Ultra-high strength medium-Mn lightweight steel by dislocation slip band refinement and suppressed intergranular ?-carbide with Cr addition

Ultra-high strength lightweight steel has great potential in the automotive industry. An ultra-high strength Fe12Mn-9Al-1.4C-3Cr austenite-based lightweight steel has been developed in the study. The alloy is designed based on the precipitation strengthening of kappa-carbides while preventing the formation of intergranular kappa-carbides by sub-rapid solidification and Cr addition. The results show that the addition of Cr element reduces C segregation at grain boundaries by expanding the solid solution ability of austenite matrix. It can effectively inhibit the precipitation of intergranular kappa-carbides at the grain boundaries. Therefore, the ductility of as-cast steel is greatly improved from 14.0% to 47.8% by Cr addition. Besides, the strain hardening ability of the alloy is also enhanced with refined slip bands. The yield strength and tensile strength of the cold rolled steel reach approximately 1.5 GPa, with an elongation up to 15%. The ultra-high strength comes from the high-density dislocation hardening and precipitation strengthening of kappa-carbides. This work provides potential alloy design and processing route for automotive applications requiring ultra-high strength and lightweight.

Automated summary

An ultra-high strength lightweight steel has been developed in this study, with improved ductility and strain hardening ability through the addition of Cr element. By carefully controlling alloy composition and processing methods, the steel achieved high elongation, yield and tensile strength of around 1.5 GPa, meeting the requirements of ultra-high strength and lightweight in automotive applications.