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

• Both macroscopic and in-situ TEM tensile tests are performed on an as-welded C-Mn steel • Dislocation bursts are directly observed and correlated to PLC serrations • Activation energies for dislocation motion reveal an interstitials-controlled DSA • HTDC-Peierls glide suppresses PLC serrations and Mn-controlled DSA • We propose a classification for DSA effects as a function of alloy chemical composition 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 423K and 623K, compared to room temperature. PLC serrations are observed in a limited temperature range, 423K and 473K. 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.