AbstractAn evaluation model is proposed for the strain and strain rate of a localised deformation band produced by an orthogonal cutting test upon a high strength low alloy steel tempered at 600°C after quenching. It can be used to determine the strain and strain rate at the first deformed zone (FDZ) in the chip and also at the second deformed zone (SDZ) at the bottom of the chip. These zones were severely deformed at high strain rates up to 4·6×104−4·2×106s−1, with strains as high as 1190–2760%. X-ray diffraction showed that the SDZ consisted of ferrite and retained austenite which was not detected in the matrix. Transmission electron microscopy and X-ray diffraction showed that cell structures in the SDZ and FDZ were ofnanocrystalline‘grains’with a high dislocation density at the‘grain’boundaries. The X-ray diffraction analysis served to check the validity of the strain evaluation model.MST/3105