Measurement of Residual Stresses in Thin-Sheet Welded Constructions of Low-Alloyed Steel

摘要

The concentrated heat source causes strong local heating of the metal during arc welding. The molten metal is cooled comparatively quickly. Its volume is reduced during solidification, shrinkage occurs and the density of the weld seam metal increases. During welding, the molten and solid metals are inseparable. During solidification in the weld seam metal and the heat-affected zone, changes of the microstructure take place that influence the nature of the distribution, the sign and value of residual stresses. Longitudinal and transverse internal stresses occur. When the stress value reaches the yield limit, plastic deformation occurs in the metal, and the shape and dimensions of the workpiece changes. Adverse tensile residual stresses reduce the vibration strength of welded constructions. The weld seam stresses differ in the gradient and complex nature of the distribution in different directions. The influence of residual stresses on the fatigue resistance will be different for various areas of a welded joint. Simulation and calculation methods do not accurately determine the value of residual stresses. The article presents the technique of residual stress measurement by an X-ray diffraction method. Residual stresses were directly determined on the surface of the weld seams. Single butt welds and single bevel butt welds of low-alloyed sheet steel with 0.9% C-2% Mn-0.8% Si have been investigated. The stress tensor at different sites of welded joints was calculated. The results demonstrate the influence of nonequilibrium crystallization on the nature of residual stresses formation. The interrelation between residual stresses and structural transformations occurring in the weld metal was shown.