Abstract
Experimental analyses of depth distributions of phase-specific residual stresses after deep rolling were carried out by means of laboratory X-ray diffraction and neutron diffraction for the two duplex steels X2CrNiMoN22-5-3 and X3CrNiMoN27-5-2, which differ significantly in their ferrite to austenite ratios. The aim of the investigation was to elucidate to which extent comparable results can be achieved with the destructive and the non-destructive approach and how the process induced phase-specific micro residual stresses influence the determination of the phase- and {hkl}-specific reference value d0, required for evaluation of neutron strain scanning experiments. A further focus of the work was the applicability of correction approaches that were developed originally for single-phase materials for accounting for spurious strains during through surface neutron scanning experiments on coarse two-phase materials. The depth distributions of macro residual stresses were separated from the phase-specific micro residual stresses. In this regard, complementary residual stress analysis was carried out by means of incremental hole drilling. The results indicate that meaningful macro residual stress depth distributions can be determined non-destructively by means of neutron diffraction for depths starting at about 150–200 µm. Furthermore, it was shown that the correction of the instrumental surface effects, which are intrinsic for surface neutron strain scanning, through neutron ray-tracing simulation is applicable to multiphase materials and yields reliable results. However, phase-specific micro residual stresses determined by means of neutron diffraction show significant deviations to data determined by means of lab X-ray stress analysis according to the well-known sin2ψ-method.
Highlights
Duplex stainless steels combine properties of austenitic and ferritic stainless steels, i.e., they generally have good mechanical properties, including high strength and ductility, and corrosion resistance is often better than in conventional austenitic steels [1,2,3]
The data show a rather large scatter that is typical for this kind of analysis and which can be explained by the rather limited statistics, not least because the assessment of whether the individual hardness value can be clearly assigned to one of the phases is based on the planar (2D)
Apart from this limitation, the levelling curves, based on regression analysis, clearly indicate that for both duplex steels the austenite phase shows a higher hardness due to work hardening induced by deep rolling as the ferrite phase
Summary
Duplex stainless steels combine properties of austenitic and ferritic stainless steels, i.e., they generally have good mechanical properties, including high strength and ductility, and corrosion resistance is often better than in conventional austenitic steels [1,2,3]. We aim at the assessment of the suitability of neutron diffraction for nondestructive analysis of phase-specific RS depth distributions that are induced by defined deep rolling treatments for commonly applied duplex stainless steels. In this methodical approach, two duplex steels were chosen that clearly differ in their phase fractions of ferrite (α-Fe) and austenite (γ-Fe). Regarding the assessment of the neutron diffraction approach determining near surface RS depth distributions induced by deep rolling of duplex stainless steel, supplementary metallographic analyses of the microstructure and phase-specific texture analysis were performed. The macro RS that are induced by deep rolling are determined by means of the incremental hole drilling method [23]
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