Stress Distributions in P91 Martensitic Steel and in AISI 316LN Steel Welds for Gen IV Nuclear Applications
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tress Distributions in P91 Martensitic Steel and in AISI 316LN Steel Welds for Gen IV Nuclear Applications P. Agostinia, G. Barbierib, R. Coppolac, *, M. Moncadab, C. Ohmsd, and R. C. Wimporye aENEA-Brasimone,
FSN–ING, CP 1, Camugnano (BO), 40032 Italy SSTP-PROMAS-MATPRO, Roma, 00123 Italy c ENEA-Casaccia, FSN–ING, Roma, 00123 Italy dEU Joint Research Centre, Petten, IET 1755ZG, The Netherlands e Helmholtz-Zentrum Berlin, Berlin, D-14109 Germany *e-mail: [email protected]
bENEA-Casaccia,
Received June 5 , 2019; revised July 29, 2019; accepted August 9, 2019
Abstract—Neutron diffraction has been used to investigate the stress field in two different welds developed for nuclear applications, namely those obtained by tungsten inert gas welding of P91 martensitic steel (Cr 9, Mn 6, Mo 1, C 0.1, and Fe bal wt %) and hybrid (laser beam and gas metal arc) welding of AISI316LN austenitic steel (17.8 Cr, 12.3 Ni, 1.7 Mn, 2.4 Mo, 0.3 Si, and Fe bal wt %). The sizes of the investigated samples were 100 × 50 × 12 mm for the P91 weld and 220 × 160 × 15 mm for the 316LN weld; unstrained references were prepared for both welds. The neutron diffraction measurements have been carried out utilizing the E3 diffractometer at the BER II reactor in Berlin, with a gauge volume of 2 × 2 × 2 mm3. Lines perpendicular to the weld direction were scanned at different depths inside the material and at different distances from the weld centerline, including the heat affected zone and the weld centerline. Strain and stress values were determined in the three principal directions. In the TIG P91 weld, the stresses are almost completely relieved after a post weld heat treatment for 2 h at 760°C. In the laser beam and gas metal arc 316LN weld not submitted to post weld heat treatment, nearly balancing longitudinal and transverse stress components as high as 300–350 MPa are found within a range of approximately 3 mm around the centerline of weld. Keywords: neutron diffraction, stress measurements, nuclear welds DOI: 10.1134/S1027451020070022
INTRODUCTION The availability of advanced welding procedures constitutes a crucial pre-requisite in the development of safe and sustainable Gen IV reactors, where structural components including a large number of welds will be simultaneously exposed to high temperature, high neutron irradiation doses and aggressive environment [1–4]. In fact, the failure in metallic components occurs very often in and around welds; therefore, their integrity is critical for the safe performance of nuclear components. It depends on a number of factors, such as residual stresses, mechanical properties of the weld, base material and heat affected zones, as well as geometrical factors which also depend on the basic material properties and on the welding process. Therefore, it is clear that the bulk characterization of nuclear welds is much more complicated than for base materials and that neutron diffraction is indispensable for such investigations [4–6]. This contribution presents experimental results obtained by neutron dif
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