Deformation studies from in situ SEM experiments of a reactor pressure vessel steel at room and low temperatures

This paper presents the strain fields acquired at micro-structural scale for a pressure vessel steel, used in the French pressurized water reactors (PWR) and designated as 16MND5 or ASTM A508cl3. The experimental observations rely on specific specimen preparation, prior crystallographic orientation characterization by means of electron backscatter diffraction (EBSD), surface patterning using lithography and chemical etching. The specimens are loaded using a miniaturized tensile stage fitted within a scanning electron microscope (SEM) chamber, and images acquired of a small area are used to measure displacement and strain fields using a Digital Image Correlation (DIC) technique. In addition, a specific setup allowed to cool down to −100°C the specimen during the whole tensile test and the image acquisition. The experimental apparatus and the kinematic field measurements are introduced in two first sections of the paper. Then the results will be presented for two experiments, one conducted at room temperature and the other at −100°C, including a comparison of strain localization features and a preliminary comparison of plasticity mechanisms.