In-Situ Analysis of Material Modifications During Deep Rolling by Synchrotron X-Ray Diffraction Experiments

The stress state achieved through elasto-plastic deformation in the deep rolling process has been analyzed with in-situ synchrotron experiment using a roller as tool. For the determination of internal material load and residual stress for specific contact parameters, the material state was analyzed via transmission synchrotron X-ray diffraction for hundreds of measurement positions below the loaded zone. From the individual diffraction rings at each point, the strain and stress fields were reconstructed as 2D mappings of the material modifications. The measured region included material in front of the roller, under the contact point as well as in the already processed near surface region. A 13 mm cylindrical tungsten carbide roller was applied on specimens of AISI 4140 steel in ferritic-pearlitic and quenched and tempered condition to compare the effect of different mechanical properties on the propagation and intensity of the stress and strain fields in the specimen during and after processing. The investigations allowed a comparison of the stress fields for the different material conditions. The results show that the mechanisms of load distribution during the process and the effect of loading stresses on the final material state and on the residual stress distribution are strongly influenced by the initial material state.