Being examined by tensile tests at 820°C with initial strain rates of 2.5×10-4 s-1, 5.0×10-3
s-1and 1.0×10-1 s-1, the hot-rolled spay formed high speed steel (SF-HSS) had superplastic properties.
With έ=2.5×10-4 s-1and 5.0×10-3 s-1, the σ-ε curves indicate that there has occurred dynamic
recrystallization at the later stage of deformation.The tensile elongation decreases monotonously with
strain rate increasing. The strain rate sensitivity m =dlogσ/dlog έ is about 0.23. In the sub-surface of
fractured SF-HSS samples with έ=2.5×10-4 s-1,, most of holes on the subsurface are observed to
distribute near the carbides and arranged along the tensile axis direction. The interface between coarse
carbides and matrix is very weak sites where the holes are easy to nucleate and connect to cracks
during deformation. In the necked region, fine carbide particles on the grain boundary have pinned the
slip of dislocations and formed dislocation wall inside the grain. Dynamic recrystallization and some
climb of dislocations has occurred. The superplastic deformation mechanism with έ=2.5×10-4 s-1 was
dislocation creep mechanism controlled by dynamic recrystallization. During deformation, the role of
some carbide in the materials was to retard the grain growth and keep SF-HSS having fine equiaxed
grain size and remain stable.
Determination of strain-rate and temperature dependent high-speed steel material data via Fe analysis of repetitive impact test imprints
