Effects of Cu addition on formability and surface delamination phenomenon in high-strength high-Mn steels

The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging. Among austenite stabilizing alloying elements in those steels, Cu has been known as an effective element to enhance tensile properties via controlling the stacking fault energy and stability of austenite. The effects of Cu addition on formability, however, have not been sufficiently reported yet. In this study, the Cu addition effects on formability and surface characteristics in the austenitic high-Mn TRIP steels were analyzed in consideration of inhomogeneous microstructures containing the segregation of Mn and Cu. To reveal determining factors, various mechanical parameters such as total elongation, post elongation, strain hardening rate, normal anisotropy, and planar anisotropy were correlated to the hole-expansion and cup-drawing test results. With respect to microstructural parameters, roles of (Mn,Cu)-segregation bands and resultant Cu-rich FCC precipitates on the formability and surface delamination were also discussed. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.