中性子回折法による溶接残留応力測定精度に関する考察 ―無ひずみ状態の格子定数の影響―

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It is required to evaluate a strain-free reference, α0, to perform accurate stress measurement using neutron diffraction. In this study, accuracy of neutron stress measurement was quantitatively discussed from α0 evaluations on a dissimilar metal butt-weld between a type 304 austenitic stainless steel and an A533B low alloy ferritic steel. A strain-free standard specimen and a sliced specimen with 10 mm thickness taken from the dissimilar metal butt-weld were utilized. In the lattice constant evaluation using the standard specimen, average lattice constant derived from multiple hkl reflections was evaluated as the stress-free reference with cancelling out an intergranular strain. Comparing lattice constant distributions in each reflection with average lattice constant distribution in the standard specimen, αFe211 and γFe311 reflections were judged as a suitable reflection for neutron strain measurement to reduce intergranular strain effects. Residual stress distribution in the sliced specimen evaluated using α0 measured here exhibited higher accuracy than that measured using strain gauges. On the other hand, α0 distributions were evaluated using the sliced specimen under the plane-stress condition. Existence of slight longitudinal residual stresses near the weld center decreased accuracy of the α0 evaluations, which means that it is required to optimize the thickness of the sliced specimen for accurate α0 evaluation under plane strain condition. As a conclusion of this study, it was confirmed that procedures of accurate α0 evaluation, optimization of the measurement condition, and multiple evaluations on the results play an important role to improve accuracy of the residual stress measurement using neutron diffraction.

中性子回折法による溶接残留応力測定精度に関する考察 ―無ひずみ状態の格子定数の影響―

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