Dynamic strain aging mechanisms in a metastable austenitic stainless steel

Discontinuous plastic flow due to dynamic strain aging (DSA) in a Fe-13Cr-3.4Mn-0.47C metastable stainless steel was studied by uniaxial tensile tests in the temperature range from 20 degrees C to 500 degrees C. A complex picture of the discontinuous flow and its disappearance in an intermediate temperature interval was interpreted in terms of an existing model, which had to be modified. Different mechanisms of DSA were proposed for different temperature intervals. DSA at temperatures up to 200 degrees C was attributed to deformation-induced martensitic transformation within glide bands. Immobilization of dislocations at martensite/austenite boundaries and emission of fresh dislocations into the adjacent austenite was considered as a major process in this temperature regime. Rapid diffusion of carbon from martensite to the martensite/austenite boundaries was considered as an additional pinning mechanism contributing to discontinuous plastic flow. Serrations on the deformation curves at temperatures between 200 degrees C and 300 degrees C were associated with dislocation pinning due to carbon diffusion in austenite. This regime of DSA did not involve high diffusivity martensite. In spite of an increase in the diffusivity of carbon in the temperature range of 350-450 degrees C, a serration-free regime was observed there. The absence of intermittent dislocation pinning/unpinning events responsible for serrations implied continuous solute drag by carbon atoms according to the Cottrell mechanism. Serrations reappeared at 500 degrees C and were attributed to dislocation pinning by substitutional chromium and manganese atoms. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Discontinuous plastic flow due to dynamic strain aging in a Fe-13Cr-3.4Mn-0.47C metastable stainless steel was studied, with different mechanisms proposed for different temperature intervals. The study identified deformation-induced martensitic transformation and carbon diffusion as key processes in DSA at various temperatures.