Decomposition of cementite in pearlitic steel due to plastic deformation

Abstract

The available experimental data and hypotheses concerning cementite decomposition during the cold work of pearlitic steels are reviewed. The results of studies performed using thermomagnetic analysis, Mössbauer spectroscopy, internal friction and APFIM are used to discuss the mechanism governing cementite decomposition. The following features of this phenomenon seem to be important: (i) the fraction of the decomposed cementite increases with the refining of the initial pearlitic structure, i.e. with the increase of the ferrite–cementite interfacial area; (ii) the decomposition effect saturates as strain increases; (iii) carbon–dislocation interaction in ferrite and MeC bonding in cementite have a strong influence on cementite decomposition. The conclusion is made that cementite decomposition is controlled by the transfer of carbon atoms from cementite to dislocations accumulated near the interface during deformation. This is because the binding enthalpy between carbon atoms and dislocations in ferrite exceeds the solution heat of cementite. Some relevant effects of cementite decomposition in practice are discussed.