Discrimination Between Cracks and Recrystallization in Steel Using Nonlinear Techniques

One major problem in ultrasonic NDT for steel products and welding inspection is that standard linear methods are often unable to distinguish the nature of signals. Partially recrystallized grains, voids, small cracks or inclusions in the piece under investigation could produce indications very similar in terms of acoustic energy reflected and ultrasonic peaks envelope. Here, we analyze the nonlinear response to ultrasonic excitations of steel bars with both kind of imperfections purposefully generated. Using the Scaling Subtraction Method as a tool for the analysis, we show differences in the nonlinear signature, which can be used to distinguish nondestructively a crack/delamination from a region with imperfect grains formation, with possible applications of this technique in the production cycle.