Abstract: An ultrasonic impact treatment method for remediating metal sensitization including introducing ultrasound compression wave energy through ultrasonic mechanical impulse impacts into an area of sensitized metal in a workpiece. The ultrasound compression wave energy and impulse impacts impart compressive residual stress to the workpiece thereby decreasing tensile stresses in the sensitized metal and modifying the grain structure of the workpiece. These changes to the structure of the workpiece combine to slow the rate of enrichment of alloying elements at grain boundaries within the area of sensitized metal, cause intergranular diffusion of alloying elements in the area of sensitized metal, return a portion of alloying elements in the area of sensitized metal to solution and reduce or eliminate substantially straight intergranular paths through the workpiece.

Abstract: This invention provides methods of treatment for welded products by pulse impact energy, preferably ultrasonic, at original production, during the active life period for maintenance and after failure in a repair stage to improve the strength at the weld sites and to fashion stress patterns that reduce stress centers and micro-stress defects. The basic method steps are nondestructive in nature, inducing interior pulse compression waves that temporarily plasticize the metal to relax stresses and redistribute stress patterns in a gradient of metallic grain structure between a higher strength substantially grainless white layer at the weld seam to an internal base metal region in the welded body. Thus, a renewed longer life span and higher strength weld joint regions are generated in welded products.