抄録
Effect of Si on the formation of Mn–C dipoles in low carbon steels has been investigated. The changes in electrical resistivity were measured at 77 and 273 K during isothermal ageing for quenched Fe–Si–Mn–C alloys containing various Si contents (0–0.8 at%). The deviation from Matthiessen’s Rule (DMR) was given by the difference between the electrical resistivities at 77 and 273 K. The DMR during ageing increased in the steels containing Si when quenched from the temperature between 673 and 973 K. Even in the Si-free steel the DMR during ageing increased when quenched from 673 and 773 K. These results showed that Mn–C dipoles retained after quenching were decomposed during ageing and single Mn atoms in solution increased. The amount of Mn–C dipoles or their binding energy increased with the increase of Si content up to 0.4 at%. It was suggested that the potential energy at the Fe–Mn, Fe–Fe and Fe–Si interstitial sites increased in that order by the addition of Si to the Fe–Mn–C system. Thus C atoms may be trapped at the Fe–Mn interstitial sites to form Mn–C dipoles. The amount and the binding energy of the Mn–C dipoles became saturated at Si contents more than 0.4 at%. The formation of dipoles at the Fe–Mn sites was considered to be restrained by repulsive interaction with excessive Si atoms.
