Bauschinger effect in structural steels and role in fabrication of line pipe: Part 1 analysis of Bauschinger effect in structural steels

Abstract

During the plastic deformation of a two-phase system containing hard particles it is important to determine the extent to which these particles support unrelaxed plastic strains. The amount of unrelaxed strain can be determined, in principle, from measurements of the behaviour of the material during reverse flow. The existence of unrelaxed plastic strains can give rise to internal stresses which not only aid flow in the reverse direction but also contribute to dimensional instabilities and to the nucleation of voids at second-phase particles. The present work illustrates that for well characterized structural materials such as carbon steels containing dispersions of cementite particles the above processes can be described in a quantitative manner based on models of heterogeneous deformation. In addition, the work indicates that for structural steels containing distributions of transformation products such as martensite and retained austenite similar conclusions can be drawn and many important facets of the behaviour of the materials such as the shape of the stress-strain curve and the magnitude of the Bauschinger effect can be analysed by reference to the volume fraction of the transformation products and the magnitude of the unrelaxed strain. The overall objective of the present study was to provide a discussion of the reverse stress-strain behaviour of structural steels in terms of basic physical models and to apply the empirical formulation of these concepts to a more practical engineering situation such as the U-O-E pipe-making operation.