A new strengthening mechanism driven by disruptive shear and solute segregation during warm rolling in 1.4 GPa class 12.5 wt% Al added-FeMnC ultra-lightweight steel

Novel strengthening of Fe-29.1Mn-12.5Al-1.35C-4.95Cr steel achieved by warm rolling was investigated. The solution-treated steel consisted of a gamma-matrix containing nano-sized kappa-carbide ((Fe,Mn) 3AlC) and elongated prior ferrite, which was transformed into FeAl-type B2 and Fe3Al-type D0(3) phases. The solution-treated steel exhibited poor strain hardening owing to glide softening associated with kappa-carbide shearing by dislocations. However, after warm rolling with a reduction ratio of 30% at 300 degrees C, the yield and tensile strengths significantly increased from 917 to 1300 MPa and 1025 to 1419 MPa, respectively. The tensile test conducted at 300 degrees C to simulate warm rolling exhibited serrated flows, indicating dynamic strain aging (DSA). Atom probe tomography exhibited that the C atoms in kappa-carbide were swept away along the slip direction by disruptive shear during rolling at 300 degrees C. The swept C atoms along the slip direction interacted strongly with dislocations at 300 degrees C, with repeated pinning and breakaway of dislocations from the C atoms. This contributed to significant strengthening owing to the formation of a solute-rich atmosphere after warm rolling. The results of the tensile tests at 300 degrees C indicated that the degree of strengthening was proportional to the pre-strain level. Tensile strength of 1.4 GPa can be achieved with good ductility (17% elongation) by warm rolling. This novel warm-rolling strengthening method expedites the potential application of Fe-29.1Mn-12.5Al-1.35C-4.95Cr as a 1.4 GPa class ultra-lightweight steel. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The strengthening effect of Fe-29.1Mn-12.5Al-1.35C-4.95Cr steel through warm rolling was investigated. After warm rolling at 300 degrees C, the steel exhibited significantly increased yield and tensile strengths. The warm rolling process caused the transformation of nano-sized carbides and elongated ferrite into different phases, leading to the strengthening of the steel.