Severe plastic deformation through adiabatic shear banding in Fe-C steels

Severe plastic deformation is observed within adiabatic shear bands in iron-carbon steels. These shear bands form under high strain rate conditions, in excess of 1000 s−1, and strains in the order 5 or greater are commonly observed. Studies on shear band formation in a ultra-high carbon steel (1.3% C) are described in the pearlitic condition. A hardness of 11.5 GPa (4600 MPa) is obtained within the band. A mechanism is described to explain the high strength based on phase transformation to austenite from severe plastic deformation and adiabatic heating. Rapid re-transformation leads to an ultra-fine ferrite grain size containing carbon principally in the form of nano-size carbides. It is proposed that the same mechanism explains the ultra-high strength of iron-carbon steels observed in ball-milling, ball drop tests and in severely deformed wires.