1998 Volume 84 Issue 12 Pages 910-917
The formation and decomposition of Mo-C dipoles during quench-aging in 0.03 mass%C steels containing from 0 to 1.01mass% Mo is discussed. The changes in electrical resistivity and its deviation from Matthiessen's rule (DMR) during aging at 523K were examined for the steels just after quenching from 973 to 273K. The difference between the electrical resistivity measured at 77K and 273K was regarded as the value of the DMR. The electrical resistivity decreases for all steels during aging. Also the DMR decreases for steels except 1.01 mass% Mo steel. The decrease in electrical resistivity and DMR is largest in 0.25mass% Mo steel. Increment of lattice constant of ferrite with increase of Mo content in 0 to 0.25mass% Mo steels aged for 105s after quenching is less than that in 0.51 to 1.01mass% Mo steels. These results can be explained from the assumption that following two reactions occur during aging, 1) Mo-C dipoles existing in quenched ferrite matrix decompose in accordance with precipitation of carbides, 2) solid solute Mo atoms in quenched ferrite matrix decrease with precipitation of carbides containing Mo. The Mo-C dipoles may be formed at the solution treatment temperature by chemical interaction between Mo and C atoms, similarly Mn-C(N) dipoles in Fe-Mn-C(N) alloys. The amount of Mo-C dipoles increases with increase of Mo content. The binding energy of a Mo-C dipole is calculated to be approximately -5.7×10-20J.
