Abstract
In the context of obtaining an excellent elongation and tensile-strength combination in the third generation of advanced high strength steel, we emphasized the practical significance of adjusting the retained austenite fraction and stability in medium-Mn steel to obtain better mechanical properties. A novel cyclic quenching and austenite reverse transformation (CQ-ART) was used to obtain a large retained austenite content in Fe-0.25C-3.98Mn-1.22Al-0.20Si-0.19Mo-0.03Nb (wt.%) Nb–Mo micro-alloyed medium-Mn steel. The results show that after twice cyclic quenching and ART, the alloy exhibited optimum comprehensive properties, characterized by an ultimate tensile strength of 838 MPa, a total elongation of 90.8%, a product of strength and elongation of 76.1 GPa%, and the volume fraction of austenite of approximately 62 vol.%. The stability of retained austenite was significantly improved with the increasing of the number of cyclic quenching. Moreover, the effects of CQ-ART on the microstructure evolution, mechanical properties, C/Mn partitioning behavior, and austenite stability were investigated. Further, the strengthening effect of microalloying elements Nb–Mo was also discussed.
Highlights
Nowadays, medium-Mn steels (~3–11 wt.% Mn) have become an appealing topic due to their high metastable retained austenite (RA) content and unique fine microstructures such as dual-phase structure or tri-phase structure [1,2,3]
Since the total amount of RA increased, the average C concentration distributed to a single austenite decreased. These results indicate that the C concentration changes slightly after cyclic quenching and austenite reverse transformation (CQ-austenite reverse transformation (ART)) treatment, grain decreased
A novel heat treatment process called cyclic quenching (CQ)-ART was studied in Fe-0.25C-3.98Mn-1.22Al0.20Si-0.19Mo-0.03Nb medium manganese transformation induced plasticity (TRIP) steel
Summary
Medium-Mn steels (~3–11 wt.% Mn) have become an appealing topic due to their high metastable retained austenite (RA) content and unique fine microstructures such as dual-phase structure (fine γ and α) or tri-phase structure (fine γ, α and/or martensite) [1,2,3]. These steels are very promising for automotive applications due to their excellent strength, elongation, crashworthiness and safety [4,5,6]. This paper draws on Metals 2019, 9, 1090; doi:10.3390/met9101090 www.mdpi.com/journal/metals
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