Residual stress evaluation with X-rays in steels having preferred orientation

Two phenomena limit the use of X-ray stress evaluation in practice: preferred orientation and coarse grained materials. Measurements with Cr-radiation and the (211)-peak showed nonlinearD vs sin ² ψ distributions in the case of a 75 pct cold-rolled steel, due to preferred orientation, and for a deep-drawing steel spotty diffraction rings on a film exposed in front of the detector, due to large grain size, were observed. However, when Mo-radiation and the (732 + 651)-peak were used, theD vs sin² ψ distributions proved to be linear, so that residual stresses could be determined. The X-ray elastic constants (XEC) needed to compute the stresses from the measured lattice strains were determined under uniaxial load using samples cut at various angles with respect to the rolling direction. For the deep drawing steel in particular, the XEC differ from the values calculated for Fe-materials having randomly oriented crystallites. Furthermore, the XEC for the two investigated steels proved to depend on the angle of sample cut with respect to the rolling direction.