Shock and spall behaviors of a high specific strength steel: Effects of impact stress and microstructure

Abstract

A series of plate-impact experiments were conducted to investigate the influences of impact stress and microstructure on the shock and spall behaviors of a high specific strength steel (HSSS). The HSSS shows a strong positive strain rate sensitivity on the yield strength. With increasing impact stress up to about 6 GPa, the spall strength is found to decrease significantly and then levels off with further increasing impact stress. This trend is proposed to be attributed to the accumulation damage within the target as the initial shock-induced compression wave propagates through the target. The microcracks are clearly observed to nucleate from the interfaces between γ-austenite and B2 phase and propagate along the interfaces or cut through the B2 phase in the HSSS during the spalling process. The Hugoniot elastic limit and the spall strength were found to be highly dependent on the microstructure. The spall strength was found to be higher when the density of the void nucleation sites is lower, indicating that the spall strength should be a microstructure parameter of the HSSS under impact tensile conditions depending on the density of phase interfaces. It was also found that there is a tradeoff between the specific yield strength and the spall strength for this HSSS; thus, the current findings should provide insights for achieving an optimal combination of both mechanical properties for impact-resistant applications by tailoring the microstructure.

Deformation mechanisms for superplastic behaviors in a dual-phase high specific strength steel with ultrafine grains

“…The details for the preparation of the HSSS can be found in our previous papers [25,26]. The hot-rolled plates with a thickness of 7.3 mm were cold rolled into a final thickness of 1.5 mm, and then were annealed at 1173 K for 15 min followed immediately by water quenching.…”

“…This HSSS shows excellent combination of specific strength and elongation when compared to the other low-density metals and alloys. In our previous research [25,26], it has been shown that this UFG HSSS should be better understood as a dual-phase microstructure since the B2 phase is deformable. Thus, the stress/strain partitioning between the constituent phases and the back-stress-induced strain hardening should play important roles during the plastic deformation for this HSSS.…”

Strain Rate Effect on Tensile Behavior for a High Specific Strength Steel: From Quasi-Static to Intermediate Strain Rates

“…Kim et al [20] has attributed the outstanding mechanical properties of this HSSS to the precipitation strengthening by the brittle B2 intermetallic compound. In our previous work [21,22], the stress/strain partitioning between the constituent phases and the back-stress-induced strain hardening have been found to play an important role during the plastic deformation for this HSSS, since the B2 phase was found to be deformable.…”

“…%) was produced using arc melting under protection of pure argon atmosphere, and the detailed procedures for preparing the hot-rolled (HR) strips can be found in our previous papers [21,22]. The HR strips with a thickness of 3.9 mm were annealed at 1000 • C for 1 h first, and then were cold rolled (CR) into a final thickness of 1.3 mm with a thickness reduction of 66%.…”

“…The tensile fracture surfaces were also characterized by scanning electron microscopy (SEM). The detailed description of the sample preparation and the operating procedures for obtaining EBSD and TEM images can also be found in our previous papers [21,22].…”