Materials Science and Engineering A 546 (2012) 263–271 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering A jo ur n al hom epage: www.elsevier.com/locate/msea Macro and intergranular stress responses of austenitic stainless steel to 90 ◦ strain path changes D. Gonzalez a,∗ , J.F. Kelleher b , J. Quinta da Fonseca a , P.J. Withers a a School of Materials, Univ. of Manchester, Grosvenor St., Manchester M1 7HS, UK b ISIS Pulsed Neutron & Muon Source, RAL, Didcot OX11 OQX, UK a r t i c l e i n f o Article history: Received 6 October 2011 Received in revised form 2 March 2012 Accepted 16 March 2012 Available online 27 March 2012 Keywords: Neutron scattering Finite element method Austenite Residual stresses Crystal plasticity Hardening a b s t r a c t Strain path history can play a crucial role in sensitising/desensitising metals to various damage mecha- nisms and yet little work has been done to quantify and understand how intergranular strains change upon path changes, or their effect on the macroscopic behaviour. Here we have measured, by neutron diffraction, and modelled, by crystal plasticity finite elements, the stress–strain responses of 316L stain- less steel over three different 90 ◦ strain path changes using an assembled microstructure of randomly oriented crystallites. The measurements show a clear Bauschinger effect on reloading that is only partially captured by the model. Further, measurements of the elastic response of different {h k l} grain families revealed an even earlier onset of yield for strain paths reloaded in compression while a strain path reloaded in tension showed good agreement with corresponding predictions. Finally, we propose that the study of strain path effects provides a more rigorous test of crystal plasticity models than conventional in situ diffraction studies of uniaxial loading. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The purpose of this paper is to contribute to our understanding of the mechanical response to non-monotonic strain paths at the granular level. In practice it is rare for metals to be deformation processed to final shape without some form of strain path change having taken place at some stage; either by 180 ◦ (e.g. tension com- pression) or 90 ◦ (say tension perpendicular to a prior tensile strain) or at some arbitrary angle. However most of our understanding of the deformation of polycrystalline metals has been acquired on the basis of uniaxial deformation, with limited attention focused on strain reversals (180 ◦ ). Consequently relatively little is known about the development of intergranular and intragranular stresses and heterogeneities as a function of complex (non 180 ◦ ) strain paths. This gap in our knowledge base is of concern because strain history can play a crucial role in sensitising/desensitising metals to various damage mechanisms. For example, prior strain path can influence stress corrosion cracking [1], most probably due, at least in part, to the inter-granular stress (IGS) acting between grains, while a reduction in the critical crack tip opening displace- ment (CTOD) has been observed in pipeline steels after tensile and ∗ Corresponding author. Tel.: +44 7961684966. E-mail addresses: david.gonzalez@postgrad.manchester.ac.uk, david 475142@hotmail.com (D. Gonzalez). compressive pre-strain, the effect being most severe for compres- sive pre-strain [2]. Similarly, a few percent of pre-strain was found to promote strain-induced ductile–brittle transition and a high compressive pre-strain found to accelerate fatigue-crack initiation and growth [2]. Further, several studies conducted under high tem- perature pressurised water nuclear reactor (PWR) environments have demonstrated the importance of strain path on cracking, for example: Couvant et al. [3] found that the complex strain paths can promote the intergranular crack initiation in 304L steels as well as 316L steels [4], while the influence of loading orientation on crack growth rates has been shown in cold-rolled Alloy 600 [5] and 304 stainless steel [6]. In general, any amount of plastic deformation in a material changes the stress required for further deformation. Typically, plas- tic strain increases the stress required for continued deformation in the same direction (i.e. strain hardening occurs), but the yield stress in other directions may be affected in more subtle ways. In particular, if the sign of the applied load is reversed after plas- tic deformation, the yield stress in the opposite direction may be reduced. This is the ‘Bauschinger effect’ (BE), named after its dis- coverer, which has been known for over a hundred years [7]. The Bauschinger effect can originate at two length scales, namely at the inter- and intra-granular levels. In polycrystalline metals heterogeneous yielding leads to inter- granular stresses (IGS), sometimes referred to as mean stresses, between crystallographic families [8,9], or between different phases [10–14], which will remain upon unloading. For certain 0921-5093/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2012.03.064