Neutronographic Analysis of Load Partitioning and Micro Residual Stress Development in Duplex Stainless Steels

Abstract

In the present work, neutronographic in situ diffraction stress analyses during uniaxial loading and subsequent unloading were carried out on the two duplex stainless steels X2CrNiMoN22-5-3 and X3CrNiMoN27-5-2 with nominal phase fractions for ferrite:austenite of 50:50% and 70:30%, respectively. In addition to the different phase fractions, the two steels also differed in their phase-specific crystallographic texture. The load-partitioning behaviour and the phase-specific micro (residual) stress evolution for total strains up to about 9% were investigated. The results indicated that for both materials under load, the phase-specific stress in the ferrite phase was significantly higher than in the austenite phase, while no texture development through the plastic deformation could be observed.

Analysis of Phase-Specific Strain Pole Figures for Duplex Steels under Elasto-Plastic Uniaxial Tension—Experiment vs. EPSC Modelling

“…However, based on Figure 6, it can already be estimated that in the present case the phase-specific strains in the ferrite phase are higher than those in the austenite phase. This would be consistent with the investigations on the same duplex stainless steel in [17].…”

“…An experimentally determined phase-specific stress could then have been derived from these. It should be noted that this stress distribution is influenced by the local phase content, the phase-specific texture and the phase-specific mechanical properties [17]. Furthermore, it must be expected that for the present microstructure the influence of the grain morphology will also affect the results [9,68].…”

“…As a further deformation mechanism, an approach to describe twinning is implemented in the present EPSC material model. However, metallographic investigations on a comparable duplex steel showed [17] that this is not a preferred deformation mechanism of the f.c.c. austenite phase in the duplex steel under consideration.…”

“…) and the used DEC. For the calculation of stresses from the elastic lattice strain using phase-specific DECs, it is expected that there exists a linear relationship between the experimentally determined lattice strain and mechanical stress. In reality, however, this is only given to a limited extent, as in the elasto-plastic stress regime the lattice strain vs. mechanical stress distributions often become significantly non-linear as, i.a., is shown in [12][13][14][15][16][17]. In the literature, this effect is generally termed the 'plastic anisotropy effect' (e.g., [12]).…”