Scanning Three-Dimensional X-Ray Diffraction Microscopy with a High-Energy Microbeam at SPring-8

Abstract

The grain-resolved residual stress (type II) in commercial-quality low carbon steel was observed using scanning three-dimensional X-ray diffraction (3DXRD) microscopy. In this method, grain orientations and lattice parameters are mapped using a monochromatic high-energy X-ray microbeam and 3DXRD-based polycrystalline indexing. Defining the reference lattice parameter a0 as the average value in the entire field of view, grain orientations and lattice parameters are converted into stress tensors, yielding a grain-resolved stress tensor map. The effectiveness of the scanning 3DXRD method was demonstrated by evaluating the residual stress in a cold-rolled low carbon steel sheet using a 50 keV microbeam at SPring-8. The area of the cross-sectional sample was 1×1 mm2, which was sufficiently larger than the grain size of about 20 μm. To produce a two-dimensional map of a circular region with a diameter of 160 μm at a pixel size of 1×1 μm2, the measurement time was about 1 h. From the stress tensor map, differences in residual stress of about 150–200 MPa between some neighboring grains were observed.