EFFECT OF MINUTE SOLUTE ELEMENTS IN THE F ERRITE MATRIX ON THE INHERENT CREEP STRENGTH OF CARBON-STEELS

One oi the present authors nas proposed a new concept about the Inhere nt creep strength determining the long term creep strength of ferritic steels. In the present study, effect of solute elements in the ferrit e matrix on the Inherent creep strength of 0.2 and 0.3 mass% carbon st eels was studied from a view point of atomic configurations such as at omic pairs. The equilibrium concentrations oi solute elements and atom ic pairs in the ferrite matrix were estimated by thermodynamic calcula tions with the sublattice model (Thermo-calc.) and the central atoms m odel, respectively. The following results are obtained; (1) The Inhere nt creep strength of carbon steels at 773K and 88MPa is proportional t o concentrations of Mn and Mo in the ferrite and inversely proportiona l to those of C and Si. (2) A good correlation is observed between the Inherent creep strength and the concentrations of Mn-C and Mo-C atomi c pairs. These atomic pairs seem to reduce the climb velocity of dislo cations due to their large interaction energies with dislocations, Thu s, it is concluded that the Inherent creep strength ol carbon steels i s controlled by Mn-C and Mo-C atomic pairs in the ferrite matrix.