An accurate evaluation of the residual stress of welded electrical steels with magnetic Barkhausen noise P. Vourna a,⇑ , A. Ktena b , P.E. Tsakiridis a , E. Hristoforou a a Laboratory of Physical Metallurgy, National Technical University of Athens, Zografos 15780, Greece b Department of Electrical Engineering, Technological Educational Institute of Sterea Ellada, Evia 34400, Greece article info Article history: Received 31 December 2014 Received in revised form 11 March 2015 Accepted 8 April 2015 Available online 23 April 2015 Keywords: Residual stress Non-oriented electrical steel Welding Magnetic Barkhausen noise X-ray diffraction abstract In the present research work the determination of residual stress distribution in welded non-oriented electrical steel samples is discussed. Tungsten Inert Gas, Plasma and Electron Beam were used as the welding methods. Residual stress was directly determined through deformation measurements and appropriate math calculations. Two methods were used: The magnetic, non-destructive method of Barkhausen noise and the semi- destructive method of X-ray diffraction. In order to evaluate accuracy and reliability of the magnetic method applied, the steel samples were subjected in both compressive and tensile stresses and the magnetic noise values were correlated to residual stress values through an appropriate calibration curve. The results were then verified by the XRD method. Then, these were further evaluated by examining the microstructure and mechan- ical properties of as received and welded samples by scanning electron microscopy and macrohardness measurements, respectively. It was found that the deviation between the two methods was within acceptable limits, thus implying potential applicability of the MBN method in non-destructive testing of materials. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The MBN signal contains information which is closely related to the microstructure [1–14] of an examined ferro- magnetic material. Thus, any change in grains configura- tion, due to the presence of stresses [15–19] or of lattice distortions, results in rearrangement of the magnetic domains’ configuration. The fore mentioned dependence of the MBN to the material’s intrinsic properties makes it a potential tool of non-destructive techniques (NDT), for the evaluation of metallurgical, microstructural, mechanical and micromag- netic parameters. The major proportion of residual stresses is introduced during common manufacturing processes. These stresses are caused by mechanical loads, temperature gradients and volumetric changes due to solid state phase transfor- mations, which result in an inhomogeneous plastic deformation process. During welding, the temperature range varies from the material’s melting point to room temperature. Additionally, the mechanical properties of the joint are temperature dependant and therefore these are often degraded in the presence of thermal gradient. Cooling to room temperature invokes stresses, which are inevitably incorporated into the material as residual stresses. Therefore, the quantitative determination of the residual stresses is important for quality, integrity and performance of the welding joints. Since the stress is an extrinsic property and cannot be directly estimated, all the methods adopted so far take into http://dx.doi.org/10.1016/j.measurement.2015.04.007 0263-2241/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +30 210 7722183, +30 6973218231. E-mail addresses: xvourna@metal.ntua.gr (P. Vourna), aktena@teihal. gr (A. Ktena), ptsakiri@central.ntua.gr (P.E. Tsakiridis), eh@metal.ntua.gr (E. Hristoforou). Measurement 71 (2015) 31–45 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement