Immersion ultrasonic technique for investigation of total welding residual stress

Abstract

Objective of this study is the prediction of total residual stress and fusion boundary in three pass welded stainless steel plates. In this work, immersion ultrasonic technique is used to measure residual stress through the thickness of the material. Two 316L stainless steel plates with the same material properties are examined. Three weld passes are applied to one of these plates and the other one is used as zero stress state reference plate. As it is well known, ultrasonic wave speed is constant for a material unless deformations such as residual stress occur. The main source of residual stress is the heat effect of welding. The relation between thermal stress and ultrasonic wave velocity variations are investigated by using ultrasonic wave velocity measurements which were done at approximately 1200 points for each plate. The differences in the ultrasonic wave velocity discriminations of two plates gave the final total residual stress distribution throughout the welded plate. Therefore the total residual stress which is the sum of longitudinal, transversal, and vertical stresses through the thickness of the plates were measured. Residual stresses are dense around weld zone due to the heat affected zone. Residual stress distribution around the weld zone also provides information about the fusion boundary. Comparison of these results with the previous studies on residual stress measurement showed that the ultrasonic immersion technique allowed more precious measurements than the measurements with couplingmaterials. This method provides a practical and accurate approach for residual stress measurements showed that fusion boundary reaches up to 20mm from weld zone center