Abstract
The strain rate effect on the tensile behaviors of a high specific strength steel (HSSS) with dual-phase microstructure has been investigated. The yield strength, the ultimate strength and the tensile toughness were all observed to increase with increasing strain rates at the range of 0.0006 to 56/s, rendering this HSSS as an excellent candidate for an energy absorber in the automobile industry, since vehicle crushing often happens at intermediate strain rates. Back stress hardening has been found to play an important role for this HSSS due to load transfer and strain partitioning between two phases, and a higher strain rate could cause even higher strain partitioning in the softer austenite grains, delaying the deformation instability. Deformation twins are observed in the austenite grains at all strain rates to facilitate the uniform tensile deformation. The B2 phase (FeAl intermetallic compound) is less deformable at higher strain rates, resulting in easier brittle fracture in B2 particles, smaller dimple size and a higher density of phase interfaces in final fracture surfaces. Thus, more energy need be consumed during the final fracture for the experiments conducted at higher strain rates, resulting in better tensile toughness.
Highlights
Metals and alloys with high strength and ductility are always desirable in applications for automobiles, aerospace and military defense
From boundaries the transmission electron microscopy (TEM) image, it can be seen that the B2 phase is much inclined to precipitate either theγ-austenite grain or triple junctions of γ-austenite matrix
The tensile behaviors of the high specific strength steel (HSSS) with ultrafine grains and dual-phase microstructure were investigated over a wide range of strain rates from 0.0006 to 56/s in the present study, and the main findings are summarized as follows: (1)
Summary
Metals and alloys with high strength and ductility are always desirable in applications for automobiles, aerospace and military defense. %), have been widely studied due to their excellent mechanical properties, such as high specific yield strengths and large uniform elongations [8,9,10,11,12,13,14,15,16,17,18,19] Most of these HSSS are based on Fe–Al–Mn–C alloy system %) has been developed [20] This HSSS with a dual-phase microstructure and ultrafine grains was found to show excellent mechanical properties, such as high specific strength and large elongation (a combination of a specific yield strength of 200 MPa·g−1 ·cm and uniform elongation of 16%, which can hardly be achieved in other high-strength steels). Kim et al [20] has attributed the outstanding mechanical properties of this HSSS to the precipitation strengthening by the brittle B2 intermetallic compound
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