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The problem of converting of the phase lattice parameters determined by the time-of-flight neutron diffraction measurements in a loaded multiphase system, to strain and subsequently to stress is discussed. An analytical formulation relating the phase applied stress -elastic strain responses in the axial (along the load direction) and transverse directions has been performed which accounts for all the sources of stress measured in the phases. The formulation was applied in the analysis of diffraction spectra from austenitic stainless steel with a martensite phase plastically induced during cyclic tensile-compressive loading. The spectra were obtained during in situ neutron diffraction stress rig experiments on the ENGIN instrument at the ISIS pulsed neutron facility, subsequent to the cyclic loading. The subsequent applied stress-elastic strain responses of the austenitic matrix and martensitic inclusions were obtained by Rietveld refinement of the spectra, and used to determine the elastic constants and residual stresses of the phases as a function of fatigue level. The data shows that the elastic properties of both phases are similar, which allows the simple determination of residual stresses. Only deviatoric components of the residual stress tensor were obtained due to the lack of an unstressed reference for both individual phases. The formation of martensite is connected with volume dilation; since the specific volume of martensite is larger than that of austenite, the martensite phase is generally in hydrostatic compression, where as the austenite is in tension. These plasticity induced phase transformation stresses are superimposed upon the deformation stresses caused by the plastic deformation occurring during low cycle fatigue, resulting in residual stresses which have a non-hydrostatic nature. We have observed that in the axial direction the deviatoric phase stress of the austenitic phase was compressive while it was tensile for the martensite phase. The axial phase stresses are mainly those due to the deformation, while the phase transformation stresses dominate in the transverse direction.

Recently, reliable and hermetic joining of stainless steel to niobium pipes has been achieved with the explosive bonding technique. Joining of these two materials are essential to ensure production of a bimetallic transition element of pipe-type for its further use as a part of charged beam acceleration systems of the new generation. A non-destructive neutron diffraction investigation of the tri-axial strains along a radial cross-sectional line through the joint section has been performed. Residual stress results indicate inherently different natures in the residual stress values within the respective pipe sections. In the external stainless steel pipe the residual stresses are tensile, showing a sudden increase to 600 MPa as the interface is approached, whilst being compressive in the internal niobium pipe, not exceeding 650 MPa. A characteristic abrupt stress discontinuity exits at the interface region.

Residual stresses in biaxially fatigued austenitic stainless steel sample of cruciform geometry Research and Development Division, NECSA Limited, Pretoria, South Africa *E-mail: taran@nf.jinr.ru Abstract. A specifically designed cruciform-shaped austenitic stainless steel AISI 321 sample was subjected to ex-situ biaxial tension-compression cycling to establish ferromagnetic martensitic phase conversion under the action of plastic deformation. The time-of-flight neutron diffraction technique was employed for in-plane residual stress determination in this sample for both the austenitic and martensitic phases. The 2D data enabled determination of macro-, micro-, hydro-and deviatoric contributions to the total phase stresses.