Deviation from Matthiessen's rule during quench-aging of Mo added low carbon steels

The formation and decomposition of Mo-C dipoles during quench-aging in 0.03 mass% C steels containing from 0 to 1.01 mass% Mo is discussed. The change s in electrical resistivity and its deviation from Matthiessen's rule (DMR) during aging at 523K were examined for the steels just after quenching fro m 973 to 273K. The difference between the electrical resistivity measured a t 77K and 273K was regarded as the value of the DMR. The electrical resisti vity decreases for all steels during aging. Also the DMR decreases for stee ls except 1.01 mass% Mo steel. The decrease in electrical resistivity and D MR is largest in 0.25 mass% Mo steel. Increment of lattice constant of ferr ite with increase of Mo content in 0 to 0.25 mass% Mo steels aged for 10(5) s after quenching is less than that in 0.51 to 1.01 mass% 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 dec ompose in accordance with precipitation of carbides, 2) solid solute Mo ato ms in quenched ferrite matrix decrease with precipitation of carbides conta ining Mo. The Mo-C dipoles may be formed at the solution treatment temperat ure by chemical interaction between Mo and C atoms, similarly Mn-C(N) dipol es 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 app roximately - 5.7 X 10(-20) J.