Application of an advanced XRD instrument for surface stress-tensor measurements on steel sheets

The three-dimensional residual-stress condition of several martensitic stainless-steel sheets (410 type) given various combinations of surface treatments was studied by an X-ray-diffraction method. The stress tensors in the near-surface region, approx 12 mu m (0.012 mm) deep, were calculated after obtaining the strain tensors through application of the differential method and an advanced X-ray-diffraction stress-measurement instrument. The advanced instrument collected the data in a few hours--a task that normally requires several days to a few weeks--and provided accuracies of the order of plus /minus 14 MPa (2 ksi). The surface treatments to the sheets included various combinations of mechanical polishing and vapor blasting; all produced substantial compressive stresses in the plane and perpendicular to the surface. The mill-annealed specimen showed nearly zero residual stress prior to mechanical polish or vapor blasting. The resulting tensor--stress data were compared with data obtained through single-exposure-technique calculations which assume a plane-stress state on the surface. 8 ref.--AA