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.