaction alone; at 275 to 300 K the Cottrell interaction appears to contribute to it too. No difference was found between the strain rate sensitivities when the carbon contents were high. This suggested that only part of the carbon atoms dissolved in the martensitic matrix participated in the redistribution of carbon atoms by their interactions with dislocations, or, possibly, that the outcome had been affected by interactions between the carbon atoms themselves.