Deformation behaviour of novel medium carbon bainitic steels with different retained austenite characteristics designed by the sparse mixed regression model

A new concept for the alloy design of advanced structural steels was figured out with the experimental elaboration of deformation behaviour in two novel medium carbon bainitic steels proposed sparse mixed regression model. Fe-0.53C-1.55Si-0.48Mn-0.59Cr-0.05Ni (wt %, Steel-A) and Fe-0.64C-1.74Si-2.11Mn-0.2Cr-0.15Ni (Steel-B) were studied. These steels were austempered to get bainite structure with retained austenite of different fraction and morphology. The chemical composition and heat treatment conditions were designed by sparse mixed regression modelling. In the Steel-A, the retained austenite fraction is 0.07 and it is in film form. In the Steel-B, the retained austenite fraction is 0.37 and most of them are in blocky form. Both the samples showed high tensile strength (>1.6 GPa) and good elongation (>12%). The Steel-A showed poor uniform elongation, but large post-uniform elongation. In the Steel-A, the retained austenite is stable during deformation, so inherent ductility of bainitic ferrite matrix largely contributed to higher post-uniform elongation. On the other hand, in Steel-B, the occurrence of deformation-induced martensitic transformation leads to large uniform elongation, through increasing the work hardening rate and delaying the onset of plastic instability.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

A new concept for the alloy design of advanced structural steels was proposed based on the experimental elaboration of deformation behaviour in two novel medium carbon bainitic steels. The chemical composition and heat treatment conditions were designed using sparse mixed regression modelling. The results showed that both steels exhibited high tensile strength and good elongation. Steel A showed greater post-uniform elongation, while Steel B showed larger uniform elongation.