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Abstract In the past decades, high Mn Al C lightweight steels have been extensively studied due to their excellent mechanical properties. However, the yield strength is usually less than 1.2 GPa for relative lower carbon content (≤1.2 wt %) steels after the general strengthening process. This study was intended to enhance the yield strength of the steel. For this purpose, a novel heterogenous lamellar microstructure was introduced in lightweight steel with the nominal component of Fe 30Mn 11Al-1.2C (wt. %), which could provide extra back stress strengthening. The microstructure consists of the lamellar fully recrystallized austenite matrix and the small volume fraction (<2%) submicron-sized ferrite which merely distributed in the fine grain layer. The formation process and the underlying strengthening mechanism of the lamellar microstructure were analyzed. Due to the synergistic strengthening of back stress, grain refinement and aging strengthening, ultrahigh yield strength (∼1.4 GPa) and greatest specific yield strength (∼220 MPa g−1 cm3) with good elongation (∼27%) were realized in the present alloy. [ABSTRACT FROM AUTHOR]

Aging treatments under three temperatures were performed to investigate the aging hardening response of high carbon high manganese austenitic Fe-30Mn-10Al-2C steel. The dramatic differences in hardness and microstructure were observed after aging under different temperatures. The aging treated at 500 ℃ had a typical aging hardness curve and the hardening response originated from the precipitation of κ-carbide, which plays an important role in performance improvement. When aging was conducted at 700 ℃, there was no significant change in hardness because a balance between aging hardening and high-temperature softening was built. On the contrary, the aging under 600 ℃ exhibited novel continuous increase in hardness and dramatic secondary hardening due to the formation of β-Mn which had an intrinsic high hardness. In addition, the β-Mn was also found after aging for long time under other temperatures. Unfortunately, the formation of β-Mn distributed along γ grain boundaries led to serious brittle fracture. For further investigation and application, the β-Mn transformation behavior was discussed based on the diffusion and redistribution of elements. Considering the dramatic difference in the formation kinetics of β-Mn depending on aging temperature, the diagram of β-Mn transformation was achieved to obtain optimized aging conditions. [ABSTRACT FROM AUTHOR]

A strategy was developed to circumvent the trade-off between the yield strength and strain hardening capability in Fe–30Mn–11Al–1.2C low-density steel by coupling two-step aging and intermediate pre-strain processes. The improvement of strain hardening capability is attributed to the non-shearable intragranular DO 3 particles. [ABSTRACT FROM AUTHOR]