Energy and velocity of sliding of edge and screw dislocations in austenite and Hadfield steel: Molecular dynamics simulation

Abstract

The sliding of edge and screw dislocations in Hadfield steel and in pure HCC iron (austenite) depending on temperature and deformation rate was studied by the method of molecular dynamics. The complete dislocation appears in the present model immediately in the form of a split into a pair of partial Shockley dislocations separated by a packing defect. The distance between partial dislocations is several nanometres. As the shear rate increases, this distance decreases. According to the data obtained, the energies of edge and screw dislocations in steel are higher than in pure austenite. The energy of the total edge dislocation in γ-iron and Hadfield steel averages 2.0 and 2.3 eV/Å, helical – 1.3 and 1.5 eV/Å respectively. Dependences of the sliding velocity of the edge and screw dislocations on the shear rate and temperature were obtained. The sliding velocity of the edge dislocation is in all cases higher than the screw one, which is explained by the difference in the propagation velocity of longitudinal and transverse waves in the material. With an increase in the shear rate, the sliding speed increases to a certain limit, depending on the propagation velocity of the corresponding elastic waves. At low and normal temperatures, the sliding velocity of dislocations in Hadfield steel is significantly (about one and a half times) lower compared to pure HCC iron. In pure iron, the sliding velocity of dislocations decreases with increasing temperature. However, for Hadfield steel, this dependence is nonmonotonic: as the temperature increases to about 500 K, the dislocation rate increases. That is probably due to the intensification of diffusion of impurity carbon atoms; then, as in iron, it decreases.