Investigation of the influence of manganese on the dynamic strain ageing of ferritic steels – Part II: Industrial alloy

Dynamic strain aging (DSA) was studied in an as-welded C-Mn steel at multiple scales, using macroscopic tensile tests, in-situ TEM tensile tests and atom probe tomography (APT). At the macroscopic scale, DSA is related to an increase in Ultimate Tensile Strength (UTS) between 423 K and 623 K, compared to room temperature. PLC serrations are observed in a limited temperature range, 423 K and 473 K. At the nano-scale, DSA manifests as a change in dislocation dynamics, namely the occurrence of dislocation bursts. Interestingly, high-temperature diffusion-controlled (HTDC) Peierls glide suppresses PLC serrations, and its velocity controls the end of DSA. Moreover, the occurrence of HTDC-Peierls glide suggests that interstitial atoms control DSA in the C-Mn weld, that being confirmed by the extracted activation energy for HTDC-Peierls glide and by APT characterizations showing the absence of Mn on dislocations. Contrary to what was observed in the Fe-3Mn-C model in the first part of this study, Mn does not influence DSA in this industrial C-Mn weld. We propose that the reduced Mn content does not lead to a sufficient anchoring of mixed dislocations, thus allowing for the occurrence of HTDC-Peierls glide. Consequently, screw dislocations, which do not attract Mn atoms, become prominent as deformation proceeds, therefore suppressing the Mn-controlled DSA. Based on these findings, we discuss previously published results regarding the manifestations of DSA in steels as a function of their chemical composition.