Experimental investigation of adiabatic shear band formation in steels

Dynamic deformation response of a high-strength, high-toughness Fe–10Ni–0.1C steel

“…The question remains why such transformed austenite does not revert to martensite on rapid cooling of the shear band as heat must be quickly extracted from it by the surrounding metal. In fact, Clos et al [7] have claimed heating and cooling rates within the band of the order of 10 7 K/s and 10 6 K/s, respectively. This is likely a consequence of the fine austenite grain size which suppresses martensite formation, and previous work on binary Fe-Ni alloys using rapid solidification processing has in fact confirmed this to be the case for grain sizes less that about 1 m [44][45][46][47]; the grain size of austenite in the shear band in this study is of the order of 300 nm.…”

“…The shear band velocity was calculated to be around 500 m/s and shear strain rate within the band was 4 × 10 5 s −1 , the latter in good agreement with the results of Giovanola [6] for a 4340 steel and of Clos et al [7] for low carbon steels.…”

“…They also claimed melting and infiltration of the molten metal into these cracks. Clos et al [7] measured the void density within the shear band (formed during dynamic deformation of two different steels) in the localization and post-localization phases and concluded that voids formed at the carbide-matrix interfaces within the shear band during the localization stage but eventually collapsed completely during the post localization phase, much like void closure during hot isostatic pressing. Timothy and Hutchings [32] have studied initiation and growth of cracks within shear bands in titanium alloys and describe the process in terms of void nucleation, coalescence and growth, the surface morphology being dependent on the density of void nucleation sites and the tensile stress state across the shear band.…”

“…Others [23,24] have claimed that they have not seen evidence for such phase transformations. Furthermore, some investigations report the absence of carbides within the band, apparently fully dissolved [7,25], while others [23,24] have observed them within the shear band. Prior to dissolution, Clos et al [7] show that the carbides are drawn out into "thin strings" from the roughly globular morphology in the undeformed state.…”

“…In many high-strength steels, the possibility of phase transformations (austenite formation in the band followed by its conversion to martensite during subsequent rapid cooling [7,[19][20][21] and in other instances, even formation and retention of ␦ ferrite [22]) occurring within the shear band as a consequence of adiabatic heating in combination with high strains has been proposed, based on inferences from post-mortem microstructural observations of shear bands. Others [23,24] have claimed that they have not seen evidence for such phase transformations.…”