Dependence of the diffraction angle on the surface microstructure of a steel sample

While the deviations from linearity of −sin²ψ curves in the case of two welded hot-rolled C40 steel bars were being studied, this paper was prompted by the observation that, at ψ = 0°, the diffraction angle 2θ depends on φ, the inclination angle of the diffraction plane with respect to an arbitrarily chosen reference plane attached to the specimen. This result is unexpected and cannot be explained by bulk structural or microstructural factors. A surface effect is offered as a possible explanation.