Microstructure, properties, and failure characteristics of medium-carbon steel subjected to severe plastic deformation

Superior strength of carbon steel with an ultrafine-grained microstructure and its enhanced thermal stability

“…Before SPD processing the samples were water-quenched with preliminary heating at 800°C for 1 h. SPD processing was conducted by high-pressure torsion (HPT) at an elevated temperature of 350°C with a number of turns N = 5 and a pressure of P = 5 GPa [13,14]. The processing was performed on disk samples with a diameter of 10 mm and a thickness of 0.2 mm.…”

“…The reason for such a deviation is the complexity of microstructures from SPD processing, which is especially typical of multiphase materials. For instance, during SPD processing of carbon steels, in addition to grain refinement, dissolution of cementite particles has been discovered [10,11], as well as formation of segregations of carbon and cementite particles at the boundaries of nanocrystalline grains formed through deformation [12][13][14][15][16]. This provides an opportunity to realize a set of strengthening mechanisms in UFG carbon steels; in particular, in addition to the grain boundary strengthening mechanism, also the dislocation strengthening, precipitate strengthening and solid solution strengthening mechanisms [12,15], as well as the new strengthening mechanism associated with solute segregation at grain boundaries [15,16], make their contributions.…”

On the microstructure and mechanical properties of an Fe-10Ni-7Mn martensitic steel processed by high-pressure torsion

“…This duplex behavior was reported also in a medium-carbon steel after applying 5 HPT turns where there was non-uniform deformation with a fracture surface having separate fragments of ~2-5 μm width with dimples developed within them [34]. It was concluded from these earlier experiments that the tensile strain accumulated on the laths of the martensite plates split the material along the grain boundaries and produced deep pits on the fracture surface [34].…”

“…The excessive reduction in the dimple size in the HPTprocessed sample by comparison with the SA sample appears to be a consequence of the very high energetic and distorted microstructure in the samples after HPT processing [15]. This duplex behavior was reported also in a medium-carbon steel after applying 5 HPT turns where there was non-uniform deformation with a fracture surface having separate fragments of ~2-5 μm width with dimples developed within them [34]. It was concluded from these earlier experiments that the tensile strain accumulated on the laths of the martensite plates split the material along the grain boundaries and produced deep pits on the fracture surface [34].…”

“…6(a-j), there is a transition in the fracture mode from necking to shearing when the sample is subjected to higher numbers of HPT turns [33]. The fracture structures after HPT processing consist of fragments which are both parts of the martensitic laths and shear bands which appear as a result of deformation accompanied by extremely fine dimples that are direct evidence for ductile fracture [34]. During the HPT process, small cave-like shear bands are produced [35] which are displayed in greater detail in Fig.…”