Neutron and X-ray residual stress analysis of steel parts produced by cold forward extrusion and tube drawing

Deformation-induced residual stresses were studied by the examples of cold forward extrusion and tube drawing of ferritic steel parts. For analysing the volume stresses in the extruded rods, neutron diffraction was applied. Therefore, the interplanar spacing d{hkl} vs. sin2 ψ up to sin2 ψ = 1 were measured for the reflections {110}–{220}, {200}, {211} and {310}. In the case of the cold-drawn tubes, stress evaluation was performed at the outer surface of the specimens by means of X-ray diffraction taking d{hkl} vs. sin2 ψ for the {200} and {211} reflections in both the axial and the tangential directions. For both metal-forming processes, the residual stress state is shown to depend in an obvious way on the degree of natural strain ϕ which is defined by the logarithmic ratio of initial and final cross-sectional areas. The results obtained are in good qualitative agreement with theoretical predictions of finite element calculations.