Electron microscopy of white-etching band generated by high-velocity parting-off of 100CrMn6 steel

High-velocity parting-off has been applied to ∅80 mm bars of pearlitic 100CrMn6, resulting in shear localisation and white-etching bands in a severely deformed region below the fracture surface. Electron microscopy showed that going from the bulk material towards the fracture surface the grains become elongated and refined. The region below the fracture surface can be divided into three subzones: 50–100 μm below the surface grains are elongated, cementite lamellae are distorted, break up and the lamellar spacing decreases. <50 μm below the fracture surface the microstructure becomes a mix of cementite lamellae and carbides in a ferrite matrix. Within the white-etching band the microstructure consists of equiaxed ferrite refined to a grain size of 50–150 nm. Several twinned regions caused by the deformation can be observed. Selected area electron diffraction and low angle convergent beam electron diffraction indicate nanocrystalline cementite dispersed in the ferrite matrix.