ON THE MEAN INTERNAL-STRESSES IN 2-DUCTILE-PHASE ALLOYS

The mean internal stresses in each microstructural element of two-duct ile-phase alloys have been theoretically calculated for Fe-Cu-Mn dual- phase steels and alpha-gamma Fe-Cr-Ni stainless steels. The results sh ow that the mean internal stress along the tensile direction in the so ftest element (EI, continuous a phase) is always negative, that in the hardest element (EII, continuous beta phase) is positive and that in the third element (EIII, an aggregate of separated alpha and beta phas es) can be either negative or positive, depending on the volume fracti on and phase contiguity of the constituent phases. The role of the mea n internal stresses is to make the plastic deformation more uniform am ong the three microstructural elements. The effects of volume fraction , phase contiguity and the difference between mechanical properties of the constituent phases on the mean internal stresses are discussed. I t is shown that the difference between the mechanical properties of th e constituent phases has a significant effect not only on the magnitud e of the mean internal stresses but also on their trend of variation w ith increasing plastic strain. It is also shown that the phase distrib ution described by the contiguity parameters does not affect very much the mean internal stresses in EI and EII at high strains, but it does affect those in EIII at high strains and those in EI, EII and EIII at low strains.