The mechanism of formation of nanostructure and dissolution of cementite in a pearlitic steel during high pressure torsion

摘要

The nanostructure and the phase composition in UIC 860V pearlitic steel, deformed by high pressure torsion in the shear stress range from 62 to 430, were studied. The refinenement of ferrite up to a grain size of 10 nm is accompanied by the total dissolution of the cementite and an increase in hardness of up to 11 GPa. The strain-induced cementite dissolution was found to be a three-stage process corresponding to the stages of nanostructure formation. The mechanism of the dissolution due to wear of cementite at the ferrite/cementite interface, followed by drage of the carbon atoms by the ferrite matrix, is discussed. The flow of carbon atoms with the ferrite phase can be considered as a mechanically driven mass transport process, quantitatively described by the mechanical diffusion parameter.