No abstract

Neutron and X-ray diffraction were used to study the residual and internal stress evolution during cold drawing in pearlitic steel wires. A selection of high strength filaments drawn to different reductions has been investigated. In order to compare the evolution of macro and micro residual phase stresses in ferrite, the lattice strain evolution has been studied in axial and transverse direction. In-situ neutron diffraction tests in "Poisson" geometry have been carried out at the TOF strain scanner POLDI at PSI, Switzerland. These tests revealed a significant scatter in mechanical response among differently oriented ferrite grains, including a peculiar response of the {200} reflection, cp. [1, 2].

This study aims to demonstrate the capability of the digital image correlation (DIC) technique for evaluating full-field residual stresses in wire and arc-additive-manufactured (WAAM) components. Investigations were carried out on WAAM steel parts (wall deposited on a substrate) with two different wall heights: 24 mm and 48 mm. Mild steel solid wire AWS ER70S-6 was used to print WAAM walls on substrates that were rigidly clamped to H-profiles. DIC was used to monitor the bending deformation of WAAM parts during unclamping from the H-profiles, and residual stresses were calculated from the strain field captured during unclamping. Residual stresses determined from the proposed DIC-based method were verified with an analytical model and validated by the results from established residual stress measurement techniques, i.e., the contour method and X-ray diffraction.

Energy dispersive synchrotron diffraction has been carried out on cold drawn pearlitic steel wires. In this paper the observed cementite peaks are analysed. For a broad range of true drawing strains sin²(Ψ) curves have been measured. The residual stress in the cementite is found to saturate after reaching a maximum at a strain of about 1.6. No indication of significant texture development in the cementite could be observed. An explanation is given in terms of possible physical mechanisms. Peak broadening was observed at the early stages of deformation.

The residual grain and phase microstress evolutions in the ferrite matrix of pearlitic wires after several steps of cold wire drawing have been studied. Energy dispersive synchrotron diffraction revealed a significant divergence in the grain microstress evolution among differently oriented ferrite grains in the high deformation regime beyond accumulated true strain level εt ≥ 2.3.The possible physical reason for the observed divergence is discussed in terms of distinct microstructure development in this stage of the cold wire drawing.