Comparison of Residual Stress Measurements on Single Bead-on-Plate Welds of a Martensitic Steel Using Neutron Diffraction

Abstract During the welding process, a material is subjected to thermal cycles with rapid heating and cooling rates resulting in residual stress in the weld and the base metal. These residual stress may affect the mechanical performance leading to premature failure of components. Therefore, it is critical to have a detailed knowledge of the residual stress distribution in the weld region as well as in the vicinity in order to predict the service life of components. Due to the high neutron penetration power, neutron diffraction is one of the most useful techniques for nondestructive evaluation of residual stress in welded regions within the bulk. In this paper, neutron diffraction was used to investigate the residual stress distribution within three single bead-on-plate welds of P91 martensitic steel. Residual stress measurements were performed at different neutron diffraction instruments and different methodology of stress determination was applied. Measurements were carried out at the diffractometers Engin-X (ISIS Neutron Source, Rutherford Appleton Laboratory), E3 (BER-II, Helmholtz-Zentrum Berlin) and SALSA (Institut Laue-Langevin). The results of the measurements presented here, were used to determine the variability of the three instruments and compare the effect of different welding parameters on residual stress. The residual stress measurements were also compared with the respective results of the Task Group 1 (TG1) of the European Network on Neutron Techniques standardization for structural integrity (NET).

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Residual Stress Measurement by Neutron Diffraction in a Single Bead on Plate Weld - Influence of Instrument and Measurement Settings on the Scatter of the Results

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.2452 ◽

2010 ◽

Vol 638-642 ◽

pp. 2452-2457

Author(s):

Carsten Ohms ◽

Robert C. Wimpory ◽

Dimitar Neov

Keyword(s):

Residual Stress ◽

Neutron Diffraction ◽

Stress Measurement ◽

Research Centre ◽

Stress Distributions ◽

Joint Research ◽

Stress Measurements ◽

Single Bead ◽

Considerable Impact ◽

The Impact

Residual stress measurements on a single bead weld on a steel plate had been performed at the High Flux Reactor of the Joint Research Centre in 2003. For these measurements a relatively old diffractometer had been used. The results obtained were characterized by significant scatter of the data, and the measurement quality suffered from the short movement ranges of the specimen positioning table as well. In 2008, a second, nominally identical, specimen from the same activity was investigated on a second diffractometer, which allowed the repetition of the residual stress measurements using different measurement settings. The present paper compares the old and the new measurement results, with a view to assessing the impact of the instrumental settings on their quality. It has been found that the overall stress distributions from the 2003 and the 2008 measurements were in fact very similar. Nevertheless, the new settings used, such as in-situ specimen rocking, extended measurement duration, increased density of measurement positions and spatial resolution among others, have been found to have considerable impact on the real and on the apparent scatter of the experimental results showing that the presented methodologies can be used for improvement of neutron diffraction measurements.

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