Mechanism of {011} martensite twinning in quenched steel

Abstract

In the lattice of the as-formed martensite ([ae]martensite) of a number of quenched steels at cryogenic temperatures a redistribution of carbon atoms can occur due to thermal activation, which results in their preferable transitions into the one octahedral interstice sublattice. Such a distribution is the most thermodynamically stable one and results from a reduction in the elastic energy determined by carbon interstitial. On the basis of crystallographic considerations, a conclusion was drawn that during the martensitic transformation a portion of the carbon atoms passes from austenite into octahedral interstices, and another part passes into tetrahedral interstices in the as-formed martensite lattice. Therefore, the [ae][prime]-[alpha] transitions was explained as the transition of carbon atoms from tetrahedral interstices into octahedral ones, i.e. as occurring by the ordering of carbon atoms, which results in increasing the martensite lattice tetragonality. In this paper, the experimental data describing the changes of the martensite crystalline structure under thermal activation are presented. Based on these data a conclusion is drawn on the possibility of forming martensite phase in the form of polysynthetic twin.