Ultrahigh Strength Induced by Superstorage Capacity of Dislocations in an Ultrafine-Grained Fe-9Mn-0.15Si-0.26C Steel

A Fe-9Mn-0.15Si-0.26C steel was prepared via warm rolling, showing the heterogeneous microstructures composed of ultrafine-grained ferrite (similar to 330 nm) and nanoscale twins (similar to 40 nm) in the lamellar austenite. We aim to improve the strain-hardening rate (SHR) via the transformation-induced-plasticity (TRIP) and twinning-induced-plasticity (TWIP) effects. The steel shows ultrahigh yield strength of 710 +/- 10 MPa and ultimate tensile strength of 2410 +/- 20 MPa, with the total elongation of 27%. Such an ultrahigh strength is rarely reported for the advanced high strength steels (AHSSs). By controlling the specific strain level, the deformation mechanisms governing the different stages of the warm-rolled steel are explored, suggesting significant differences compared to the typical structural metallic alloys. The uplifted stress-strain curve and continuously increasing hardening curve can be attributed to the continuous martensite transformation and twinning process during the whole strain, and the moderate stability of austenite has played a role. In addition, the geometrical necessary dislocation, rho(GND), is 1.04 X10(15) m(-2) in the fractured specimen (epsilon = 27%), leading to a strain hardening of 1753 MPa.

Automated summary

By controlling the specific strain level, the deformation mechanisms of the warm-rolled steel were studied, revealing the steel's ultrahigh strength and ductility, which differs significantly from typical structural metallic alloys.