Kohsuke \nameTagashira1, Noriyuki \nameSumita2, Hisashi \nameHayakawa2 and Kazuyuki \nameKikuchi1
1Department of Mechanical Engineering, Muroran Institute of Technology, Muroran
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. In the Si-free steel the DMR decreased during the ageing when quenched from 823 and 973 K, whereas the DMR increased when quenched from 673 and 773 K. This result showed that Mn-C dipoles retained after quenching were decomposed during ageing and single Mn atoms in solution increased. The amount of Mn-C dipole or its binding energy increased with the increase of Si content up to 0.4 at%. It was suggested that the potential energies 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 were trapped at the Fe-Mn interstitial sites, accelerating the formation of Mn-C dipoles. The amount and the binding energy of the Mn-C dipole became saturated with the Si content in excess of 0.4 at%. The formation of dipoles at the Fe-Mn sites was considered to be restrained by the repulsive interaction with excessive Si atoms.
low carbon steel, manganese-carbon dipole, electrical resistivity, deviation from Matthiessen's rule, iron-silicon-manganese-carbon alloy, quench-ageing, solute chemical interaction, binding energy
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