Analysis of structure and deformation behavior of AISI 316L tensile specimens from the second operational target module at the Spallation Neutron Source

Abstract

Please cite this article as: M.N. Gussev, D.A. McClintock, F.A. Garner, Analysis of structure and deformation behavior of AISI 316L tensile specimens from the second operational target module at the AbstractIn an earlier publication, tensile testing was performed on specimens removed from the first two operational targets of the Spallation Neutron Source (SNS). There were several anomalous features in the results. First, some specimens had very large elongations (up to 57%) while others had significantly smaller values (10-30%). Second, there was a larger than the usual amount of data scatter in the elongation results. Third, the stress-strain diagrams of nominally similar specimens spanned a wide range of behavior ranging from expected irradiation-induced hardening to varying levels of force drop after yield point and indirect signs of "traveling deformation wave" behavior associated with strain-induced martensite formation. To investigate the cause(s) of such variable tensile behavior, several specimens from Target 2, spanning the range of observed tensile behavior, were chosen for detailed microstructural examination using electron backscatter diffraction (EBSD) analysis. It was shown that the steel employed in the construction of the target contained an unexpected bimodal grain size distribution, containing very large out-of-specification grains surrounded by "necklaces" of grains of within-specification sizes. The large grains were frequently comparable to the width of the gauge section of the tensile specimen. The propensity to form martensite during deformation was shown to be accelerated by radiation but also to be very sensitive to the relative orientation of the grains with respect to the tensile axis. Specimens having large grains in the gauge that were most favorably oriented for production of martensite strongly exhibited the traveling deformation wave phenomenon, while those specimens with less favorably oriented grains had lesser or no degree of the wave effect, thereby accounting for the observed data scatter.

Structure and mechanical properties of improved cast stainless steels for nuclear applications

“…The role of Cu is negative and can be roughly estimated as ~(-34) MPa/1%. A similar result -N increasing deformation hardening ratehas been previously reported [20] for non-irradiated 316-series stainless steels with regular grain size. Since grain size decrease leads to increase of deformation hardening rate [19], it is possible to expect that grain size refinement will lead to an additional increase of k-parameter for the modified steels investigated in the present work.…”

“…additions of N, Mn, and Cu might cause significant changes in stacking fault energy (SFE) and lead to the changes in the deformation mechanisms. 316L steel deformed at room temperature may exhibit both twinning and martensitic transformation [20], and it was important to evaluate the deformation mechanisms in the modified steels. Copper [21], manganese and nitrogen [9] stabilize austenite against martensitic transformation at room temperature.…”

Model for deformation-induced martensitic transformation in irradiated materials

“…The propensity of DIMT is accelerated by neutron or ion irradiation, generating a much more significant volume fraction of α′-martensite (body-centred cubic structure, BCC) phase from the γ-austenite (face-centred cubic structure) matrix than their unirradiated counterpart during post-irradiation mechanical tests [9,26]. In the irradiated AustSSs with complex deformation microstructures, the dominant role of deformation-induced α′-martensite has been found with increasing irradiation dose [9,14,26,27]. Furthermore, an intensely localized martensitic transformation moving along the sample similar to a deformation band is reported repeatedly in neutron-irradiated AustSSs [9,28].…”

Is duplex stainless steel more corrosion resistant than 316L in aqueous acid chloride-containing environments at temperatures higher than 100°C?

“…These modified steels are known as the 300 series [1]. In these steels, the austenitic phase is stable at room temperature, but martensitic phase can be formed by transformation induced by plasticity (the TRIP effect), which occurs when the steel is subjected to external stresses leading to elastic or plastic deformation [2 -4].…”