The role of stress-induced ordering of interstitials in the deformation of Fe[sbnd]Ni[sbnd]C martensites

Abstract

Unaged martensite specimens of Fe-18 wt. % Ni alloys containing 0·005, 0·1, 0·2 and 0·4 wt. % C have been deformed in compression. The temperature and strain-rate dependence of the flow stress have been measured at five different temperatures, from 77°k to 293°k. Except for the purest alloy, and at temperatures T > 160°k, the changes in strain rate were accompanied by stress transients of high amplitude. At T > 250°k, the strain-rate sensitivity of the flow stress was negative. These results are explained in terms of the Snoek ordering of carbon atoms around moving dislocations, and it is shown that they are in agreement with theoretical calculations (Schoeck and Seeger 1959). At low temperatures (T< 160°k), where the influence of stress-induced ordering is negligible, the strain-rate sensitivity of the flow stress increased with carbon content, in agreement with the predictions of a model of point defect hardening (Guiu 1969 b).